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Støve M.P.1, Hirata R.P.2, Palsson T.S.2
1University College North Denmark, Department of Physical Therapy, Aalborg, Denmark, 2Aalborg University, Department of Health Science and Technology (SMI), Aalborg University, Denmark, Aalborg, Denmark
Background: Stretching is commonly used in relation to exercise as well as rehabilitation where the purpose is to improve function, reduce painful symptoms and to prevent injury. The mechanisms underlying stretching have been thoroughly examined but the increase in joint mobility following stretching is commonly related with changes in the viscoelastic properties of the muscle tendon unit or an acute neuromuscular relaxation. However, such explanations have been negated which calls for alternative explanatory model. Stretch-tolerance is defined as the ability to tolerate the discomfort related to a muscle stretch and has been suggested to depend on sensitivity of peripheral nociceptors. This will indicate that by reducing the input caused by peripheral nociceptive afferents, the stretch tolerance could be increased. The nervous system has an inbuilt ability to modulate pain via supraspinally mediated endogenous pain inhibition or facilitation. Whether such a mechanism affects the stretch-tolerance during a passive muscle stretch is however unclear but knowledge regarding this can give valuable information about the mechanisms underlying the effect of muscle stretches.
Purpose: To measure the passive range of motion (PROM) during a muscle stretch, comparing individuals where conditioned pain modulation (CPM) is induced with a control group.
Methods: Thirty-four healthy male individuals were included in the study which was conducted in a single session. Participants were randomly allocated into a control group (n=17) or the CPM group (n=17). Subjects were seated in a Biodex System 4 Pro (Biodex Medical Systems, New York, USA) in reclined position with their upper body, thighs and pelvis securely fixated. The Biodex system was adjusted so that it slowly pulled the lower leg from flexion towards extension of the knee. The subjects were asked to indicate when they reached the threshold between stretch and pain (Stretch-Pain Threshold, SPT) upon which the movement stopped and the joint angle was registered (PROM). Two measurements were performed with a 5 minute break between measurements. During the break, subjects in the CPM group were asked to submerge their non-dominant hand in ice water (1°-4°C) and hold it there for 2 minutes. Following the break, the second measurement of PROM was performed where participants indicated their SPT as before. All subjects were blind to their performance between the two measurement. The difference in joint angles between the two measurements was extracted and used for group comparison.
Results: A statistically significant difference was found between the CPM group and controls after stretching (Independent samples t-test: P 0.05).
Conclusion(s): This study demonstrated that the stretch-pain threshold can be increased by engaging conditioned pain modulation.
Implications: These findings indicate that pain is a significant contributor to the range of motion available during a muscle stretch. The results are in line with more recent findings which have questioned that increased PROM is a result of changes in the muscles mechanical properties. The current findings imply that modulation of pain during stretching may explain the improvements in PROM which is an important point to consider when prescribing stretches as part of a rehabilitation regime.
Funding acknowledgements: Department of Health Science and Technology (SMI), Aalborg University, University College North Denmark. The authors have no conflicts of interest.
Topic: Sport & sports injuries
Ethics approval: This study protocol was approved by the Regional Ethics Committee (N-20160019)
All authors, affiliations and abstracts have been published as submitted.
