The effects of 5 weeks of unilateral lower limb suspension (ULLS) and flywheel resistance exercise (RE) on skeletal muscle protein composition were examined in thirty-one subjects (40 +/- 8y), divided into three groups: ULLS, ULLS+RE, and RE. Pre and post biopsy samples were examined for protein concentration, myosin heavy chain (MHC) and actin concentration. VL protein concentration of the three groups did not change. Soleus protein concentration following ULLS decreased (p<0.05). MHC and actin content of the VL and soleus were unaltered. Muscle mass changed from pre to post: ULLS -11% (VL), -11% (soleus), both p<0.05; ULLS+RE +9%, p<0.05; RE +6%, P<0.05. Therefore, the increase or decrease in VL muscle mass over 5 weeks occurred while maintaining protein, MHC and actin. However, soleus muscle atrophy occurred at the expense of other muscle proteins, since MHC and actin were maintained and protein concentrations decreased.