Venceslav Kapus

Evaluation of mean power spectral frequency of EMG signal during 100 metre crawl

Abstract The aim of our study was to compare mean frequency (MNF) decrease in some upper body muscles during a 100-metre all-out crawl by using two different normalization methods: firstly, when MNF at the end of swimming (MNFSend) was normalized with respect to its initial value at the beginning and expressed with a fatigue index (FI) labelled FIstart, and secondly when MNFmin was used to calculate FImin. MNFmin presented the lowest MNF obtained during isometric contractions until exhaustion executed on land after swimming for each of three observed muscles – 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 FIstart; however, when FImin values were compared differences between the muscles were found (P<0.05). The triceps brachii (TB) and the upper part of the latissimus dorsi muscles (LD1) showed the lowest FImin (40.0±15.7 and 40.7±24.4 respectively), which implied that MNFSend obtained from these muscles most closely approached their respective MNFmin 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 FImin (isometric versus dynamic) might represent a drawback to our study, but this approach could be acceptable when between-muscle comparisons are made.

The Influence of Reduced Breathing During Incremental Bicycle Exercise on Some Ventilatory and Gas Exchange Parameters

The purpose of this study was to examine the ventilatory, gas exchange, oxygen saturation and heart rate response to reduced breathing frequency during an incremental bicycle exercise. Eight healthy male subjects performed an incremental bicycle exercise test on an electromagnetically braked cycle ergometer twice: first with continuous breathing (CB), and second with reduced breathing frequency (B10), which was defined as 10 breaths per minute. As work rates increased, significantly higher VE, Vco2 and R were measured during the exercise with SB than during the exercise with B10. Consequently, PETco2 and PETo2 were higher and lower, respectively, during the exercise with B10 than during the exercise with SB at 150 W. In addition, HR was greater during the exercise with SB than during the exercise with B10; significant differences were achieved at 90, 120 and 150W. However, Vo2 showed no significant difference between the exercises in two different breathing conditions. In summary, reduced breathing frequency during the incremental bicycle exercise decreased VE and consequently decreased So2 and increased PETco2. However, it seemed that this degree of breathing reduction did not influence on aerobic metabolism due to unchanged Vo2.

Change of mean frequency of EMG signal during 100 meter maximal free style swimming

Changes in EMG signal spectral parameters of some arm muscles were monitored during 100 m maximum front crawl swimming. MNF linearly decreased at approxi- mately the same extent in all observed muscles during swim- ming and no plateau of stabilized MNF values was observed at the end of swim. Yet, when normalized with respect to the endurance level MNF value obtained with the 90-second maximal voluntary isometric contraction after swimming, some differences between the analyzed muscles were shown.