Metabolically assessed muscle fibre recruitment in brief isometric contractions at different intensities

• Published in: European journal of applied physiology 2004-08, Vol.92 (4-5), p.485-492
• Main Authors: Beltman, J G M, de Haan, A, Haan, H, Gerrits, H L, van Mechelen, W, Sargeant, A J
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphatases - physiology; Adult; Biopsy; Creatine - physiology; Electromyography; Female; Histocytochemistry; Humans; Isometric Contraction - physiology; Leg - physiology; Male; Muscle Fibers, Skeletal - enzymology; Muscle Fibers, Skeletal - metabolism; Muscle Fibers, Skeletal - physiology; Muscle, Skeletal - enzymology; Muscle, Skeletal - physiology; Phosphocreatine - physiology
• ISSN: 1439-6319; 1439-6327
• DOI: 10.1007/s00421-004-1105-6

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