The present study aimed to investigate differences among the soleus (Sol), medial gastrocnemius (MG) and tibialis anterior (TA) in electromyogram (EMG) activities during ambulatory condition without any moderate to high intensity exercise. From 10:00 to 17:00, seven healthy graduate students participated in EMG recordings, which included the measurements during maximal voluntary efforts. During the long-term EMG recoding, the subjects were instructed to perform normal daily routines, including desk work and the attendance of lectures. EMG signals from the three muscles were averaged every 0.1s and expressed as a percentage (%MVE) of those obtained with maximal voluntary efforts, averaged over 1s. An EMG burst which had an amplitude >2%MVE and a duration >0.1s was defined as muscular activity. Regardless of muscles examined, the amplitude of the greater part of all bursts observed over the recording time was less than 30%MVE. The summed duration of all bursts over the recording time was significantly greater in Sol than in MG and TA, without a significant difference in the summed number of all bursts among the three muscles. The percentage of the summed duration of bursts at less than 10%MVE to that over the recording time was significantly higher in Sol and TA than in MG, but the corresponding value at 20< or =%MVE<30 was lower. Thus, EMG responses during ambulatory condition without any moderate to high intensity exercise differed among the three muscles, even between synergists: Sol was predominantly activated with low burst amplitudes as compared to MG.