Effect of swim taper on whole muscle and single muscle fiber contractile properties

Purpose: To examine the changes in whole muscle function and single cell co ntractile properties of Type I and II muscle fibers from the deltoid muscle of highly trained swimmers before and after a 21-d reduction in training v olume (taper). Methods: Six college male swimmers (age, 20 +/- 1 yr; height , 187 +/- 2 cm, weight, 79 +/- 3 kg, fat, 7 +/- 1%) who had been, on averag e, swimming 6200 m.d(-1) for 5 months before the taper participated in this investigation. Results: Whole muscle power increased (P < 0.05) 17% and 13 % on 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 dia meter, whereas Type IIa fibers were 11% larger (P < 0.05) after taper. Peak force (Po) of the Type I fibers was unaffected by the taper but increased (P < 0.05) from 0.63 +/- 0.02 to 0.82 +/- 0.05 mN in the IIa fibers. Howeve r, the specific force (Po/CSA) of the IIa fibers was unchanged. Shortening velocity (Vo) was 32% and 67% faster (P < 0.05) in the Type I and IIa fiber s, respectively. Although Type I fiber power was unaltered, the IIa fibers increased 2.5-fold from 24.6 +/- 2.8 to 56.2 +/- 3.9 <mu>N. FLs(-1). When p ower was normalized for cell size, the power was still elevated twofold. Co nclusions: These data suggest that tapering induces alterations in the cont ractile properties of single muscle fibers. Further, it appears that the Ty pe IIa fibers are more affected than the Type I fibers by the taper. The in creased size, strength, velocity, and power of the IIa fibers may be respon sible for the improvements in whole muscle strength and power after the tap er.