Abstract

Physically active young men were studied in terms of muscle fibre type distribution in the vastus lateralis muscle and performance capacity during various types of short term exercise. The percentage of fast twitch (FT) muscle fibres averaged 49 (range 10-79) in the studied muscle. Muscle force (torque) was recorded during repeated isokinetic knee extensions. The torque decline was taken as criterion for muscle fatigue and was found to be more pronounced in individuals with muscles rich in FT and/or FTb muscle fibres. As shown by EMG in individuals characterized by a high percentage of Ft fibres, mean power frequency decreased to a higher extent as compared to individuals with a high percentage of ST fibres. Lactate concentration was relatedto FT fibres in the activated muscle. This seems to indicate a higher rate of lactate production in FT fibres. After 25 maximal repeated contractions, a relationship between force decline and FT/ST lactate ratio was demonstrated. Asimilar relationship was also demonstrated for LGHtot and M-LDH ratios, indicating a close relationship between the metabolic profile of the different fibre types, muscle metabolism and muscle function. Lactate accumulation and associated metabolic changes interfering with the contractile mechanism is suggested to beresponsible for muscle fatigue in the situations described here. Verf.-Referat