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No description available.

Near Infrared Spectroscopy (NIRS) is a non-invasive technique which can be used to monitor changes in oxygen saturation and haemoglobin concentration in the muscle microvasculature during exercise. The recent development of reliable portable NIRS devices presents the opportunity to measure muscle oxygenation and blood flow in-vivo during simulated competition in a realistic sporting setting. Therefore, portable NIRS was used to monitor right and left leg quadriceps oxygenation and blood volume changes during simulated competition in short-track speed skating, across a range of race distances. During race simulation over 500m in male subjects, linear regression analysis revealed asymmetry between right and left vastus lateralis muscle oxygen saturation (TSI%) data: TSI% decreased to a plateau after 8s, after which right leg TSI% remained constant throughout the rest of the simulation (slope value = 0.01), whereas left leg TSI% increased steadily (slope value = 0.16), leading to a significant asymmetry (p<0.05) in the final lap. Although total muscle haemoglobin concentration decreased equally in both legs at the start of the simulation, during the course of subsequent laps there was a strong asymmetry during cornering; when skaters travelled solely on the right leg there was a decrease in its haemoglobin concentration whereas an increase was seen in the left leg. This difference was attributed to the differing technical demands placed on the two legs during cornering at high speeds. When comparisons were made between NIRS-derived changes over 3 race distances in males and females, it was shown that neither race distance nor sex had a significant effect on the magnitude of maximal muscle desaturation (~TSlmax). Linear regression analysis revealed asymmetry between right and left leg desaturation in males during the final stages of skating across each race distance, but not in females. Thus, NIRS-derived measurements of local muscle oxygenation can provide insight into velocity and pacing changes in speed skating, and technical differences between male and female skaters. Comparison between skating and cycling data revealed that NIRS-detected leg asymmetry was due to the specific demands of short-track speed skating. However, heterogeneity between individuals is not specific to the mode of exercise. Finally, the possibility of using portable NIRS to monitor adaptations to endurance training in . . elite biathletes was examined. Training did not significantly affect muscle oxygen saturation levels during submaximal treadmill running, although it did reduce blood lactate values. Comparison of data for males and females revealed a significant effect of adipose tissue thickness on magnitude of tissue saturation change during running. The results presented here suggest that the utility ofNIRS as a tool for monitoring peripheral adaptations to training interventions in elite athletes is still subject to debate. However, this thesis does show that portable NIRS can be used in a variety of sporting contexts as a viable tool to address questions relating to the supply and utilisation of oxygen in specific muscles during dynamic exercise in the field.

It has always been of great interest for scientists to study human performance and fatigue in order to better understand the limiting factors and determinants, which ultimately rule exercise tolerance in humans. In the last decades, the focus has moved to study fatigue and human performance not only from a physiological point of view but also to integrate it with psychophysiological mechanisms in order to reach a fuller understanding of fatigue processes and its implications on exercise performance. The aim of this thesis was to analyse the most prominent models of exercise tolerance and delineate psychological and physiological factors determining and/or limiting exercise performance. Moreover, the role of "effort" and its implications for exercise tolerance has been defined and elucidated. In chapter 2, it has been shown that maximal voluntary cycling power measured before and immediately after exhaustive cycling exercise does not decrease below the constant power at which participants were cycling at exhaustion. Such decrease in power, therefore, does not explain and challenge the traditional assumptions that in high intensity aerobic exercise muscle fatigue causes exhaustion, which occurs when the power generated from the muscles does not match any longer the power required by the task. Moreover, this study suggests the implication of other psychobiological variables such as rating of perceived exertion as important determinant and main limiting factor of exercise tolerance In chapter 3 has been tested the hypothesis that rating of perceived exertion and naturally occurring muscle pain, the two main perceptual determinants influencing physical performance have a different impact on physical performance. Muscle pain unpleasantness (Cook's scale) and rating of perceived exertion (RP E) (Borg's scale) were rated during a high intensity aerobic cycling test. During the cycling task, a constant increase in RPE was reported until subjects withdrew exercise while naturally occurring muscle pain rating increased at a moderate level without reaching the maximal rating. These findings suggest a high correlation between rating of perceived exertion and high intensity cycling at exhaustion and minimize the impact of naturally occurring muscle pain as limiting factor in aerobic performance. In chapter 4 it has been tested the validity and efficacy of a novel protocol to measure neural correlates of rating of perceived exertion using functional magnetic resonance imaging (fMRI). By comparing two different conditions: Fatigued leg vs. Non fatigued Leg, nine participants performed a series of leg extensions tasks alternating both legs. During this task, brain activation was measured using a 3 Tesla fMRI scanner and rating of perceived exertion has been recorded. Main results have shown an increase in rating of perceived exertion concomitantly to an increase in central motor command across the series of leg extension task performed and a significant activation of the cingulate gyrus and insular cortex has been detected when comparing higher ratings of effort compared to lower ones. These new findings may help the understanding of the neurobiology of perceived exertion and the brain areas and neural processes implicated with an increase of the rating of perceived exertion. Moreover, it elucidates the role of effort-based decisionmaking mechanisms related with perceived exertion. Overall, our findings showed the validity of a more psychophysiological approach to study complex processes of fatigue and to delineate main determinants involved in human performance with particular attention to the rating of perceived exertion. It redefined the role and the impact of exercise-related muscle pain in endurance performance. Finally, it proposes new neurophysiological insights into the origin and development of perceptions of effort in the brain. iii

The accurate measurement of physical activity in children and adolescents is very difficult and there is currently no ideal method for use in this area of research that measures all facets of physical activity behaviour. The primary aim of this study was to develop and evaluate an Internet-based self-report, the ActiLog. Secondary aims were to evaluate the use of heart rate monitoring and accelerometry for measuring physical activity in adolescents.

A series of experiments were conducted to investigate the effect of the perception of stimuli external to the body on the perception of effort, and its subsequent effect on athletic pacing. An initial study investigated the pacing and ratings of perceived exertion (RPE) during an ultra-distance triathlon. This revealed that RPE scores follow a linear rate of increase throughout the event, but also that this increase displays a number of perturbations. Run pace followed a positive profile, suggesting a constant re-assessment of pace by the participants, by a process of comparison of the rate of increase in RPE with the perception of progress through the event. How athletes do this was investigated further. The next study examined the role of optic flow on RPE. This showed that slow optic flow reduced RPE, with there being a number of possible mechanisms. These were further explored in a study into the effect of optic flow upon distance perception, RPE, and pacing. This revealed an altered perception of distance, but, an unaltered freely-chosen work rate. It also revealed a divergence between visual perception and action. These results are discussed in the context of existing cognitive models of pacing. A final study revealed that the visual perception of gradient altered RPE, but, that this occurred without interaction with the effect of optic flow on RPE, suggesting that they act via separate mechanisms. The results are discussed in the context of theories of perceptual experience and athletic pacing.

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Walking and cycling are considered very important behaviours in public health. This thesis is a study of the measurement of walking, cycling and overall travel behaviour. In the first part I present a systematic review of studies comparing Global Positioning System (GPS) measured travel to self-report. I found 12 results from eight eligible studies. All studies showed self-reported journey times were greater than GPS measured times. The differences ranged from over-reporting of +2.2 to +13.5 minutes per journey. In the second part of this thesis, I describe the development of a feasible, valid and reliable method for measuring travel with automated wearable cameras (SenseCam) through field testing and two pilot studies. I compared my new method to direct observation (considered a criterion measure) and found very good agreement and reliability (inter-rater, intra-rater and inter-measure). I also present an ethical framework for the measurement of health-related behaviours using automated wearable cameras. In the third part of the thesis, I report findings from an experiment designed to assess a well known UK travel diary (The National Travel Survey). Across four locations (Oxford, UK; Romford, UK; San Diego, USA; and Auckland, New Zealand) I collected 3-4 days of SenseCam and travel diary data from n=84 participants (convenience sample). Compliance with the collection protocol was high and inspection of the crude results suggests relative agreement between measures. Analysis of matched pairs of measurements (n=1,127 journeys) suggests a significant positive bias on self-reported durations (2:08 minutes; 95% CI = 1:48 to 2:28; 95% limits-of-agreement = -9:10 to 13:26). These results suggest self-reported journey exposure is valid at a population level, though corrections according to my reported bias could be considered. The large limits of agreement on duration estimates suggest self-report may be unsuitable for assessment of individual travel behaviour.

La surveillance de l’activité physique et des comportements sédentaires, et la question de leur mesure, sont primordiales dans un contexte où les sociétés modernes favorisent l’augmentation de l’incidence de nombreuses maladies associées à un mode de vie sédentaire. Objectif : L’objectif de cette thèse était d’approfondir les connaissances sur la surveillance et la mesure de l’activité physique et des comportements sédentaires. Méthodes : Quatre études ont été réalisées. Deux travaux analysent et discutent le système français de surveillance de l’activité physique et des comportements sédentaires des adultes et des jeunes. Une étude teste les propriétés psychométriques du questionnaire mondial sur la pratique d’activités physiques (GPAQ). Enfin, une revue de la littérature analyse le contenu des questionnaires disponibles pour mesurer les comportements sédentaires. Résultats : Les deux études portant sur la surveillance observent un manque d’homogénéité et de constance dans le choix des outils de mesure qui limite le suivi de l’évolution des pratiques. L’étude sur le GPAQ révèle des résultats, en termes de reproductibilité et de validité, similaires aux valeurs habituellement observées. Enfin, la revue de littérature a mis en évidence que les questionnaires mesurant les comportements sédentaires présentent des différences en termes de population cible, période de rappel, nombre d’item, et caractéristiques des comportements sédentaires mesurés. Conclusion : Des recommandations ont été formulées afin d’améliorer la mesure et la surveillance de l’activité physique et des comportements sédentaires en France / Physical activity and sedentary behaviors are major health determinants and are being surveyed worldwide. Objective: The aim of this thesis was to contribute to the surveillance and measurement of physical activity and sedentary behaviors. Method: This thesis includes four studies. The first study analyzes and discusses the present situation of French national surveillance studies. The second study presents the results from the first French report card on physical activity for children and adolescents. The third study discusses the validity and reliability properties of the French version of the Global Physical Activity Questionnaire (GPAQ). The fourth study examines the content of questionnaires measuring sedentary behaviors. Results: Studies 1 and 2 reported measurement issues impairing the overall data quality, inter-study comparisons and survey of changes over time. The study of GPAQ reported limited but acceptable reliability and validity for the measurement of physical activity and sedentary time in France. Finally, the systematic review on sedentary behaviors questionnaires reported large differences in the population targeted (ex: adults, youth, elderly), recall frame (ex: previous day, last 7 days, last month), the number of item (from 1 to more than 100), and the sedentary behaviors characteristics measured (from only sitting time to up to 27 sedentary behaviors). Conclusion: The work realized during this thesis allows the formulation of recommendations to improve the surveillance of physical activity and sedentary behaviors in France