Is there a relationship between isometric hamstrings-to-quadriceps torque ratio and athletes’ plyometric performance?

BACKGROUND: The application of the modified reactive strength index (RSI(mod)) and isometric hamstrings to quadriceps (H:Q) torque ratio to monitoring the athletes’ performance is well established, but their relationship to each other still remains unknown. Therefore, the purpose of this investigation was to clarify whether there is a relationship between RSI(mod) and the isometric H:Q torque ratio. METHODS: Twenty-one male recreational athletes (age, 24.89 ± 4.46 years; weight, 74.11 ± 8.66 kg; height, 179.78 ± 6.76 cm) volunteered to participate in this research. Their isometric H:Q torque ratio via hand-held dynamometer and jumping performance variables during the stop jump (STJ), double leg-drop vertical jump (DL-DVJ), and single leg-drop vertical jump (SL-DVJ) tasks were measured. Also, the RSI(mod) was calculated by dividing the vertical jump height by the time to take-off. Pearson correlation coefficients were used to determine the relationship between the RSI(mod) and jumping performance variables. RESULTS: The result showed a significant strong positive relationship between the H:Q torque ratio and STJ performance based on the RSI(mod) (p = .027, r = .724). Although, there was a moderate positive relationship between the H:Q torque ratio and jumping height of the STJ task, but it wasn’t statistically significant (p = .096, r = .588). Also, no significant relationship was found between the H:Q torque ratio and all jumping performance variables of the DL-DVJ and SL-DVJ tasks (p ≥ .05). CONCLUSION: The current study exhibited that the isometric H:Q torque ratio correlates to STJ performance based on RSI(mod) but not to SL-DVJ and DL-DVJ. Notably, the difference in results between jumping tasks can be attributed to the complexity of the movement, which means that the RSI(mod) is probably related to other factors. Therefore, the isometric H:Q torque ratio used to monitor the athletes’ performance couldn’t independently represent the jumping performance that is determined by RSI(mod).