Abstract

The aim of the study was to examine whether increased neural tension during passive hamstring stretching contributes to stretch-induced strength loss. Eleven healthy subjects performed maximal isometric knee flexion contractions (100°, 80°, 60° and 20°) before and after a series of hamstring stretches (six 1-min stretches), performed in either a spinal neutral position or a neural tension position. Effect of stretch technique (neutral or neural tension) on passive resistance to stretch, strength-induced strength loss and electromyography activity during strength tests was assessed with repeated measures analysis of variance. Passive resistance to stretch was reduced by 19% after the series of stretches (p=0.001) with no difference between neutral or neural tension stretches (p=0.41). Stretch-induced strength loss was greater (p=0.043) after the neural tension stretches (13%) vs the neutral stretches (5%). There was an apparent rightward shift in the length tension curve after neutral stretches with a 15% strength loss at muscle lengths shorter than optimum, and a 10% gain in strength at muscle lengths longer than optimum (p<0.001). This effect was not apparent after neural tension stretches where strength loss was 21% at muscle lengths shorter than optimum and 9% at muscle lengths longer than optimum. The addition of neural tension to hamstring stretching increased stretch-induced strength loss but this was not associated with observable neural inhibition. The absence of a rightward shift in the length-tension curve after neural tension stretching indicates that muscle fibre shortening during isometric contractions was unaffected, presumably because tendon-aponeurosis compliance was not increased.