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| CYCLING EFFICIENCY IS RELATED TO THE PERCENTAGE OF TYPE-I MUSCLE-FIBERS |
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| Author(s): COYLE EF, SIDOSSIS LS, HOROWITZ JF, BELTZ JD |
| Source: MEDICINE AND SCIENCE IN SPORTS AND EXERCISE Volume: 24 Issue: 7 Pages: 782-788 Published: JUL 1992 |
| Times Cited: 237 References: 24 |
| Abstract: We determined that the variability in the oxygen cost and thus the caloric expenditure of cycling at a given work rate (i.e., cycling economy) observed among highly endurance-trained cyclists (N = 19; mean +/- SE; VO2max, 4.9 +/- 0.1 l.min-1: body weight, 71 +/- 1 kg) is related to differences in their % Type I muscle fibers. The percentage of Type I and II muscle fibers was determined from biopsies of the vastus lateralis muscle that were histochemically stained for ATPase activity. When cycling a Monark ergometer at 86 RPM at work rates eliciting 52 +/- 1, 61 +/- 1, and 71 +/- 1% VO2max, efficiency was determined from the caloric expenditure responses (VO2 and RER using open circuit spirometry) to steady-state exercise. Gross efficiency (GE) was calculated as the ratio of work accomplished.min-1 to caloric expenditure. min-1, whereas delta efficiency (DE) was calculated as the slope of this relationship between approximately 50 and 70% VO2max. The Type I fibers ranged from 32 to 76% and DE when cycling ranged from 18.3 to 25.6% in these subjects. The % Type I fibers was positively correlated with both DE (r = 0.85; P < 0.001; N = 19) and GE (r = 0.75; P < 0.001; N = 19) during cycling. Additionally, Type I fibers was positively correlated with GE (r = 0.74; P < 0.001; N = 13) measured during the novel task of two-legged knee extension; performed at a velocity of 177 +/- 6-degrees.s-1 and intensity of 50 and 70% of peak VO2 for that activity. Therefore, the relationship between muscular efficiency and muscle fiber type is not specific to cycling. We conclude that muscular efficiency varies greatly in highly endurance-trained cyclists and most of this variability appears to be related to differences in their % Type I muscle fibers. Therefore, when endurance-trained men exercise under these conditions, Type I muscle fibers appear to be substantially more efficient than Type II muscle fibers, possibly as a result of a lower rate of ATP turnover as reflected by a lower VO2 while performing exercise at a given power output. |
| Document Type: Article |
| Language: English |
| Reprint Address: COYLE, EF (reprint author), UNIV TEXAS, DEPT KINESIOL & HLTH EDUC, HUMAN PERFORMANCE LAB, BELLMONT 222, AUSTIN, TX 78712 USA |
| Publisher: WILLIAMS & WILKINS, 351 WEST CAMDEN ST, BALTIMORE, MD 21201-2436 |
| Subject Category: Sport Sciences |
| IDS Number: JC413 |
| ISSN: 0195-9131 |
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| | | | | | | | | Record from Web of Science® | | | | | | | | | |