Affiliations: [a] Institute of Movement and Neuroscience, German Sports University, Cologne, Germany | [b] Institute of Biomechanics and Orthopaedics, German Sports University, Cologne, Germany | [c] Faculty of Medical Engineering and Technomathematics, Aachen University of Applied Science, Jülich, Germany
Correspondence:
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Corresponding author: Lars N. Heinke, Institute of Movement and Neuroscience, German Sports University, Am Sportpark Müngersdorf 6, 50933 Cologne, North Rheine-Westfalia, Germany. Tel.: +49 221 4982 3322; Fax: +49 221 4973 3454; E-mail: l.heinke@dshs-koeln.de.
Abstract: BACKGROUND: Muscle stretch reflexes are widely used to examine neural muscle function. The knowledge of reflex response in muscles crossing the shoulder is limited. OBJECTIVE: To quantify reflex modulation according to various subject postures and different procedures of muscle pre-activation steering. METHODS: Thirteen healthy male participants performed two sets of external shoulder rotation stretches in various positions and with different procedures of muscle pre-activation steering on an isokinetic dynamometer over a range of two different pre-activation levels. All stretches were applied with a dynamometer acceleration of 104∘/s2 and a velocity of 150∘/s. Electromyographical response was measured via sEMG. RESULTS: Consistent reflexive response was observed in all tested muscles in all experimental conditions. The reflex elicitation rate revealed a significant muscle main effect (F (5,288) = 2.358, ρ= 0.040; η2= 0.039; f= 0.637) and a significant test condition main effect (F (1,288) = 5.884, ρ= 0.016; η2= 0.020; f= 0.143). Reflex latency revealed a significant muscle pre-activation level main effect (F (1,274) = 5.008, ρ= 0.026; η2= 0.018; f= 0.469). CONCLUSION: Muscular reflexive response was more consistent in the primary internal rotators of the shoulder. Supine posture in combination with visual feedback of muscle pre-activation level enhanced the reflex elicitation rate.
