Changes in the CSAs and comparison of hamstring and gastrocnemius cross sectional areas during the experimental periods. Cross-sectional area (μm2) of the control group (a), sham-operated group (b), and immobilized group (c). The ratio of the immobilized side CSA to the sham side CSA (%) (d). Values are presented as mean + SD; **, hamstring vs gastrocnemius at the same time point (P < 0.01); §, 1 week vs 16 weeks of hamstring (P < 0.01). Significant differences were found the CSAs between the hamstring and the medial gastrocnemius muscles at each time point in the all groups, except for at 1 week in the control group. The ratio was significantly lower after 16 weeks than after 1 week for the hamstring but not for the gastrocnemius. The myofiber CSAs of the hamstring were larger than those of the gastrocnemius at each time point in all groups, except for at 1 week in control group.