Nine men volunteered to undergo 10% downhill (DT) or 10% uphill (UT) treadmill training at 60% VO2max for 12 minutes on two consecutive days. Four days later the downhill run (DR) was repeated. All subjects reported considerable muscular soreness following DT but not UT. When DR followed UT muscular soreness was again reported but not when DR followed DT. Peak knee flexion and extension moment of force data at five angular velocities, ranging from 0.52-4.71 rad s-1, were reduced following DR regardless of whether soreness was present. During each run VO2 was stable during UT but drifted upwards during DT and DR. This increase in VO2 was not due to changes in the stride frequency since the stride frequency remained nearly constant on all days except for the second day of the DT when an increase of 20 strides per minute occurred; this was the only day the subjects ran while sore. It was concluded that two 12 minute bouts of downhill running were sufficient to protect against the occurrence of muscular soreness in subsequent downhill run. However, this training was insufficient to prevent a 2-3 day loss of muscular strength. These results support the hypothesis that the sensation of delayed onset muscle soreness and the temporary strength loss associated with eccentric contraction have different physiological causes.