Hamstrings to quadriceps peak torque ratios diverge between sexes with increasing isokinetic angular velocity

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Summary

Our purpose was to determine if females demonstrate decreased hamstrings to quadriceps peak torque (H/Q) ratios compared to males and if H/Q ratios increase with increased isokinetic velocity in both sexes. Maturation disproportionately increases hamstrings peak torque at high velocity in males, but not females. Therefore, we hypothesised that mature females would demonstrate decreased H/Q ratios compared to males and the difference in H/Q ratio between sexes would increase as isokinetic velocity increased. Studies that analysed the H/Q ratio with gravity corrected isokinetic strength testing reported between 1967 and 2004 were included in our review and analysis. Keywords were hamstrings/quadriceps, isokinetics, peak torque and gravity corrected. Medline and Smart databases were searched combined with cross-checked bibliographic reference lists of the publications to determine studies to be included. Twenty-two studies were included with a total of 1568 subjects (1145 male, 423 female). Males demonstrated a significant correlation between H/Q ratio and isokinetic velocity (R = 0.634, p < 0.0001), and a significant difference in the isokinetic H/Q ratio at the lowest angular velocity (47.8 ± 2.2% at 30°/s) compared to the highest velocity (81.4 ± 1.1% at 360°/s, p < 0.001). In contrast, females did not demonstrate a significant relationship between H/Q ratio and isokinetic velocity (R = 0.065, p = 0.77) or a change in relative hamstrings strength as the speed increased (49.5 ± 8.8% at 30°/s; 51.0 ± 5.7% at 360°/s, p = 0.84). Gender differences in isokinetic H/Q ratios were not observed at slower angular velocities. However, at high knee flexion/extension angular velocities, approaching those that occur during sports activities, significant gender differences were observed in the H/Q ratio. Females, unlike males, do not increase hamstrings to quadriceps torque ratios at velocities that approach those of functional activities.

Introduction

Decreased hamstrings strength relative to the quadriceps (H/Q) is implicated as a potential mechanism for increased lower extremity injuries.1, 2 Imbalances in hamstrings to quadriceps strength (i.e., hamstrings to quadriceps peak torque ratios, H/Q < 0.75) and bilateral hamstrings strength (dominant leg flexor >15% stronger than non-dominant) correlate to greater incidence of lower extremity injury in female collegiate athletes.2

Male and female relative hamstrings to quadriceps strength profiles diverge significantly during and following puberty.3 Isokinetic dynamometer measurements show that male athletes demonstrate significantly greater hamstrings peak torques with increasing maturity, while peak hamstrings torque remains stable with increasing maturational stage in female athletes.3 Thus, it appears that decreased hamstrings strength and H/Q ratios of female athletes relative to males may be related to the development of neuromuscular imbalances associated with the onset on maturation. These neuromuscular imbalances may increase injury risk in pubertal and post pubertal female athletes.3, 4, 5

Isokinetic testing assesses the ability of the agonist-antagonist musculature to co-contract during reciprocal extension–flexion motions. This assesses the ability of the antagonists (hamstrings) to “brake” the movement of the agonist (quadriceps).6 However, in contrast, the agonist of the ACL is the hamstrings, while the antagonist is the quadriceps, which increases strain on the ACL at the lower half of the knee flexion range (0–45°). Therefore, dynamic anterior–posterior stability, as well as abduction–adduction and internal–external rotational stability during multi-planar movements, is contingent upon hamstrings co-activation to resist anterior translation and tibial rotation resulting from quadriceps contraction and is likewise potentially dependent on H/Q ratio.7

The general purpose of this study was systematically to evaluate the literature to determine relative hamstrings to quadriceps strength of males and females. The specific purpose was to evaluate the cumulative isokinetic data, to determine if there were differences in isokinetic H/Q ratios between genders and to evaluate the effects of increased isokinetic velocity on these measures. Maturation disproportionately increases hamstrings peak torque at high velocity in males, but not females.3 These differences have not been reported at low velocities. Therefore, we hypothesised that mature females would demonstrate decreased H/Q ratios compared to males and the difference in H/Q ratio between sexes would increase as isokinetic velocity increased.

Section snippets

Methods

Medline, accessed through Pubmed, and Smart databases were searched, combined with cross-checked bibliographic reference lists of the publications, to determine studies to be included in this review. Investigations that analysed the H/Q ratio by the use of gravity corrected isokinetic strength testing and that evaluated an uninjured population of females and/or males reported between 1967 and 2004 were eligible for inclusion, as were studies analysing isokinetic strength and/or H/Q ratio for

Results

Twenty-two studies were included in this review and analysis based on the inclusionary and exclusionary criteria. These are presented in Table 1. The included studies contained a total of 1568 subjects (1145 male, 423 female). Isokinetic testing velocities ranged from 30°/s to 360°/s. The total mean H/Q ratios across all velocities were 51.9 ± 8.0% for females and 60.7 ± 9.5% for males (p  0.001).

The findings showed a significant correlation between H/Q ratio and isokinetic velocity in males (R = 

Discussion

The goal of this study was to review the effects of gender on H/Q ratio. An analysis of the published literature was employed to determine whether or not females and males respond to increased isokinetic angular velocity with increased hamstrings torque relative to their quadriceps torque. Review and analysis of the gravity-corrected isokinetic data published in the literature demonstrated significantly different changes in H/Q ratio with increased isokinetic velocity between males and females.

Acknowledgements

The authors would like to acknowledge funding support from National Institutes of Health Grant R01-AR049735 (TEH). In addition, we would like to acknowledge Paul Succop, Ph.D., for assistance with the statistical analysis. We would also like to acknowledge the assistance of Tiffany Evans for assistance with preparation and Thomas Guidone, PT, for critical reading of the manuscript.

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