EFFECT OF SWIM TAPER ON HUMAN SINGLE MUSCLE FIBER CONTRACTILE PROPERTIES

Abstract

220 The goal of this project was to test the hypothesis that changes in the contractile properties of type I and II fibers from the deltoid muscle of swimmers before and after a 21-d taper contribute to the increased whole muscle power and faster swim performances following taper. Six college male swimmers (age, 20 ± 1 yr; height, 187 ± 2 cm, weight, 79± 3 kg, fat, 7 ± 1%) who had been training 6200 m/d for 5 months before the taper participated in this investigation. Whole muscle power increased (p<0.05) 17% and 13% during the swim bench and swim power tests, respectively. Swim times improved by 4% (range: 3.0-4.7%; p<0.05). There was no change in type I fiber diameter, while type IIa fibers were 7% larger(p<0.05) after taper. Type I peak tension (Po) was similar after taper, while the IIa fibers increased (p<0.05) from 72 ± 5 to 83 ± 6 mg. The specific tension (Po/CSA) of the IIa fibers was unchanged. Shortening velocity (Vo) was 37% and 55% faster (p<0.05) in the type I and IIa fibers, respectively. While type I fiber power was unaltered, the IIa fibers increased from 26.8 ±3.5 to 65.5 ±3.4 μN·FL/s (p<0.05). These data suggest that taper induced alterations in the contractile properties of muscle fibers may contribute to faster swim performances. Further, it appears that the type IIa fibers are more affected than the type I fibers by the taper. The increased size, strength, velocity, and power of the IIa fibers may be responsible for the improvements in whole muscle strength and power following the taper.