High levels of clenbuterol have been shown to preserve muscle mass and function during disuse. In this study we report that a low dose of clenbuterol (10 microg/kg per day) lessened the loss of in situ soleus muscle isometric force normalized to wet muscle weight (P(o)/g wet weight) by 8% and reduced isometric fatigue by approximately 30% in senescent rats after 21 days of hindlimb suspension (HS). Clenbuterol did not reduce the loss of relative force in the soleus of adult rats or the plantaris of old or adult rats. Furthermore, clenbuterol failed to improve muscle force or isometric fatigue in the soleus of adult rats or in the plantaris of either age group after HS. We conclude that low levels of clenbuterol reduce muscle fatigue in slow muscles during disuse and this beta-agonist may also have therapeutic value for reducing fatigue in slow muscles (e.g., postural muscles) in the elderly during disuse.