Author(s): POLSPOEL, M., REILLY, T., VAN TIGGELEN, D., CALDERS, P., Institution: MILITARY HOSPITAL QUEEN ASTRID , Country: BELGIUM, Abstract-ID: 2118

INTRODUCTION:
Wrist worn accelerometers are widely used in sport and exercise science to classify physical activity intensity. Most applications rely on fixed absolute cut points derived from general populations. However, during high intensity exercise, these thresholds may not accurately reflect relative physiological effort. The purpose of this study was to compare absolute and individualized wrist accelerometer cut points during a maximal 2400 m running test.
METHODS:
Seventy four active adults (43 men, 31 women; age 39.3 +/- 9.3 years) performed a maximal 2400 m run while wearing a non dominant wrist ActiGraph GT9X accelerometer and a chest worn heart rate monitor. Raw acceleration was processed as gravity corrected vector magnitude units. Absolute cut points were compared with individualized cut points derived from the mean of the three highest consecutive one minute epochs during the test. Agreement with heart rate based intensity classification was evaluated using Cohen kappa, intraclass correlation coefficients, and receiver operating characteristic analysis. Statistical significance was set at p < 0.05.
RESULTS:
Participants achieved near maximal physiological effort (peak heart rate 187 +/- 11 bpm; 95 +/- 4 percent of age predicted maximum). Using absolute thresholds, only 34.5 percent of participants were classified as predominantly vigorous during the maximal effort, while 47.3 percent were predominantly classified as light intensity. Individualized cut points improved agreement with heart rate based intensity. Kappa increased from 0.31 to 0.74 (p < 0.001). Intraclass correlation improved from 0.52 (95 percent CI 0.35 to 0.66) to 0.81 (95 percent CI 0.73 to 0.87). Discriminatory ability improved from AUC 0.68 (95 percent CI 0.58 to 0.78) to AUC 0.89 (95 percent CI 0.82 to 0.96).
CONCLUSION:
Absolute wrist accelerometer cut points substantially underestimated vigorous intensity during maximal running. Individualized calibration based on maximal performance improved agreement with physiological intensity and reduced misclassification at the upper intensity spectrum.