In the Syrian hamster, winter seasonal inhibition of reproduction occurs in response to decreasing day-length. This inhibitory response is modulated by nonphotic cues. In particular, access to a running-wheel has been shown to produce incomplete gonadal regression. The present study sought to determine whether this occurs as a consequence of wheel-effect on adaptation of the circadian system to short days, or whether downstream physiological responses are involved. Short day adaptation of the circadian clock, which is located in the suprachiasmatic nucleus of the hypothalamus (SCN), was tested using the lengthening of the photosensitive phase of the SCN (assayed by the light-induced c-Fos expression in the SCN) as parameter. We found that wheel-running activity does not inhibit the integration of the photoperiodic change by the SCN even if complete testicular regression is prevented. Moreover, this exercise was even capable of accelerating the lengthening of the photosensitive phase after the transfer to short day-length. Thus, even though wheel-running activity inhibits the short photoperiod induced gonadal regression, it acts on the SCN to accelerate the integration of the photoperiodic change by the biological clock.