Changes in ventilation related to changes in electromyograph activity during repetitive bouts of isometric exercise in simulated sailing

Abstract

This study examined the control of ventilation during repetitive bouts of isometric exercise in simulated sailing. Eight male sailors completed four successive 3-min bouts of similar isometric effort on a dinghy simulator; bouts were separated by 15-s rest intervals. Quadriceps muscle integrated electromyograph activity (iEMG) was recorded during each bout and expressed as a percentage of activity during maximal voluntary contraction (%iEMGmax). From the first to the fourth bout, the 3-min mean averages for ventilation and for %iEMGmax increased from 19.8 (SEM 1.1) to 37.5 (SEM 3.0) l.min-1 and from 31 (SEM 4) to 39 (SEM 4)% respectively; also, ventilation and %iEMGmax over each minute throughout the four bouts were significantly correlated (r = 0.85; P < 0.05). Progressive hyperventilation reduced the mean end-tidal partial pressure of carbon dioxide from 5.0 (SEM 0.3) kPa during bout 1 to 4.3 (SEM 0.4) kPa during bout 4 [37.7 (SEM 2.0) to 32.4 (SEM 3.0) mmHg]. From the first to the fourth bout the end-of-bout blood lactate concentration did not increase significantly although the concentration from the third bout onwards was significantly greater than at rest. The results suggested that the development of muscle fatigue, which was enhanced by the insufficiency of recovery during the 15-s intervals and mirrored in the progressive increase in iEMG, was linked with stimuli causing progressive hyperventilation. Though these changes in ventilation and iEMG could not be associated with changes in blood lactate concentration, they could both have been related to accumulating metabolites within the muscles themselves.

Assessment of physiological demand in kitesurfing

“…Consequently, the [La b ] values may be related to the specific isometric effort component which characterizes the kitesurfing position. In the present study, the [La b ] responses are in good agreement with those reported in dinghy sailing during which [La b ] values hardly exceed 3 mmol l -1 either on water or in the laboratory, suggesting a limited oxygen deficit (e.g., Vogiatzis et al 1995Vogiatzis et al , 1996. Within this framework, Spurway (2007) recently indicated that the prolonged isometric effort resulted in a large increase in blood pressure and HR commonly accompanied by low or moderate increments in _ VO 2 and [La b ] responses.…”

Electromyogram as an indicator of neuromuscular fatigue during incremental exercise

“…The main factors are probably``a decrease in muscle pH and elevated extracellular potassium concentration'' as stated by Vogiatzis et al (1996). The fall in muscle pH causing inhibition in metabolic regulation as well as a decrease in the excitability of the muscle cell leads to a decrease in the mechanical eect of the contraction.…”

“…Moreover, the variations in [K + ] themselves represent a stimulus. The cellular variations in [K + ] stimulate muscular chemosensitive groups III and IV nerve ®bres, and similarly have been shown to take part in ventilation regulation (Vogiatzis et al 1996). It has been suggested that this action is probably strengthened by the stimulation of arterial chemoreceptors (Paterson and Nye 1991 Busse et al (1991).…”

Human Physiology

“…Physiology (1996) 491T.P stimulation has, however, been proposed to account for the recurrence of hyperventilation reported to occur early in the recovery; this was associated with decreasing arterial pH and could be attributed to release of metabolic products from previously underperfused muscle (Poole et al 1988). We have reported a comparable pattern on cessation of isometric exercise in simulated dinghy sailing (Vogiatzis et al 1995). If such stimuli were acting at the arterial chemoreceptors, the response should be abolished or delayed in hyperoxia.…”