This study examined the effect of unilateral lower limb suspension (ULLS) on neuromuscular function in humans. Eight subjects (31 +/- 4 years old) performed all ambulatory activity on crutches for 6 weeks while wearing a shoe with a 10-cm sole on the right foot to unweight the left lower limb. Knee extensor (KE) torque during eccentric, concentric, and isometric actions, and electromyography (EMG) of m. vastus lateralis (m. VL), m. gastrocnemius medialis (m. GM) and m. soleus (m. SL) during isometric actions were assessed pre-ULLS, post-ULLS, and after 4 d of recovery. Average muscle cross-sectional area (CSA) of the KE was measured pre- and post-ULLS and that of the ankle extensors (AE) post-ULLS using magnetic resonance imaging. Strength of the KE of the suspended left limb was reduced (p less than 0.05) 21 and 15%, respectively, after ULLS and 4 d later. Average muscle CSA of the left KE decreased (p less than 0.05) 16%. The KE of the non-suspended right limb showed no changes in muscle CSA. Thus, average muscle CSA of the KE of the suspended limb was 17% less (p less than 0.05) than that of the non-suspended limb. Average muscle CSA of the AE, likewise, was smaller (18%, p less than 0.05) in the left than right leg after ULLS. Maximal integrated EMG of VL and overall mean power frequency of GM and SL for submaximal isometric actions were both decreased (p less than 0.05) post-ULLS.(ABSTRACT TRUNCATED AT 250 WORDS)