The effects of Blue Calorad supplementation on exercise performance and skeletal muscle metabolic potential

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The effects of Blue Calorad supplementation on

exercise performance and skeletal muscle metabolic

potential

Mémoire

Emma Galbraith

Maîtrise en kinésiologie - avec mémoire

Maître ès sciences (M. Sc.)

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The effects of Blue Calorad® supplementation

on exercise performance and skeletal muscle

metabolic potential

Mémoire

Emma Jane Galbraith

Sous la direction de :

Professeur François Billaut, directeur de recherche

Professeur Denis R. Joanisse, co-directeur de recherche

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Résumé

Plusieurs facteurs peuvent limiter la capacité, ou le désir, d’un individu d’effectuer un exercice physique. Entre autres, la perception de la difficulté de l’effort et une faible résistance à la fatigue peuvent limiter la performance tant chez des athlètes d'élite que des individus sédentaires. Les athlètes, les entraîneurs, les médecins et autres intervenants sont donc continuellement à la recherche d’interventions pouvant améliorer la capacité à l’effort et la résistance à la fatigue neuromusculaire. De nombreux travaux démontrent que l'augmentation de l'apport en substrat énergétique au niveau du muscle actif et des niveaux de la machinerie métabolique, soit des activités à la hausse d’enzymes clés impliquées dans le métabolisme énergétique, pourraient réduire les effets néfastes d'une activité physique inhabituelle, améliorant ainsi la tolérance à l'exercice et la performance globale. Cette performance est souvent évaluée au moyen de la puissance aérobie maximale (PAM), soit la quantité de travail produit au niveau du muscle squelettique dans les conditions de consommation maximale d’oxygène au niveau de l’organisme dans son ensemble. La résistance à la fatigue est, de son côté, souvent évaluée par la durée ou le travail total qui peut être fournit dans un effort d’intensité dans le temps. Outre l’entraînement, l’apport nutritionnel, incluant l’utilisation de compléments nutritionnels, peut également améliorer la résistance à la fatigue et la PAM globale en modifiant, entre autres, le potentiel métabolique des muscles squelettiques.

Le complément alimentaire Blue Calorad® (BC) est un breuvage contenant du collagène de milieu marin hydrolysé, de l'extrait de myrtille et des polyphénols combinés dans une formule brevetée. Il a été rapporté que ce médicament réduit le stress induit par l'exercice, améliore l'endurance et la récupération grâce à des effets antifatigue. Ces allégations proviennent cependant des rapports anecdotiques des consommateurs. Par conséquent, une évaluation objective des effets et des mécanismes potentiels sous-jacents de ces effets s’impose. Il est plausible que le Blue Calorad® ait des effets sur la performance car, individuellement, les ingrédients du produit, dont les bleuets, le collagène et les polyphénols, amélioreraient la santé et la capacité d'exercice chez des modèles humains et animaux en bonne santé. Les adaptations physiologiques aiguës et chroniques induites par ces éléments modulent certains mécanismes qui se révèlent limitants pour la performance. L'étude présentée dans l’article de ce mémoire a examiné l’hypothèse selon laquelle le Blue Calorad® agit de la sorte.

Nos résultats démontrent que la consommation ad libitum de Blue Calorad®, pendant une durée de 5 semaines chez des rattes non entraînées, permet d’augmenter leur performance sur tapis roulant en ralentissant l’apparition de la fatigue. Cette amélioration de la performance n’a pas été accompagnée

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de changements significatifs des paramètres physiologiques choisis, soient la composition corporelle, certaines variables plasmatiques, le glycogène musculaire et plusieurs éléments de la machinerie musculaire squelettique des métabolismes anaérobie et aérobie. Ces résultats appuient les rapports anecdotiques des consommateurs du produit et suggèrent que le Blue Calorad® pourrait produire un effet ergogénique chez l’humain, bien que les mécanismes de son action demeurent inconnus.

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Abstract

Maximal aerobic power (MAP), the ability of the muscles to use oxygen received from the heart and the lungs to produce energy, is an important determinant of performance among both athletes at the elite level and sedentary individuals seeking to partake structured physical activity. Athletes, coaches, physicians and others use varied interventions to enhance performance, with the goal of delaying the onset of fatigue. Many authors have suggested that increasing energy supply and upregulating activities of key enzymes involved in the skeletal muscle metabolism could mitigate the deleterious impact of unaccustomed physical activity thereby improving exercise and overall performance. Aside from physical training, a well-structured and balanced nutrition plan may also enhance exercise tolerance and overall MAP by altering anaerobic and aerobic skeletal muscle metabolic potential.

Blue Calorad® (BC), is a liquid dietary supplement containing marine hydrolyzed collagen, blueberry extract, and polyphenols combined in a proprietary formula, which has been reported to reduce exercise-induced stress and enhance endurance and recovery via its potential anti-fatigue effects. Claims surrounding this product are based solely on anecdotal evidence provided by consumers and therefore, potential mechanisms behind its effects have yet to be discovered. BC has yet to be tested in humans. However, blueberries, collagen and polyphenols have been reported to enhance health and exercise capacity in both healthy human and animal models. The acute and chronic physiological adaptations induced by these elements mimic some of the mechanisms that prove to be limiting to overall physical performance and when enhanced these could thereby potentiate the effects of an increased performance. The study presented later in this paper examined this hypothesis.

Our results suggest that ad libitum consumption of BC over a 5-week period in sedentary female rats increases performance during two MAP tests. Although the BC supplementation did not clearly enhance the chosen physiological parameters such as body composition, plasma variables, muscle glycogen and ultimately anaerobic and aerobic mechanisms related to skeletal muscle metabolic potential, the increased performance responses could prove beneficial to sedentary individuals or those seeking to newly partake in a physical activity regime.

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Table of figures

Figure 1. Relative risks of all-cause mortality among participants with various risk factors when

stratified according to their exercise capacity (Myers et al., 2002) ... 6

Figure 2. Correlation between ratings of perceived exertion (RPE) and time to exhaustion (Marcora

and Staiano 2010) ... 11

Figure 3. Relationship between peak power (PP) and percentage of body fat (BF) (Maciejczyk et al.

2014a) ... 14

Figure 4. The Wasserman gears: Conceptual models illustrating the interdependence of ventilation,

circulation, tissue metabolism and overall energy balance in the mitochondria to cell function that defines the essential pathways to VO2max (Poole et al., 2007). ... 20

Figure 5. Illustration of the major energy systems contributing to ATP provision during maximal

aerobic power testing (Thériault 1997). ... 21

Figure 6. The three energy systems and their contribution of total energy supply during any

duration of maximal exercise (Gastin 2001). ... 22

Figure 7. Relative increase in energy derived from carbohydrate (CHO) utilization and decline in

energy from oxidation of lipid (fat) utilization as function of relative power output. At crossover point, increments in relative exercise intensity result in increasingly greater dependence on CHO and less dependence on fat. Even though on absolute scale training results in rightward curve shifts, on a relative basis training probably has minimal effects on curves relative to aerobic power (Brooks and Mercier 1994). ... 24

Figure 8. Compiled data from several studies illustrating the variations of muscle glycogen storage

according to fatigue status, training status and dietary carbohydrate intake (Hearris et al. 2018) ... 25

Figure 9. Glycolytic enzyme activity changes induced by chronic electrical muscle stimulation (Jan

Henriksson, 1992). ... 26

Figure 10. (A) Electron micrography image of MitoVD in a pre-sample and (B) EM image of

MitoVD in a pre-sample from the same subject; x- and y-pixel size is 4.14 nm, arrows point to examples of mitochondria, and asterisk is placed near a fat droplet (Meinild Lundby et al. 2018). ... 29

Figure 11. Illustration of the relationship between CS activity of the vastus lateralis and varying

exercise volume in humans (Bishop et al. 2019). Sprint Interval Training (SIT), High-Intensity Interval Training (HIIT), Moderate-Intensity Continuous Training (MICT), or MICT + HIIT. Dashed, colored lines connect groups that performed different types of training within the one study. ... 30

Figure 12.The influence of endurance exercise training on maximal COX and CS activities (Zoladz

et al. 2016) ... 31

Figure 13. Changes in pain on movement related to collagen hydrolysate consumption compared to

controls (Bello and Oesser 2006) ... 47

Figure 14. Change in percentage of fat-free mass and fat mass after 12 weeks of collagen

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List of Tables

Table 1. List of nutritional facts and ingredients of Blue Calorad® food supplement. ... 37 Table 2. Characteristics and results of studies regarding the effects of blueberry consumption on

exercise performance. ... 41

Table 3. Characteristics and results of studies regarding the effects of collagen hydrolysate

consumption on exercise performance. ... 49

Table 4. Characteristics and results of studies regarding the effects of BCAA consumption on

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List of

abbreviations

AA: amino acids AG: adaptive gait AMA: arm muscle area

AMPD1: adenosine monophosphate deaminase 1 ATP: adenosine triphosphate

ATP-PCr: alactic component of the anaerobic system AUC: area under the curve

BAC: bioactive compound BB: blueberry

BBB: blood brain barrier

BBE-H: high dosage of blueberry extract BBE-L: low dosage of blueberry extract BBE-M: medium dosage of blueberry extract BCAA: branched chain amino acid

BCAT: branched-chain-amino-acid aminotransferase BC: body composition

BC: Blue Calorad®

BCKDH: branched-chain α-ketoacid dehydrogenase complex BCP: bioactive collagen peptides

BF: body fat

ß-HADH: 3-beta-hydroxyacyl-CoA dehydrogenase β -NGF: beta nerve growth factor

BL: blood lactate BM: body mass BMI: body mass index BP: blood pressure BW: body weight CAC: citric acid cycle CAFF: caffeine

CAVI: cardio-ankle vascular index

CDC: Center for Disease Control and Prevention CHD: coronary heart disease

CHO: carbohydrate CK: creatine Kinase

COPD: chronic obstructive pulmonary disorder COX: cytochrome-c oxidase

CO2: carbon dioxide CP: collagen peptides

CPT: carnitine palmitoyl transferase CRP: C-reactive protein,

CS: citrate Synthase CT: control

β-CTX: bone turnover C-terminal telopeptide of type 1 collagen CVD: cardiovascular disease

[C]: concentration D: day

DBP: diastolic blood pressure

DOMS: delayed onset of muscle soreness DLM: dual-leg lean mass

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EC: eccentric training

EC: enzyme commission number EM: electron micrography image ES: effect size

ETC: electron transport chain F: female

FADH: flavin adenine dinucleotide

fCSA: muscle fiber cross-sectional area

FEV1: forced expiratory volume in one second FFA: free fatty acids

FFM: fat-free mass FM: fat mass

FMD: flow-mediated dilation F-TRP: tryptophan

FVC: forced vital capacity

F2-isoprosponate: marker of oxidative stress g: gram

GAPDH: glyceraldehyde phosphate dehydrogenase GPX: glutathione peroxidase

GS: glycogen synthase

GTND: glycerine trinitrate-induced dilation G6P: glucose-6-phospahte dehydrogenase h: hours

HDL: high-density lipoprotein HIIT: high-intensity interval training HK: hexokinase

HOMA-IR: homeostatic assessment model of insulin resistance IGS: International Genetic Standardization

IL : interleukin Ile : isoleucine IL-6 : interleukin-6 IL-10: interleukin-10 IR: insulin resistance km: kilometers L: liters

LDL: low-density lipoprotein LE: light exercise

Leu: leucine

LF-fed ZFR: low-fat fed Zucker-fatty rats LIPA: low-intensity physical activity LEA: low energy availability m: meters

M: male

MAP: maximal aerobic power MCP: monocyte chemoattractant

MCVC: dietary supplement containing mucopolysaccharides, type 1 collagen, and vitamin C MDA: malondialdehyde

MEF50: maximum expiratory flow at 50% of VC METs: metabolic equivalents

MICT: moderate-intensity Continuous Training min: minutes

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MitoP: mitochondrial profile

MitoLV: mitochondrial length density MitoVD: mitochondrial volume density mg: milligrams

ml : millilitres

mmol/L: millimoles per litre

mmHg: millimeter of mercury

MMP: matrix metalloproteinases MP: mean power

MST: motivational self-talk

MVPA: moderate to vigorous physical activity NADH: nicotinamide adenine dinucleotide

nm: nanometre

OA: osteoarthritis O2: oxygen

P1NP: N-terminal propeptides of type 1 pro-collagen PCH: pharmaceutical-grade collagen hydrolysate PEF: peak expiratory flow

PFK: phosphofructokinase PHOS: glycogen phosphorylase PI: physical Inactivity

PINP: procollagen I intact N-terminal PLAC: placebo

PP: peak power PS: passive stretching

SAC: systemic arterial compliance SB: sedentary Behaviour

SBP: systolic blood pressure SD : standard deviation

SDH : succinate dehydrogenase SHGT: sustained hand-grip test SIT: sprint interval training SOD: superoxide dismutase RCTs: randomized controlled trial RET: resistance exercise training RM: maximum repetition RPE: rate of perceived exertion Rpm: rate per minute

TAS: total antioxidant status TCA: tricarboxylic acid cycle TLM: total lean mass

TNF-!: tumor necrosis factor

TT: time trial

TT : mutant homozygotes

Val : valine

VAS : visual analogue scale VC: vital capacity

VE: pulmonary ventilation

VEGF: vascular endothelial growth factor

VISA-A: Victorian Institute of sports assessment-Achilles VLDL: very low-density lipoprotein

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VO2max: maximal oxygen consumption Wk: week

WOMAC: Western Ontario McMaster Osteoarthritis Index WWI: World War I

Y: year

5-HT: serotonin

5-OHMU: marker of oxidative stress µmol: micromole %: percentage =: no change ↑: increase ↓: decrease °C: degree Celsius

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I would like to dedicate this master’s thesis to

all of those who share the same passion

about the physical inactivity epidemic and

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Acknowledgements

To my director, Dr. François Billaut, thank you. For everything. I express my infinite gratitude and recognition to the researcher who gave me this golden opportunity to not only pursue a master’s degree but also a passion. Thank you for the ceaseless support, outstanding sense of humour, contagious passion and for the several insightful discussions which sparked interest and further questioning throughout the realization of this project.

I thank my co-director, Dr. Denis Joanisse who has contributed extensively to my professional as well as personal self-growth as a beginner in research. The realization of this project would have not been possible without your knowledgeable insight, guidance and of course infectious determination and passion for pursuing scientific research.

I am indebted to all the team in the Kinesiology Department at the Université Laval. In your attention to detail, your dedication and your support you go above and beyond. Dr. Pascale Mauriège, Dr. Patrice Brassard, Pénélope Paradis-Dechênes, Elisa Marin Couture Tremblay. I thank you. Your display of passion through your energy and ability to connect with what you love, sparks an awakening not only within me but within the multitude of students whom have had the occasion of crossing your very paths. Your constant encouragement and support are memorable and for that, I thank you all of you.

To Marie-Pierre Pelletier and Nadine Duperon, thank you for all your excellent work, mindful counsel, enthusiasm and great humour. It is much appreciated.

Throughout the pursuit of this academic journey, nobody has been more important to me than my family. I thank my parents, Doug and José, two younger sisters, Abby and Mollie, and lastly my grandmother, Marylou Galbraith, those who instilled my desire for success and whose love and kindness are with me in whatever I decide to pursue and accomplish.

You have all provided unending inspiration, there are not enough words to describe.

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Foreward

The article inserted in chapter 2 of this master’s thesis is entitled Greater aerobic performance with Blue Calorad® consumption is not related to changes in muscle metabolic potential. I am the first author of the article, as I completed the final analysis of data, drafted the first version of the manuscript and participated in elaborating the final version of the work. Dr. Erick Couillard collected and did the preliminary analysis of data. With the previously established experimental protocol and collected data, we further analyzed the data for any errors or other potentially significant relationships. The manuscript is expected to be soon submitted to the international peer-reviewed journal Applied Physiology, Nutrition and Metabolism (APNM).

François Billaut, Ph. D., professor and researcher in the Department of Kinesiology at Université Laval and researcher at the Research Center of the Institut universitaire de cardiologie et de Pneumology de Québedc-Université Laval, is the director of my master’s work. He contributed greatly to each stage of the project, particularly to the development of the research protocol and the revision of the article.

Denis R Joanisse, Ph.D., is a professor and researcher in the Department of Kinesiology at Université Laval and a researcher at the Research Center of theInstitut universitaire de cardiologie et de Pneumology de Québedc-Université Laval. He and his research assistant Erick Couillard generated the original project idea and protocol with research support provided through a company. Professor Joanisse, acted as co-director of my master’s work, and played a major role in the critical revision of the article.

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Introduction

Muscle fatigue diminishes the ability to maintain the required force or expected force output during a given activity. It is a common feature of sport and exercise activities, and its associated perception is heavily influential on the level of adherence and dedication to training (Reichert et al. 2007; Rimmer et al. 2012). Specifically, in the untrained population, a significant negative impact associated with the sedentary lifestyle is the alterations in exercise capacities which can be traced to limitations of the musculoskeletal system, for example, at the biochemical level of the skeletal muscle or its capillarization (Bloomfield 1997; Bogdanis 2012; Burgomaster et al. 2006; Figueiredo et al. 2009; McLeay et al. 2012). Ultimately influencing the ability to maintain the required power output and ability to recover (McAnulty et al. 2011; McLeay et al. 2012; Ping and Hong-mei 2011; Swamy et al. 2011). Similarly, the access and capacity to mobilize energy substrates proves to be an ongoing challenge while exercising (McAnulty et al. 2011; McLeay et al. 2012; Ping and Hong-mei 2011; Swamy et al. 2011). The development of locomotor muscle fatigue during whole-body exercise is highly sensitive to the availability of substrates and modified enzyme activities, as well as more efficient motor recruitment and enjoyment from exercising mediated through the central nervous system (Meeusen 2014). Whatever the causes, increased muscle fatigability negatively impacts exercise tolerance, not only limiting adherence to structured physical activity programs, but also impairing the ability of the skeletal muscle to recover and sustain increased force or power levels (McAnulty et al. 2011; McLeay et al. 2012).

Increasing energy supply and upregulating activities of key enzymes involved in the skeletal muscle metabolism aids in mitigating the deleterious impact of unaccustomed physical activity and, therefore, significant research has been devoted to identifying interventions that alleviate the stress of exercise thereby improving exercise tolerance (Clark et al. 2008; McAnulty et al. 2011; McLeay et al. 2012; Naderi et al. 2018). With this being said, there is a scope to develop time and efficient nutritional strategies to facilitate adherence to structured physical activity. Blue Calorad® is a liquid dietary supplement containing hydrolyzed marine collagen, blueberry extract, and polyphenols combined in a proprietary formula, which has been suggested to reduce exercise-induced stress and enhance endurance and recovery via its potential anti-fatigue effects. Claims surrounding this product are solely anecdotal, as provided by consumers. Therefore, objective evaluation of the effects of this product and of its potential mechanisms of action are needed and warranted.

The possible ergogenic effects of Blue Calorad® appear plausible, as studies on some of its individual components are positive for such effects. Thus, when administered independently, blueberries or

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collagen hydrolysate have been reported to enhance health and exercise capacity in healthy human and rodent models (Clark et al. 2008; McAnulty et al. 2011; McLeay et al. 2012; Park et al. 2018; Ping and Hong-mei 2011). Although both elements may delay skeletal muscle fatigue, the existing literature does not provide a clear picture of their physiological impacts on the anaerobic and aerobic metabolic potential of the skeletal muscle and suffers from one or more shortcomings. For example, some studies have incorporated only short duration exercise protocols in varying environmental conditions (McAnulty et al. 2004; McLeay et al. 2012; Ping and Hong-mei 2011), while others extend over a minimum of 6 weeks (Clark et al. 2008; McAnulty et al. 2011; McLeay et al. 2012). Certain studies used forced aerobic exercise modalities such as treadmill running or swimming (McAnulty et al. 2011; Ping and Hong-mei 2011), while others used resistant training protocols to evaluate muscle recovery (McLeay et al. 2012). Quantification of optimal dosage has also yet to be determined, some studies administering blueberries in varying forms and amounts (140 g (Park et al. 2018), 150 g (McAnulty et al. 2014), 200 g (McLeay et al. 2012) 250 g (McAnulty et al. 2011) and 375 g (McAnulty et al. 2011)), as well as in an acute or chronic manner. Animals are also often force-fed a greater product to weight ratio of a given substance compared to their human counterparts (Bo 2015; Ping and Hong-mei 2011).

Despite these shortcomings, the theoretical framework supporting the potential ergogenic impact of Blue Calorad® supplementation on exercise performance currently exists. Because it is difficult to isolate the objective effects from placebo effects in human subjects, the use of an animal model is suggested as a suitable and desirable first approach to establish whether Blue Calorad® can improve aerobic performance. Such models also allow studies into mechanisms that could explain any performance gain, such as increase in muscle metabolic potential. This master’s thesis sought to verify the hypothesis that Blue Calorad® improved performance using such an approach.

The first chapter of this master’s thesis is a comprehensive literature review exposing the current state of knowledge regarding the major determinants of overall exercise capacity and the ability to attain maximal aerobic power, including supplements such as Blue Calorad® and the individual benefits of marine collage hydrolysate, blueberries and polyphenols consumption. The details of the study conducted as part of this thesis are then presented in subsequent chapters. This is the first study to evaluate the effect of ad libitum Blue Calorad® consumption on performance and aerobic and anaerobic skeletal muscle potential. The findings presented at the end of the manuscript make a definite contribution to the knowledge currently available regarding blueberry, collagen hydrolysate

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and polyphenol consumption as well as Blue Calorad® consumption and its potential ergogenic effect.

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1.1 Physical Activity and Exercise Training

In spite of the well-recognized benefits of physical activity (PA) and exercise, millions of people are physically inactive. More importantly, the associated cardio-metabolic diseases and obesity are still-growing health and financial threats to our society. Despite considerable efforts to reduce the burdens of these diseases through diet and exercise, only a small percent of subjects achieves their goals, and even fewer maintain these over the medium- or long-term. Several factors appear to limit long-term adherence to physical activity programs, including the time investment and perceived discomfort associated with weight reduction or metabolic improvement (Reichert et al. 2007). Finding ways to optimise the benefit/time invested ratio is therefore of great interest, and several studies have demonstrated the benefits of high-intensity interval exercise in this regard (Burgomaster et al. 2006; Gibala 2007; Nybo et al. 2010). However, it is important to keep in mind that the second most cited barrier to partake in physical activity programs is the lack of enjoyment due to perceived effort (Reichert et al. 2007), which is why researchers and health professionals are seeking other solutions.

The recognition that the human body is highly adaptable and efficient for light or vigorous movement dates from antiquity. More importantly, the importance of movement to maintain health, vitality and one’s physique has been acknowledged throughout history (Paffenbarger et al. 2001) and clearly acknowledged by today’s physicians and society. Nevertheless, too few participate in activities they know to be beneficial. Physical activity and exercise training are terms that fit together structurally while providing support for their differences on a conceptual level. Both terms will be briefly defined in order to establish clear differences between them and paint the picture of their importance on overall health.

1.1.1 Definition of Physical Activity

PA is defined as all leisure and non-leisure body movements resulting in an increased energy output from the resting condition (Warburton et al. 2006a). It is often categorized with the following formula (Caspersen et al. 1985):

kcalsleep + kcaloccupation + kcalleisure = kcaltotal daily physical activity

PA is also characterized by its modality, frequency, intensity, duration, and context of practice (Caspersen et al. 1985). Further subdividing leisure time PA into categories like sports and conditioning exercises is also possible using this formula (Caspersen et al. 1985):

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kcalsleep + kcalocupation+ kcalconditioning + kcalhousehold+kcalother = kcaltotaldailyphysicalactivity

Findings from systematic reviews confirm that PA is associated with numerous health benefits in school-aged children, adults as well as the elderly (Groessl et al. 2019; Janssen and Leblanc 2010; Reiner et al. 2013; Warburton et al. 2006a). The dose-response relationship between PA and health in these reviews suggests the more PA performed, the greater the health benefit and decreased risk of death (Figure 1). To further emphasize the overwhelming evidence supporting the benefits of PA, physical inactivity (PI) and

sedentary behaviour (SB) have emerged over the last decade as specific risk factors for morbidity and mortality (Després 2016; Lavie Carl et al. 2019). It is currently suggested that adults from ages 18-64 years should accumulate at least 150 minutes of moderate- to vigorous-intensity aerobic PA per week, in bouts of 10 min or more. In addition, guidelines suggest it is also beneficial to add muscle and bone strengthening activities using major muscle groups, at least 2 days per week. Although experts continue to debate on the optimal PA level, the “movement mindset” is crucial considering the alarming rates of deaths attributed to PI in the past decade (Després 2016).

It is important to view PA as a continuum. This provides a way of categorizing activities that requires different amounts of energy expenditure. The PA continuum does not solely encompass exercise activity, it also includes non-exercise activities, such as house chores and standing. On the lower end of the continuum lies SB and on the higher end lies moderate to vigorous physical activity (MVPA). It is important to note that SB and PA are not the opposite of each other. In other words, a person can be classified as both active and sedentary. While individuals are classified as active when they reach PA recommendations for their age, this does not prevent them from possibly also devoting a significant part of their time to SB (Thivel et al. 2018). Which means, devotion to any waking behaviours categorized by an energy expenditure lesser than 1.5 METs, while sitting, reclining, or in a lying posture (Tremblay et al. 2017).

Figure 1. Relative risks of all-cause mortality among participants with various risk factors when stratified according to their exercise capacity (Myers et al., 2002)

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1.1.2 Definition of Exercise Training

Like PA, several reviews have clearly illustrated that taking part in regular ET, specifically aerobic exercise training, aids in attenuating the onset or reversing to development of physical and mental diseases in both sexes across a wide age range (Franklin et al. 2003; Lees and Hopkins 2013; Reed et al. 2018). Both PA and ET involve any bodily movement produced by skeletal muscles that expends energy, but ET distinguishes itself from the less structured and unplanned PA. The reasoning behind ET is unique and regularly performance oriented. For the purpose of this thesis, we will follow the definition that ET is a “subset of physical activity that is planned, structured and repetitive and has a final or an intermediate objective to improve or maintain physical fitness” (Caspersen et al. 1985; Després 2016; Warburton et al. 2006b). The formula below demonstrates that PA and ET are indeed related due to their shared elements; however, ET remains a subcategory (Caspersen et al. 1985):

kcalexercise + kcalnon-exercise = kcaltotal daily physical activity

Thus, according to their powerful ability to counteract the onset and early development of diseases, it is not surprising that PA and ET have been and still are intense topics of scientific and clinical research. PA and ET can both improve health and performance. The following section will first define exercise capacity and maximal aerobic power (MAP) and highlight the possible effects of acute exercise or regular PA and ET on the determinants of MAP

.

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1.2 Exercise and Maximal Aerobic Power

Activity status (PA and ET) and exercise capacity (e.g., MAP or maximal oxygen intake) are not only associated with increased physical performance, but also with numerous beneficial effects promoting longevity and well-being. This section will first briefly define exercise capacity and its clinical importance, define maximal aerobic power (MAP) and explore the benefits of ET or regular PA in relation to major determinants of MAP. Additionally, MAP and its relationship with the skeletal muscle will be explored further in section 3.

1.2.1 Definition of Exercise Capacity and Fatigue

In order to objectively measure an individual’s level of physical fitness, we measure someone’s ability to exercise until exhaustion, a state of extreme physical or mental fatigue. This is known as exercise capacity (EC). Both central and peripheral systems play pivotal roles in the development of exercise fatigue in as much that the term “fatigue” is still subdivided in relation to the location of inhibition to perform a task; there exists both peripherally and centrally mediated fatigue. Because fatigue is mediated through two key systems, in order to arrive at a reliable and meaningful result about an individual’s level of exercise performance, it is important to keep in mind that complementary approaches (such as interview and direct laboratory measurement (maximal oxygen consumption (VO2max)) are necessary.

Peripherally mediated fatigue is generally defined as the inability to maintain the required force or expected force or power output or any decline in muscle performance associated with muscle activity at the original intensity (Bogdanis 2012; Fitts 1994). Whereas central fatigue is defined as any exercise-induced reduction in maximal voluntary contraction force that is not accompanied by the same reduction in maximal evocable force. Enough evidence exists suggesting that mechanisms of the central nervous system (CNS) are also part of the manifestation of fatigue, but peripheral fatigue remains the type of fatigue most frequently measured seeing as it can be objectively quantified. Objective measurements of peripheral fatigue often include substrate depletion, metabolic acidosis and neuromuscular transmission disturbances.

Much like a high exercise capacity is associated with better performance and health (Myers et al. 2002), a reduced or evident deterioration in exercise capacity is often an indicator of a disease progression or dysfunction in endocrine, metabolic, hematologic, neuromuscular or physiological systems, as well as cardiovascular or pulmonary disorders (Goldstein 1990; Myers et al. 2002). In

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fact, exercise capacity has been recognized as an important prognostic factor in patients with cardiovascular disease (Goldstein 1990; Myers et al. 2002; Peterson et al. 2008). The wealth of data supporting the fact that exercise capacity is a strong predictor of health outcomes emphasizes the value of exercise tests as inexpensive and non-invasive clinical tools (Myers et al. 2002). Depending on the availability of facilities, budget and the level of medical support, exercise testing can be assessed on cycle and arm cranking ergometers and treadmills (walking or running tests depending on the population being assessed). Among the existing exercise tests, we will focalize on MAP (also known as VO2max) throughout the remainder of the master’s thesis.

1.2.2 Definition of Maximal Aerobic Performance

Maximal aerobic performance is most often expressed as the maximal volume of oxygen consumed (VO2max) during an incremental exercise test. It can also be expressed as MAP, the power output

achieved at VO2max

.

VO2max is the point at which oxygen uptake no longer increases (or increases only

marginally) with an increase in workload. These measures are used to determine the level of cardiorespiratory fitness and allow comparisons between various individuals or populations in both exercise performance and clinical settings. Cardiorespiratory fitness reflects the coordinated response of several body systems leading to VO2max, notably the cardiovascular, pulmonary, neural, and muscle

systems (Goldstein 1990). It is important to keep in mind that this measurement can be affected by numerous factors, including age, conditioning status, the presence of disease, and medications (deJong 2011).

Maximal aerobic performance is but evaluated by maximal exercise testing (increasing the intensity of the test to the physiological maximal ability of the individual), but it can also be estimated from submaximal tests (deJong 2011). Objective measurement of cardiorespiratory fitness can be evaluated using numerous exercise modalities, such as arm cranking (Sawka et al. 1983), leg cycling and treadmill walking and running (Davis et al. 1976). As each modality involves a set of active muscles and can be load bearing (body supporting) or not, their absolute VO2max or MAP values will differ accordingly. In most clinical settings, VO2max is determined with a progressive treadmill test (the intensity of the required work increasing over time by either increasing the speed or the incline of the treadmill until volitional fatigue), and this objective and direct laboratory measurement approach is considered by many as the “gold-standard” (Carlson 1995). Several factors can influence maximal aerobic performance, some of these are explored below.

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A plethora of data suggest that structured and planned PA improves maximal exercise performance. The following section will briefly explore some of the key determinants that limit this performance, and that can be targets for improvement following PA.

1.2.3.1 The mind and maximal aerobic performance

Many studies have focused on potential limiting mechanisms related to respiration, cardiovascular function and, skeletal muscle metabolism while often neglecting the power of the mind. Undoubtedly, these three systems play key roles in performance but the extent of psychological contribution (task disengagement or “giving up” (Marcora and Staiano 2010)) to exercise performance decrement remains highly debated.

Perception of effort and motivation during high-intensity aerobic exercise are two potential psychological elements with the ability to influence exercise tolerance (Marcora and Staiano 2010; Meeusen 2014; Noakes 2008; Reichert et al. 2007). As subjects approach the end of high-intensity aerobic exercise, increases in blood lactate and heart rate are often accompanied by increases in ratings of perceived exertion (RPE) (Marcora and Staiano 2010). In a study seeking to shed light on the “mind over muscle” debate, researchers demonstrated that higher levels of perceived effort were associated with earlier rates of cessation during a cycling time to exhaustion test. Authors further concluded that exercise tolerance in highly motivated subjects was ultimately limited by perception of effort (Figure 2).

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Figure 2. Correlation between ratings of perceived exertion (RPE) and time to exhaustion (Marcora and Staiano 2010)

In line with this account, evidence supports the importance of cognitive activity to overall performance (Clare et al. 2014). After subjecting 20 experienced runners to two 3,000-m runs on an indoor track, one after cognitive fatigue (watching a movie about World War I (WWI)), and the other under non-fatigued condition, researchers concluded pre-exercise cognitive activity contributed to a performance decrement by increasing the perception of exertion and leading to lesser performance on the running task. From another performance viewpoint, data support the relationship between the tendency of athletes to change pace during competitive simulations, how they feel momentarily (RPE) and to how much of the event remains (de Koning et al. 2011). In brief, these data support the concept that muscular power output during high-intensity exercise performance is actively regulated in an anticipatory manner that accounts for both the momentary sensations the athlete is experiencing as well as the relative amount of a competition to be completed.

The willingness to continue exercising when subjected to a state of fatigue requires a certain level of motivation (Barte et al. 2019). Considering their findings, Marcora and Staiano further supported their results with studies testing the effect of psychostimulants on time to exhaustion (Marcora and Staiano 2010). When presented with an ultimatum (external motivational stimulus), increases in performance have been noted. For instance, in a “money versus pain” experimental study, Cabanac

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noted a linear relationship between the time tolerated in a painful position and the logarithm of the amount of monetary compensation offered (Cabanac 1986). Further, in extreme heat conditions, motivational self-talk (MST), a top-down regulation strategy requiring participants to continuously reappraise negative self-talk and bottom-up feedback with self-contextualized motivational statements, is effective in altering the internal psychophysiological control of exercise and plays a role in improving endurance capacity and executive function (Wallace et al. 2017). Moreover, a study which investigated the effects of motivation on fatigue-induced performance decrements in soccer concluded that motivation plays a crucial role in performance under fatigue. Findings indicated that players in the motivation group were able to counteract performance decrements under fatigue. These findings support the idea that motivation, and not only physiological factors, play a crucial role in determining performance decrements under fatigue (Barte et al. 2019).

Although there is a growing wealth of data describing, and at times supporting, the role of psychological phenomena known to impact exercise performance, additional research is warranted to clarify the precise nature of the psychological response to maximal aerobic exercise. Although inconclusive, some studies have attempted to explore the effects of varying nutritional supplements and/or interventions on the chemical disposition of the brain. Hydration status, branched chain amino acids (BCAA) such as tyrosine, caffeine, carbohydrate supplementation are all methods that have been studied on potential central fatigue mechanisms (Meeusen 2014). The lack of congruency between nutritional studies leaves a window of opportunity for future research regarding nutritional supplementation and exercise performance. Elaborations regarding this topic will be discussed in section 1.4 and 1.5.

1.2.3.2 Body composition and maximal aerobic performance

Body composition describes the distribution of body mass into different compartments, notably fat mass and lean mass, the latter including notably muscle, bone and water masses. Both body composition and body mass are thus closely related and are both key determinants of exercise performance. This comes as no surprise, since performing a given exercise with extra weight to support will translate to greater workload and thus require increased muscular effort (Salvadori et al. 1992). In any given sport or structured PA, body mass and body composition will affect performance in a positive or negative way depending on the subject’s disposition. For example, in aerobic sports like track and field or marathon running, a significantly increased body mass is a limiting factor due to mechanical and gravitational reasons, each deployment of effort requiring supplementary muscle work to counter the workload imposed by the additional mass. However, a low body mass can also

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be problematic, often leading to overuse injury or amenorrhea, the latter a common disorder among elite female distance athletes (Torstveit and Sundgot-Borgen 2005). Therefore, optimizing body composition by promoting the correct balance between muscle mass and whole-body mass is key in order to enhance and sustain aerobic performance over the long-term.

Evidence suggests that both body fat and lean body mass can adversely affect aerobic performance results in both adults and children (Maciejczyk et al. 2014a; Maciejczyk et al. 2014b; Thomas et al. 1999). A study investigating the associations between skeletal muscle mass, BF and training characteristics with running times in master athletes (age > 35 years) in half-marathon, marathon and ultramarathon races concluded that having more skeletal muscle mass did not provide a clear performance advantage. Rather, varying BF percentages in conjunction with training programs were directly related to both volume capability, endurance, and speed during training in all classes of marathoners (Knechtle et al. 2012). Similar results have been shown in short bouts of maximal exercise relying on anaerobic energy systems. In a study quantifying the influence of increased body mass and body composition on cycling anaerobic power, no significant differences were seen between groups in peak power and mean power when presented relative to lean body mass. Therefore, it seems that it is not body mass but rather body composition that affects peak power (Figure 3). Increased body mass, resulting from increased lean body mass, does not adversely affect cycling anaerobic power, but a body mass increase resulting from an increase in body fat may adversely affect peak power. From this study it was inferred that coaches and athletes should avoid excess body fat to maximize cycling anaerobic power (Maciejczyk et al. 2015).

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Figure 3. Relationship between peak power (PP) and percentage of body fat (BF) (Maciejczyk et al. 2014a)

Studies in animals also support an influence of body composition on exercise performance. For example, in addition to confirming that red blood cells from the splenic reserve constitute an important factor in the horse's ability to achieve a high V̇O2max, researchers investigating the relationship between body composition, blood volume and maximal oxygen uptake indicated that V̇O2max in the horse is significantly related to fat‐free mass, independent of body mass (Kearns et al. 2002). Therefore, lean body mass may be a more appropriate basis for assessing metabolic function in the athletic horse.

In short, it is clear that body composition, and in particular BF percentage, is an important determinant of exercise performance whether exercise is mainly anaerobic or aerobic, in both humans and animals. If this specific determinant is optimized, performance can be increased.

1.2.3.3 The cardiovascular system and maximal aerobic performance

The cardiovascular system is composed of three crucial components, the pump (heart), a system of channels (blood vessels) and a fluid medium (blood). Its functions are separated into the following five main categories: delivery of nutrients, removal of carbon dioxide and metabolic by-products and transports hormones from endocrine glands to their target receptors, maintaining body temperature and the blood’s buffering capabilities which help control the body’s pH levels and, lastly, preventing

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dehydration and infection by maintaining appropriate fluid levels (Wilmore and Costill 1994). Ultimately, this system must be able to respond immediately to any changes made to the human body because virtually every cell depends on this system in one way.

Partaking in regular structured PA and ET has many benefits on cardiovascular health (Nystoriak and Bhatnagar 2018). It is well-established that systemic hypertension (high blood pressure) is an independent predictor of premature death and disability from cardiovascular complications (Mensah 2002). It results in part from the hardening and thickening of the arteries, limiting circulation throughout the body. Blood pressure increases dramatically to meet the body’s needs during PA, but studies have confirmed a notable decrease in blood pressure (BP) within two to four hours following exercise (Thompson et al. 2001). Further, a meta-analysis comprehending 72 studies, 105 different groups and 3936 participants concluded that dynamic aerobic endurance training decreased resting BP through a reduction in systemic vascular resistance, where the sympathetic nervous system and the renin–angiotensin system appear to be involved (Fagard 2006). Additionally, chronic exercise has been associated with decreased arterial stiffness. A study investigating the effects of ET on total systemic arterial compliance (SAC) in humans highlighted three main findings, 1) ET increases SAC 2) that the increase in SAC is greater than that due to changes in BP and is likely to include a component due to change in intrinsic arterial compliance; and 3) that the induced change in SAC is linearly related to change in VO2max (Cameron and Dart 1994).

With the evidence above, short and long-term PA and ET can minimize factors associated with poor cardiovascular health and improve the efficacy of the overall cardiovascular system. Despite its potential for remodelling and improvement, the cardiovascular system remains a physiological determinant of exercise performance, often responsible for individual differences in aerobic performance. In any given physical effort, oxygen demands increase throughout the body and namely in surrounding tissues. More energy is needed thus metabolic processes accelerate, creating more waste in addition to amplifying the level of hemodynamic stresses. As a result, changes are made to the parameters of the cardiovascular system like heart size, stroke volume, heart rate, cardiac output, blood flow, BP and blood volume in order to normalize stresses and meet the demands placed upon it by carrying out its functions with maximum capacity (Nystoriak and Bhatnagar 2018; Wilmore and Costill 1994). Among all parameters, evidence suggests that cardiac output, defined as the total volume of blood pumped by the ventricle per minute, is the primary factor explaining interindividual differences in VO2max (Bassett and Howley 2000; Thomas et al. 1999). Cardiac output is the product of heart rate (HR) and stroke volume and is potentially influenced by either maximal heart rate (HR)

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or stroke volume (SV). HR has shown to vary considerably less in comparison to maximal stroke volume (SV) when comparing sedentary and trained men and women (Bassett and Howley 2000). SV, the amount of blood pumped per heartbeat, has been shown to increase during rest, submaximal and maximal exercise. In a study investigating the physiological determinants of MAP in healthy 12-year-old boys, the results of which showed that maximal SV, related to body size provided the only physiological explanation for differences in VO2max. When boys of high and low cardiorespiratory fitness were compared, differences in maximal SV reflected values at rest.

Thus, although regular exercise is associated with significant reduction among the risk factors related to poor cardiovascular health, dyslipidemia, arterial stiffness and systemic hypertension, certain parameters of the cardiovascular system like cardiac output remains a physiological determinant limiting aerobic performance across varying populations.

1.2.3.4 The respiratory system and maximal aerobic performance

Put simply, we cannot live without oxygen. Our cells depend on it for survival. The respiratory system is crucial for breathing (also referred to pulmonary ventilation) and the lungs serve in its primary function by soliciting the exchange between fresh surface air while removing waste gases from the body. The respiratory system allows individuals to obtain oxygen from the external environment and supply it to the cells, and to remove carbon dioxide from the body produced by cellular metabolism. Its functions include gas exchange, acid-base balance, phonation, pulmonary defense and metabolism, and the handling of bioactive materials (Wilmore and Costill 1994).

Among potential exercise performance limiting factors, the availability and turnover of oxygen plays a major role. Oxygen transport from the atmosphere to the mitochondria of the skeletal muscle involves several systems and processes, including respiration, blood circulation, and skeletal muscle uptake of circulation oxygen. In subject populations suffering from pulmonary dysfunctions or athletes training in high altitude conditions where oxygen consumption is limited, the respiratory system can pose several limits on performance (Faulkner et al. 1968; Mälkiä and Impivaara 1998). Much like skeletal muscles, respiratory muscles can fatigue and be trained to increase strength and endurance. Accordingly, studies have examined the importance of the respiratory system as a potential limiting factor for exercise performance (Boutellier and Piwko 1992; Boutellier et al. 1992; Verges et al. 2008). All three studies have provided evidence illustrating that the respiratory system has the potential to limit a subject’s endurance for submaximal exercise (i.e., at 64% peak oxygen consumption), whether that individual be sedentary or trained. Comparatively, several studies have highlighted that for healthy individuals exercising at sea level, the respiratory system does not appear

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to be an important limiting factor for performance. This is supported by studies revealing that pulmonary ventilation can be increased to a greater extent than the cardiovascular capacity to distribute oxygen to active muscle (Bassett and Howley 2000; Burton et al. 2004; Wilmore and Costill 1994), and that its function is enough to cope with the demands associated with pulmonary ventilation and gas exchange even during intense exercise (Amann 2012).

Taking part in regular ET or PA improves functional parameters related to the respiratory system. For example, most research indicates that PA and good physical fitness are connected with improved ventilation of the lungs (Boutellier and Piwko 1992; Cheng et al. 2003; Pelkonen et al. 2003). In a study estimating the correlation between the functional parameters of the respiratory system and the level of PA and body composition in the adult rural population, parameters of the respiratory system (forced expiratory volume in one second (FEV1), peak expiratory flow (PEF), MEF50 (maximum expiratory flow at 50% of VC)) show the highest correlations with parameters of muscle strength (Rozek-Piechura et al. 2014). In addition to supporting the increase in functional parameters of the respiratory system, this study notes increased muscle strength in physical active individuals compared to their less-active counterparts. Further, results from a 25-year longitudinal study concluded that PA (walking and cycling) may delay the decline in pulmonary function occurring in middle and old age (Pelkonen et al. 2003). Specifically, during the first 10 years, FEV (forced expiratory volume) was 9.8 ml per year less among men in the highest tertile of baseline PA than in men in the lowest tertile. Lastly, cross-sectional and longitudinal data presented in a report emphasized that men who remained active had higher FEV1 and forced vital capacity (FVC) compared to their sedentary counterparts (Cheng et al. 2003). Thus, it is evident that regular PA and ET can greatly impact the efficacy of the respiratory system by improving its functional parameters.

Depending on a subject’s physical and environmental conditions, the respiratory system can pose several limitations on the body resulting in an affected exercise performance. PA and ET improve parameters related to respiratory function but to what extent the lungs limit exercise performance in sedentary healthy individuals is still a matter of debate. Unlike the cardiovascular system, it is unlikely to be a major limitation to performance in healthy individuals.

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1.2.3.5 The skeletal muscle system and maximal aerobic performance

“The stones themselves reveal the construction history, stops and starts, damage and rebuilding, extensions in times of prosperity.”

Ken Follett, Pillars of the Earth

If we compare the human body to the cathedral from Ken Follett’s novel Pillars of the Earth and our muscles to the stones used to build this religious monument, we soon realize that stones and muscles are similar on a multitude of levels. There is a beginning and an end to muscular development and function, our muscles carry our stories of injury and recovery and muscle tissue has allowed humans to propel itself forward and achieve unimaginable athletic performances.

Of the three types of muscle tissue, skeletal muscle is of primary importance in movement and performance, as it is responsible for voluntary movements. To do so, skeletal muscles are dependent on the CNS, requiring motoneuron signaling to initiate contraction. They also must act in concert with the circulatory system in order to obtain required elements for function, such as oxygen or substrates such as carbohydrates or lipids that can fuel metabolism directly or serve to build intracellular reserves for future metabolic needs. Structurally, skeletal muscle tissue per se consists of several elongated cells known as muscle fibers. These cells contain many contractile protein structures (sarcomeres) arranged in parallel structures known as myofibrils. Surrounding each cell and the whole tissue is a complex extracellular support matrix of collagenous fibres, and these are continuous with the tendons that can be attached to bones at the muscle extremities.

Much evidence supports changes at the skeletal muscle level contributing to improved performance following ET and PA. For example, studies have established that exercise or selected structured PA can induce skeletal muscle hypertrophy (D'Antona et al. 2006; Hermansen and Wachtlova 1971; Konopka and Harber 2014), alter muscle fiber type distribution (Andersen and Henriksson 1977; Bogdanis 2012) and increase mitochondrial density as well as its enzyme activities (Bogdanis 2012; Wilmore and Costill 1994). ET and PA have also been associated with increased capillarization thus blood flow and myoglobin content (Andersen and Henriksson 1977; Hermansen and Wachtlova 1971; Wilmore and Costill 1994). All these elements aid skeletal muscle to counteract the early onset of fatigue and increase performance.

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In addition to improving cardiovascular and respiratory systems, it is evident that ET and regular PA can improve a set of factors related to the skeletal muscle, its surrounding capillary bed and its metabolic machinery (Bogdanis 2012). This indicates that there is potential for improvements and that it also has the potential to pose several limits on performance. Among sedentary or physically inactive individuals, perceived discomfort associated with weight reduction and metabolic improvement (Reichert et al. 2007) is heavily influential on the level of adherence dedicated to training. Since this master’s thesis focalizes on optimizing/facilitating performance and alleviating stress of exercise to thereby improve exercise tolerance among sedentary individuals, our primary interest in section 3 will be to shed light on these physiological factors and how exactly they may pose limitations on exercise performance in varying healthy populations.

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1.3 Skeletal muscle limitations related to maximal aerobic performance

The mechanisms that regulate MAP are multifactorial (Figure 5) and key studies, both longstanding and recent, have illustrated that VO2max is mainly limited by central factors like maximum cardiac output and oxygen carrying capacity (Bassett and Howley 2000; do Nascimento Salvador et al. 2019; Poole et al. 2007).

Figure 4. The Wasserman gears: Conceptual models illustrating the interdependence of ventilation, circulation, tissue metabolism and overall energy balance in the mitochondria to cell function that defines the essential pathways to VO2max (Poole et al., 2007).

However, most research also implicates peripheral (muscle) factors as limiting performance. Whether it be at the central or peripheral levels, the specific factors limiting exercise performance in any given situation are not fully understood and will certainly vary between individuals. Nevertheless, at the peripheral level, certain studies have highlighted potential limitations to perform at maximal capacity originating in skeletal muscle (Hagerman et al. 2000; Poole et al. 2007; Weiss et al. 2017). This section will examine peripheral and metabolic factors limiting performance of the skeletal muscle. Potential peripheral sites for VO2max limitation include notably muscle oxygen diffusion capacity (indicated in part by the extent of the capillary bed surrounding muscle fibers), muscle mitochondrial content (often assessed as maximal activities of a number of mitochondrial enzymes such as citrate synthase), as well as substrate availability and handling during exercise (Bassett and Howley 2000).

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The section below will first elaborate on the three energy systems necessary for adenosine triphosphate ATP production and highlight how mitochondrial enzymatic activities, substrates availability (glycogen and lipid levels) and capillary density can limit exercise performance.

1.3.1 Energy systems and adenosine triphosphate (ATP) provision

First and foremost, in order for muscle contractile activity to be maintained for longer than a few seconds, ATP must be supplied at a rate equivalent to demand. Depending on duration and intensity of exercise, the pathways and substrates used for the production of ATP will differ. The capacity for ATP production of these different pathways can vary significantly following PA and ET and can also be influenced by other multiple factors (Figure 5). Of interest, nutrition can significantly influence substrate availability and use and will be discussed in sections 4 and 5 of this master’s thesis

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Figure 5. Illustration of the major energy systems contributing to ATP provision during maximal aerobic power testing (Thériault 1997).

During exercise, the three major energy systems that contribute to ATP provision are oxidative phosphorylation (the aerobic energy pathway), the ATP-PCr system (alactic component of the anaerobic system) and anaerobic glycolytic system (lactic, anaerobic system). It is important to keep

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in mind that all three major energy pathways are functioning harmoniously at all times regardless of the given muscular effort (Figure 6). However, depending on intensity and duration of a given exercise and/or PA, one pathway may contribute more compared to another. Nevertheless, the body does not heavily rely on the anaerobic system for energy provision during maximal aerobic type exercises. It has been estimated that during VO2max testing, the anaerobic system contributes approximately 5-14% of total ATP provision (Bertuzzi et al. 2013).

Figure 6. The three energy systems and their contribution of total energy supply during any duration of maximal exercise (Gastin 2001).

The anaerobic energy system does not require oxygen to function and can be subdivided into two sub-systems. The first is the simplest, the alactic element (ATP-PCr system). This is the main energy system solicited during explosive exercise and high-intensity exercise lasting for a few seconds. The ATP-PCr system remains nonetheless active during aerobic efforts. To prevent the muscle cells from depleting their ATP at the beginning of maximal or near maximal contractions, phosphocreatine (PCr), another energy-rich phosphate molecule located within the muscle cell itself, can be used to regenerate ATP at a very rapid rate. Phosphocreatine has its phosphate group transferred to adenosine diphosphate (ADP) to yield ATP and creatine, in a reaction catalyzed by creatine kinase (CK; enzyme commission number (EC) 2.7.3.2). The activity of CK is very high in muscle in order to match the regeneration of ATP during the most vigorous muscle contractions. However, with high potential comes quick depletion. This explains why this metabolic pathway is heavily solicited only during