Esforços físicos prolongados em ritmo dinâmico parecem promover menor demanda metabólica, estresse fisiológico e cardiovascular comparado a tarefas em ritmo constante. Contudo, os mecanismos não são completamente descritos. Além disso, sugere-se que o tempo que o indivíduo é capaz de suportar um exercício em intensidade máxima (TLim[FCmax]) correlaciona-se com o desempenho no ciclismo. Assim, os objetivos do presente estudo foram verificar como a estratégia de prova (EP) influencia nas respostas fisiológicas, no controle autonômico cardiovascular e no desempenho de tarefas aeróbias subseqüentes. Adicionalmente, verificar se o Lim[FCmax] correlaciona-se com o desempenho em teste contrarelógio de 3 km (CR3KM). Participaram desse estudo oito ciclistas treinados masculinos. Após avaliações antropométricas e familiarização com os cicloergômetros, os indivíduos foram submetidos: (i) teste máximo progressivo para determinação da potência aeróbia máxima e dos limiares metabólicos; (ii) teste TLim[FCmax]; (iii) teste de 20 km adotando diferentes EP, mas mantendo a potência média em todas as sessões; (iv) teste CR3KM realizado 30 minutos após as EP. A frequência cardíaca (FC), a variabilidade da FC, a percepção de esforço (PSE) e o lactato sanguíneo [Lac] foram registrados em todas as situações experimentais. A transformada de Fourier e a amostragem entrópica foram empregadas para analisar a VFC, ao passo que a FC foi descrita por função exponencial. Adicionalmente, a ANOVA two way (estratégia de prova x distância) e a correlação produto momento de Pearson foram utilizadas para comparações estatísticas. Para todas as análises, foi assumido um p < 0,05. Os principais achados foram que o TLim[FCmax] não correlacionou-se o desempenho do CR3KM, a EP não modificou o teste CR3KM subseqüente. No entanto, houve menores incrementos de [Lac], FC e PSE na EP positiva. Possivelmente o início rápido na EP positiva reduz o déficit anaeróbio de oxigênio, reduzindo a contribuição glicolítica nesse período inicial. Finalmente, a VFC apresentou menor complexidade imediatamente após a tarefa, comparado ao repouso e aos minutos finais de recuperação, indicando maior redundância do sistema na tentativa de evitar eventos catastróficos ao organismo / Prolonged physical efforts in variable pacing promote lower metabolic demand, physiological and cardiovascular stress compared with workouts in even pacing. However, the mechanisms is not completely understanding. Additionally, one suggests that the period of time that someone can support exercises in maximal intensity (TLim[FCmax]) could be correlate with performance on the cycling. Thus, the objectives of this study were verified if the pacing strategy (EP) could influence the physiological responses, cardiovascular autonomic control and the performance of the subsequent aerobic exercises. Additionally, to verify the correlation between TLim[FCmax] with the performance on time trials of 3 km (CR3KM). Eight male trained cyclists took part of this study. After anthropometric tests and familiarization with the ergometers, the subjects were submitted: (i) maximal progressive test to determinate the maximal aerobic power and metabolic thresholds; (ii) TLim[FCmax] test; (iii) 20 km test taken different EP, but keeping the average power output in all sessions; (iv) CR3KM test performed 30 minutes after EP. The heart rate (FC), the heart rate variability (VFC), the perceived of effort (PSE) and the blood lactate [Lac] were recorded in all experimental tests. The fast Fourier transformer and the sample entropy were used to analyze the VFC, whilst the FC was analyzed employing exponential function. Further, the ANOVA two way (pacing strategy x distance) and the Pearson product moment correlation were used to statistical comparison. For all the analysis, we assumed p < 0,05. The mains finding were that TLim[FCmax] did not correlate with performance on the CR3KM and the EP did not modify the subsequent CR3KM test . However, there was lower increment for [Lac], FC and PSE on positive EP. Possibly the fast start in the positive EP reduce the anaerobic oxygen deficit, narrowing the glycolytic contribution on the initial effort. Finally, the VFC showed lower complexity immediately after the workout than the rest and the last minutes of recovery, suggesting higher redundancy of the system, probably trying avoid catastrophic occurrence to the organism

Esforços físicos prolongados em ritmo dinâmico parecem promover menor demanda metabólica, estresse fisiológico e cardiovascular comparado a tarefas em ritmo constante. Contudo, os mecanismos não são completamente descritos. Além disso, sugere-se que o tempo que o indivíduo é capaz de suportar um exercício em intensidade máxima (TLim[FCmax]) correlaciona-se com o desempenho no ciclismo. Assim, os objetivos do presente estudo foram verificar como a estratégia de prova (EP) influencia nas respostas fisiológicas, no controle autonômico cardiovascular e no desempenho de tarefas aeróbias subseqüentes. Adicionalmente, verificar se o Lim[FCmax] correlaciona-se com o desempenho em teste contrarelógio de 3 km (CR3KM). Participaram desse estudo oito ciclistas treinados masculinos. Após avaliações antropométricas e familiarização com os cicloergômetros, os indivíduos foram submetidos: (i) teste máximo progressivo para determinação da potência aeróbia máxima e dos limiares metabólicos; (ii) teste TLim[FCmax]; (iii) teste de 20 km adotando diferentes EP, mas mantendo a potência média em todas as sessões; (iv) teste CR3KM realizado 30 minutos após as EP. A frequência cardíaca (FC), a variabilidade da FC, a percepção de esforço (PSE) e o lactato sanguíneo [Lac] foram registrados em todas as situações experimentais. A transformada de Fourier e a amostragem entrópica foram empregadas para analisar a VFC, ao passo que a FC foi descrita por função exponencial. Adicionalmente, a ANOVA two way (estratégia de prova x distância) e a correlação produto momento de Pearson foram utilizadas para comparações estatísticas. Para todas as análises, foi assumido um p < 0,05. Os principais achados foram que o TLim[FCmax] não correlacionou-se o desempenho do CR3KM, a EP não modificou o teste CR3KM subseqüente. No entanto, houve menores incrementos de [Lac], FC e PSE na EP positiva. Possivelmente o início rápido na EP positiva reduz o déficit anaeróbio de oxigênio, reduzindo a contribuição glicolítica nesse período inicial. Finalmente, a VFC apresentou menor complexidade imediatamente após a tarefa, comparado ao repouso e aos minutos finais de recuperação, indicando maior redundância do sistema na tentativa de evitar eventos catastróficos ao organismo / Prolonged physical efforts in variable pacing promote lower metabolic demand, physiological and cardiovascular stress compared with workouts in even pacing. However, the mechanisms is not completely understanding. Additionally, one suggests that the period of time that someone can support exercises in maximal intensity (TLim[FCmax]) could be correlate with performance on the cycling. Thus, the objectives of this study were verified if the pacing strategy (EP) could influence the physiological responses, cardiovascular autonomic control and the performance of the subsequent aerobic exercises. Additionally, to verify the correlation between TLim[FCmax] with the performance on time trials of 3 km (CR3KM). Eight male trained cyclists took part of this study. After anthropometric tests and familiarization with the ergometers, the subjects were submitted: (i) maximal progressive test to determinate the maximal aerobic power and metabolic thresholds; (ii) TLim[FCmax] test; (iii) 20 km test taken different EP, but keeping the average power output in all sessions; (iv) CR3KM test performed 30 minutes after EP. The heart rate (FC), the heart rate variability (VFC), the perceived of effort (PSE) and the blood lactate [Lac] were recorded in all experimental tests. The fast Fourier transformer and the sample entropy were used to analyze the VFC, whilst the FC was analyzed employing exponential function. Further, the ANOVA two way (pacing strategy x distance) and the Pearson product moment correlation were used to statistical comparison. For all the analysis, we assumed p < 0,05. The mains finding were that TLim[FCmax] did not correlate with performance on the CR3KM and the EP did not modify the subsequent CR3KM test . However, there was lower increment for [Lac], FC and PSE on positive EP. Possibly the fast start in the positive EP reduce the anaerobic oxygen deficit, narrowing the glycolytic contribution on the initial effort. Finally, the VFC showed lower complexity immediately after the workout than the rest and the last minutes of recovery, suggesting higher redundancy of the system, probably trying avoid catastrophic occurrence to the organism

The study dealt with the influence of exercise on the autonomic nervous system (ANS) and with factors that may influence the results. ANS function was measured in 183 young, healthy participants, before and after a twelve week standardised, medium-to-high volume physical training programme, in a controlled environment. The effects of the training programme were assessed on resting ANS functioning, during standing and on the response to an orthostatic challenge. ANS function was assessed by means of heart rate variability (HRV) determination. HRV was quantified by three different analytical techniques, i.e., time domain analysis (RR, STDRR, RMSSD and pNN50), frequency domain analysis (LF,LFnu, HF, HFnu and LF/HF) and Poincaré plot analysis (SD1 and SD2). The influence of technical variations, such as variations in tachogram length and period of recording, as well as the influence of pre-intervention values of physiological variables, such as blood pressure, BMI, VO2 max and ANS functioning, on the response to the exercise intervention, were assessed. Results on the exercise intervention showed: <ul><li> Increased supine, as well as standing, parasympathetic cardiac control as indicated by time domain, frequency domain and Poincaré analyses. </li><li> Decreased sympathetic control in the supine position and increased sympathetic control during rising and standing. </li><li> Increased vagal withdrawal, as well as increased sympathetic control during the first phase of the orthostatic response to rising from the supine position. </li><li> Only an exercise-induced increase in sympathetic control when the orthostatic response was measured as the difference between standing and supine. </li></ul> Results on exercise-induced changes in sympathetic and parasympathetic ANS control differ, depending on posture. It is suggested that the effects of an exercise intervention on sympathetic and parasympathetic ANS control of the heart should be assessed from measurements in the supine, in the standing, and in response to an orthostatic stressor. It is further suggested that information obtained during rising will give additional information on the response of the ANS. This study showed that technical as well as physiological variations may lead to differences in the outcome of HRV studies. Results from the technique evaluation showed that the length and period of tachogram recordings should be standardised, especially during an orthostatic challenge. Starting the recording too late will miss out on the initial response to a change in body position. Longer recording times will represent the mean of HRV values obtained during the orthostatic response and that obtained after stabilisation in the standing position. Investigations into the influence of pre-intervention physiological status on exercise-induced changes showed: <ul><li> Baseline ANS functioning is a significant contributor to variations in the ANS response to an exercise intervention. </li><li> Pre-intervention values for physiological variables, such as blood pressure, BMI and VO2 max do not have a significant influence on the HRV response to exercise in young, healthy individuals of average fitness</li><li> Regression analyses confirm the correlation results, i.e. that baseline ANS function is a significant predictor of the ANS response to exercise. </li><li> However, regression results indicated that the combination of pre-intervention values for LFms2, HFms2, BMI, VO2 max, gender and blood pressure, contributes only between 12.83% and 29.82%, depending on the HRV variable, to the exercise induced changes in the autonomic nervous system. </li></ul> / Thesis (PhD)--University of Pretoria, 2011. / Physiology / unrestricted