Muscle pain, fatigue and performance in motor impairments
Dep of Sports Science and Clinical Biomechanics, Faculty of Health, University of Southern Denmark, Odense, Denmark.
Muscle fatigue and pain both have an impairing effect on motor performance and force generating capacity. It is evident that pain is associated with decreased maximal voluntary force in the affected muscle group both regarding work related pain and specific conditions like myalgia, impingement, and chronic neck pain. Fatigue as a precursor of pain causes some of the same effects with a decreased force response to maximal stimulation and a longlasting depression of force output evoked during low frequency stimulation1.
Specifically, for myalgic muscles case-control studies have shown mechanical insufficiencies such as lower static, dynamic, and repetitive contraction force as well as lower rate of force development. In contrast, both voluntary activation and muscle thickness seem to be maintained at the same level as in healthy controls2.
The underlying cause for lower force generation may be found in motor control as well as in metabolic and algesic responses to sustained low force contractions. Motor control on a single motor unit level shows activation patterns including doublets that may impair muscle Ca metabolism during repetitive contractions3. Disturbed intracellular Ca regulation has recently been confirmed in an animal model on work related pain. Human micro dialysis studies show that repetitive low force contraction does involve anaerobic metabolism with an increase in nociceptive substances such as lactate and glutamate in healthy and more so in myalgic muscles.
In contrast, most recently, intervention studies among patient groups have shown that specific exercise training can be tailored to effectively reverse pain conditions and motor impairment4.
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2. Beck KT, Larsen CM, Sjøgaard G, Holtermann A, Taylor JL, Søgaard K. (2017) Voluntary activation of the trapezius muscle in cases with neck/shoulder pain compared to healthy control. 2017 J Electromyogr Kinesiol. 2017 Oct;36:56-64.
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- Søgaard K and Sjøgaard G. (2017) Physical activity as cause and cure of muscular pain: evidence of underlying mechanisms. Exerc Sport Sci Rev. 2017 Jul;45(3):136-145.