The aim of this thesis was to directly test the key underpinnings of recent propositions for systems of central control of exercise regulation. Fatigue and exercise tolerance have traditionally been explained through peripheral mechanisms, such as excitation-contraction coupling failure and the inability to supply sufficient metabolic substrate to contracting muscle in order to meet increasing energy demand. More recently, models of central control, which are proposed to regulate exercise intensity in an anticipatory/feedforward manner, with the ultimate aim of avoiding physiological ‘catastrophe’, have received a great deal of attention. This thesis investigated several of the key requirements and mechanisms stated in these models. The central governor model (CGM) and teleoanticipation are stated to use a combination of prior experience and distance knowledge of an exercise bout to work in a feedforward manner, so that a pacing strategy is set before exercise commences which ensures the bout is completed in an optimum time but in the absence of premature fatigue. Study one examined the influence of distance knowledge, prior experience and distance feedback on the setting and regulation of a pacing strategy in 4 km time trial (TT) cycling in trained cyclists (n = 18). When performing 4 × 4 km TT intervals, it was found that prior experience of the exercise (in the absence of distance feedback and distance knowledge) allowed the creation of a pacing strategy that produced a performance which was as competitive as cyclists who were provided with prior experience, distance knowledge and distance feedback. The difference in TT completion time between groups (CON = feedback group, EXP = no feedback group) was reduced with subsequent TT (CON TT1 367 ± 21 s; EXP TT1 409 ± 45 s; CON TT2 373 ± 19 s; EXP TT2 389 ± 30 s; CON TT3 375 ± 18 s; EXP TT3 383 ± 26 s; CON TT4 373 ± 20 s; EXP TT4 373 ± 14 s), so that by the final TT, completion time between groups was almost exactly the same. It was concluded that when sufficient prior experience is attained in the absence of distance knowledge and feedback, a successful pacing strategy can be set. In order for pacing to be set prior to an exercise bout and adjusted in a feedforward/anticipatory manner during exercise, an internal mechanism must exist which monitors the passage of time. Study two examined the accuracy and robustness of this ‘internal clock’ by assessing cyclist’s (n = 16) ability to gauge the distance they had cycled during repeated 4 km and 6 km TT. The internal clock was shown to be inaccurate to absolute measures of distance, but showed a calibration capacity following experience of a TT of unknown distance (24.6 ± 18.2 % error in distance judged completed vs. 8.2 ± 5.5 % error in distance judged completed). This process was fragile and occurred in the absence of any significant performance improvement. It was concluded that relative quantities appear more important in creating a pacing strategy, and that times are of greater importance than distances. Study three examined the influence of comparative performance feedback in a field setting in 4 km track TT cycling in trained cyclists (n = 5). Correct feedback produced a significantly faster TT time (t4 = -3.10, p < 0.05) than non-contingent feedback (341 ± 8 s vs. 350 ± 12 s), with differences in mean lap speed apparent between the conditions at the start of the TT (t4 = 4.71, p < 0.05) and at the end of the TT (t4= 3.45, p < 0.05; t4 = 3.30, p < 0.05). The study provided empirical support for the assumption that performance feedback is advantageous during exercise and provided insights into past and present exercise comparison and its role on the setting of a pacing strategy. A central component of the CGM and theories of central exercise regulation is the role of afferent feedback during exercise and the premature termination of exercise before a true maximum intensity has been reached. Study four used acetaminophen to blunt cyclists’ (n = 13) pain response during ten mile (16.1 km) TT in order to disrupt the afferent feedback processes. When using acetaminophen, cyclists produced significantly faster (t12 = 2.55, p < 0.05) TT completion times (1575 ± 96 s) than under a placebo condition (1605 ± 122 s). When using acetaminophen, cyclists had a higher power output during the middle section of the TT (F1, 12 = 4.79, p < 0.05), yet showed no significant difference in RPE (F1,12 = 0.72, p > 0.05) or pain scores (F1,12 = 0.30, p > 0.05). It was concluded that acetaminophen reduced levels of pain during the TT, thereby disrupting the comparative afferent feedback mechanism and allowing cyclists access to a ‘metabolic reserve’. The research presented has advanced our knowledge and supported propositions of models of central control and regulation during exercise. The research has provided further insight in the role of prior experience, distance knowledge, distance feedback, the internal clock, performance feedback and afferent feedback on the setting and maintenance of a pacing strategy in 4, 6 and 16.1 km TT cycling.

The Borg Rating of Perceived Exertion (RPE) scale is a primary tool for researchers and practitioners in exercise science to describe the intensity level subjects are experiencing when participating in exercise sessions. It has recently been suggested that RPE is not simply the direct result of interpretation of physiological changes as originally postulated, but is also influenced by affect, past experience, and time to completion, a concept coined as teleoanticipation. The purpose of this study was to determine the role of teleoanticipation in a sedentary population, by examining the effect unexpected increases in exercise duration on rating of perceived exertion and affect during low intensity treadmill walking. Based on the findings of prior studies, it is expected that the unexpected duration session will elicit higher RPE values and lower affect scores as measured by the feeling scale (FS) than the expected duration session. Ten participants between the ages of 18 and 45 years participated in the study. All participants were sedentary or insufficiently active with respect to physical activity for at least six months prior to the beginning of the study. Only participants with low to moderate risk according to the American College of Sports Medicine (ACSM) guidelines were admitted. All volunteers participated in one familiarization session followed by two trials of treadmill exercise. The familiarization trial was used to determine the treadmill speed in subsequent trials. All experimental trials were 30 minutes in length in partial accordance with ACSM guidelines, but the third trial in each group was presented as being 20 minutes and was extended to 30 minutes using a deception procedure employed in related research. Participants were informed at the 20-minute mark that the session would be extended to 30 minutes. Speed remained constant during both experimental trials. RPE and heart rate were recorded every minute to preclude volunteers from noticing the difference an increased interest in RPE responses around the 20-minute mark. Affect was measured by way of the feeling scale (FS) every other minute during the experimental trials. Blood pressure was recorded every five minutes to ensure participant safety. Results indicated a significant main effect for time for RPE (p = 0.001); however, there was no significant main effect for time and no interaction for RPE (p > 0.05) and no significant main effect and no interaction for FS. The primary finding from this investigation was that unexpected exercise durations have no affect on RPE or FS at low intensities in untrained, sedentary populations. Results suggest there may be a threshold of intensity required for a teleoanticipatory effect. More research is needed to further compare these effects with those of moderately and highly trained populations in medium or high intensity situations.

No description available.

The aim of this thesis was to investigate the extent of peripheral and central components in the development of fatigue during maximal exercise. Fatigue during maximal and supramaximal exercise has traditionally been modelled from the peripheral context of an inadequate capacity to supply metabolic substrate to the contracting muscles to meet the increased energy demand. However, there are a number of observations that are not compatible with the peripheral fatigue model but which support a reduced central drive during exercise acting to prevent organ failure that might occur should the work be continued at the same intensity. Candidates for the role of “exercise stopper” have been identified as mechanical forces, teleoanticipation, cardiovascular capacity and dyspnoea. We explored these various possibilities in order to determine the most likely cause of exercise cessation during high intensity exercise.The development of a plateau in oxygen consumption during maximal incremental exercise has traditionally been used as evidence that an oxygen deficiency in the exercising muscles causes the termination of exercise. However, the incidence of this “plateau phenomenon” depends largely on mode of exercise, testing protocol and sampling frequency. The aim of this study was to examine whether the development of the “plateau phenomenon” is an artefact of pedalling cadence. In the first study nine healthy individuals performed in random order a maximal incremental ramp test (0.5 W.s-1) on four occasions at a fixed cadence of 60, 80 or 100 rpm and at a self-selected cadence. Oxygen consumption (VO2), CO2 production (VCO2), minute ventilation (VE) and heart rate were measured throughout each trial and averaged over 30 s. Cadence was recorded every second. Neither VO2max nor peak power output were different between trials. Submaximum VO2, VCO2 and VE were not influenced by cadence. A plateau in oxygen consumption was observed in 14% of the trials. Cadence declined significantly towards the end of the self-selected cadence trial (p < 0.05). This ramp protocol produces a low incidence of the “plateau phenomenon” and the measured physiological variables are unaffected by cadence. Furthermore, only one subject displayed this phenomenon on more than one occasion. This confirms that the “plateau phenomenon” is an artefact of the testing protocol. The significant fall in cadence in anticipation of exercise termination during the self-selected cadence trial indicates the presence of a neural regulation, which would lead to a “plateau phenomenon” in those cycle tests in which the work rate is cadence-dependent.The purpose of the second study was to assess whether pacing strategies are adopted during supramaximal exercise bouts lasting longer than 30 s. Eight healthy males performed six Wingate Anaerobic Tests (WAnT). Subjects were informed that they were performing four 30 s WAnT and a 33 s and 36 s WAnT. However, they actually completed two trials of 30, 33 and 36 s each. Temporal feedback in the deception trials was manipulated so that subjects were unaware of the time discrepancy. Power output (PO) was determined from the angular displacement of the flywheel and averaged over 3 s. The peak power (PPI), mean power (MPI) and fatigue (FI) indices were calculated for each trial. Power output was similar for all trials up to 30 s. However, at 36 s the PO was significantly lower in the 36 s deception trial compared to the 36 s informed trial (392 ± 32 W vs 470 ± 88 W) (p < 0.001). The MPI was significantly lower in the 36 s trials (714 ± 76 W and 713 ± 78 W) compared to the 30 s trials (745 ± 65 W and 764 ± 82 W) although they were not different at 30 s (764 ± 83 W and 755 ± 79 W). The significant reduction in FI was greatest in the 36 s deception trial. In conclusion, the significant reduction in PO in the last six seconds of the 36 second deception trial, but not in the 36 second informed trial, indicates the presence of a pre-programmed 30 second “end point” based on the anticipated exercise duration from previous experience. Furthermore the similarity in pacing strategy in all informed trials suggests that the pacing strategy is centrally regulated and is independent of the total work to be performed.Athletes adopt a pacing strategy to delay fatigue and optimise athletic performance. However, many current theories of the regulation of muscle function during exercise do not adequately explain all observed features of such pacing strategies. We studied power output, oxygen consumption and muscle recruitment strategies during successive 4km cycling time trials to determine whether alterations in muscle recruitment by the central nervous system could explain the observed pacing strategies. Seven, highly trained cyclists performed three consecutive 4 km time trial intervals, each separated by 17 minutes. Subjects were instructed to perform each trial in the fastest time possible, but were given no feedback other than distance covered. Integrated electromyographic (iEMG) readings were measured at peak power output and for 90 s before the end of each trial. Subjects reach a VO2max in each interval. Time taken to complete the first and third intervals was similar. Peak power output was highest in the first interval but average power output, oxygen consumption, heart rate and postexercise plasma lactate concentrations were not different between intervals. Power output and iEMG activity rose similarly during the final 60 s in all intervals but were not different between trials. The similar pacing strategies in successive intervals and the parallel increase in iEMG and power output towards the end of each interval suggests that these pacing strategies could not have been controlled by peripheral mechanisms. Rather, these findings are compatible with the action of a centrally regulated that are recruited and de-recruited during exercise. The extent to which peripheral feedback influences recruitment patterns could not be determined from these experiments.The fourth study examined whether the supplementation of inspired air with a hyperoxic mixture results in a dose-dependent increase in peak work rate and maximal oxygen consumption (VO2max) during a ramp test to volitional exhaustion. To avoid the methodological disadvantages associated with breathing the gas mixtures from mixing bags, the trials were performed in a sealed chamber in which the oxygen fraction (FIO2) in the ambient air was altered and subjects were able to inhale directly from the environment. The three oxygen fractions in which the subjects exercised were 21% (room air), 35 or 60%. Arterial blood sampling occurred at rest and every 3 min during the trial. The blood was analysed for the partial pressure of oxygen (pO2), and carbon dioxide (pCO2); pH; oxygen saturation (sO2); haemoglobin saturation (O2Hb); and lactate concentrations. Expired gas and heart rate were measured continuously. Arterial sO2 and O2Hb were elevated in both hyperoxic conditions and did not fall throughout either trial. However in the normoxic trial sO2 and O2Hb declined over the duration of the trial. Lactate concentrations and pH were similar between all trials. VO2max was significantly higher with an FIO2 of 35 and 60% but was not different between hyperoxic conditions. Maximal ventilation (VEmax), carbon dioxide production (VCO2max) and heart rate were similar for all trials. Peak power output was increased in the trained athletes in the 60% FIO2 trial. Since the plateau phenomenon occurred infrequently in all trial (~9%) and the effect of hyperoxia on performance was less than the changes in blood oxygen carrying capacity, we conclude that hyperoxia improved exercise performance not solely by increasing oxygen delivery to the exercising muscles.In order to be able to directly compare the results from studies using different equipment it is important to know the interchangeability of the results from the machines. The fifth study tested the reliability and interchangeability of the two automated metabolic gas analyser systems that would be used in this series of studies at a range of submaximal workloads. Eight highly trained cyclists performed two incremental submaximal cycle ergometer tests. For each session either a Schiller CS-200 or a Vmax Series 229 automated gas analyser was used for expired gas analysis. Data for oxygen consumption (VO2), CO2 production (VCO2), minute ventilation (VE) and respiratory exchange ration (RER) were averaged for each of the five stages (200, 250, 275, 300 and 325 W). The VO2, VE and RER were similar between trials at all workloads. However, VCO2 was significantly lower in the Schiller trial at workloads above 200 W (p < 0.05). Although there was a significant correlation between the two automated systems for the measured parameters (VO2 = 0.78; VCO2 = 0.80; VE = 0.82; RER = 0.72) (p < 0.05), a Bland-Altman plot revealed that the limits of agreement between the two systems were unacceptably large (VO2 = 0.53 to 1.30 L.min-1; VCO2 = 0.55 to 0.64 L.min-1; VE = -22.3 to 30.3 L.min-1; RER = - 0.03 to 0.13). The co-efficient of variation within the analysers was insignificant for both systems. Both the systems provide reliable measures of expired gas parameters. However, care should be taken in directly comparing studies that have used the two different systems due to the poor agreement between the systems.The factors causing the termination of maximal exercise at sea level are unknown. A widely held view is that skeletal muscle anaerobiosis consequent to an inadequate oxygen delivery to the exercising muscles limits exercise. However, there is also evidence that respiratory muscle fatigue at the high ventilatory volumes achieved during maximal exercise delivery and respiratory muscle work on maximal exercise performance, we exercised 8 highly trained cyclists in a pressure-sealed chamber in which O2 concentrations were manipulated and helium (He) was substituted for nitrogen in the ambient air in order to reduce the work of breathing during exercise. This system ensured that external inspiratory and expiratory resistance was minimised and identical in all experimental conditions and approximated conditions present during usual exercise. During trials with O2 enriched ambient air the peak work rate increased (451 ± 58 W vs. 429 ± 59 W). Neither maximum nor submaximal oxygen consumption was altered in FIO2 of 35% (5.0 ± 0.6 l.min-1) compared to 21% (4.9 ± 0.7 l.min- 1). Substituting helium for nitrogen had no additional effect on work (453 ± 56 W) or VO2max (4.9 ± 0.7 l.min-1) beyond those observed for the hyperoxic conditions. Although submaximum VE was reduced with helium, VEmax was unchanged. Since exercise was terminated at the same peak work rate (± 5 W) in the two hyperoxic conditions we postulate that the actual work rate may be the sensed variable that determines maximal exercise performance. The findings from these studies suggest that the maintenance of physiological homeostasis and the avoidance of organ and cellular damage are of fundamental importance during maximal exercise. This is achieved through central regulation of work output based, possibly, on afferent information from the mechanoreceptors in the exercising skeletal muscles or alternatively, the extent of motor unit recruitment during maximal exercise may be hardwired in the central nervous system in a system of feed-forward control.

Estratégia de corrida é forma pela qual os corredores distribuem a velocidade durante uma competição. Objetivando otimizar a utilização dos recursos energéticos, bem como melhorar o desempenho geral na prova, durante uma corrida de 5 km os atletas comumente adotam uma estratégia caracterizada por um início em alta velocidade, seguido por um trecho intermediário em velocidade inferior, e finalmente os atletas aumentam a velocidade quando se aproximam dos 400 m finais da prova. Sabe-se que o treinamento intervalado de alta intensidade (TIAI) realizado ao longo de 3 a 6 semanas é capaz de promover melhoras significativas nas variáveis fisiológicas determinantes do desempenho aeróbio, tais como VO2max, EC, VP, e OBLA. Uma vez que os atletas monitoram a PSE baseado em sinais internos (fisiológicos) e externos (ambiente), e desta forma alteram a velocidade para evitarem o término prematuro do exercício, acredita-se que melhoras em tais variáveis fisiológicas possam permitir que os corredores modifiquem a estratégia de corrida. Portanto, o principal objetivo do presente estudo foi analisar a influência de quatro semanas de TIAI sobre a PSE e também sobre a estratégia de corrida adotada por corredores durante um teste contra-relógio de 5 km (T5). Vinte sujeitos, homens, corredores recreacionais de longa distância foram distribuídos de forma contrabalançada em grupo controle (CON, n = 10; 33,5 ± 6,2 anos) e grupo treinamento intervalado (TINT, n = 10; 32,9 ± 8,6 anos). TINT realizou uma sessão de TIAI duas vezes por semana, enquanto que CON manteve seu programa regular de treinamento. Antes e após o período de intervenção, os corredores realizaram: 1) um teste incremental até exaustão para se obter o início do acúmulo de lactato sanguíneo (OBLA), o consumo máximo de oxigênio (VO2max), e a velocidade pico em esteira (VP); 2) um teste submáximo de carga constante para se medir a economia de corrida (EC); 3) e um teste contra-relógio de 5 km (T5) em pista para se estabelecer a estratégia de corrida. O programa de TIAI produziu uma melhora relevante no VO2max (effect size = 0,219), OBLA (effect size = 0,489), EC (effect size = -0,593), e VP (effect size = 0,622). Não foram detectadas alterações significativas na estratégia de corrida, TT5, VT5 e PSET5 durante o T5, comparando ambas as condições (pré e pós-treinamento) ou entre os grupos (TINT e CON; P > 0,05). Esses achados sugerem que melhoras nas variáveis fisiológicas induzidas por um programa de quatro semanas de TIAI não são acompanhadas por alterações similares na PSE e na estratégia de corrida durante um teste contra-relógio de 5 km / Pacing strategy has been defined as the manner by which the runners distribute their speed during a competition. In order to optimize the use of the energetic resources, as well as improve the general race performance, during a 5-km running race, athletes usually adopt a pacing strategy characterized by a fast start (400 m), followed by a period of slower speed during the middle (400 4600 m), and a significant increase in running speed during the last part of the race (400 m). It is well recognized that high-intensity interval training (HIIT) performed along 3 to 6 weeks is able to promote significant improvements in physiological variables determinants of endurance performance, such as VO2max, RE, PTS, and OBLA. Since athletes monitor their RPE based on the internal (physiological) and external (environment) signals, and change their running speed in order to prevent a premature exercise termination, its believed that improvements in such physiological variables could enable athletes to modify the pacing strategy. Thus, the main purpose of this study was to analyze the influence of 4 weeks of high-intensity interval training (HIIT) on the rating of perceived exertion (RPE) and the pacing strategy adopted by runners during a 5-km running time-trial (T5). Twenty male, recreational long-distance runners were randomly assigned into control group (CG, n = 10) or high-intensity interval-training group (HIITG, n = 10). The HIITG performed a high-intensity interval-training session twice per week, while CG maintained its regular training program. Before and after the training period, the runners performed the following tests: 1) an incremental exercise test to exhaustion to measure the onset of blood lactate accumulation (OBLA), maximal oxygen uptake (VO2max), and peak treadmill speed (PTS); 2) a submaximal speed-constant test to measure the running economy (RE); 3) a 5-km running time-trial on an outdoor track to establish pacing strategy. HIIT program produced a relevant improvement on the VO2max (effect size = 0.219), OBLA (effect size = 0.489), RE (effect size = -0.593), and PTS (effect size = 0.622). There were no significant differences on pacing strategy, TT5, ST5 and RPE response during the 5-km running time-trial between both conditions (pre- and post-training) or between groups (HIITG and CG; P > 0.05). These findings suggest that improvements on the physiological variables induced by a 4-week HIIT program are not accompanied by similar modifications on the RPE and running pacing strategy during a 5-km running time-trial

Estratégia de corrida é forma pela qual os corredores distribuem a velocidade durante uma competição. Objetivando otimizar a utilização dos recursos energéticos, bem como melhorar o desempenho geral na prova, durante uma corrida de 5 km os atletas comumente adotam uma estratégia caracterizada por um início em alta velocidade, seguido por um trecho intermediário em velocidade inferior, e finalmente os atletas aumentam a velocidade quando se aproximam dos 400 m finais da prova. Sabe-se que o treinamento intervalado de alta intensidade (TIAI) realizado ao longo de 3 a 6 semanas é capaz de promover melhoras significativas nas variáveis fisiológicas determinantes do desempenho aeróbio, tais como VO2max, EC, VP, e OBLA. Uma vez que os atletas monitoram a PSE baseado em sinais internos (fisiológicos) e externos (ambiente), e desta forma alteram a velocidade para evitarem o término prematuro do exercício, acredita-se que melhoras em tais variáveis fisiológicas possam permitir que os corredores modifiquem a estratégia de corrida. Portanto, o principal objetivo do presente estudo foi analisar a influência de quatro semanas de TIAI sobre a PSE e também sobre a estratégia de corrida adotada por corredores durante um teste contra-relógio de 5 km (T5). Vinte sujeitos, homens, corredores recreacionais de longa distância foram distribuídos de forma contrabalançada em grupo controle (CON, n = 10; 33,5 ± 6,2 anos) e grupo treinamento intervalado (TINT, n = 10; 32,9 ± 8,6 anos). TINT realizou uma sessão de TIAI duas vezes por semana, enquanto que CON manteve seu programa regular de treinamento. Antes e após o período de intervenção, os corredores realizaram: 1) um teste incremental até exaustão para se obter o início do acúmulo de lactato sanguíneo (OBLA), o consumo máximo de oxigênio (VO2max), e a velocidade pico em esteira (VP); 2) um teste submáximo de carga constante para se medir a economia de corrida (EC); 3) e um teste contra-relógio de 5 km (T5) em pista para se estabelecer a estratégia de corrida. O programa de TIAI produziu uma melhora relevante no VO2max (effect size = 0,219), OBLA (effect size = 0,489), EC (effect size = -0,593), e VP (effect size = 0,622). Não foram detectadas alterações significativas na estratégia de corrida, TT5, VT5 e PSET5 durante o T5, comparando ambas as condições (pré e pós-treinamento) ou entre os grupos (TINT e CON; P > 0,05). Esses achados sugerem que melhoras nas variáveis fisiológicas induzidas por um programa de quatro semanas de TIAI não são acompanhadas por alterações similares na PSE e na estratégia de corrida durante um teste contra-relógio de 5 km / Pacing strategy has been defined as the manner by which the runners distribute their speed during a competition. In order to optimize the use of the energetic resources, as well as improve the general race performance, during a 5-km running race, athletes usually adopt a pacing strategy characterized by a fast start (400 m), followed by a period of slower speed during the middle (400 4600 m), and a significant increase in running speed during the last part of the race (400 m). It is well recognized that high-intensity interval training (HIIT) performed along 3 to 6 weeks is able to promote significant improvements in physiological variables determinants of endurance performance, such as VO2max, RE, PTS, and OBLA. Since athletes monitor their RPE based on the internal (physiological) and external (environment) signals, and change their running speed in order to prevent a premature exercise termination, its believed that improvements in such physiological variables could enable athletes to modify the pacing strategy. Thus, the main purpose of this study was to analyze the influence of 4 weeks of high-intensity interval training (HIIT) on the rating of perceived exertion (RPE) and the pacing strategy adopted by runners during a 5-km running time-trial (T5). Twenty male, recreational long-distance runners were randomly assigned into control group (CG, n = 10) or high-intensity interval-training group (HIITG, n = 10). The HIITG performed a high-intensity interval-training session twice per week, while CG maintained its regular training program. Before and after the training period, the runners performed the following tests: 1) an incremental exercise test to exhaustion to measure the onset of blood lactate accumulation (OBLA), maximal oxygen uptake (VO2max), and peak treadmill speed (PTS); 2) a submaximal speed-constant test to measure the running economy (RE); 3) a 5-km running time-trial on an outdoor track to establish pacing strategy. HIIT program produced a relevant improvement on the VO2max (effect size = 0.219), OBLA (effect size = 0.489), RE (effect size = -0.593), and PTS (effect size = 0.622). There were no significant differences on pacing strategy, TT5, ST5 and RPE response during the 5-km running time-trial between both conditions (pre- and post-training) or between groups (HIITG and CG; P > 0.05). These findings suggest that improvements on the physiological variables induced by a 4-week HIIT program are not accompanied by similar modifications on the RPE and running pacing strategy during a 5-km running time-trial