Prolonged muscle disuse leads to muscle atrophy and decrease in force. We compared effects of 21 day bed rest (BR) on muscle excitability and force in upper and lower extremities. Voluntary (EMG) and evoked (m-wave) muscle activity were recorded in 8 subjects before BR, at the day after the BR as well as 5 days after the BR (REG) in m. gastrocnemius (GA), m. vastus lateralis (VL) and m. biceps brachii (BB). Torque and EMG were measured during sets of 3 maximum isometric contraction at different angles. During breaks m-waves were excited. In VL the torque decreased after the BR from 261±7 to 205±7 Nm (P<0.05) and partly recovered during REG to 234±7 Nm (P<0.05). The median power frequency of the EMG (MF) was lower after the BR (84±2 vs. 94±2 Hz). The duration of the m-wave increased from 20.1±0.2 to 20.8±0.2 ms (P<0.05) after the BR. Both parameters did not recover during REG. In GA decrease in torque was about 14% (P<0.05), the MF was not different, the m-wave duration rose from 13.5±0.3 to 14.6±0.3 ms (P<0.05). There were no changes in torque and properties of electrical activity in BB. Our data show that the decrease in force in postural muscles due to BR is accompanied by signs of decrease in the muscle excitability. The different behaviour of the EMG and m-wave in comparison to the torque during the recovery period points out the additional factors determining the effects of BR on muscle function.