Title

Time Motion Analysis and Hip Abductor Strength Changes in Netball

Date of Award

2011

Degree Type

Thesis

Degree Name

Master of Science

School

School of Exercise and Health Sciences

Faculty

Faculty of Computing, Health and Science

First Advisor

Dr Sonya Girdler

Abstract

Netball is the most popular sport among females in Australia, with an estimated one million registered players nation wide. Despite its popularity, there are limited published studies about the physical and biomechanical demands of netball. This thesis assessed the type and frequency of lateral and landing movements that occur during a netball game (Study 1), examined the validity and reliability of handheld dynamometry to measure hip abductor strength that has been shown to be associated with the risk of non-contact anterior cruciate ligament injuries (ACL) injuries (Study 2), and investigated changes in hip abductor strength following a netball game (Study 3). In Study 1, the frequency of sidesteps, crossover cuts and lands during a netball game was analysed for five recorded netball games, and was compared across the five positional groups centre (C), wing attack (WA), wing defence (WD), goal attack (GA), and goal defence (GD). Average number of movements per game was 2668 of which C performed 27%, which was significantly (p < 0.05) greater compared with the other positions. Significantly (p < 0.05) more sidesteps and crossover cuts occurred at the small angle of cut (0°- 45°) compared to the large angle of cut (45° - 180°), and significantly (p < 0.05) more single leg lands occurred than double leg. Shuffles were used significantly (p < 0.01) more compared to all other lateral and landing movements. It was concluded that C performed significantly more lateral and landing movements, which may increase their level of fatigue and susceptibility to non-contact anterior cruciate ligament injuries. Across all positions single leg landings occurred more often than double leg landings, and are known to increase loads on the knee. Although the majority of change of direction movements occurred at the smaller angle there was a considerable amount performed with the greater angle, which has also been related to increased knee loads. The reported information provides context on which playing positions may be more susceptible to non-contact knee injuries and which movements may increase fatigue with a presumed increased risk of non-contact knee injuries. Although more research is needed in this area, this information is important in developing training to decrease knee injury risk. In Study 2, nine women (18 - 29 years) performed three maximal isometric contractions of the hip abductors at 0°, 15° and 30° of hip abduction on an isokinetic dynamometer, and a handheld dynamometer attached to the isokinetic dynamometer. The correlation assessed by a Pearson product-moment correlation coefficient (r) between the dynamometers was high (r = 0.9) at 0°, low at 15° (r = 0.69) and absent at 30° (r = 0.12). Reliability of the handheld dynamometer based on intraclass correlation coefficient (R) was moderate for 0° (R = 0.80) and 30° (R = 0.88) but poor at 15° (R = 0.55) for within-day (1 h apart), and moderate for 0° (R = 0.89) and 15° (R = 0.76), and good at 30° (R = 0.96) for between-days (1 week apart). The coefficient of variation was less than 7% for all angles. The handheld dynamometer’s surface area was increased by modification, and validity and reliability were re-assessed using another 10 (19-28 years) women. The correlation between the dynamometers improved at 15° (r = 0.9) and 30° (r = 0.8), and the reliability was high at all angles (R > 0.9, CV = 5%). It was concluded that the handheld dynamometer with modification could be used to reliably measure hip abduction isometric strength at different angles. Study 3 investigated changes in maximum voluntary hip abductor isometric strength before, within 5 min and 10 min after a netball game using the modified handheld dynamometer for 30 recreational netball players (18 - 34 years). For each time point, two 3 s maximum contractions at 15° of hip abduction with a 60 s rest between contractions were measured. A Category Ratio 10 scale was used to assess rate of perceived exertion (RPE) 30 min after the game. Hip abduction strength decreased (p < 0.01) by 12.0 ± 7.4% from pre (20.9 ± 3.2 kg) to post game (18.4 ± 3.1 kg) and was still lower (p < 0.01) than baseline at 10 minutes post game (19.5 ± 3.5 kg). The average RPE was 4.5 ± 2.2, and a low correlation (r = 0.39, p < 0.01) was evident between RPE and the decrease in the strength immediately post-game. These results show that a netball game induces neuromuscular fatigue to the hip abductors, which could increase the risk of non-contact ACL injuries.

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