RT3 accelerometer shoulder activity: Discrimination of activity levels by the RT3 accelerometer for the assessment of shoulder physical activity (SPA)

We investigated whether the RT3 accelerometer can be used to discriminate and characterize the different levels of shoulder physical activity (SPA) in both patients and healthy adults. Twenty healthy adults and 20 patients with shoulder disorders (SDs) performed activities at 5 levels of difficulty (easy, easy–moderate, moderate, hard–moderate, hard) with the same RT3 accelerometer fixed on the arm. The Vector Magnitude (VM) is the square root of the sum of squares from each axis to determine the overall magnitude of activity. The SPA counts of healthy group were significantly higher than the patient group in every level except easy (31–38 VM counts difference, p < 0.01). For both groups, the hard task demonstrated higher counts as compared to the other tasks. The easy task showed lower counts as compared to the other tasks. In the patient group, significant correlation between FLEX-SF scores and counts from the RT3 (R = −0.72, p < 0.05) was found in the moderate tasks. The results of this study showed that RT3 can be a potential measurement tool to (1) characterize the difference of SPA between two groups; and (2) partially discriminate the different levels of SPA. The correlations between self-reported function scores and SPA RT3 counts are dependent on self-reported task difficulty.