Abstract
This study investigated the recruitment of type I, IIA and IIAX fibres after seven isometric contractions at 40, 70 and 100% maximal voluntary knee extension torque (MVC, 1 s on/1 s off). Biopsies of the vastus lateralis muscle were collected from seven subjects at rest and immediately post-exercise. Fibre fragments were dissected from the freeze-dried samples and characterized as type I, IIA and IIAX using mATPase staining. Phosphocreatine (PCr) and creatine (Cr) content were measured in the remaining part of characterized fibres. A decline in the ratio of PCr to Cr (PCr/Cr) was used as an indication of activation. The mean peak torques were, respectively, 39 (2), 72 (2) and 87 (6)% MVC. Cumulative distributions of type I and IIA fibres were significantly shifted to lower PCr/Cr ratios at all intensities (Kolmogorov-Smirnov test, P < 0.05). The cumulative distribution of type IIAX fibres showed a significant leftward shift only at 87% MVC (P < 0.05). A hierarchical order of fibre activation with increasing intensity of exercise was found, with some indication of rate coding for type I and IIA fibres. Evidence for activation of type IIAX fibres was only found at 87% MVC. © Springer-Verlag 2004.
Original language | English |
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Pages (from-to) | 485-492 |
Number of pages | 8 |
Journal | European journal of applied physiology |
Volume | 92 |
Issue number | 4-5 |
Early online date | 1 Aug 2004 |
DOIs | |
Publication status | Published - Aug 2004 |
Keywords
- Adenosine Triphosphatases/physiology
- Adult
- Biopsy
- Creatine/physiology
- Electromyography
- Female
- Histocytochemistry
- Humans
- Isometric Contraction/physiology
- Leg/physiology
- Male
- Muscle Fibers, Skeletal/enzymology
- Muscle, Skeletal/enzymology
- Phosphocreatine/physiology