ENZYME ADAPTATIONS OF HUMAN SKELETAL-MUSCLE DURING BICYCLE SHORT-SPRINT TRAINING AND DETRAINING

The effect of sprint training and detraining on supramaximal performan ces was studied in relation to muscle enzyme adaptations in eight stud ents trained four times a week for 9 weeks on a cycle ergometer. The s ubjects were tested for peak oxygen uptake ((V) over dot O-2peak), max imal aerobic power (MAP) and maximal short-term power output ((W) over dot(max)) before and after training and after 7 weeks of detraining. During these periods, biopsies were taken from vastus lateralis muscle for the determination of creatine kinase (CK), adenylate kinase (AK), glycogen phosphorylase (PHOS), hexokinase (HK), phosphofructokinase ( PFK), lactate dehydrogenase (LDH) and its isozymes, 3-hydroxy-acyl-CoA dehydrogenase (HAD) and citrate synthase (CS) activities. Training in duced large improvements in (W) over dot(max) (28%) with slight increa ses (3%) in (V) over dot O-2peak (P < 0.10). This was associated with a greater glycolytic potential as shown by higher activities for PHOS (9%), PFK (17%) and LDH (31%) after training, without changes in CK an d oxidative markers (CS and HAD). Detraining induced significant decre ases in (V) over dot O-2peak (4%), MAP (5%) and oxidative markers (10- 16%), while (W) over dot(max) and the anaerobic potential were maintai ned at a high level. This suggests a high level in supramaximal power output as a result of a muscle glycogenolytic and glycolytic adaptatio n. A long interruption in training has negligible effects on short-spr int ability and muscle anaerobic potential. On the other hand, a persi stent training stimulus is required to maintain high aerobic capacity and muscle oxidative potential. This may contribute to a rapid return to competitive fitness for sprinters and power athletes.