The Effects of Skeletal Muscle Contractions and Paralysis on Physiological Responses to Head Immersion in Pekin Duck

Abstract This study investigated whether increases and decreases in pectoral muscle metabolism influence underwater endurance time and cardiovascular responses to head submersion in Pekin ducks. Muscle metabolic rate (anaerobic ATP synthesis) was estimated using 31 P magnetic resonance spectroscopy, and was manipulated by direct electrical stimulation and by pharmacological paralysis. These manipulations had no significant effect on underwater endurance times or cardiovascular responses to head immersion (heart rate, mean arterial blood pressure). Anaerobic ATP synthesis was not detectable in paralyzed muscle during head immersion, implying that muscle metabolic rate was reduced to less than 10% of normal resting values. Despite this, underwater endurance times were not significantly extended. We conclude that muscle metabolic rate per se does not influence the maximum breath-hold time in this species.