Breakpoints in Ventilation, Cerebral and Muscle Oxygenation, and Muscle Activity During an Incremental Cycling Exercise

Abstract

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The aim of this study was to locate the breakpoints of cerebral and muscle oxygenation and muscle electrical activity during a ramp exercise in reference to the first and second ventilatory thresholds. Twenty-five cyclists completed a maximal ramp test on an electromagnetically braked cycle-ergometer with a rate of increment of 25W/min. Expired gazes (breath-by-breath), prefrontal cortex and vastus lateralis (VL) oxygenation (Near-infrared spectroscopy) together with electromyographic Root Mean Square activity for the VL, rectus femoris (RF) and biceps femoris (BF) muscles were continuously assessed. There was a non-linear increase in both cerebral deoxyhemoglobin (at 56±13% of the exercise) and oxyhemoglobin (56±8% of exercise) concomitantly to the first ventilatory threshold (57±6% of exercise, p>0.86, Cohen’s d0.8). We identified one threshold only for muscle parameters with a non-linear decrease in muscle oxyhemoglobin (78±9% of exercise), attenuation in muscle deoxyhemoglobin (80±8% of exercise), and increase in electromyographic activity of VL (89±5 % of exercise), RF (82±14 % of exercise) and BF (85±9 % of exercise). While the thresholds in muscle oxygenation and RF electromyographic activity were contemporary to V-T2 (d0.6). Our results suggest that the metabolic and ventilatory events characterizing this latter cardiopulmonary threshold may affect both cerebral and muscle oxygenation levels, and in turn, muscle recruitment responses.

Keywords

• Electromyography
• Cycling
• ventilatory threshold
• maximal oxygen consumption
• near infra red spectroscopy