Unilateral Eccentric Strength Training of the Human Quadriceps: Effect of Loading on Muscle Strength and Size

Abstract

Eccentric resistance training is effective at increasing muscular volume, force and power production. Eccentric contractions cause augmented myofibrillar tearing leading to greater potential for trained musculature to enhance repair. However, it is unclear what eccentric training protocol is most effective at stimulating significant physiological adaptations related to volume, force and power. PURPOSE: To examine the effect of variable eccentric resistance training loads on parameters of muscular fitness in the human quadriceps. METHODS: Maximum voluntary contraction (MVC), thigh circumference (TC), and strength-to-lean body mass ratio (MVC:LBM) were assessed in nineteen college-aged adults (six men, thirteen women) who completed eight weeks of unilateral strength training of the knee extensors. Subjects were randomly assigned to one of four training groups: eccentric high (EH, 90% 1-RM, N = 5), eccentric medium (EM, 70% 1-RM, N = 6), eccentric low (EL, 50% 1-RM, N = 4), or control (CON, concentric contractions at 50% 1-RM, N = 4). Subjects in each group performed four sets of ten repetitions, two times per week, for eight consecutive weeks. MVC, TC and MVC:LBM were measured before and after the eight week training program. RESULTS: There were no significant differences between trained and untrained legs for any measure (P > 0.05). However, when trained leg group comparisons of MVC and MVC:LBM change were made, EH (26 ± 14 vs. 51 ± 31 N, 0.53 ± 0.20 vs. 0.98 ± 0.41 N/kg) showed a significantly greater increase at post-testing compared to EM (42 ± 8 vs. 47 ± 7 N, 0.72 ± 0.17 vs. 0.81 ± 0.16 N/kg), EL (65 ± 10 vs. 64 ± 11 N, 1.10 ± 0.08 vs. 1.06 ± 0.09 N/kg), and CON (36 ± 8 vs. 36 ± 9 N, 0.77 ± 0.17 vs. 0.73 ± 0.20 N/kg) groups (P < 0.05). CONCLUSIONS: Our findings indicate that training at a relatively high load (90% 1-RM) is more effective than training at lower loads for increasing knee extensor force production, independent of any significantly correlated changes in whole-muscle size, over eight weeks of unilateral eccentric strength training of the quadriceps. However, because trained and untrained legs within groups exhibited similar increases in strength after the training period, the results are inconclusive.