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
