Influence of the time when weight bearing is started on disuse atrophy in rat soleus muscle

Prevention of disuse muscle atrophy is an important problem in physical therapy. Although several reports have been published concerning the effect of weight bearing on the prevention of disuse atrophy of lower extremity muscles, few basic clinical data are available. The present study was undertaken to examine differences in the progression of disuse muscle atrophy in terms of the time when weight bearing is started. The experimental materials consisted of the soleus muscles of 30 male Wistar rats (weight: 220 ± 6 g). The rats were divided into the control group (CON) and the experimental group, and disuse muscle atrophy caused by non-weight bearing was induced by hindlimb suspension for two weeks in the latter group. The experimental group was subdivided into four groups: no weight bearing permitted (SUS), and daily weight bearing permitted from 1, 4 and 7 days after the start of suspension (1-D, 4-D and 7-D). The relative weight of the soleus muscles did not differ for CON and 1-D or for 7-D and SUS. The mean cross-sectional area of type I fibers was 68% of that of CON for 1-D, 61% for 4-D, 52% for 7-D and 52% for SUS. This parameter showed significant differences any two groups, except for between 7-D and SUS. The results were regarded as normal in view of differences in the total time of weight bearing. The data also suggested that disuse muscle atrophy can be prevented quantitatively if weight bearing is initiated from the day following the start of suspension, and that early start of weight bearing is more effective for controlling atrophy progression.