The Role Of Neural Tension In Hamstring Flexibility

Abstract

PURPOSE: The Slump Test is used to assess adverse neural tension in patients with low back and hamstring injuries, and involves tensioning the neural tissues by flexing the cervical and thoracic spine during hamstring stretch. It is not known if this neural tension increases resistance to stretch. Therefore, the purpose of this study was to determine if neural tension, via the Slump Test, during passive hamstring stretch, affects maximum range of motion (ROM), stretch discomfort, resistance to stretch, or the electromyographic (EMG) response to stretch in healthy subjects. METHODS: Resistance to stretch, EMG response, ROM and stretch discomfort were measured bilaterally during passive hamstring stretches with and without neural tension (n=8, age 39±13 yr, weight 154±24 lb). Stretches were performed on an isokinetic dynamometer (5°/s) with subjects seated, the test thigh flexed 45° above the horizontal, and the seat back at 90° to the horizontal. Knees were passively extended from 90° flexion to maximum stretch tolerance. Starting leg (right or left) and test sequence (stretch with or without neural tension) were alternated between subjects (each stretch separated by 4 min). Stretch-induced EMG signals were normalized to maximum contractions performed prior to stretches. For neural tension stretches the cervical and upper thoracic spine were manually flexed by a physical therapist (Slump Test). RESULTS: Maximum ROM was 8±5° less for the stretches with neural tension versus stretches without neural tension (P<0.01). Stretch discomfort and EMG response were not different between stretches with and without neural tension (discomfort: 7±1 vs. 6±2, P=0.29; EMG: 3±5% vs. 5±5%, P=0.1). Resistance to stretch was progressively greater with increasing ROM for stretches with neural tension versus without neural tension (P<0.001). During the neural tension stretches resistance to stretch at maximum ROM was 12% greater than resistance at the same angle during stretches without neural tension (P<0.05). CONCLUSIONS: Maximum ROM was decreased and passive resistance to stretch was increased by increasing neural tension during passive hamstring stretch. This effect was not due to an increased EMG response to stretch. These data indicate that passive extensibility of neural tissues can limit hamstring flexibility.