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 contractile 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 volume (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 average, swimming 6200 m x 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 diameter, 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. However, 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 fibers, 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 microN x FL x s(-1). When power was normalized for cell size, the power was still elevated twofold.

CONCLUSIONS

These data suggest that tapering induces alterations in the contractile properties of single muscle fibers. 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 after the taper.

Effect of resistance training on single muscle fiber contractile function in older men

The purpose of this study was to examine single cell contractile mechanics of skeletal muscle before and after 12 wk of progressive resistance training (PRT) in older men (n = 7; age = 74 +/- 2 yr and weight = 75 +/- 5 kg). Knee extensor PRT was performed 3 days/wk at 80% of one-repetition maximum. Muscle biopsy samples were obtained from the vastus lateralis before and after PRT (pre- and post-PRT, respectively). For analysis, chemically skinned single muscle fibers were studied at 15 degrees C for peak tension [the maximal isometric force (P(o))], unloaded shortening velocity (V(o)), and force-velocity parameters. In this study, a total of 199 (89 pre- and 110 post-PRT) myosin heavy chain (MHC) I and 99 (55 pre- and 44 post-PRT) MHC IIa fibers were reported. Because of the minimal number of hybrid fibers identified post-PRT, direct comparisons were limited to MHC I and IIa fibers. Muscle fiber diameter increased 20% (83 +/- 1 to 100 +/- 1 microm) and 13% (86 +/- 1 to 97 +/- 2 microm) in MHC I and IIa fibers, respectively (P < 0.05). P(o) was higher (P < 0.05) in MHC I (0.58 +/- 0.02 to 0.90 +/- 0.02 mN) and IIa (0.68 +/- 0.02 to 0.85 +/- 0.03 mN) fibers. Muscle fiber V(o) was elevated 75% (MHC I) and 45% (MHC IIa) after PRT (P < 0.05). MHC I and IIa fiber power increased (P < 0.05) from 7.7 +/- 0.5 to 17.6 +/- 0.9 microN. fiber lengths. s(-1) and from 25.5 to 41.1 microN. fiber lengths. s(-1), respectively. These data indicate that PRT in elderly men increases muscle cell size, strength, contractile velocity, and power in both slow- and fast-twitch muscle fibers. However, it appears that these changes are more pronounced in the MHC I muscle fibers.

Influence of sodium on glucose bioavailability during exercise

To examine the influence of beverage sodium content on glucose bioavailability during exercise, six trained men were studied during 30 min of cycle ergometer exercise at 65% VO2max. Immediately prior to exercise, subjects ingested 400 ml of a 10% glucose solution containing 100 microCi of D-(3-3H]-glucose, with a sodium concentration of either 0, 25, or 50 mmol.l-1. Trials were conducted in the morning after an overnight fast and in randomized order at least 1 wk apart. Blood samples were obtained from a forearm vein before and during exercise and subsequently analyzed for plasma glucose and 3H-glucose activity and blood lactate. No differences in oxygen uptake, heart rate, or blood lactate were observed between trials. Resting plasma glucose levels were not different between trials. The increases in plasma glucose and the plasma accumulation of 3H-glucose were similar in the three trials. These results indicate that alterations in beverage sodium content, from 0-50 mmol.l-1, have no effect on glucose bioavailability, as measured by increases in plasma glucose and 3H-glucose activity during moderate intensity exercise.