PERFORMANCE AND FIBER CHARACTERISTICS OF HUMAN SKELETAL-MUSCLE DURINGSHORT SPRINT TRAINING AND DETRAINING ON A CYCLE ERGOMETER

The ergometric effect of sprint training and detraining was studied in relation to muscle fibre changes in seven students trained during 9 w eeks 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 f rom vastus lateralis muscle at rest for histochemical analysis. The tr aining-induced shift of the force-velocity relationship was such that the increase in maximal velocity (v(max)) was greatest against high br aking forces (FB) With unchanged v(max) with no load. This was associa ted with higher maximal power output (28%) and peak force (16%). The i ncreased 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) o ver bar max) At the same time, a considerable hypertrophy in fast twit ch b (FTb) fibres was observed. All these changes were maintained afte r detraining. The training-induced changes in v(max) reached against F -B.(W over bar max)(v(m,(W) over bar max)) allowed us to produce evide nce for two particular sub-groups in which inverse fibre conversions w ere observed. In subgroup A? the lowered post-training v(m (W) over ba r max) was associated with a decrease in both FTa and FTb fibres. Conv ersely, the v(m,(W) over bar max) increase in subgroup B was associate d with a higher percentage of FT fibres as the result of increased FTa fibres and decreased FTb fibres. Thus, the fibre hypertrophy associat ed with a unidirectional fibre translation [FTb --> FT2 --> slow twitc h (ST)] toward fibres with a high thermodynamic efficiency would resul t mainly in increased force qualities, whereas the bidirectional fibre translation (ST --> FTa <-- FTb) would allow enhancement of both forc e and velocity properties.