Comprehensive isokinetic analysis of hamstring and quadriceps strength profiles in football players

Abstract

Football players experience increased risks of lower limb injuries, particularly hamstring strains and knee ligament damage, often attributed to muscle imbalances. This study aimed to conduct a detailed isokinetic assessment of the knee joint, focusing on both kicking and supporting legs, involving 24 football players from the university football team of SWU “Neofit Rilski”. The objective was to monitor the physiological and biomechanical characteristics of the thigh musculature. Isokinetic measurements of knee joint extensors (quadriceps) and flexors (hamstrings) strength were conducted bilaterally at angular velocities of 60, 180, and 300 °/s A comparative analysis included traditional parameters - peak torque (PT, Nm), average power (AP, W) and total work (TW, J) - together with additional parameters such as time to peak torque (TPT) and acceleration time (AcT). Conventional H/Q ratios were used for quadriceps and hamstring strength balance evaluation, and potential side-to-side strength deficits were calculated. Results indicated that the kicking leg (KL) demonstrated significant strength superiority (Wilcoxon, p < 0.05) compared to the supporting leg (SL). PT values in both antagonist groups were reduced when compared to those in other studies. Additionally, at low speeds (60 °/s), the time to PT was significantly prolonged, distinguishing these football players from their professional counterparts. Differences in time parameters, work capacity, and power at moderate velocity – 180o/s, were observed in both muscles’ groups, with the SL having lower values compared to the KL. At 60o/s and 300o/s the extensors of the SL had a longer time to reach AcT and TPT and a more reduced AP than the KL. The TW of Q and H is greater in the KL compared to the SL. The H/Q ratios between KL and SL, at all three measured speeds, fell below normal balance values, with nearly 75% of players exhibiting unilateral asymmetry in the KL and approximately 85% in the SL. This study provides evidence that a comprehensive isokinetic assessment, considering both traditional and additional parameters, is beneficial for university footballers. The findings revealed potential risks and susceptibility to noncontact knee injuries, offering valuable insights for the development of targeted training and therapy programmes.