Purpose To investigate the effects of caffeine on performance, neuromuscular fatigue and perception of effort during high-intensity cycling exercise in moderate hypoxia. Methods Seven adult male participants firstly underwent an incremental exercise test on a cycle ergometer in conditions of acute normobaric hypoxia (fraction inspired oxygen = 0.15) to establish peak power output (PPO). In the following two visits, they performed a time to exhaustion test (78 ± 3% PPO) in the same hypoxic conditions after caffeine ingestion (4 mg kg⁻¹) and one after placebo ingestion in a double-blind, randomized, counterbalanced cross-over design. Results Caffeine significantly improved time to exhaustion by 12%. A significant decrease in subjective fatigue was found after caffeine consumption. Perception of effort and surface electromyographic signal amplitude of the vastus lateralis were lower and heart rate was higher in the caffeine condition when compared to placebo. However, caffeine did not reduce the peripheral and central fatigue induced by high-intensity cycling exercise in moderate hypoxia. Conclusion The caffeine-induced improvement in time to exhaustion during high-intensity cycling exercise in moderate hypoxia seems to be mediated by a reduction in perception of effort, which occurs despite no reduction in neuromuscular fatigue.

The aims of this study were to verify the relationship between rating of perceived exertion (RPE) and electromyography (EMG) increases during exhaustive constant-load cycling bouts and, to compare and to correlate the power outputs corresponding to perceived exertion threshold (PET) and neuromuscular fatigue threshold (NFT). 11 men completed 3–4 different exhaustive constant-load cycling bouts on a cycle ergometer, being RPE and EMG measured throughout the bouts. The linear regression of the RPEslope and EMGslope against the power output identified the PET and NFT intensity, respectively. There was a significant relationship between RPEslope and EMGslope (R²=0.69; P<0.01). However, the linearity of RPEslope (R²=0.93±0.07) was significantly higher (P<0.001) than EMGslope (R²=0.63±0.25). In addition, the RPEslope and EMGslope were related to time to exhaustion (r=−0.59 and r=−0.60; P<0.001). There was no significant difference (P=0.42) between PET (201.5±27.9W) and NFT (210.3±22.6W) and they were significantly correlated (r=0.78; P=0.005). Therefore, the RPE and EMG increases during exhaustive constant-load cycling bouts are related and, PET and NFT intensities are similar and closely associated.

Frequency domain analyses of changes in electromyographic (EMG) signals over time are frequently used to assess muscle fatigue. Fourier based approaches are typically used in these analyses, yet Fourier analysis assumes signal stationarity, which is unlikely during dynamic contractions. Wavelet based methods of signal analysis do not assume stationarity and may be more appropriate for joint time-frequency domain analysis. The purpose of this study was to compare Short-Time Fourier Transform (STFT) and Continuous Wavelet Transform (CWT) in assessing muscle fatigue in isometric and dynamic exercise. The results of this study indicate that CWT and STFT analyses give similar fatigue estimates (slope of median frequency) in isometric and dynamic exercise (P<;;003E;0.05). However, the results of the variance was lower for both types of exercise in CWT compared to STFT (P<;;0.05) indicating more variability in the EMG signal analysis using STFT. Thus, the stationarity assumption may not be the sole factor responsible for affecting the Fourier based estimates.

This study investigated the acute effect of a low‐volume static and dynamic stretching on maximal isometric peak force (MIPF), time to maximal isometric force (TMIF), rate of force production (RFP) and average amplitude of the surface EMG (AvgEMG) of the main agonist muscles acting on the bench press maximum isometric force exercise. Thirty subjects were randomly divided into three groups: static stretch (SG: 22.8±5.6 years, 176.6±3.5 cm, 74.4±5.9 kg), dynamic stretch (DG: 21.4±3.9 years, 178.4±7.2 cm, 71.7±8.2 kg) and control group (CG: 20.4±3.6 years, 179.8±5.8 cm, 74.4±9.8 kg). SG performed two 30‐s repetitions and DG performed 10 repetitions of each of the two different exercises for the pectoralis major and triceps brachii. The MIPF, TMIF, RFP and AvgEMG of the pectoralis major (sternocostal part) and triceps brachii (long and lateral head) were measured before and immediately after the stretching protocols. A significant decrease in the MIPF from pre‐ to post‐stretching was observed in both SG (p <0.001) and DG (p <0.05). No significant differences were found in the CG for all force parameters. No significant differences in the TMIF and RFP from pre‐ to post‐stretching were found in the three groups. The SG showed a significant (p <0.05) decrease in the AvgEMG of the three muscles, whereas no significant differences were found for the DG and CG. These findings suggest that a low‐volume static and dynamic stretching adversely affects efforts of muscle maximal strength of the upper limb muscles studied, but it does not seem to affect TMIF or RFP.

This study compared the activation pattern and the fatigue rate among the superficial muscles of the quadriceps femoris (QF) during severe cycling exercise. Peak oxygen consumption (V̇o2peak) and maximal accumulated oxygen Deficit (MAOD) were established by 10 well-trained male cyclists (27.5 ± 4.1 years, 71.0 ± 10.3 kg, 173.4 ± 6.6 cm, mean V̇o2peak 56.7 ± 4.4 ml·kg−1·min−1, mean MAOD 5.7 ± 1.1 L). Muscle activity (electromyographic [EMG] signals) was obtained during the supramaximal constant workload test (MAOD) and expressed by root mean square (RMS) and median frequency (MF slope). The RMS of the QF, vastus lateralis (VL) and vastus medialis (VM) muscles were significantly higher than at the beginning after 75% of exercise duration, whereas for the rectus femoris (RF), this was observed after 50% of exercise duration (p ≤ 0.05). The slope of the MF was significantly higher in the RF, followed by the VL and VM (−3.13 ± 0.52 vs. −2.61 ± 0.62 vs. −1.81 ±0.56, respectively; p < 0.05). We conclude that RF may play an important role in limiting performance during severe cycling exercise....