VALIDATION OF ENERGY EXPENDITURE PREDICTION ALGORITHMS IN ADULTS USING THE ACTICAL ELECTRONIC ACTIVITY MONITOR

Abstract

PURPOSE The purpose of this study was to validate the use of the Actical (Mini Mitter Co., Inc., Bend, OR) electronic activity monitor for predicting energy expenditure (EE) in healthy adults. METHODS Twelve men (Mean±SD: 33.5±7.8 yrs, 83.0±8.7 kg) and 12 women (39.3±10.2 yrs, 68.9±5.3 kg) visited the lab once to perform 9 activities: Typing, hand writing, card sorting, floor sweeping, carpet vacuuming, table surface dusting, and treadmill walking (5 mins each at 67 and 80.4 m/min) and jogging (5 mins at 120.6 m/min). Subjects wore Actical monitors on the non-dominant wrist, on the ankle of the same side of the body, and on the right hip just posterior to the iliac crest during all activities. Actual EE was determined using the VmaxST portable metabolic system (SensorMedics Corp., Yorba Linda, CA) which was carried in a small pack and worn on the back during all activities (equipment mass = 1.14 kg). The last two 60 sec sample averages from both the metabolic system (units of METs) and the Actical monitors (units of counts/min) were extracted from the raw data and used to generate separate MET prediction algorithms (standard linear regression procedures) for each monitor location. Each algorithm included: 1) Lower Actical cutoff value (< 250–500 counts/min; no prediction equation applied); 2) Equation predicting METs between the lower cutoff and an upper cutoff (1200–1500 counts/min); 3) Equation predicting METs higher than the upper cutoff. Predicted METs from each algorithm was compared with actual METs using PPM correlations, SEE, and standard residual analyses. RESULTS Algorithms for the ankle (R = 0.77, SEE = ±1.4 METs, P < 0.001), hip (R = 0.94, SEE = ±0.8 METs, P < 0.001), and wrist (R = 0.90, SEE = ±1.0 METs, P < 0.001) monitors provided reasonably accurate predictions of METs. CONCLUSIONS Though the hip and wrist locations appear to be most promising, further research should verify this in field settings. This study was funded by a grant from the Mini Mitter Co., Bend, OR.