Accelerometer output and its association with energy expenditure during manual wheelchair propulsion

Study design:This is an experimental design.Objectives:This study examined the association between rates of energy expenditure (that is, oxygen consumption (VO 2)) and accelerometer counts (that is, vector magnitude (VM)) across a range of speeds during manual wheelchair propulsion on a motor-driven treadmill. Such an association allows for the generation of cutoff points for quantifying the time spent in moderate-to-vigorous physical activity (MVPA) during manual wheelchair propulsion.Setting:The study was conducted in the University Laboratory.Methods:Twenty-four manual wheelchair users completed a 6-min period of seated rest and three 6-min periods of manual wheelchair propulsion on a motor-driven wheelchair treadmill. The 6-min periods of wheelchair propulsion corresponded with three treadmill speeds (1.5, 3.0 and 4.5 mph) that elicited a range of physical activity intensities. Participants wore a portable metabolic unit and accelerometers on both wrists. Primary outcome measures included steady-state VO 2 and VM, and the strength of association between VO 2 and VM was based on the multiple correlation and squared multiple correlation coefficients from linear regression analyses.Results:Strong linear associations were established between VO 2 and VM for the left (R=0.93±0.44; R 2 =0.87±0.19), right (R=0.95±0.37; R 2 =0.90±0.14) and combined (R=0.94±0.38; R 2 =0.88±0.15) accelerometers. The linear relationship between VO 2 and VM for the left, right and combined wrists yielded cutoff points for MVPA of 3659 ±1302, 3630±1403 and 3644±1339 counts min -1, respectively.Conclusion:We provide cutoff points based on the linear association between energy expenditure and accelerometer counts for estimating time spent in MVPA during manual wheelchair propulsion using wrist-worn accelerometry. The similarity across wrist location permits flexibility in selecting a location for wrist accelerometry placement.