Growth in rats (Rattus norvegicus BERKENHOUT) 3. Development of the musculoskeletal system

Growth of limb bones and the semitendinosus muscle as well as fibre differe ntiation within this muscle were investigated in male and female inbred F34 4/Shoe Wistar rats from birth to 119 days (bones) respective 249 days (musc le measurements). Characteristics of their growth curves were evaluated usi ng the modified JANOSCHEK growth curve. Sigmoid growth patterns were found except for femur width which showed exponential growth. The growth in lengt h of the forelimb bones pre ceded that of corresponding hindlimb bones duri ng early half of growing by around five days Within a limb, the more distal elements finish their growth earlier. A sexual dimorphism in skeletal size and both muscle weight and length was present except for the bones of the Metapodium and most obvious after 50 days of age. At birth, only oxidative fibres were found in the M. semitendinosus. Glycolytic fibres could be dete cted surely above day 29, at day 39 the fibre type frequency resembled that of adults. Glycolytic fibres were already larger when occurring. This diff erence increased during growth. However, the principal growth patterns are similar for both fibre types.