Recruitment of the Serratus Anterior as an Accessory Muscle of Ventilation during Graded Exercise

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Abstract
The role of the serratus anterior (SA) as an accessory muscle of ventilation and its physiologic significance under exercising conditions remains unclear. Recent investigations have utilized the measurement of SA as an analog for respiratory muscle oxygenation. The purpose of this investigation was to examine the action of the serratus anterior via surface electromyography (EMG) and near infrared spectroscopy (NIRS) during exercise while controlling for muscular effort not related to ventilation. Nine healthy volunteers (age = 24.4 +/- 0.5 years, VO2max = 3.416 +/- 0.35 l min(-1); VEpeak = 127.5 +/- 13.1 l min(-1); TVpeak = 2.844 +/- 0.226 l) completed a graded exercise test to volitional exhaustion on a cycle ergometer. The subjects' arms were folded and relaxed at the abdomen to minimize muscular effort resulting from scapular stabilization during pushing/forward flexion of the arms associated with cycle ergometry. VO2 and V were monitored breath-by-breath throughout exercise. EMG was recorded over the right SA, and a near infrared probe was placed over the left SA. No significant differences were observed throughout the graded exercise test for tissue oxygenation (StO2) (n = 6, F[1.532, 7.661] = 0.895, P > 0.05, eta2 = 0.15) or EMG (n = 9, F[1.594, 12.75] = 3.067, P > 0.05, eta2 = 0.27). Although the recruitment of the SA has been postulated to aid in ventilation in various postures and disease states, it is concluded that it shows little muscular effort in healthy subjects during upright cycling. Additional research is needed to conclude the pertinence of utilizing StO2 of the SA as an analog for respiratory muscle oxygenation.

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