Tri-Axial Dynamic Acceleration as a Proxy for Animal Energy Expenditure; Should We Be Summing Values or Calculating the Vector? PLOS One 7: e31187

Dynamic body acceleration (DBA) has been used as a proxy for energy expenditure in logger-equipped animals, with researchers summing the acceleration (overall dynamic body acceleration- ODBA) from the three orthogonal axes of devices. The vector of the dynamic body acceleration (VeDBA) may be a better proxy so this study compared ODBA and VeDBA as proxies for rate of oxygen consumption using humans and 6 other species. Twenty-one humans on a treadmill ran at different speeds while equipped with two loggers, one in a straight orientation and the other skewed, while rate of oxygen consumption ( _VO2) was recorded. Similar data were obtained from animals but using only one (straight) logger. In humans, both ODBA and VeDBA were good proxies for _VO2 with all r 2 values exceeding 0.88, although ODBA accounted for slightly but significantly more of the variation in _VO2 than did VeDBA (P,0.03). There were no significant differences between ODBA and VeDBA in terms of the change in _VO2 estimated by the acceleration data in a simulated situation of the logger being mounted straight but then becoming skewed (P = 0.744). In the animal study, ODBA and VeDBA were again good proxies for _VO2 with all r 2 values exceeding 0.70 although, again, ODBA accounted for slightly, but significantly, more of the variation in _VO2 than did VeDBA (P,0.03). The simultaneous contraction of muscles, inserted variously for lim