Micromeasuring Studies on Age Changes in Human Major and Minor Pectoral Muscles

Micromeasuring studies have been made on the age changes of the surgically resected 180 major pectoral muscles (29-81 years) and 200 minor pectoral muscles (26-80 years). The microscopic defferentiation between type I and II fibers was made by the immunohistochemical demonstration of β-enolase in the paraffin sections with indirect antibody method. The age related decrease in weight of the muscles was marked after 60 years of age in the pectoralis major, but not significant in the minor. Number of both type I and II muscle fibers in the major and the minor pectoral muscles was significantly decreased after 60 years of age. On the other hand, size of type I fibers was increased markedly after 60 years of age in the pectoralis minor, but slightly after 70 years in the major. Size of the type II fibers was decreased significantly with age in the pectoralis minor, but did not significantly change in the major. The differences in the age changes between major and minor pectoral muscles are considered to be due to their functional situation.