Effect of Three Different Muscle Action Training Protocols on Knee Strength Ratios and Performance

Hamstring to quadriceps (H:Q) ratios are often used to assess strength imbalances. The aims of this study were to compare 3 different muscle action training protocols on H:Q strength balance and functional performance. Forty untrained men (age: 22.87 +/- 2.28 years, mass: 70.66 +/- 11.049 kg, ht: 174.29 +/- 6.90 cm) performed 6 weeks of training on an isokinetic dynamometer. They were randomly assigned to one of 4 groups; concentric quadriceps and concentric hamstring (CON/CON), eccentric quadriceps and eccentric hamstring (ECC/ECC), concentric quadriceps and eccentric hamstring (CON/ECC), or no training. Mixed Factor analyses of variance were used to compare interactions for variables pretest and posttest between groups (p < 0.05). The ECC/ECC group showed significant increases in H:Q functional ratio (pre = 0.73 +/- 0.092, post = 0.87 +/- 0.098), ECC peak torque (PT) (pre = 226.44 +/- 67.80 N.m, post = 331.74 +/- 54.44 N.m), isometric PT (IPT) (pre = 173.69 +/- 41.41 N.m, post = 203.091 +/- 30.82 N.m), countermovement jump (CMJ) (pre = 52.73 +/- 6.95 cm, post = 58.16 +/- 6.10 cm), and drop jump (DJ) (pre = 52.91 +/- 6.080 cm, post = 58.20 +/- 7.72 cm), whereas the CON/CON group increased the rate of torque development (pre = 152.19 +/- 65.0074 N.m.s(-1), post = 225.26 +/- 88.80 N.m.s(-1)). There were no differences between groups for CON PT, squat jump, conventional ratio or 40 m sprint. Our findings suggest that ECC/ECC training may be the most effective at increasing functional H:Q strength ratios, as well as ECC PT, IPT, CMJ, and DJ performance. Eccentric training increases ECC PT, thereby increasing the functional H:Q ratio. Eccentric training also improves vertical jumping involving ECC actions. CON/CON training may be more effective at increasing explosive muscle strength.