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 (mean ± S.E.M. peak oxygen uptake [V_O2peak] = 50.0 ± 1.9 ml^.kg^-1.min^-1) cycled at >90% V_O2peak 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 (P_ga) after the nerve roots supplying the abdominal muscles were magnetically stimulated at 1 through 25 Hz. Immediately after exercise there was a decrease in P_ga at all stimulation frequencies (mean -25 ± 4%; P < 0.001) that persisted up to 30 min post-exercise (-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 P_ga 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.