Evidence of residual force enhancement for multi-joint leg extension |
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| Authors: | Daniel Hahn Wolfgang Seiberl Susanne Schmidt Katrin Schweizer Ansgar Schwirtz |
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| Affiliation: | 1. Canadian Centre for Activity and Aging, School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada;2. School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada;3. Department of Human Physiology, University of Oregon, Eugene, OR, United States;4. Human Performance Laboratory, University of Calgary, Calgary, Alberta, Canada;5. School of Physical Therapy, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada;6. Department of Anatomy and Cell Biology, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada;1. Faculty of Kinesiology, Human Performance Laboratory, University of Calgary, Calgary, Alberta, Canada;2. Canadian Centre for Activity and Aging, School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, Canada;3. Department of Anatomy and Cell Biology, The University of Western Ontario, Canada;4. School of Physical Therapy, Faculty of Health Sciences, The University of Western Ontario, Canada |
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| Abstract: | Force enhancement is a well accepted property of skeletal muscle and has been observed at all structural levels ranging from single myofibrils to voluntarily activated m. quadriceps femoris in vivo. However, force enhancement has not been studied for multi-joint movements like human leg extension; therefore knowledge about its relevance in daily living remains limited. The purpose of this study was to determine whether there is force enhancement during maximal voluntary multi-joint leg extension. Human leg extension was studied (n=22) on a motor driven leg press dynamometer where external reaction forces under the feet as well as activity of 8 lower extremity muscles were measured. In addition, torque in the ankle and knee joints was calculated using inverse dynamics. The steady-state isometric force, joint torques, and muscle activation after active stretch (20° stretch amplitude at 60°/s) were compared with the corresponding values obtained during isometric reference contractions. There was consistent force enhancement during and following stretch for both forces and joint torques. Potentiation during stretch reached values between 26% and 30%, while a significant force enhancement of 10.5–12.3% and 4.3–7.4% remained 0.5–1 and 2.5–3 s after stretch, respectively. During stretch, EMG signals of m. gastrocnemius medialis and lateralis were significantly increased, while following stretch all analyzed muscles showed the same activity as during the reference contractions. We conclude from these results that force enhancement exists in everyday movements and should be accounted for when analyzing or modelling human movement. |
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