Performance and fibre characteristics of human skeletal muscle during short sprint training and detraining on a cycle ergometer

Abstract

The ergometric effect of sprint training and detraining was studied in relation to muscle fibre changes in seven students trained during 9 weeks on a cycle ergometer. Before and after training and after 7-week detraining, they performed a force-velocity test on a friction-loaded cycle ergometer. On these three occasions, muscle samples were taken from vastus lateralis muscle at rest for histochemical analysis. The training-induced shift of the force-velocity relationship was such that the increase in maximal velocity (v _max ) was greatest against high braking forces (F _B) with unchanged v _max with no load. This was associated with higher maximal power output (28%) and peak force (16%). The increased maximal mean power output to reach a maximal velocity during a short sprint was obtained against a 23% higher optimal F _B(F _B,¯˙W _max ). At the same time, a considerable hypertrophy in fast twitch b (FT_b) fibres was observed. All these changes were maintained after detraining. The training-induced changes in v _max reached against F _B,¯˙W_max(v _m, ¯˙W_max) allowed us to produce evidence for two particular sub-groups in which inverse fibre conversions were observed. In subgroup A, the lowered post-training v _m, ¯˙W_max was associated with a decrease in both FT_a and FT_b fibres. Conversely, the v _m, ¯˙W_max increase in subgroup B was associated with a higher percentage of FT fibres as the result of increased FT_a fibres and decreased FT_b fibres. Thus, the fibre hypertrophy associated with a unidirectional fibre translation [FT_b→FT_a→ slow twitch (ST)] toward fibres with a high thermodynamic efficiency would result mainly in increased force qualities, whereas the bidirectional fibre translation (ST→FT_a←FT_b) would allow enhancement of both force and velocity properties.