DisclosuresThis project did not receive any funding and has no conflicts of interest to report. The results of the present study do not constitute endorsement by ACSM. AbstractPurpose: Few studies have assessed neuromuscular fatigue after self-paced locomotor exercise; moreover, none have assessed the degree of supraspinal fatigue. This study assessed central and peripheral fatigue after self-paced exercise of different durations. Methods:Thirteen well-trained male cyclists completed 4 km, 20 km and 40 km simulated time-trials (TTs). Pre-and immediately post-TT (< 2.5 min), twitch responses from the knee-extensors to electrical stimulation of the femoral nerve and transcranial magnetic stimulation of the motor cortex were recorded to assess neuromuscular and corticospinal function. Results: Time to complete 4 km, 20 km and 40 km was 6.0±0.2 min, 31.8±1.0 min and 65.8±2.2 min, at average exercise intensities of 96%, 92% and 87% of V O2max, respectively. Exercise resulted in significant reductions in maximum voluntary contraction, with no difference between TTs (-18%, -15% and -16% for 4, 20 and 40 km respectively). Greater peripheral fatigue was evident after the 4 km (40% reduction in potentiated twitch) compared to the 20 km (31%) and 40 km TTs (29%). In contrast, longer TTs were characterized by more central fatigue, with greater reductions in voluntary activation measured by motor nerve (-11% and -10% for 20 km and 40 km vs. -7% for 4 km) and cortical (-12% and -10% for 20 km and 40 km vs. -6% for 4 km) stimulation. Conclusions: These data demonstrate fatigue after self-paced exercise is taskdependent, with a greater degree of peripheral fatigue after shorter, higher intensity (~6 min) TTs and more central fatigue after longer, lower intensity TTs (>30 min). Words: 254

The significant reduction in power output in the last 6 s of the 36-s deception trial, but not in the 36-s informed trial, indicates the presence of a preprogrammed 30-s "end point" based on the anticipated exercise duration from previous experience. The similarity in pacing strategy suggests that the pacing strategy is centrally regulated.

The prevalence of allergy in recreational marathon runners was similar to that in elite athletes and higher than that in the general population. There was a strong association between a positive AQUA and URT symptoms. The low proportion of households in which both runners and nonrunners were symptomatic suggests that the nature of symptoms may be allergic or inflammatory based rather than infectious. Allergy is a treatable condition, and its potential effect on performance and health may be avoided by accurate clinical diagnosis and management. Both athletes' and coaches' awareness of the potential implications of poorly managed allergy needs to be raised.

The increase in power output and the parallel upward trend in iEMG at the end of each interval indicate that the iEMG changes "tracked" the power output changes dynamically and that therefore the observed pacing strategies were not regulated by peripheral mechanisms. Rather, these findings are compatible with the action of a centrally regulated mechanism that alters the number of motor units that are recruited and de-recruited during exercise based upon peripheral feedback or anticipatory feed-forward.