INTRODUCTION: Conventional and functional knee strength ratios, defined using peak joint moment of the flexors and extensors, are used in practice to estimate injury risk (Baroni et al., 2020). Despite literature commonly reporting these values there remains uncertainty regarding their functional value (Kellis et al., 2022). It has been suggested that using a time-series metric from angle-specific joint moments might be more successful at identifying injury risk (Read et al., 2022). Therefore, the aim of this study was to compare discrete strength ratios commonly used in practice with angle-specific ratios to determine the differences between the two measures. METHODS: Twenty-eight footballers were recruited from the same English Premier League club (age: 22±4 y; stature: 1.81±0.07 m; body mass: 75.2±6.8 kg). Isokinetic testing was conducted for the knee flexors and extensors in a concentric motion at two angular velocities (60°/s and 240°/s) and in an eccentric motion (for the knee flexors only) at one angular velocity (30°/s) using an isokinetic dynamometer (Biodex Medical Systems). Conventional, discrete H:Q ratio`s (c HQR-D) were calculated as the ratio between peak joint moment in the flexors and extensors at 60°/s. Functional, discrete H:Q ratio`s (f HQR-D) were calculated as the peak joint moment in the flexors during the eccentric condition (30°/s) and the extensors at 240°/s. Angle-specific ratios (cHQR-AS and fHQR-AS) were computed as the ratio between flexor and extensor joint moments for all angles where both muscle groups were in the isokinetic range. Mean absolute residuals were then computed to compare between discrete and angle specific ratios. RESULTS: Peak joint moment for flexors and extensors at 60°/s was 129.4±21.6 and 240.9±35.6 Nm, respectively (cHQR-D = 0.54±0.07). Eccentric peak joint moment for the flexors was 165.9±34.6 Nm, and concentric peak moment for the extensors at 240°/s was 145.3±18.4 Nm (fHQR-D = 1.15±0.21). Throughout the isokinetic range, average cHQR-AS ranged from 0.41-0.98 with a mean absolute residual of 0.11±0.11 versus cHQR-D. In comparison, the average fHQR-AS ranged from 0.98-1.33 with a larger mean absolute residual of 0.26±0.14 versus fHQR-D. CONCLUSION: Neither conventional nor functional discrete ratios were fully representative of angle-specific ratios throughout the isokinetic range. However, the average residual for the conventional ratio was lower than the functional ratio, despite a greater range of values for cHQR-AS. Suggesting that discrete conventional ratios are more representative of angle-specific ratios over a greater range of joint angles, compared to discrete functional ratios. Furthermore, discrete functional ratios are not representative of angle specific functional ratios, which could mask athletes who may have fHQR deficits and may be at risk of injury.
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