The aim of this study was to evaluate muscle fatigue in upper body muscles during 100-m all-out front crawl. Surface electromyogram (EMG) was collected from the pectoralis major, latissimus dorsi and triceps brachii muscles of 11 experienced swimmers. Blood lactate concentration level increased to 14.1 ± 2.9 mmol l(-1) 5 min after the swim. The velocity, stroke length and stroke rate calculated based on video analysis decreased by 15.0, 5.8 and 7.4%, respectively, during the swim. EMG amplitude of the triceps and the lower part of the latissimus muscles increased, whilst the mean power frequency (MNF) of all muscles significantly decreased by 20-25%. No significant differences in the relative MNF decrease were observed amongst the muscles; however, the differences in the rate of the MNF decrease between the lower part of the latissimus and the triceps brachii muscles were found (P < 0.05). The time of rest between the muscle activation of the two consecutive arm strokes at the end of swimming was extended (P < 0.05). It was concluded that 100-m all-out crawl induced significant fatigue with no evident differences amongst the analysed muscles.

The aim of our study was to compare mean frequency (MNF) decrease in some upper body muscles during a 100-metre allout crawl by using two different normalization methods: firstly, when MNF at the end of swimming (MNF Send ) was normalized with respect to its initial value at the beginning and expressed with a fatigue index (FI) labelled FI start , and secondly when MNF min was used to calculate FI min . MNF min presented the lowest MNF obtained during isometric contractions until exhaustion executed on land after swimming for each of three observed muscles Á triceps brachii (TB), latissimus dorsi (LD) and pectoralis major (PM). Eleven experienced swimmers participated in the study and surface electromyography (EMG) signals from TB, the upper and lower parts of LD (LD1 and LD2 respectively) and the upper and lower parts of PM (PM1 and PM2 respectively) were recorded during both swimming and isometric contractions. Results showed no differences in FI start ; however, when FI min values were compared differences between the muscles were found (P B 0.05). The triceps brachii (TB) and the upper part of the latissimus dorsi muscles (LD1) showed the lowest FI min (40.0915.7 and 40.7924.4 respectively), which implied that MNF Send obtained from these muscles most closely approached their respective MNF min values during swimming. This might suggest that these muscles fatigued more than other observed muscles. The use of a different type of muscle contraction for calculating FI min (isometric versus dynamic) might represent a drawback to our study, but this approach could be acceptable when between-muscle comparisons are made.

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Introduction: Hypoxia has not been detected only during altitude exercise but also during specific conditions during exercise at sea level, such exercise with reduced breathing frequency (RBF). Training with RBF is often referred to as "hypoxic training". It was thought that, by limiting inspired air, the reduction of oxygen available for muscular work would result and therefore cause muscle hypoxia, similar to that experienced at altitude. Therefore, the aim of this study was to examine the possible effect of RBF on ventilatory parameters, blood gases, oxygen saturation and some metabolic responses during the constant load exercise to exhaustion. Methods: Eight healthy male subjects performed an incremental cycling test with RBF at 10 breaths per minute. A constant load test with RBF (B10) was then performed to exhaustion at the peak power output obtained during the incremental test. Finally, the subjects repeated the constant load test with the spontaneous breathing (SB) using the same protocol as B10. Results: RBF during the constant load exercise resulted in a profound reduction in V E , when compared to the spontaneous breathing, despite significantly increases in V T. Consequently, there were significantly lower SO 2 and PO 2 and higher PCO 2 during B10 than during SB. However, there were no significant differences in VO 2 and [LA-] between different breathing conditions. Conclusions: Therefore, it may be concluded that RBF during the constant load exercise induced marked hypoventilation and consequently hypoxia and hypercapnia. However, it seemed that this degree of the breathing reduction did not influence on aerobic metabolism due to unchanged VO 2 and [LA-].

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