Fatiguability and Fibre Composition of Human Skeletal Muscle

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Abstract
The vastus lateralis muscle (25-65% fast twitch, FT, muscle fibers) was investigated in 10 male subjects (25-40 yr). Fatiguability was assessed as the decline in maximal force (in percent of initial values) with 50 repeated isokinetic knee-extensions at fast angular velocity (3.14 rad/s). Each contraction lasted 0.5 s and the rest periods were about 0.7 s. Every subject was tested on 2 occasions and the SD for a single determination of fatiguability was 1.4%. The average decline in force after 50 contractions was about 45%. The individual values varied and a linear correlation was present between fatiguability and percent FT fibers (r = 0.86, P < 0.01). Development of fatigue in human skeletal muscle performing repeated fast dynamic contractions with maximal effort was most marked in muscles with a high proportion of FT fibers.