The global intent of this research was to confirm the validity of the interpolated twitch technique (ITT) to voluntary torque model (first study) and then to utilize this technique in developing definitive criterion measures enhancing the study of training strategies on central fatigue (second study) and velocity specific (third study) voluntary activation (VA) and force production outcomes. The first study assessed the contribution of non-stimulated synergists to the non-linearity of the ITT voluntary torque relationship for elbow flexion contraction. Since multiple synergist stimulation was found not to significantly improve the ITT to voluntary torque relationship, follow-up pilot work was conducted in which the quadriceps femoris was identified as a valid ITT test model muscle. The first training study investigated the effects of high volume, maximum voluntary isometric contraction (MVIC) resistance training of the quadriceps femoris on MVIC levels of force and VA prior to, during, and recovery from a standardized fatigue test protocol. Results showed significant increases in pre-fatigue MVIC VA and force, increases in resistance to early fatigue, but also increased overall rate of fatigue resulting in non-significant changes in total force volume and endurance time. Post-fatigue analysis showed significant training increases in rate and level of recovery for both MVIC VA and force production. The second training study investigated the effects of high resistance ramp versus ballistic type MVIC strength training of the quadriceps femoris on central adaptations in submaximal and maximal levels of MVIC VA and force production. Results showed similar ramp and ballistic group training increases in MVIC force and VA on both ramp and ballistic tests. Ballistic group, ballistic test change scores were significant but not for the ramp test, suggesting ballistic group test-training specificity. The ballistic group showed significant force increases on the submaximal 150ms ballistic test, while the ramp group showed non-significant training changes, further supporting test-training specificity for the ballistic group. Results support utility of the ITT and provide valuable information with regard to training and test-training specificity considerations.

Caffeine consistently enhances endurance performance in temperate environmental conditions, while far less research has examined its ergogenic and physiological effects during prolonged exercise in the heat. Despite the performance benefit of an acute caffeine doses being less pronounced in regular caffeine users versus those not habituated to the drug, few studies have examined the influence of a prolonged period of controlled caffeine intake on endurance performance. The endogenous trace amine octopamine is purported to possess stimulant-like properties and influence fat metabolism, although no study has examined these effects in humans. The aim of this thesis was to further characterise the performance and physiological effects of caffeine during prolonged exercise, while elucidating a potential ergogenic role for octopamine. The first two studies investigated the ergogenic and thermoregulatory effects of low to moderate caffeine doses during prolonged cycle exercise in the heat. Chapter 4 demonstrated that 3 mg kg-1 caffeine, administered either as a single or split-dose (2 x 1.5 mg kg-1) before exercise, improved endurance performance without influencing thermoregulation during prolonged exercise at a fixed work-rate. Dividing the caffeine bolus appeared to confer an additional performance benefit, suggesting repeated low dose may potentiate the efficiency of the same total caffeine dose under these conditions. Chapter 5 demonstrated that a 6 mg kg-1 caffeine dose improved endurance cycle performance without differentially influencing thermoregulation than placebo. The level of habituation to caffeine influences the ergogenic effect of an acute dose, yet previous studies have employed sub-chronic supplementation protocols. Chapter 6 investigated the effect of a twenty-eight day supplementation period on endurance cycle performance. Habituation to caffeine attenuated the ergogenic effect of an acute caffeine dose, without any change in circulating caffeine, substrate oxidation or hormonal concentrations. In chapter 7 the performance and metabolic effects of octopamine was investigated. Octopamine supplementation did not influence performance, hormonal concentrations or substrate oxidation, likely due to low serum concentrations of the drug.

O objetivo do presente estudo foi analisar os efeitos da execução prévia de exercício físico e cognitivo sobre os componentes central e periférico da fadiga neuromuscular durante um teste contrarrelógio de 4 km de ciclismo. Para tanto, oito ciclistas treinados (n = 8) participaram de três diferentes estudos. No estudo 1, os atletas realizaram o teste contrarrelógio após assistir documentário (CON) ou após tarefa cognitiva (TC). No estudo 2, o teste de 4 km de ciclismo foi realizado após 100 drop jumps (DJ), 48 horas após 100 drop jumps (48h-DJ) e sem a realização prévia de exercício (CON). No estudo 3, o teste contrarrelógio foi realizado após fadiga prévia de membros superiores (FB) e inferiores (FP) e sem fadiga prévia (CON). Em todos os estudos, parâmetros de fadiga central e periférica foram avaliados por meio da técnica de estimulação elétrica no nervo femoral em repouso, pré e pós 4km de ciclismo. Estudo 1: O desempenho foi similar (P> 0,05) entre CON (376 ± 26,9 s) e TC (376,3 ± 26 s). Do mesmo modo, não encontramos diferenças significativas (P> 0,05) para parâmetros de fadiga central e periférica entre CON e TC. Estudo 2. O desempenho foi significativamente (P< 0,05) prejudicado em DJ (-2,3%) e houve uma tendência em 48h-DJ (-1,8%). A redução no desempenho em 48h-DJ foi devido à menor potência na parte inicial da prova (P< 0,05). Em DJ a piora no desempenho foi em decorrência de menor potência (P< 0,05) na parte inicial e final da prova. Houve uma exacerbada (P< 0,05) fadiga periférica após o contrarrelógio em DJ (1Hzpot= -44,7%) comparado com CON (1Hzpot= -20,1%). Além disso, significante fadiga de baixa frequência foi observada em DJ comparado com CON. Por outro lado, parâmetros de fadiga central e periférica apresentaram valores similares entre CON e 48h-DJ (P> 0,05). No entanto, foi encontrado aumento significativo (P< 0,05) na dor muscular tardia em 48hDJ comparado com CON e DJ. Estudo 3: O desempenho foi reduzido em FP (-2,3%) e FB (-1,5%) quando comparado com CON. O menor desempenho nas condições FP e FB foi acompanhado por redução na potência (P< 0,05) na parte inicial (condição FP) e na parte final (condições FP e FB) a prova. Ao final dos 4 km de ciclismo, os participantes apresentaram menor (P< 0,05) fadiga periférica em FB (1Hzpot= -11,9%) comparado com CON (1Hzpot= -20,1%). Em FP, houve maior fadiga periférica em comparação a condição CON e FB. Em conclusão, os resultados destes estudos sugerem que apenas a execução prévia de exercício envolvendo a musculatura utilizada no ciclismo promove alterações nos componentes periféricos da fadiga neuromuscular após 4 km de ciclismo / The aim of this study was to analyze the effects of previous execution of physical exercise and cognitive on the central and peripheral components of the neuromuscular fatigue during a 4 km cycling time trial. Eight trained cyclists (n = 8) participated of three different studies. In study 1, the athletes performed the 4 km cycling time trial test after watching a documentary (CON) or after a cognitive task (CT). In study 2, the 4-km cycling test was performed after 100 drop jumps (DJ), 48 hours after 100 drop jumps (48h-DJ) and without previous exercise (CON). In study 3, the time trial was performed after pre-fatigue of the upper (FU) and lower (FL) body and without prefatigue (CON). In all studies, central and peripheral fatigue parameters were evaluated via electrical stimulation in femoral nerve at rest, before and after 4km cycling. Study 1: Performance was similar (P> 0.05) between CON (376 ± 26.9 s) and TC (376.3 ± 26 s). Likewise, we found no significant differences (P> 0.05) for parameters of central and peripheral fatigue between CON and CT. Study 2: Performance was significantly (P< 0.05) impaired in DJ (-2.3%) and there was a trend in 48h-DJ (-1.8%). This reduction in performance in 48h-DJ was due to a lower power at first part of the time trial (P< 0.05). In DJ condition, loss in performance was due to lower power (P< 0.05) at the start and end phases of the test. There was exacerbated (P <0.05) peripheral fatigue after the time trial in DJ (1Hzpot = -44.7%) compared to CON (1Hzpot = 20.1%). Furthermore, a significant low frequency fatigue was observed in DJ compared to CON. On the other hand, central and peripheral fatigue parameters showed similar values between CON and 48h-DJ (P> 0.05). However, a significant increase in delayed onset muscle soreness was found in 48h-DJ than CON and DJ. Study 3: Performance was reduced in FU (-2.3%) and FL (-1.5%) compared to CON. The lowest performance was accompanied by a reduction in power (P< 0.05) in the initial (FL) and final (FL and FU phases of the time trial. After 4 km cycling, participants had a lower (P< 0.05) peripheral fatigue in FU (1Hzpot = -11.9%) compared with CON (1Hzpot = -20.1%). In FL, there was a greater peripheral fatigue compared to CON and FB condition. In conclusion, the results of these studies suggest that only the previous execution of exercise involving the muscles used in cycling causes changes in the peripheral components of the neuromuscular fatigue after 4 km of cycling

The reticular-activating hypofrontality model of acute exercise (RAH) predicts exercise-induced hypoactivity in frontal cortex which mediates executive function. Connors Continuous Performance Test (CCPT) was used to investigate changes in executive function during- and post treadmill running in healthy volunteers (n=30, 15 male). In a randomized order, subjects performed the CCPT at rest, during low- (LI; 63% maximal heart rate; MHR) and moderate intensity (MI; 75% MHR). Separately, subjects then performed isocalorifically matched exercise bouts of LI, MI and high intensity interval training (HIT) consisting of 4x4 min with 90% MHR and 3 min recovery at 60-70% MHR. Repeated measures ANOVAs revealed main effects of exercise intensity for reaction time RT during- (p≤0.001) and post exercise (p≤0.0001). Subsequent analyses showed an overall increase of RT during exercise compared to rest (p≤0.005). RT decreased significantly from rest to post exercise levels in an exercise intensity dependent, linear fashion (p≤0.0001). Commission errors showed a non significant linear trend to increase both during (p=0.057), and post exercise (p=0.052) as a function of intensity. In a follow up study, we sought to relate observed exercise effects to frontal cortex activity through the use of transcranial direct current stimulation (tDCS) (n=4) and transcranial magnetic stimulation (TMS) over the dorsolateral prefrontal cortex (DLPFC). Prior to TMS stimulation cortical excitability was estimated post running through motor-evoked potentials (MEP) elicited from the primary motor cortex (M1) induced by single burst TMS and measured in the first dorsal interosseous (FDI) muscle using electromyography. At rest, inhibitory cathodal tDCS with left DLPFC cathode and right supraorbital anode led to improved reaction time and increased amount of commission errors, whereas anodal stimulatory tDCS in the immediate post exercise period was unable to recover the post exercise effect. Continuous theta burst stimulation over the left DLPFC post running further impaired inhibitory control and facilitated reaction time. Different findings during- and after- exercise suggests that potential contributing mechanisms such as computational and metabolic factors may be differentially active during these respective conditions. Furthermore, the fact that an inhibitory TMS protocol pronounced the post running effects even more and that we were able to mimic the reported RAH effects at rest with inhibitory frontal tDCS, but observed different patterns during exercise, suggests that the latter state cannot be fully explained by reducing activity in the left frontal cortex alone. Failure to modify the after exercise effect with stimulatory tDCS also supports an interplay of different factors and might emphasize the strong, robust effects of exercise that cannot simply be attenuated by current application. Increases in MEP post running for 35min paired with the observed performance decrements imply an excited state of M1 and might serve as an explanatory cross-link to central fatigue suggesting that a hypofrontal state might enhance the motor cortical drive to activate muscles.

Resumo: O objetivo principal desta tese foi investigar a causa e a conseqüência da fadiga em countermovement jumps realizados em diferentes razões de esforço e pausa. Esses objetivos foram testados utilizando dois estudos experimentais. O primeiro estudo comparou as causas da fadiga em protocolos de fadiga de curta (=10 min) e longa duração (=20 min), manipulando as durações da pausa entre countermovement jumps. Os resultados indicaram que, após a realização do protocolo de fadiga de curta duração, houve redução da contração isométrica voluntária máxima para extensão do joelho acompanhada por fadiga central e periférica. Por outro lado, após a realização do protocolo de fadiga de longa duração, a redução da contração isométrica voluntária máxima para extensão do joelho foi associada apenas à fadiga periférica. No segundo estudo foi utilizado um protocolo de fadiga para o sistema neuromuscular similar ao primeiro estudo, tendo como objetivo investigar o padrão de movimento sob fadiga. O tempo e a seqüência da relação inter-segmental do movimento e da ativação muscular permaneceram inalteradas sob a condição de fadiga. Entretanto, alguns ajustes no controle de countermovement jumps realizados sob a condição de fadiga foram observados, provavelmente na tentativa de manter a altura do salto vertical. Entre alguns ajustes, é possível destacar um aumento na flexão das articulações e na duração do salto vertical. Esses resultados foram similares independentemente da razão de esforço e pausa utilizada para induzir fadiga em countermovement jumps. Considerando ambos os estudos experimentais, os resultados da presente tese sugerem que a causa da fadiga em countermovement jumps é tarefa-dependente. Isso significa que dependendo do protocolo de indução de fadiga utilizado, a causa da fadiga pode ser alterada de central para periférica, por exemplo... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This thesis explored the cause of fatigue in countermovement jump performed under different intensities and its influence upon movement pattern. These aims were tested using two experimental studies. The first one aimed to compare the causes of fatigue development during a short- (=10 min) and a long-term (=20 min) countermovement jump protocols through the manipulation of resting interval. The results indicated that after short-term fatigue protocol, maximal voluntary isometric contraction reduction was accompanied by central and peripheral fatigue. On the other hand, after long-term fatigue protocol, maximal voluntary isometric contraction reduction was accompanied by peripheral fatigue. The second study used similar exercise protocol to induce fatigue on neuromuscular system. It was aimed to investigate the movement pattern of countermovement jump throughout fatigue exercise protocols. The timing and sequencing of inter-segmental movement and of muscle activation remained relatively unaltered under fatigue. However, in order to sustain required jump height, few adjustments were performed on control and on coordination of fatigued jumps, such as increased joint flexion and earlier initiation of joint extension. This result was quite similar irrespective of fatigue-induced exercise intensities. Considering both experimental studies, the results of present thesis suggest that the cause of fatigue in countermovement jump is task-dependent in which depends on what fatigue protocol is used, thereby the cause of fatigue can move from one site to another. Even with the neuromuscular system impaired, there was not change on the movement pattern of countermovement jump, irrespective of exercise duration and cause of fatigue. However, adjustments on control and coordination of countermovement jump were performed in order to compensate the force loss and to maintain the targeted jump height. / Orientador: Eduardo Kokubun / Coorientador: José Angelo Barela / Banca: André Luiz Félix Rodacki / Banca: Ana Maria Forti Barela / Banca: Carlos Ugrinowistch / Doutor

Cette thèse porte sur l’étude des mécanismes de régulation du niveau de fatigue périphérique à l’exercice et sur les conséquences de cette régulation sur la capacité de performance motrice. Nous avons tout d’abord démontré que la puissance est étroitement régulée au cours de sprints répétés – épreuve au cours de laquelle la commande motrice est recrutée à son niveau maximal volontaire – de sorte qu’un seuil critique de fatigue périphérique ne soit jamais dépassé. Nous avons ensuite montré qu’il existe un lien étroit entre l’atteinte de ce seuil critique de fatigue et l’arrivée à une phase de plateau de puissance développée au cours de sprints répétés, indépendamment de la durée de la récupération entre les sprints. Ces résultats ont permis de démontrer que le niveau d'activité de la commande motrice centrale et la puissance sont régulés au cours de sprints répétés dans le but de limiter le niveau de fatigue périphérique à un niveau seuil. Le rôle de ce mécanisme régulateur est cependant dépendant de la nature de la tâche. Nous avons en effet montré que l’arrêt de l’effort d’un exercice de squat isométrique, conduit jusqu'à épuisement, est associé à une défaillance de l’activation centrale volontaire, qui précède l'atteinte du seuil critique de fatigue. Enfin, l'application de ces données et concepts théoriques à l'exercice réalisé sur une plateforme à instabilité servo-assistée (imoove) a permis de montrer que ce type d’outil permet un recrutement accru des muscles posturaux et de l’équilibre comparé à un exercice réalisé sur une surface stable, sans compromettre la fatigue et le recrutement des muscles locomoteurs, déterminants des adaptations positives à l'entraînement. / This doctorate thesis focused on the mechanisms involved in the control of peripheral fatigue during exercise and on the consequences of this regulation on exercise tolerance. We first demonstrated that performance during repeated sprints – a trial during which the central motor drive is activated at its maximal voluntary level – is tightly regulated to avoid the development of peripheral fatigue beyond a critical threshold. We then showed that the attainment of the plateau phase of performance, characterized by a constant power output until the last sprint, was closely linked to the attainment of the critical threshold of peripheral fatigue, independently of the recovery duration between sprints. These firsts results demonstrated that central motor drive and power output are regulated during repeated sprints in order to limit the development of peripheral fatigue beyond a critical threshold. However, the role of this regulatory mechanism is task-dependent. Indeed, we showed that time to task failure during the first repetitions of a sustained submaximal isometric contraction is likely associated with failure in central activation of motor units, which precede the attainment of the critical threshold of peripheral fatigue. We then developed applied research protocols on imoove, a servo-assisted instability device for training composed by a board that can move in the three-dimensional plans. Because greater trunk and ankle muscles activity was achieved in imoove without compromising lower limb muscles activity and fatigue, this device may provide sufficient muscle overload to simultaneously develop locomotor, postural and balance muscles.

Made available in DSpace on 2014-06-11T19:30:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-07-26Bitstream added on 2014-06-13T19:19:34Z : No. of bitstreams: 1 pereira_g_dr_rcla.pdf: 601547 bytes, checksum: 78fe39c887efbb78c46303cff6e30a46 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O objetivo principal desta tese foi investigar a causa e a conseqüência da fadiga em countermovement jumps realizados em diferentes razões de esforço e pausa. Esses objetivos foram testados utilizando dois estudos experimentais. O primeiro estudo comparou as causas da fadiga em protocolos de fadiga de curta (=10 min) e longa duração (=20 min), manipulando as durações da pausa entre countermovement jumps. Os resultados indicaram que, após a realização do protocolo de fadiga de curta duração, houve redução da contração isométrica voluntária máxima para extensão do joelho acompanhada por fadiga central e periférica. Por outro lado, após a realização do protocolo de fadiga de longa duração, a redução da contração isométrica voluntária máxima para extensão do joelho foi associada apenas à fadiga periférica. No segundo estudo foi utilizado um protocolo de fadiga para o sistema neuromuscular similar ao primeiro estudo, tendo como objetivo investigar o padrão de movimento sob fadiga. O tempo e a seqüência da relação inter-segmental do movimento e da ativação muscular permaneceram inalteradas sob a condição de fadiga. Entretanto, alguns ajustes no controle de countermovement jumps realizados sob a condição de fadiga foram observados, provavelmente na tentativa de manter a altura do salto vertical. Entre alguns ajustes, é possível destacar um aumento na flexão das articulações e na duração do salto vertical. Esses resultados foram similares independentemente da razão de esforço e pausa utilizada para induzir fadiga em countermovement jumps. Considerando ambos os estudos experimentais, os resultados da presente tese sugerem que a causa da fadiga em countermovement jumps é tarefa-dependente. Isso significa que dependendo do protocolo de indução de fadiga utilizado, a causa da fadiga pode ser alterada de central para periférica, por exemplo... / This thesis explored the cause of fatigue in countermovement jump performed under different intensities and its influence upon movement pattern. These aims were tested using two experimental studies. The first one aimed to compare the causes of fatigue development during a short- (=10 min) and a long-term (=20 min) countermovement jump protocols through the manipulation of resting interval. The results indicated that after short-term fatigue protocol, maximal voluntary isometric contraction reduction was accompanied by central and peripheral fatigue. On the other hand, after long-term fatigue protocol, maximal voluntary isometric contraction reduction was accompanied by peripheral fatigue. The second study used similar exercise protocol to induce fatigue on neuromuscular system. It was aimed to investigate the movement pattern of countermovement jump throughout fatigue exercise protocols. The timing and sequencing of inter-segmental movement and of muscle activation remained relatively unaltered under fatigue. However, in order to sustain required jump height, few adjustments were performed on control and on coordination of fatigued jumps, such as increased joint flexion and earlier initiation of joint extension. This result was quite similar irrespective of fatigue-induced exercise intensities. Considering both experimental studies, the results of present thesis suggest that the cause of fatigue in countermovement jump is task-dependent in which depends on what fatigue protocol is used, thereby the cause of fatigue can move from one site to another. Even with the neuromuscular system impaired, there was not change on the movement pattern of countermovement jump, irrespective of exercise duration and cause of fatigue. However, adjustments on control and coordination of countermovement jump were performed in order to compensate the force loss and to maintain the targeted jump height.

Les objectifs de ce travail de thèse étaient d’évaluer les effets des différences (i) de niveau de force, en utilisant différents groupes et longueurs musculaires, et (ii) de profil métabolique entre enfants pré-pubères et adultes sur les différences de développement et d’origine de la fatigue neuromusculaire, ainsi que (iii) d’accroître nos connaissances sur les mécanismes de la fatigue neuromusculaire chez l’enfant pré-pubère. Les résultats de ce travail montrent que les différences de niveau de force pourraient être un facteur expliquant les différences de développement et d’origine de la fatigue neuromusculaire entre enfants et adultes. Toutefois, ce facteur n’est pas suffisant pour expliquer toutes les différences de fatigue entre ces deux populations. En effet, nos résultats soulignent aussi que les différences de profil métabolique pourraient être impliquées de façon importante dans les différences de développement et d’origine de la fatigue neuromusculaire entre enfants et adultes. Par ailleurs, les résultats de nos études rapportent que les enfants présentent généralement une fatigue périphérique plus faible par rapport aux adultes au profit d’une fatigue centrale plus importante suite à un protocole de fatigue maximal intermittent. Cette moindre fatigue périphérique est associée à une moindre altération des propriétés contractiles et du couplage excitation-contraction, et à une meilleure adaptation de l’oxygénation musculaire chez l’enfant pré-pubère. Nos résultats semblent suggérer que la fatigue spinale ne permettrait pas d’expliquer les différences de fatigue centrale entre enfants et adultes et donc que la fatigue centrale plus importante des enfants pourrait être attribuée à une fatigue supra-spinale plus élevée. / The aims of this PhD thesis were to evaluate the effects of differences of (i) force level, throughout different muscle groups and muscle lengths, and (ii) metabolic profile on the differences of development and etiology of the neuromuscular fatigue between prepubertal children and adults, as well as (iii) to improve our knowledge of the mechanisms of neuromuscular fatigue in children. The results of this PhD thesis showed that force level differences could be a factor underpinning the differences in the development and etiology of neuromuscular fatigue between children and adults. However, this factor cannot fully account for differences in fatigue between both populations. Indeed, our results also highlighted that metabolic profile differences could explain the difference of development and etiology of neuromuscular fatigue between children and adults. Additionally, the results of this thesis showed that children exhibit lower peripheral fatigue and greater central fatigue than adults after an intermittent maximal exercise. This lower peripheral fatigue was associated with a lower alteration of the contractile properties and excitation-contraction coupling, and a better adaptation of the muscle oxygenation in prepubertal children. Our results suggest that spinal fatigue could not explained the differences in central fatigue between children and adults, and that the greater central fatigue in children could be attributed to a greater supra-spinal fatigue.

A presente tese investigou o efeito da ingestão de cafeína no desempenho no ciclismo, no recrutamento muscular, na contribuição energética, no lactato sanguíneo, nas respostas fisiológicas e perceptivas e no desenvolvimento de fadiga central e periférica em diferentes modelos de exercício aeróbio de alta intensidade. Nove ciclistas do sexo masculino (32,3 ± 6,0 anos de idade, 79,3 ± 6,8 kg, 181,2 ± 7,9 cm e VO2máx 55,2 ± 5,7 mL.kg-1.min-1) completaram 11 sessões experimentais. Os participantes foram submetidos a testes contrarrelógio de 4.000 m, testes com carga constante até a exaustão realizados na potência média do contrarrelógio (313 ± 41 W e 100 ± 10 rpm), e ainda testes com carga constante com tempo fixo correspondente a 60% do tempo sustentado no teste de carga constante até a exaustão (237,2 ± 56,0 s). Os participantes ingeriram cápsulas contendo placebo ou cafeína (5 mg.kg-1 de massa corporal) 60 minutos antes da realização dos testes, em ordem contrabalançada e em um modelo duplo-cego. Respostas cardiorrespiratórias e perceptivas foram mensuradas durante os testes. Lactato sanguíneo foi coletado antes e após o exercício. Avaliações neuromusculares foram realizadas através de estimulação elétrica no nervo femoral nos momentos Baseline (previamente à ingestão da cápsula), Pré-EX (uma hora após a ingestão, antes do exercício), e Pós-EX (2 min após o exercício). A ingestão de 5 mg.kg-1 de cafeína melhorou o desempenho no teste contrarrelógio de 4.000 m de ciclismo (-6,9 ± 7,4 s; p = 0,024), devido a um aumento na contribuição anaeróbia. O desempenho no teste com carga constante até a exaustão também foi melhor após a ingestão de cafeína (+134,3 ± 81,5 s; p = 0,001), mas neste caso acompanhado por maior contribuição aeróbia. A ingestão de cafeína previamente a realização do exercício proporcionou efeito ergogênico no teste contrarrelógio de 4.000 m e no teste de carga constante até a exaustão, sem alterar o limiar de fadiga periférica. Entre os componentes periféricos avaliados, a taxa máxima de desenvolvimento de força reduziu significativamente menos após o teste de carga constante até a exaustão na condição cafeína, mesmo como o tempo de exercício prolongado, e também reduziu significativamente menos após o teste de carga constante e tempo fixo, o que sugere que a cafeína pode ter alterado o processo acoplamento excitação-contração, o que resultou em atraso da fadiga periférica. Além disso, no teste com carga constante até a exaustão, a disposição e a sensação de prazer foram maiores após a ingestão de cafeína, sugerindo que neste modelo de exercício estas variáveis perceptivas também podem ter contribuído para o efeito ergogênico da cafeína observado no desempenho. Em conclusão, este estudo demonstrou que a cafeína melhorara o desempenho no ciclismo em ambos os modelos de exercício aeróbio de alta intensidade, sendo no contrarrelógio devido ao aumento da quantidade total de energia anaeróbia e no carga constante até a exaustão nas variáveis perceptíveis e alteração no acoplamento excitação-contração, sem alterar o limiar de fadiga periférica / The present thesis investigated the effect of caffeine on cycling performance, muscle recruitment, energetic contribution, blood lactate, physiological and perceptual responses and the development of central and peripheral fatigue in different models of high-intensity aerobic exercises. Nine male cyclists (32.3 ± 6.0 years old, 79.3 ± 6.8 kg, 181.2 ± 7.9 cm and VO2max 55.2 ± 5.7 mL.kg-1.min-1) completed 11 experimental sessions. The participants performed 4,000 m cycling time trial, constant-load to exhaustion in the average power output of the time trial (313 ± 41 W and 100 ± 10 rpm), and also performed constant-load with fixedtime corresponding to 60% of the time sustained in the constant-load to exhaustion (237.2 ± 56.0 s). Participants ingested capsules containing placebo or caffeine (5 mg.kg-1 body weight) 60 minutes prior to the tests, in a counterbalanced order and in a double-blind model. Cardiorespiratory and perceptual responses were measured during the tests. Blood lactate was collected before and after exercises. Neuromuscular assessments were performed via electrical femoral nerve stimulation at Baseline (prior to capsule ingestion), Pre-EX (one hour after capsules ingestion, before exercise), and Post-EX (2 min after exercise). 5 mg.kg-1 of caffeine improved their performance in the 4,000 m cycling time trial (-6.9 ± 7.4 s; p = 0.024), due to an increase in anaerobic contribution. The performance in the constant-load to exhaustion was also enhanced after caffeine intake (+134.3 ± 81.5 s; p = 0.001), but in this case accompanied by greater aerobic contribution. Caffeine intake prior to cycling performance provided an ergogenic effect in the 4,000 m time trial and in the constant-load to exhaustion, without altering the critical threshold of peripheral fatigue. Among the peripheral components evaluated, the maximum rate of force development significantly reduced less after the constant-load to exhaustion in the caffeine condition, even as the prolonged exercise time, and also reduced significantly less after the constant-load with fixed-time, which suggests that caffeine may have altered the excitation-contraction coupling, which resulted in delayed peripheral fatigue. In addition, during the constant-load to exhaustion test, the felt arousal and feeling were higher after the caffeine, suggesting that in this exercise model these perceptions may also have contributed to the observed ergogenic effect of caffeine on the cycling. In conclusion, this study demonstrated that caffeine improved the cycling performance in both models of high-intensity aerobic exercise, being in the time-trial due to the increase of the total amount of anaerobic energy and the constant load until the exhaustion due to alteration in the perceptible variables and in the excitation-contraction coupling, without change the peripheral fatigue threshold

L’objectif général de ce travail doctoral était de comparer les effets de la fatigue musculaire des quadriceps femoris après un exercice musculaire volontaire (VOL) et un exercice musculaire électroinduit (ES) sur le contrôle postural bipodal, ainsi que sur la fatigue centrale. Les résultats montrent qu’à l’issue d’une tâche fatigante unilatérale ou bilatérale, l’exercice ES dégrade davantage la force usculaire que l’exercice VOL. Cependant, le contrôle postural bipodal est indifféremment perturbépar les deux exercices. En outre, les vitesses de récupération des capacités posturales et de force musculaire ne diffèrent pas à l’issue des exercices. Par ailleurs, l'exercice VOL altère davantage la commande centrale que l'exercice ES (immédiatement à l’issue de l’effort), tandis que celui-ci retarde l’apparition de la fatigue centrale et la maintient plus longuement. Etant donné que l'exercice VOL estinduit par la commande centrale et que l'exercice ES est généré par une stimulation artificielle externe, on peut émettre l’hypothèse que l'exercice VOL produit essentiellement une fatigue supraspinale, tandis que l'exercice ES engendre surtout une fatigue spinale. / The overall objective of this thesis was to compare the effect of fatigue of the quadriceps femoris after fatiguing voluntary contractions (VOL) and fatiguing neuromuscular electrical stimulation (ES) on bipedal postural control, and central fatigue. The results show that after unilateral or bilateral muscle fatigue, the ES exercise affected the muscle strength more than the VOL exercise. However, bipedal postural control was similarly deteriorated for both exercises. Moreover, the recovery speeds of postural control and muscle strength abilities did not differ for the both exercises. In addition, the VOL exercise alters central drive quicker than the ES exercise immediately after their completion while the ES exercise delays and prolongs the central fatigue. As the VOL exercise is induced by central command and the ES exercise is generated by artificial external stimulation, one can hypothesize that the VOL exercise especially produces supraspinal fatigue, while the ES exercise especially engenders spinal fatigue.