BrJ Sports Med 1996;30:313-318 Effect of passive stretching and jogging on the series elastic muscle stiffness and range of motion of the ankle joint

Objective-To determine the effect of stretching and jogging on the series elastic muscle stiffness of the plantar flexors and on the range of dorsiflexion at the ankle joint. Methods-24 healthy subjects participated in this study. Each subject undertook all of the following protocols, in random order: (1) stretching protocol: five 30 s static stretches with 30 s rest between stretches; (2) aerobic jogging protocol: subjects ran on a treadmill for 10 min at 60% of their maximum age predicted heart rate; (3) combined protocol: subjects ran first and then stretched. A damped oscillation technique was used to measure the series elastic stiffness of the plantar flexors. Dorsiflexion of the ankle was assessed with a weights and pulley system that moved the ankle joint from a neutral position into dorsiflexion passively. Electromyography was used to monitor the activity of the plantar and dorsiflexors during these procedures. The statistical analysis of these data involved an analysis of covariance Results-For decreasing series elastic muscle stiffness running was more effective than stretching (P < 0.05). In contrast, the results for range of motion showed that the combination protocol and the stretching only protocol were more effective than the running only protocol (P < 0.05) for increasing dorsiflexion range of motion at the ankle. Conclusions-Both jogging and static stretching exercises appear to be benefiNeuromuscular cial to individuals participating in sportResearch Unit, School ing activities. of Physiotherapy, (BrJ Sports Med 1996;30:313-318) Faculty ofHealth Studies, Auckland . Insttut ofTecnolgyKey terms: warm up; stretching; muscle stiffness; joint Institu e fTechnology, rag ofmto Auckland, range of motion New Zealand P J McNair S N Stanley Extensibility in soft tissues is related to the Correspondence to: Peter J McNair PhD, Neuromuscular Research Unit, School of Physiotherapy, Faculty of Health Studies, Auckland Institute of Technology, Private Bag, Auckland, New Zealand. Accepted for publication 9 July 1996 resistance of tissue as it lengthens. The ratio of the change in force to the change in length of the tissue is termed muscle stiffness,l the reciprocol of which is termed compliance. A muscle that is more compliant will lengthen with less resistance. Resistance to stretch will be determined by both mechanical and neural factors. With regard to the former, muscle and tendon are composed of varying amounts of collagen, polysaccharides, and water, and these constituents mainly determine the mechanical behaviour of these tissues.' In this respect, the muscle and tendon have elastic and viscous properties, and these can be represented as springs and damping pots respectively.2 As fig 1 shows, tendon is modelled as lying in series with the contractile elements (actin and myosin), while endomysial, perimysial, and epimysial connective tissues lie in parallel with the contractile elements. As all of these structures are viscoelastic, their resistance to lengthening is dependent on the time over which they are deformed and the rate at which the forces are applied to the tissues.' With respect to neurological factors, stretching muscle increases the discharge of muscle spindles.' The reflex response to a transient stretch has been shown to increase the stiffness of muscle considerably in both isolated preparations4 and in vivo muscle testing.5 The stiffness of the musculotendinous tissues will thus also be determined by the level of muscle activation. As muscle activation increases, the contractile elements stiffen, and at maximum isometric tension, contractile element stiffness can be of a similar magnitude to that of the tendon.6 The aetiology of muscle and tendon strains is thought to be multifactorial.' Among the factors implicated in these injuries is a loss of extensibility in the soft tissues.8 "Warm up" activities-which typically include aerobic and stretching exercises-have been advocated as an effective means of decreasing the incidence of muscle and tendon strains, the rationale being that aerobic exercises lead to increased temperatures in the tissues and this effect enhances the extensibility of the tissue. Indeed it has been shown that a muscle preconditioned by isometric contractions requires Parallel element (eg: endomysium, perimysium, epimysium) Contractile element Series elastic element (eg: tendon) Figure 1 A mechanical model of the viscoelastic properties of a musculotendinous unit. Elastic elements are represented as springs, while damping elements are represented as damping pots. 313 group.bmj.com on June 22, 2017 Published by http://bjsm.bmj.com/ Downloaded from