Effect of long-term muscle paralysis on human single fiber mechanics

• Published in: Journal of applied physiology (1985) 2007-01, Vol.102 (1), p.340-349
• Main Authors: Malisoux, Laurent, Jamart, Cecile, Delplace, Krystel, Nielens, Henri, Francaux, Marc, Theisen, Daniel
• Format: Article
• Language: English
• Subjects: Adult; Biological and medical sciences; Biomechanical Phenomena; Biopsy; Calcium - pharmacology; Comparative analysis; Fundamental and applied biological sciences. Psychology; Humans; Male; Muscle Contraction - drug effects; Muscle Contraction - physiology; Muscle Fibers, Skeletal - chemistry; Muscle Fibers, Skeletal - pathology; Muscle Fibers, Skeletal - physiology; Muscular system; Myosin Heavy Chains - analysis; Myosin Heavy Chains - metabolism; Paralysis; Paraplegia - pathology; Paraplegia - physiopathology; Quadriceps Muscle - pathology; Quadriceps Muscle - physiopathology; Spinal cord injuries; Spinal Cord Injuries - pathology; Spinal Cord Injuries - physiopathology; Studies
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00609.2006

Institut d'Éducation Physique et de Réadaptation, Faculté de Médecine, Université Catholique de Louvain, Louvain-la-Neuve, Belgium Submitted 1 June 2006 ; accepted in final form 3 October 2006 This study compared human muscles following long-term reduced neuromuscular activity to those with normal functioning regarding single fiber properties. Biopsies were obtained from the vastus lateralis of 5 individuals with chronic (>3 yr) spinal cord injury (SCI) and 10 able-bodied controls (CTRL). Chemically skinned fibers were tested for active and passive mechanical characteristics and subsequently classified according to myosin heavy chain (MHC) content. SCI individuals had smaller proportions of type I (11 ± 7 vs. 34 ± 5%) and IIa fibers (11 ± 6 vs. 31 ± 5%), whereas type IIx fibers were more frequent (40 ± 13 vs. 7 ± 3%) compared with CTRL subjects ( P < 0.05). Cross-sectional area and peak force were similar in both groups for all fiber types. Unloaded shortening velocity of fibers from paralyzed muscles was higher in type IIa, IIa/IIx, and IIx fibers (26, 65, and 47%, respectively; P < 0.01). Consequently, absolute peak power was greater in type IIa (46%; P < 0.05) and IIa/IIx fibers (118%; P < 0.01) of the SCI group, whereas normalized peak power was higher in type IIa/IIx fibers (71%; P < 0.001). Ca 2+ sensitivity and passive fiber characteristics were not different between the two groups in any fiber type. Composite values (average value across all fibers analyzed within each study participant) showed similar results for cross-sectional area and peak force, whereas maximal contraction velocity and fiber power were more than 100% greater in SCI individuals. These data illustrate that contractile performance is preserved or even higher in the remaining fibers of human muscles following reduced neuromuscular activity. chemically skinned fibers; unloaded shortening velocity; fiber power; passive tension; spinal cord injury Address for reprint requests and other correspondence: D. Theisen, 1, place P. de Coubertin, B-1348 Louvain-La-Neuve, Belgium (e-mail: daniel.theisen{at}uclouvain.be )