Structure and function of the ankle dorsiflexor muscles in young and moderately active men and women

• Published in: Journal of applied physiology (1985) 2003-12, Vol.95 (6), p.2416-2424
• Main Authors: Holmback, Anna Maria, Porter, Michelle M, Downham, David, Andersen, Jesper L, Lexell, Jan
• Format: Article
• Language: English
• Subjects: Adult; Ankle; Ankle - anatomy & histology; Ankle - physiology; Basic Medicine; Biological and medical sciences; Body Height - physiology; Body Weight - physiology; Female; Fundamental and applied biological sciences. Psychology; Fysiologi; Gender differences; Humans; Magnetic Resonance Imaging; Male; Medical and Health Sciences; Medicin och hälsovetenskap; Medicinska och farmaceutiska grundvetenskaper; Men; Motor Activity - physiology; Muscle Contraction - physiology; Muscle Fibers, Skeletal - physiology; Muscle, Skeletal - anatomy & histology; Muscle, Skeletal - cytology; Muscle, Skeletal - physiology; Muscular system; Myosin Heavy Chains - metabolism; NMR; Nuclear magnetic resonance; Organ Size - physiology; Physiology; Sex Characteristics; Women; Young adults
• ISSN: 8750-7587; 1522-1601; 1522-1601
• DOI: 10.1152/japplphysiol.00517.2002

Departments of 1 Physical Therapy and 5 Rehabilitation, Lund University Hospital, SE-22185, and 6 Department of Community Medicine, Lund University, SE-22100 Lund, Sweden; 2 Faculty of Physical Education and Recreation Studies, University of Manitoba, Winnipeg, Canada, R3T 2N2; 3 Department of Mathematical Sciences, University of Liverpool, Liverpool L69 7ZL, United Kingdom; 4 Copenhagen Muscle Research Centre, Department of Molecular Muscle Biology, DK-2100 Copenhagen, Denmark; and 7 Department of Health Sciences, Luleå University of Technology, SE-96136 Boden, Sweden Submitted 13 June 2002 ; accepted in final form 9 July 2003 The aim was to investigate determinants of ankle dorsiflexor muscle (DF) strength and size in moderately active young men and women ( n = 30; age 20–31 yr). Concentric (Con) and eccentric (Ecc) strength were measured isokinetically. Magnetic resonance imaging was used to determine the muscle cross-sectional area (CSA). Multiple biopsies were obtained from the tibialis anterior muscle to determine total numbers, areas (Area I and II) and proportions (Prop I and II) of type I and II fibers, respectively, and relative contents of myosin heavy chain (MHC) isoforms MHC 1 , MHC 2a , and MHC 2x . Women had lower Con and Ecc strength (24 and 27%; P < 0.01), smaller CSA (19%; P < 0.001), lower Ecc DF specific strength (strength/CSA) (10%; P < 0.01), and smaller Area I and Area II (21 and 31%; P < 0.01) than men. Prop I, MHC 1 , estimated total number of fibers, and Con DF specific strength were similar for both sexes. Con DF strength was up to 72% determined by CSA and Prop I, and Ecc DF strength was up to 81% determined by CSA, Prop I, and sex; variables other than CSA explained at most 9%. Body weight and fiber areas explained >50% of the variation in CSA. In conclusion, CSA was the predominant determinant of DF strength, CSA was to a great extent determined by the body weight and the sizes of muscle fibers, and sex differences in Ecc specific strength require further study. magnetic resonance imaging; skeletal; muscle contraction; muscle fibers; sex characteristics Address for reprint requests and other correspondence: A. M. Holmbäck, Dept. of Physical Therapy, Lund Univ. Hospital, SE-221 85 Lund, Sweden (E-mail: anna_maria.holmback{at}sjukgym.lu.se ).