The effect of dietary restriction on muscle fibre length in mice

The dietary intake of male mice from a line selected for high body-weight was restricted to 60% by weight of the ad lib. intake of the control litter-mates between days 21 and 42 post partum. One group was killed and compared with controls at 42 d of age. A further group then resumed ad lib. feeding. Mice which had regained the control body-weight by 61 d of age were killed and also compared with controls. Muscle weight, fibre length, sarcomere length, sarcomere number per fibre, actin length and myosin length were measured in the biceps brachii and tibialis anterior muscles. Muscle weight, fibre length and the number of sarcomeres per fibre were significantly reduced in both muscles following dietary restriction, but regained their control values following a resumption of normal feeding. The other indices remained unchanged throughout the study. The pattern of fibre length changes, due entirely to alterations in sarcomere number, is similar to that reported previously during growth, senescence and immobilization and following selection for high and low body-weights.