Effects of strength training and immobilization on human muscle fibres

Seven healthy male subjects were studied under control conditions and following 5–6 months of heavy resistance training and 5–6 weeks of immobilization in elbow casts. Cross-sectional fibre areas and nuclei-to-fibre ratios were calculated from cryostat sections of needle biopsies taken from triceps brachii. Training resulted in a 98% increase in maximal elbow extension strength as measured by a Cybex dynamometer, while immobilization resulted in a 41% decrease in strength. Both fast twitch (FT) and slow twitch (ST) fibre areas increased significantly with training by 39% and 31%, respectively. Immobilization resulted in significant decreases in fibre area by 33% for FT and 25% for ST fibres. The observed nuclei-to-fibre ratio was 10% greater following the training programme. However, this change was non-significant. There was also a nonsignificant correlation between the magnitude of the changes in fibre size and the changes in maximal strength following either training or immobilization.