Single-Fiber MHC Polymorphic Expression Is Unaffected by Sprint Cycle Training

• Published in: Medicine and science in sports and exercise 2005-07, Vol.37 (7), p.1133-1137
• Main Authors: Parcell, A C, Sawyer, R D, Drummond, MJ, O'Neil, B, Miller, N, Woolstenhulme, M T
• Format: Article
• Language: English
• ISSN: 0195-9131
• DOI: 10.1249/01.mss.0000170123.27209.el

The present investigation examined single-fiber MHC alterations in response to high-intensity, short-duration, sprint cycle training. Ten untrained college-age male subjects participated in 8 wk of a progressive sprint cycle training program. Training involved 15-s maximal sprints separated by 5 min of rest beginning with four sprints x 2 d in week 1 and increasing to six sprints x 3 d at week 8. Muscle samples from the vastus lateralis were obtained before and after training. A 30-s sprint cycle test was used to evaluate performance before and after training. For the 30-s sprint, mean power and total work increased from pre to post. Single-fiber analyses revealed a reduction in the MHC IIx isoform (2.0 plus or minus 1.0 to 0.2 plus or minus 0.1%, pre to post, P < 0.05) and an increase in MHC IIa (P = 0.08), whereas there was no change in hybrid fiber composition (total hybrids = 24%). Generally, MHC IIa content increased and MHC IIx decreased (P < 0.05) as demonstrated by homogenate analyses of tissue samples. We report that as little as 32 min of high-intensity sprint cycle training over 8 wk is sufficient to improve sprinting performance. This training response is accompanied by an increase in MHC IIa and reduction in MHC IIx content of the vastus lateralis. However, short-duration, high-intensity, sprint cycle training does not cause a reduction in hybrid muscle fiber content.