Changes in muscle thickness of gastrocnemius and soleus associated with age and sex.

Gastrocnemius and soleus in the triceps surae have functional and histological differences.We therefore investigated age-related changes in muscle thickness of these two muscles, as well as the difference in these changes between men and women.Participants comprised 847 healthy adults aged 20 to 79 years. A B-mode ultrasound scanner, with participants sitting on a chair, was used to measure muscle thickness from the midpoint of the gastrocnemius medialis muscle at the level of maximum girth (target point). The ratio of muscle thickness to height was calculated. The inter-rater and intra-rater reliability of measuring muscle thickness with the ultrasound scanner and the validity of the target point were demonstrated before the examination.Gastrocnemius was significantly thinner in women aged 60 or older and in men aged 50 or older, compared with their counterparts in their 20s. For soleus, no significant differences in thickness were found among the age groups in either sex. Decline in muscle thickness from age 40-79 was greater for gastrocnemius than for soleus.These results confirm that gastrocnemius starts to deteriorate earlier and atrophies at a faster pace than soleus. A significant sex difference was found only in the onset age of gastrocnemius deterioration, which was earlier in men than in women.