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PURPOSE: The study aimed to establish the test-retest reliability and convergent validity of PlayerLoad™ (triaxial-accelerometer data) during a standardized bout of treadmill running. METHODS: Forty-four team-sport players performed 2 standardized incremental treadmill running tests (7-16 km/h) 7 d apart. Players' oxygen uptake (VO2; n = 20), heart rate (n = 44), and triaxialaccelerometer data (PlayerLoad; n = 44) measured at both the scapulae and at the center of mass (COM), were recorded. Accelerometer data from the individual component planes of PlayerLoad (anteroposterior PLAP, mediolateral PLML, and vertical PLV) were also examined. 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 vs 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 VO2, 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 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-athletes contrasts in loading and when using recordings from the scapulae to identify lower-limb movement patterns.
Barrett et al. (Tue,) studied this question.