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Lack of Neuromuscular Origins of Adaptation After a Long-Term Stretching Program

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https://ir.library.oregonstate.edu/concern/articles/d504rm102

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  • Context: Static stretching is commonly used during the treatment and rehabilitation of orthopedic injuries to increase joint range of motion (ROM) and muscle flexibility. Understanding the physiological adaptations that occur in the neuromuscular system as a result of long-term stretching may provide insight into the mechanisms responsible for changes in flexibility. Objective: To examine possible neurological origins and adaptations in the la-reflex pathway that allow for increases in flexibility in ankle ROM, by evaluating the reduction in the synaptic transmission of la afferents to the motoneuron pool. Design: Repeated-measures, case-controlled study. Setting: Sports medicine research laboratory. Participants: 40 healthy volunteers with no history of cognitive impairment, neurological impairment, or lower extremity surgery or injury within the previous 12 mo. Intervention: Presynaptic and postsynaptic mechanisms were evaluated with a chronic stretching protocol. Twenty subjects stretched 5 times a wk for 6 wk. All subjects were measured at baseline, 3 wk, and 6 wk. Main Outcome Measures: Ankle-dorsiflexion ROM, H-max:M-max, presynaptic inhibition, and disynaptic reciprocal inhibition. Results: Only ROM had a significant interaction between group and time, whereas the other dependent variables did not show significant differences. The experimental group had significantly improved ROM from baseline to 3 wk (mean 6.2 +/- 0.9, P < .001), 3 wk to 6 wk (mean 5.0 +/- 0.8, P < .001), and baseline to 6 wk (mean 11.2 +/- 0.9, P < .001). Conclusions: Ankle dorsiflexion increased by 42.25% after 6 wk of static stretching, but no significant neurological changes resulted at any point of the study, contrasting current literature. Significant neuromuscular origins of adaptation do not exist in the la-reflex-pathway components after a long-term stretching program as currently understood. Thus, any increases in flexibility are the result of other factors, potentially mechanical changes or stretch tolerance.
  • This is the author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Human Kinetics, Inc. and can be found at: http://www.humankinetics.com/.
  • Keywords: lower extremity, flexibility, Hoffmann reflex, soleus, ankle
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  • Hayes, B. T., Harter, R. A., Widrick, J. J., Williams, D. P., Hoffman, M. A., & Hicks-Little, C. A. (2012). Lack of neuromuscular origins of adaptation after a long-term stretching program. Journal of Sport Rehabilitation, 21(2), 99-106.
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  • 21
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  • 2
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