STRETCHING ACUTE

RESPONSES TO STRETCHES

WITH ISOKINETIC DYNAMOMETERS

Traditional, isokinetic dynamometers have been used to measure variables associated with strength, power and endurance, while the effects of stretching have often only involved goniometric measurements of range of motion. However, in recent years a number of studies have made use of isokinetic dynamometers to measure the amount of resistance occurring as a joint moves through its range of motion. The combination of these variables has provided a greater understanding of the effects of stretching. Furthermore, dynamometers can be used as training equipment to facilitate improvements in range of motion. This paper will examine the findings of studies that have utilised dynamometers primarily to investigate the acute adaptations that occur when we stretch.

By Dr Peter McNair, PhD

Most commonly these studies have been undertaken at the ankle and knee joint and typically involve the joint being moved to a percentage level of maximum range of motion. Figure 1 shows a typical torque-angle curve as a joint moves to 80% of maximum range of motion. The curve is characterised by a non linear region earlier in the range of motion in which the resistive torque to lengthening is low. During this time un-crimping is occurring in the collagen fibrils. Thereafter, a greater rate of increase in resistive torque is encountered, and the relationship between the resistive torque and motion is more linear. Increased lengthening and slippage of collagen fibrils and the redistribution of mobile molecules and fluid in the tissues is thought to be responsible for the changes observed in this region.

In such stretches, the variables of interest are the maximum force, stiffness, and the passive energy absorbed as measured by the area under the torque-angle curve. In many instances, researchers may select a particular region of the torque-angle curve to measure stiffness and passive energy absorbed (eg. final 50% or 10% of the range of motion). Some researchers (1) have been interested in the forces recorded when the joint is moved back to the starting position. In doing so, they are investigating mechanical energy loss and can calculate the energy lost in the system. More recently, some authors (2) have calculated damping coefficients associated with the viscous properties of the tissues from these curves. These measures are related to the shock absorbing properties of the muscles.

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Following an acute stretching session (eg. 3 times 30 second sportEX medicine 2007:34(Oct):6-9