Activation of Mechanoreflex, but not Central Command, Delays Heart Rate Recovery after Exercise in Healthy Men.

This study tested the hypotheses that activation of central command and muscle mechanoreflex during post-exercise recovery delays fast-phase heart rate recovery with little influence on the slow phase. Twenty-five healthy men underwent three submaximal cycling bouts, each followed by a different 5-min recovery protocol: active (cycling generated by the own subject), passive (cycling generated by external force) and inactive (no-cycling). Heart rate recovery was assessed by the heart rate decay from peak exercise to 30 s and 60 s of recovery (HRR30s, HRR60s fast phase) and from 60 s-to-300 s of recovery (HRR60-300s slow phase). The effect of central command was examined by comparing active and passive recoveries (with and without central command activation) and the effect of mechanoreflex was assessed by comparing passive and inactive recoveries (with and without mechanoreflex activation). Heart rate recovery was similar between active and passive recoveries, regardless of the phase. Heart rate recovery was slower in the passive than inactive recovery in the fast phase (HRR60s=20±8vs.27 ±10 bpm, p<0.01), but not in the slow phase (HRR60-300s=13±8vs.10±8 bpm, p=0.11). In conclusion, activation of mechanoreflex, but not central command, during recovery delays fast-phase heart rate recovery. These results elucidate important neural mechanisms behind heart rate recovery regulation.

Stretch-shortening cycle exercise produces acute and prolonged impairments on endurance performance: is the peripheral fatigue a single answer?

OBJECTIVE: This study aimed to verify the acute and prolonged effects of stretch-shortening cycle exercise (SSC) on performance and neuromuscular function following a 4-km cycling time trial (4-km TT). METHODS: On separate days, individuals performed a 4-km TT without any previous exercise (CON), immediately (ACUTE) and 48 h after (PROL) SSC protocol (i.e., 100-drop jumps). Neuromuscular function was measured at baseline SSC (baseline), before (pre-TT) and after (post-TT) 4-km TT. Muscle soreness and inflammatory responses also were assessed. RESULTS: The endurance performance was impaired in both ACUTE (- 2.3 ± 1.8%) and PROL (- 1.8 ± 2.4%) compared with CON. The SSC protocol caused also an acute reduction in neuromuscular function, with a greater decrease in potentiated quadriceps twitch-force (Qtw.pot - 49 ± 16%) and voluntary activation (VA - 6.5 ± 7%) compared for CON and PROL at pre-TT. The neuromuscular function was fully recovered 48 h after SSC protocol. Muscle soreness and IL-10 were elevated only 48 h after SSC protocol. At post-TT, Qtw.pot remained lower in ACUTE (- 52 ± 14%) compared to CON (- 29 ± 7%) and PROL (- 31 ± 16%). CONCLUSION: These findings demonstrate that impairment in endurance performance induced by prior SSC protocol was mediated by two distinct mechanisms, where the acute impairment was related to an exacerbated degree of peripheral and central fatigue, and the prolonged impairment was due to elevated perceived muscle soreness.

Mental fatigue does not alter performance or neuromuscular fatigue development during self-paced exercise in recreationally trained cyclists.

PURPOSE: The purpose of this study was to investigate the effects of mental fatigue, characterized by a subjective feeling of tiredness, on the development of neuromuscular fatigue during a 4-km cycling time trial (4-km TT). METHODS: Eight recreationally trained male cyclists performed a 4-km TT after either performing a prolonged cognitive task (mental fatigue) or after viewing emotionally neutral documentaries (control). The neuromuscular function of the knee extensors was assessed using electrical nerve stimulation at baseline, before (pre-TT), and after (post-TT) the 4-km TT. Rating of perceived exertion (RPE) and physiological variables were periodically measured during 4-km TT. RESULTS: Subjective ratings of fatigue increased significantly only after a prolonged cognitive task (P = 0.022). Neuromuscular function at baseline was similar between conditions and remained unchanged at pre-TT. Time to complete the 4-km TT was similar between control (376 ± 27 s) and mental fatigue (376 ± 26 s). There was no significant difference between conditions for RPE, [Formula: see text], [Formula: see text], and HR throughout the exercise. The 4-km TT-induced similar decrease (from baseline to post-TT) in maximal voluntary contraction (mental fatigue - 11 ± 10%, control - 16 ± 12%), twitch force (mental fatigue - 26 ± 16%, control - 24 ± 17%), and voluntary activation (mental fatigue - 5 ± 7%, control - 3 ± 2%) for both conditions. CONCLUSION: Mental fatigue induced by prolonged cognitive task does not impair performance nor alter the degree of central and peripheral fatigue development during self-paced exercise in recreationally trained cyclists.

CONTRARRELÓGIO DE CICLISMO DE MÉDIA DISTÂNCIA: DETERMINAÇÃO E REPRODUTIBILIDADE DE PARÂMETROS DERIVADOS DA DISTRIBUIÇÃO DE POTÊNCIA / TIME TRIAL IN MIDDLE DISTANCE CYCLING: DETERMINATION AND REPRODUCIBILITY OF PARAMETERS DERIVED FROM THE POWER DISTRIBUTION

RESUMO A escolha do pacing é determinante para o sucesso esportivo, mas a análise de pequenas alterações no pacing necessita de mais estudos. O objetivo deste estudo foi determinar parâmetros na curva de desempenho em contrarrelógio de ciclismo para investigar variações dopacing e sua reprodutibilidade. A análise por trechos da prova também foi realizada. 19 ciclistas amadores realizaram dois testes de 4-km, no qual foram analisados parâmetros nas curvas de desempenho individuais e a potência média dos trechos da prova. O tempo e a potência média foram similares entre os testes. Não houve diferença entre os parâmetros observados na curva de desempenho comparando o teste 1 e 2, mas estes mostraram alto valor de erro típico da medida. A análise por trechos da prova foi mais consistente, sendo uma opção para analisar o pacing. Apesar de um desempenho consistente no contrarrelógio de 4-km, os parâmetros determinados apresentaram grande variação intraindividual.

ABSTRACT The selection of pacing is determinant for the sport success, but the analysis of modest variations in pacing requires further studies. The purpose of this study was to determine parameters in the performance curve on cycling time trial to investigate pacing variations and reproducibility. The test sections analysis was also performed. 19 amateur cyclists performed two tests of 4-km, in which parameters were analyzed in the individual performance curves and the average power of the test sections. The time and the average power were similar between tests. There was no difference between the parameters observed in the performance curve comparing the test 1 and 2, but these showed a high value of typical error. The test portions analysis was more consistent, with an alternative to analyze pacing. Despite consistent performance in time trial 4-km, the parameters determined varied widely between individuals.

High Carbohydrate Diet Induces Faster Final Sprint and Overall 10,000-m Times of Young Runners.

This study analyzed the pacing employed by young runners in 10,000 m time-trials under 3 dietary regimens of different carbohydrate (CHO) intakes. Nineteen boys (13-18 years) ate either their normal CHO diet (56% CHO), high (70% CHO), or low (25% CHO) CHO diets for 48 hr; the boys then performed a 10,000 m run (crossover design). The high CHO diet led to faster final sprint (14.4 ± 2.2 km·h⁻¹) and a better performance (50.0 ± 7.0 min) compared with the low CHO diet (13.3 ± 2.4 km·h⁻¹ and 51.9 ± 8.3 min, respectively, p < .05). However, the final sprint and performance time in the high CHO or low CHO diets were statistically not significantly different from the normal CHO diet (13.8 ± 2.2 km·h⁻¹ and 50.9 ± 7.4 min; p > .05). CHO oxidation rate during the constant load exercise at 65% of VO2max was elevated in high CHO diet (1.05 ± 0.38 g·min⁻¹) compared with low CHO diet (0.63 ± 0.36 g·min⁻¹). The rating of perceived exertion increased linearly throughout the trial, independently of the dietary regimen. In conclusion, the high CHO diet induced higher CHO oxidation rates, increased running speed in the final 400 m and enhanced overall running performance, compared with low CHO.

Pontos de transição da frequência cardíaca em teste progressivo máximo / Transition points of heart rate in maximum progressive test

Foi realizada análise do comportamento da frequência cardíaca (FC) e identificação dos pontos de inflexão (PIFC) e de deflexão da FC (PDFC) em teste progressivo máximo, em sujeitos do sexo feminino e masculino. Vinte universitários foram submetidos ao teste em cicloergômetro. A FC foi monitorada para posterior análise e identificação dos pontos de transição (PT). A FC apresentou comportamento sigmóide, com identificação de PT em todos os sujeitos, sendo: a) em 65% PIFC (64 ± 27W; 29 ± 9%Pmáx e 126 ± 12bpm; 66 ± 5%FCmáx) e PDFC (177 ± 45W; 81 ± 10%Pmáx e 178 ± 8bpm; 93 ± 4%FCmáx); b) em 30% apenas PIFC (80 ± 32W; 36 ± 14%Pmáx e 125 ± 13bpm; 66 ± 5%FCmáx) e c) em 5% o PDFC isolado (103W; 57%Pmáx e 150bpm; 82%FCmáx). O PIFC foi encontrado em carga significativamente inferior ao PDFC, sem diferenças na carga e FC relativas entre os sexos.

Was analyzed the Heart Rate (HR) behavior and identified the HR inflection points (HRIP) and deflection points (HRDP) in a maximum progressive test, using female and male subjects. Twenty university students were submitted to a maximum progressive test. The HR was monitored to posterior analysis and identification of the transition points (TP). The subjects' HR showed sigmoid behavior, with TP identification in all subjects, being: a) in 65% HRIP (64 ± 27W; 29 ± 9% Pmax and 126 ± 12bpm; 66 ± 5% HRmax) and HRDP (177 ± 45W; 81 ± 10%Pmax and 178 ± 8bpm; 93 ± 4%Hrmax); b) in 30% only the HRIP (80 ± 32W; 36 ± 14%Pmax and 125 ± 13bpm; 66 ± 5%HRmax) and c) in 5% HRDP isolated (103W; 57%Pmax and 150bpm; 82%HRmax). The HRIP was found in significantly lower load than HRDP and there were no differences in the load and HR relative between genders.