ADAPTATIONS IN MUSCLE-FIBER CHARACTERISTICS INDUCED BY PHYSICAL-ACTIVITY IN PIGS

The influence of regular exercise training and physical activity on di stribution of muscle fibre types, fibre cross-sectional areas and the number of adjacent capillaries per fibre type and per fibre (capillari zation) teas studied in Jive muscles from 48 female and 48 entire male pigs. In the growth interval from 30 to 100 kg, the pigs were subject ed to one of three treatments: individual housing in pens of 2.5 m(2) (treatment C), individual housing and treadmill trail-ring for 15 min/ day at a speed of 4 km/h, 5 days/week for a period of 70 days (treatme nt T), and housing in large pens (36 m(2), 40 pigs per pen) allowing f br spontaneous physical activity (treatment Fl. In m. longissimus dors i, treatment F increased the ratio of fast-twitch oxidative (FTa-) to fast twitch glycolytic (FTb-) fibres, elevated the mean fibre cross-se ctional area and the number of capillaries per fibre. In m. biceps fem oris (BF) from female pigs, the only adaptation found was a marked tra ining-induced (treatment T) increase in the cross-sectional area of th e slow-twitch (ST-) fibres. In m, semitendinosus and BF from male pigs , treatments T and F increased the ratio of FTa- to FTb-fibres. Both t raining and spontaneous activity increased the proportion of ST-fibres in m. trapezius thoracis (0.48 in treatment C, 0.53 in T and 0.52 in F). Conversely in m. psoas major, treatment F increased the proportion of FTa-fibres (0.15 in C and 0.19 in F) at the Expense of ST- and int ermediate FTc-fibres. Spontaneous activity induced ST-fibre hypertroph y in the five muscles. For several muscles, the mean fibre cross-secti onal area was significantly higher in female than in male pigs.