Using an Accelerometer to Predict Mechanical Load of Physical Activities in Adults

Abstract

PURPOSE: The accepted method for quantifying impact forces on the lower skeleton involves force plates to quantify ground reaction forces (GRF) in a lab. This method is not feasible in free-living situations. Developments in accelerometer (accel) technology may provide the ability to evaluate the effects of mechanical loading on bone. Technology is preferred over a compendium approach since the GRF of activities such as jumping, jogging depend on the actual execution of the movement. The purpose of this project was to validate an accel for the prediction of mechanical load by comparing its output to GRF. METHODS: Participants (n=20 males, 20 females; 18 to 39 yr) completed 10 repetitions of 9 activities (stand, walk, jog, run, 15 cm jump, step down from curb, drop down from curb, forward hop, side hop) on a force plate with an accel on their right hip. The activities were categorized as standing, ambulation, and jumping and used with 59 accel variables to predict mechanical load. Models were fit using the randomForest package in R using 10-fold cross-validation. Model performance was assessed using coefficient of determination (R2) and median absolute error. RESULTS: The percentage of variation explained by the models ranged from 0.32 to 0.78 with median absolute errors ranging from 0.20 to 0.49. The best model (Model 2) contained the known activity categories and accel variables, but is not realistic for free-living situations where activity categories will not be known. The best free-living model was Model 5, which used derived activity categories and accel variables.Table: No title available.CONCLUSION: Models containing the accel variables performed better than those containing only activity categories. The accel data can be used to predict categories and GRF. Accels provide valuable objective information when evaluating mechanical loading on bone and should be used when examining bone-strengthening physical activity in free-living situations.