Journal of Applied Physiology AJP: Endocrinology and Metabolism
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J Appl Physiol 107: 1413-1419, 2009. First published September 17, 2009; doi:10.1152/japplphysiol.00555.2009 Free Article
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Effect of contrasting physical exercise interventions on rapid force capacity of chronically painful muscles

Lars L. Andersen,1 Jesper L. Andersen,2 Charlotte Suetta,2 Michael Kjær,2 Karen Søgaard,3 and Gisela Sjøgaard3

1National Research Centre for the Working Environment, Copenhagen; ; 2Institute of Sports Medicine Copenhagen, Bispebjerg Hospital, Copenhagen; and ; 3University of Southern Denmark, Institute of Sports Science and Clinical Biomechanics, Odense, Denmark

Submitted 23 May 2009 ; accepted in final form 10 September 2009

Rapid force capacity of chronically painful muscles is inhibited markedly more than maximal force capacity and is therefore relevant to assess in rehabilitation settings. Our objective was to investigate the effect of two contrasting types of physical exercise on rapid force capacity, as well as neural and muscular adaptations in women with chronic neck muscle pain. A group of employed women (n = 42) with a clinical diagnosis of trapezius myalgia participated in a 10-wk randomized controlled trial; specific strength training of the neck/shoulder muscles, general fitness training performed as leg-bicycling; or a reference intervention without physical activity. Maximal voluntary shoulder abductions were performed at static angles of 35° and 115° with simultaneous recording of electromyography (EMG) in the trapezius and deltoid. Maximal muscle strength and activation (peak torque and peak EMG) as well as rapid muscle strength and activation [rate of torque development (RTD) and rate of EMG rise] were subsequently determined. Trapezius muscle fiber characteristics were determined with ATPase histochemistry. Significant changes were observed only in the specific strength training group. Whereas peak torque increased 18–29% (P < 0.01), RTD increased 61–115% (P < 0.001). Peak EMG and rate of EMG rise increased correspondingly (P < 0.05–0.001), and trapezius type II muscle fibers hypertrophied 20% (P < 0.001). In conclusion, rapid force capacity of chronically painful muscles is highly responsive to rehabilitation with specific strength training. The underlying mechanisms were related to both pain reduction and general neuromuscular adaptations to strength training. Potentially, the present method can be a useful clinical screening tool of muscle function in rehabilitation settings.

rate of force development; rehabilitation; myalgia; electromyography; histochemistry; rate of torque development


Address for reprint requests and other correspondence: L. L. Andersen, National Research Centre for the Working Environment, Lersø Parkalle 105 DK 2100 Copenhagen Ø, Denmark (e-mail: LLA{at}nrcwe.dk).






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