| Summary: | The aim of the thesis was to examine the utility of tri-axial accelerometer data (PlayerLoad™) during soccer, including its reliability, validity, and determinants, with special reference to potential implications for fatigue management and injury risk. The aims of the first experimental study (chapter 3) were to: 1) establish the test-retest reliability oftri-axial accelerometer data during a standardized bout of treadmill running; 2) examine the effect of accelerometer location upon PlayerLoad™ data; and 3) investigate the convergent validity of Player Load™ using heart rate and rate of pulmonary oxygen uptake (V0₂) as criterion measures of exercise intensity. Forty-four team-sports players performed two standardized incremental treadmill running tests (7-16 km·h⁻¹) 7 d apart. Players' V0₂ (n=20), heart rate (n=44), and tri-axial accelerometer data (n=44) were measured at both the scapulae (SCAP) and at the centre of mass (COM). A cumulative vector magnitude (PlayerLoad™ [PLvM]) together with individual-component planes of PlayerLoad™ (anterior-posterior PlayerLoad™ [PLAP ], medial-lateral PlayerLoad™ [PLML] and vertical Player Load™ [PLv]) were examined. PlayerLoad™ and its individual planes showed moderate to high test-retest reliability (ICC: 0.80-0.97; CV: 4.2-14.8%) at both unit locations. PlayerLoad™ was significantly higher at COM versus scapulae (223.4 ± 42.6 vs. 185.5 ± 26.3 au; p = 0.001). The percentage contributions of individual planes to PlayerLoad™ were higher for PLML at the COM (scapulae: 20.4 ± 3.8%; COM: 26.5 ± 4.9%; p = 0.001), but lower for PLv (scapulae: 55.7 ± 5.3%; COM: 49.5 ± 6.9%; p = 0.001). Between-subject correlations between PlayerLoad™ and V0₂, and between PlayerLoad™ and heart rate, were trivial to moderate (r = -0.43 to 0.33), whereas within-subject correlations were nearly perfect (r = 0.92 to 0.98). PlayerLoad™ had a moderate to high degree of test-retest reliability and demonstrated convergent validity with measures of exercise intensity on an individual basis. However, caution should be applied in making between-athlete contrasts in loading, and when using recordings from the scapulae to identify lower-limb movement patterns. Further research is required to investigate if multidirectional movements observed in team sports, such as soccer, effect the reliability of PlayerLoad™ Experimental study 2 (Chapter 4) aimed to examine the PLvM and the individual planars response to a 90-min laboratory controlled soccer match-play simulation. Five semi-professional and 15 university soccer players completed three trials (one familiarisation, two experimental) of SAFT⁹⁰ PlayerLoad™ and its individual planes were measured continuously using micromechanical-electrical systems (MEMS) positioned at the scapulae (SCAP) and near the centre of mass (COM). PlayerLoad™ and its individual planars showed moderate and high test-retest reliability at both locations (ICC: 0.80-0.99). No between-half differences in PLvM were observed; however, within-half increases were recorded at the COM, but only during the first half at the SCAP. Greater contributions to PLvM were provided by PLv and PLML when derived from the SCAP and COM, respectively. PLvM (COM: 1451 ± 168; SCAP: 1029 ± 113), PLAr (COM: 503 ± 99; SCAP: 345 ± 61), PLML (COM: 712 ± 124; SCAP: 348 ± 61) and PLv (COM: 797 ± 184; SCAP: 688 ± 124) were significantly greater at the COM compared to the SCAP. Player Load™ and its individual planes are reliable measures during SAFT⁹⁰ and detected within-match changes in movement strategy when the unit was placed at the COM, which may have implications for fatigue management. Inferring alterations in lower-limb movement strategies from MEMS units positioned at the SCAP should be undertaken with caution. Further research is warranted to examine the between-match variability of PlayerLoad™ and its individual planes during actual soccer match play. The principle aim of the third experimental study (Chapter 5) was to examine the within-match patterns of locomotor efficiency in professional soccer, determined as the ratio between tri-axial accelerometer data (PlayerLoad™) and locomotor activities. Secondary aims were to assess the between match variability and determinants of PlayerLoad™ during soccer match play. PlayerLoad™ and its individual planes were recorded during 86 competitive soccer matches in 63 English Championship players (574 match observations). PlayerLoad™, together with the locomotor activity (total distance covered [TDC]) were determined in 15-min segments. Locomotor efficiency was calculated using the ratio of PLvM and TDC (Player Load™ per metre). The proportion of variance explaining the within-match trends in PLvM, PLAr, PLML, PLv, and TDC was determined owing to matches, individual players, and positional role. PLvM, PLAr, PLML, PLv and TDC decreased after the initial 15-min match period (P=0.001; ƞ²=0.22-0.43, large effects). PL: TDC increased in the last 15 minutes of each half (P=0.001; ƞ²= 0.25, large effect). The variance in PLvM during soccer match-play was explained by individual players (63.9%; P=0.001) and between-match variation (21.6%; P=0.001), but not positional role (14.1 %; P= 0.36). Locomotor efficiency is lower during the latter stages of each half of competitive soccer match-play, a trend synonymous with observations of increased injury incidence and fatigue in these periods. Locomotor efficiency may be a valuable metric to identify fatigue and heightened injury risk during soccer training and match-play. In summary, Player Load™ has a moderate to high degree of test-retest reliability and near perfect convergent validity in comparison to HR and V02 at both the SCAP and COM during incremental treadmill running. Moderate to high test-retest reliability was further observed during SAFT⁹⁰ For both treadmill running and SAFT⁹⁰ , PlayerLoad™ was underestimated when worn at the SCAP in comparison to the COM, with different loading contributions observed in the three planes. Caution should be applied in making between-athlete contrasts in loading, and when using recordings from the SCAP to identify lower-limb movement patterns due to this underestimation. However, locomotor efficiency was lower during the latter stages of each half of SAFT⁹⁰ and competitive soccer match-play, a trend synonymous with observations of increased injury incidence and fatigue in these periods. Hence, locomotor efficiency may be a valuable metric to identify fatigue and heightened injury risk during soccer training and match-play.
|
|---|
