Effects of Short Term Stretching on Ankle Stiffness and Range of Motion in People with Multiple Sclerosis
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Hypertonia is seen in 85% of people with Multiple Sclerosis (pwMS) resulting in disability and functional restrictions. Hypertonia can be caused by increases in passive stiffness and enhanced stretch reflexes (spasticity) and is frequently managed clinically using passive stretches. However, the optimal parameters of stretching such as the applied torque and stretch duration remain unclear. During commonly prescribed ankle plantarflexor stretches pwMS produced higher torques when standing in a weight bearing position compared to stretches applied using the upper limbs. Stretches could be held for 120 seconds on average and stretch duration was mainly limited by fatigue. People with higher disability tended to favour more supported stretching positions. The effects of stretching for either 30 or 10 minutes using a customised motor at three torque levels covering the range that MS participants could produce was investigated. Compared to the 10 minute stretch, greater reductions in passive stiffness and greater increases in range of movement (ROM) were seen immediately following the 30 minute stretch with the effects being sustained for the 30 minute post stretch period. Higher levels of applied torque resulted in a greater change in ROM however; there was no effect of applied torque on passive stiffness. Stretch reflex mediated stiffness was unaffected by the stretching intervention and showed transient post stretch increases. Ultrasonography was used to investigate changes in muscle–tendon length and strain in pwMS and controls and following stretching. PwMS showed evidence of stiffer muscles and increased tendon length at baseline compared to controls. Following a 10 minute stretch overall muscle length did not increase in pwMS, although increases in strain in the musculotendinous junction region were observed suggesting that more proximal regions of the muscle was likely to have contributed significantly to overall stiffness. This work highlights that stretch duration and levels of applied torque are critical factors in determining the effectiveness of stretches. The pathological mechanisms underlying hypertonia at a molecular and structural level and the effects of stretching on components of the musculo-tendinous structure and on functional ability should be ascertained.
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