The purpose of the present study was to investigate the role of reciprocal inhibition in the regulation of antagonistic ankle muscles during bicycling. A total of 20 subjects participated in the study. Reciprocal inhibition was induced by stimulation of the Peroneal Nerve (PN) at 1.2 x threshold for the M-response in the Tibialis Anterior muscle (TA) and recorded as a depression of the rectified Soleus (SOL) EMG. Recordings were made during tonic plantar flexion and during bicycling at an ergometer-bicycle. During tonic contraction the amount of inhibition in the SOL EMG was linearly correlated to the amount of background EMG. This linear relation was used to calculate the expected amount of reciprocal inhibition at corresponding EMG levels during bicycling. During the early phase of down-stroke of bicycling at 60 revolutions per minute (RPM) and an external load of 1.0 kg the amount of recorded reciprocal inhibition was significantly smaller than that calculated from the linear relation during tonic contraction. In 9 subjects the SOL Hreflex was used to evaluate the amount of inhibition. At a short conditioning-test-interval (2-3 ms) the PN stimulation depressed the SOL H-reflex when the subjects were at rest. This shortlatency inhibition was absent during down-stroke, but appeared during upstroke just prior to and during TA activation. A positive linear relation was found between the level of SOL background EMG in early down-stroke and the external load (from 0.5 to 2.5 kg) as well as the rate of pedaling (from 30 to 90 RPM at 1.0 kg external load). The amount of inhibition in the SOL EMG when expressed as a percentage of the background EMG activity decreased significantly with increasingload. During increased pedaling rate, a similar decrease was seen but it did not reach a statistically significant level. The data illustrate that reciprocal inhibition of the soleus muscle is modulated during bicycling being small in down-stroke when the SOL muscle is active and large in upstroke where the muscle is inactive and its antagonist becomes active. The depression of the inhibition in relation to increased load and pedaling rate likely reflects the need of reducing inhibition of the SOL motoneurons in order to ensure a sufficient activation of the muscle.