The Effect of Adverse Neural Tension on Hamstring Strength in Rugby Players
Michael B. Fox1, Dominic Mazza1, Susan Y. Kwiecien2, Malachy P. McHugh, FACSM2.
PURPOSE:The slump test is used to assess adverse neural tension in patients with low back or hamstring injuries. Hamstring stretching with the addition of neural tension causes acute strength loss (McHugh et al 2013). The purpose of this study was to assess whether rugby players presenting with a positive neural tension sign had associated hamstring weakness.
METHODS:The slump test and hamstring strength were assessed in 30 rugby players in preseason (age 26±5 yr, height 183±8 cm, weight 93±12 kg). The slump test was performed in sitting using cervical and thoracic flexion, and ankle dorsiflexion to increase neural tension during active knee extension. A positive sign was defined as pain or discomfort during knee extension in the slump position with or without dorsiflexion. Isometric hamstring strength was assessed in sitting, with the thigh flexed to 45o and the trunk flexed to 90° relative to the horizontal (Biodex System 2). Two contractions were performed at 100°, 80°, 60° and 40° knee flexion. Torque was corrected for limb mass and passive muscle tension. History of prior hamstring strain was documented. The effect of adverse neural tension and previous hamstring strain on angle specific hamstring strength was assessed by angle by group anova.
RESULTS:Ten of 30 players had a positive neural tension sign (5 bilateral = 15 positive neural tension signs). Fifteen players reported a previous hamstring strain (4 bilateral = 19 previous strains). Five of 19 previously injured hamstrings had a positive neural tension sign vs. 10 of the 41 uninjured hamstrings (P=0.9). Hamstring strength at longer muscle lengths was significantly lower in limbs with a positive neural tension sign versus the limbs with negative tests (angle by group P=0.013); 19% lower at 40° (long), 10% lower at 60°, 5% lower at 80°, 4% higher at 100° (short). Previous hamstring strain did not affect hamstring strength (angle by group P=0.99; group effect P=0.94).
CONCLUSIONS:These rugby players had a high prevalence of adverse neural tension (33%) and previous hamstring strain injury (50%). While previous injury did not impact hamstring strength, adverse neural tension caused marked hamstring weakness in the lengthened state. These results highlight the importance of identifying adverse neural tension in athletes at a high risk of hamstring strain injury.
1 Sports Therapy and Rehabilitation, New York, NY.
2 Nicholas Institute of Sports Medicine and Athletic Trauma, Lenox Hill Hospital, New York, NY.