Stretching at the ankle joint: viscoelastic responses to holds and continuous passive motion

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Abstract
To compare the effect of static holds and continuous passive motion on stiffness and force relaxation of the soft tissue structures resisting ankle joint dorsiflexion. This study used a randomized repeated measures trial design. Twenty-four asymptomatic subjects (15 males and 8 females) with a mean age of 26 yr participated. A Kin-Com dynamometer was used to measure the stiffness and force relaxation response of tissues about the ankle joint in response to a plantar flexor stretch. A comparison was made of the response for a 1 x 60-s hold, 2 x 30-s holds, 4 x 15-s holds, and continuous passive motion for 60 s. All subjects undertook all conditions. The main outcome measures were 1) stiffness at the ankle joint as it moved to 80% of the maximum range of dorsiflexion, and 2) the decrease in force at 80% of the maximum range of motion of the ankle joint. Stiffness was decreased significantly (P < 0.05) for the continuous passive motion condition only. The mean magnitude of the decrease in stiffness was 16%. Across hold times, force decreased significantly (P < 0.05). Bonferonni contrasts indicated that there was a significant difference (P < 0.05) between the continuous passive motion condition and all other hold conditions. There were no significant differences (P > 0.05) between the 4 x 15-s, 2 x 30-s, and 1 x 60-s holds. The magnitude of the decline in force was 10.5%, 21.5%, 21.7%, and 19% for the 0-, 15-, 30-, and 60-s holds, respectively. The greatest decreases in tension were achieved in the first 20 s of a hold. If decreasing stiffness is a key aim of a stretching program, the findings indicate that continuous motion is more effective than holds. In contrast, if relaxation of peak tension is the main aim, then holds are most effective.

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