Article Text

Role of neural tension in stretch-induced strength loss
  1. J Tallent1,
  2. B Greene2,
  3. C D Johnson2,
  4. M P McHugh2
  1. 1Northumbria University, School of Psychology and Sports Sciences, Newcastle upon Tyne, UK
  2. 2Nicholas Institute of Sport Medicine and Athletic Trauma, Lenox Hill Hospital, New York, USA

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.

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