NEUROMUSCULAR EFFECTS OF THERAPEUTIC MUSCLE STRETCH
PALMER, G.J., UNIVERSITY OF AUCKLAND, NEW ZEALAND. Dawson, N.J.
Research to date regarding therapeutic muscle stretch has been concerned with determining which method of stretch is the safest and/or the most effective in increasing range of movement. The cellular adaptations to muscle and especially tendon stretch are well documented. However, relatively few studies have documented the neuromuscular consequences of therapeutic muscle and tendon stretch. Those that have done have measured neuromuscular variables during muscle stretch. This study found, and was concerned with measuring the long- term neuromuscular effects of pass (PASS) and contract-relax (C-R) therapeutic muscle stretch. Soleus motorneuron excitability as indexed by the H-reflex was measured before and after PASS and C-R stretches to the soleus muscle. Results show a significant long-lasting decrease in H and M thresholds following these manoeuvres i.e. a concomitant decrease and increase in average H-wave and M-wave amplitudes respectively. Experiments were also performed to control for the effect of time i.e. no intervention, and for potential surface electrode movement during stretch i.e. intramuscular wire electrode experiments.
Early results from a further set of experiments show that electromechanical delay (E.M.D.), muscle contractility and H-reflex threshold were concomitantly affected by the muscle stretch techniques. The hypothesis to explain these changes may involve stretch-induced alterations in motoneuron excitability, synaptic transmission, muscle fibre membrane excitability, excitation-contraction coupling and contractility. Resulting from the "re-setting" of previously contracted areas of sarcomeres within the stretch muscle.
A SIMPLE METHODE FOR ESTIMATING ANKLE DORSIFLEXIOR MUSCLE STRENGTH
Ken-Ichi Sakamoto(Yamaguchi Univ. Sch. Med. Ube, Japan), Fujio Sakamoto, Nobusada Ishiko (Minami Kyushu Rehabil. Hosp., Kagoshima, Japan), Kazuto Tenma (Nagasaki Rehabil. Sch., Nagasaki, Japan)
We developed an apparatus that allows weight-lifting tasks of the ankle dorsiflexior muscle to assess the dynamic maximum strength (DMS), dynamic endurance (DD), and static endurance(SD) of the muscle under exercises of three types; single and 30 successive twitches with a rate of 30-60/min, and sustained concentric contraction of more than 30sec in duration. In the first and second type of exercises, DMS corresponding to each type was expressed by the maximal amount of work (in 10-1 joule) in the relationship between the work needed for weight-lifting and the weight of load( 0.9-7.9 Kg), whereas, in the second and third type, DD and SD were expressed, respectively, by the weight of load at which susceptibility of the muscle declined to 50% of the initial in the endurance-load relationship. In either type of exercises, the work(W) of a single twitch done against a load (L in Kg) was expressed by the formula, W = L X d, where "d" represents the distance (cm) between the resting and elevated positions of a load.
Healthy human subjects with and without trained leg muscles could perform all the three types of exercises with which two DMSs, DD, and SD can readily be obtained. However, in patients with deteriorated leg muscles, DMS based on single twitch, and SD could only be obtained, since most of them were difficult to repeat weight-lifting tasks at a constant rate. Our apparatus thus proved it useful in evaluating the muscle strength of a wide variety, ranging from a few to several hundreds X 10-1 joules.