Relationship Between Power Output And iEMG In Differently Paced 4000-m Cycling Time Trials

Abstract

Recent studies have investigated neuromuscular activity during bouts of high intensity exercise (St. Clair Gibson et al., 2001; Kay et al., 2001; Ansley et al. 2004) using measurements of the iEMG of the rectus femoris (RF) muscle. They have suggested the presence of a central control mechanism which allows completion of the activity without the development of physiological damage or premature fatigue. This suggestion is supported by observations that iEMG changes in parallel with power output (St. Clair Gibson et al., 2001; Ansley et al., 2004). PURPOSE The present study investigated the influence of different pacing strategies on neuromuscular activity and power output during 4000-m cycling time trials. METHODS Based on the results of a familiarization trial (FA), 8 male cyclists performed an even paced 4000-m time trial (EVEN), a 'submaximal first half' 4000-m time trial (SUB) and a 'supra-maximal first half' 4000-m time trial (SUPRA) in random order. In the SUB trial, the subjects rode the first 2000-m 5% slower than in the FA trial. In the SUPRA trial, they cycled the first 2000-m 5% faster. The remaining 2000-m of the SUB and SUPRA trials, subjects tried to finish as fast as possible. iEMG of the RF, vastus lateralis (VL) and biceps femoris (BF) muscle was measured during the time trials, as was power output (PO). RESULTS In the SUB trial, PO increases in the second half of the race (283.2W vs. 347.4W, p = 0.00). In the EVEN trial, PO remained constant (333.7W vs. 318.4W, p = 0.12) and in the SUPRA trials, PO decreased (355.0W vs. 297.0W, p = 0.00). In contrast to this, in all muscles, an increase in iEMG over the course of the time trial was found in all conditions. Only for the RF muscle in the EP condition, this was not the case (see figure).FigureCONCLUSION Our data do not support the suggestion that iEMG decreases in all muscles during time trials when PO is decreasing. This was evident only in the RF. As such, our data do not support the hypothesis of a central governor.