Objective Assessment of Strength Training Exercises using a Wrist-Worn Accelerometer

The 2008 Physical Activity Guidelines for Americans recommend that all adults perform muscle-strengthening exercises to work all of the major muscle groups of the body on at least 2 d.wk(-1), in addition to aerobic activity. Studies using objective methods of monitoring physical activity have focused primarily on the assessment of aerobic activity. To date, a method for assessing resistance training (RT) exercises has not been developed using a wrist-worn activity monitor. Purpose: The purpose of this study was to examine the use of a wrist-worn triaxial accelerometer-based activity monitor for classifying upper-and lower-body dumbbell RT exercises. Methods: Sixty participants performed 10 repetitions each of 12 different upper-and lower-body dynamic dumbbell exercises. Algorithms for classifying the exercises were developed using two different methods: support vector machine and cosine similarity. Confusion matrices were developed for each method, and intermethod reliabilities were assessed using Cohen's kappa. A repeated-measures ANOVA was used to compare the predicted repetitions, identified from the largest acceleration peaks, with the actual repetitions. Results: The results indicated that support vector machine and cosine similarity accurately classified the 12 different RT exercises 78% and 85% of the time, respectively. Both methods struggled to correctly differentiate bench press versus shoulder press and squat versus walking lunges. Repetition estimates were not significantly different for 8 of the 12 exercises. For the four exercises that were significantly different, the differences amount to less than 10%. Conclusion: This study demonstrated that RT exercises can be accurately classified using a single activity monitor worn on the wrist.