PlayerLoadTM: Reliability, Convergent Validity, and Influence of Unit Position During Treadmill Running

Barrett, S., Midgley, A., Lovell, R.

Purpose: This study aimed to assess the test-retest reliability and convergent validity of PlayerLoadTM, measured using a triaxial accelerometer, during a standardized bout of treadmill running.
Methods: Forty-four team-sport players completed two standardized incremental treadmill running tests (speeds ranging from 7 to 16 km/h) seven days apart. Oxygen uptake (V02; n = 20), heart rate (n = 44), and triaxial accelerometer data (PlayerLoad; n = 44) recorded at both the scapulae and the center of mass (COM) were collected. The accelerometer data from the individual planes of PlayerLoad (anteroposterior [PLap], mediolateral [PLMl], and vertical [PLv]) were also analyzed.
Results: Moderate to high test-retest reliability was observed for PlayerLoad and its individual planes (ICC .80-97, CV 4.2-14.8%) at both unit locations. PlayerLoad was significantly higher at COM compared to the scapulae (223.4 ± 42.6 vs 185.5 ± 26.3 arbitrary units; P = .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 = .001) but lower for PLV (scapulae 55.7% ± 5.3%, COM 49.5% ± 6.9%; P = .001). Between-subjects correlations between PlayerLoad and V02, and between PlayerLoad and heart rate were trivial to moderate (r = -.43 to .33), whereas within-subject correlations were nearly perfect (r = .92-98).
Conclusions: PlayerLoad demonstrated moderate to high test-retest reliability and showed convergent validity with measures of exercise intensity on an individual basis. However, caution is warranted when making between-athletes contrasts in loading and when using recordings from the scapulae to identify lower-limb movement patterns.

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