Date of Award

2014

Degree Type

Thesis

Degree Name

Master of Science (Exercise and Sports Science)

School

School of Exercise and Health Science

Faculty

Health, Engineering and Science

First Advisor

Professor Ken Nosaka

Second Advisor

Associate Professor Michael Newton

Abstract

Global positioning system (GPS) with a triaxial accelerometer is widely used to monitor movements of athletes in games and training, and “body load” (BL) representing the accumulation of the rate of changes in three planes of movements is obtained to determine the training load of a session. Deceleration, change of directions and stopping require eccentric contractions of leg muscles, potentially causing muscle damage and affecting athletic performance. Thus, it is important to monitor eccentric loading in games and training. A variable known as “eccentric index” (EI) purports to be a better representation of eccentric loading than BL. However, it is not known whether BL or EI accurately represents eccentric loading. The present study compared BL and EI during a drill consisting of several movements requiring eccentric contractions of leg muscles (Study 1), and monitored BL and EI over four training sessions of football (soccer) together with changes in maximal voluntary contraction (MVC) strength of the knee extensors and muscle soreness of the thigh muscles before and after each training session (Study 2).

In Study 1, 11 university students performed a drill consisting of 3 segments separated by 2 vertical jumps (segment 1: 70 m, segment 2: 50 m, segment 3: 60 m) with several movements including half turns (approximately 45°), 90° and 180° turns and a stop for a total distance of 180 m. All subjects performed the drill at 30%, 60% and 100% of their perceived maximal velocity, 2 trials for each velocity with a 5-min rest between trials. The same trials were repeated on two different days separated by at least 2 days. The time to complete the drill was measured by timing gates, and the time to complete each segment and entire distance, BL (GPSports, Australia) and EI (Athletic Data Innovations, Australia) of each segment were calculated from the GPS/accelerometer data using a specific software. One-way ANOVA compared the three velocities and three segments for the time, BL and EI, and a Pearson product-moment correlation was used to examine the relationships between them. The time to complete the drill was 102.9 ± 15.2 s for 30%, 56.3 ± 5.6 s for 60%, and 42.6 ± 3.1 s for maximum (100%) velocity, with each significantly different from the others (p

In Study 2, 6 state league level outfield football (soccer) players were monitored for 4 training sessions, each lasting for 90-120 minutes. BL and EI were calculated as per Study 1 and MVC strength and muscle soreness were assessed before and 1 day after each training session. BL and EI were similar across the 4 sessions; however a large variability in the EI was evident among the players. It was found that a high EI player had a high total mechanical work (total accumulation of changes of directions, accelerations and decelerations). No significant correlation was found between BL and EI, indicating that BL and EI showed different aspects of the movements. No significant changes in MVC strength and muscle soreness were observed after any training session, suggesting that muscle damage was not induced, because of the protective effect conferred by regular training.

From the two studies, it was concluded that EI was a better marker to quantify eccentric load than BL, however it is still unclear how accurately EI represents actual muscle damage of leg muscles, which warrants further studies

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