The relationship between isokinetic knee extensor and flexor muscle strength and vertical jump performance in university rugby union players of the North-West University

摘要

Introduction: Rugby is a professional sport which places emphasises on strength, power, speed and endurance. Therefore the accurate assessment of rugby performance is very important for sports and exercise therapists to enable peak performance for the players. Lower limb strength is often tested by means of isokinetic testing, whilst functional power is tested by means of the vertical jump test. Sophisticated equipment used in the measurement of performance indicators, are often not available in smaller communities and rural areas. A good correlation between laboratory testing and functional testing could be of great value for determining performance in less fortunate communities.udAim of Study: To determine the relationship between isokinetic strength testing of the quadriceps and hamstring muscle groups and vertical jump performance in rugby players.udMethods: Fifty one male, rugby players who were part of the Varsity Cup Tournament in (2011) participated in this study. Ethical approval was given by the Human Research Ethics Committee (HREC) of the University of Witwatersrand. Height and weight were measured. Isokinetic knee extensor and flexor strength was tested (Biodex system 4 dynamometer TM ) at 60˚/sec (5 repetitions), 180˚/sec (10 repetitions) and 300˚/sec (15 repetitions). A single leg vertical jump was done using the Vertec and the performance was assessed as maximal height jump in centimetres. Descriptive statistics (mean and standard deviation) are reported for all outcomes. The SPSS software (IBM. SPSS version 21) was used for analysis. A Pearson's Product Moment Correlation coefficient was calculated between the isokinetic parameters of quadriceps and hamstring muscles and the vertical jump height and power (watts). An independent t-test and a paired t-test were used to calculate the differences between the forward and backline players and the dominant (Dom) and non-dominant (ND) legs.udResults: The mean age of the participants was 21.4 ± 1.2 years; they were 1.83 ± 7.4m tall and weighed 99.3 ± 13.8kg. There were 26 forward players (mean height of 1.88 ± 7.2m and mean weight of 109.9 ± 10.3kg) and 25 backline players (mean height of 1.80 ± 5.5m and mean weight of 88.3 ± 6.1kg). The forwards were significantly taller and heavier than the backline players (p = 0.0001). The forwards produced significant greater peak power in the vertical jump than the backline players in both the dominant and non-dominant legs (p=0.0001). The PT (Nm) decreased as the angular velocity increased from 60˚/sec to 300˚/sec. A significant negative correlation (r = - 0.313; p = 0.025) between peak torque (PT) concentric strength from the hamstrings at 60º/sec and the vertical jump height on the non-dominant side were found. Quadriceps PT to vertical power at the higher velocities showed significant correlations at 180º/sec (dominant: r = 0.294; p = 0.011) udand 300º/sec (dominant: r = 0.352; p = 0.011; non-dominant: r = 0.293; p = 0.037). No significant correlations were found between peak torque and vertical jump height when corrected for body weight. When correlating PT and vertical jump power corrected for body weight significant negative correlations was found at 180º/sec (dominant: r = 0.319; p = 0.022; non-dominant: r = 0.305; p = 0.030) for the hamstrings.udConclusion: The findings from the presented study found no significant correlation between lower limb isokinetic knee muscle torque parameters and vertical jump performance in rugby union players. Future research should investigate the relationship between isokinetic testing and vertical jump height by including the parameters of a multi joint mechanism.