The Effect Of An Eccentrically-biased Hamstring Strengthening Home Program On Knee Flexor Strength And The Length-tension Relationship
Karl F. Orishimo, Malachy P. McHugh, FACSM.
Rehabilitation emphasizing eccentrically-biased exercises requiring no equipment have been shown to result in a more rapid return to sports after hamstring strains. However, the actual training stimulus for such exercises and their effect on the length-tension relationship has not been established.
Purpose: To assess the effects of a 4-week, home-based, eccentric hamstring strengthening program on knee flexion strength and the length-tension relationship. We hypothesized that this protocol would improve strength and produce a rightward-shift in knee flexor length-tension relationship.
Methods: 10 healthy, uninjured subjects (8M, 2F) participated in this study. Baseline isometric strength was assessed with subjects seated in a dynamometer with the hip flexed to 50 degrees from horizontal. Knee flexion strength was measured at 90, 70, 50 and 30 degrees of knee flexion. Hamstring flexibility was also measured as the angle of maximum knee extension tolerated in this position. Following the baseline test, subjects were given a progressive training program of four exercises to be performed three times per week for 4 weeks. The 4 exercises were (1) standing hip extension with elastic resistance, (2) standing trunk flexion (The Diver), (3) standing split (The Glider), and (4) supine eccentric bridge (The Slider). Following completion of the training program, strength and flexibility tests were repeated. A Training (pre to post) by Angle repeated-measures ANOVA was used to assess the effects of the training program on knee flexion strength and the length-tension relationship.
Results: Maximum knee extension angle (i.e. hamstring flexibility) was increased by 5.7±6.6 degrees following the training protocol (p = 0.001). Knee flexor strength improved by 7.9% (p = 0.033), although this improvement was not angle-specific (Training by Angle p = 0.641). Neither baseline flexibility (p = 0.292) nor baseline strength (p = 0.599) affected the improvement in knee flexion strength.
Conclusions: This short term home training program resulted in a small but significant strength improvement but without shifting the length-tension relationship to greater strength at longer muscle lengths. The training stimulus might be improved by identifying exercises with greatest hamstring activation and elongation.
Nicholas Institue of Sports Medicine and Athletic Trauma, Lenox Hill Hospital, New York, NY.