Separating movement and gravity components in an acceleration signal and implications for the assessment of human daily physical activity.
van Hees VT, Gorzelniak L, Dean León EC, Eder M, Pias M, Taherian S, Ekelund U, Renstrom F, Franks PW, Horsch A, and Brage S
PLoS ONE. Dec 2012
(DOI : 10.1371/journal.pone.0061691)