Exercise-induced abdominal muscle fatigue in healthy humans

Abstract

Exercise-induced abdominal muscle fatigue in healthy humans. J Appl Physiol 100: 1554–1562, 2006. First published January 19, 2006; doi:10.1152/japplphysiol.01389.2005.—The abdominal muscles have been shown to fatigue in response to voluntary isocapnic hyperpnea using direct nerve stimulation techniques. We investigated whether the abdominal muscles fatigue in response to dynamic lower limb exercise using such techniques. Eleven male subjects [peak oxygen uptake (V˙ O2 peak) 50.0 1.9 (SE) ml kg 1 min 1] cycled at 90% V˙ O2 peak to exhaustion (14.2 4.2 min). Abdominal muscle function was assessed before and up to 30 min after exercise by measuring the changes in gastric pressure (Pga) after the nerve roots supplying the abdominal muscles were magnetically stimulated at 1–25 Hz. Immediately after exercise there was a decrease in Pga at all stimulation frequencies (mean 25 4%; P 0.001) that persisted up to 30 min postexercise ( 12 4%; P 0.001). These reductions were unlikely due to changes in membrane excitability because amplitude, duration, and area of the rectus abdominis M wave were unaffected. Declines in the Pga response to maximal voluntary expiratory efforts occurred after exercise (158 13 before vs. 145 10 cmH2O after exercise; P 0.005). Voluntary activation, assessed using twitch interpolation, did not change (67 6 before vs. 64 2% after exercise; P 0.20), and electromyographic activity of the rectus abdominis and external oblique increased during these volitional maneuvers. These data provide new evidence that the abdominal muscles fatigue after sustained, high-intensity exercise and that the fatigue is primarily due to peripheral mechanisms.