Instant of chair-rise lift-off can be predicted by foot-floor reaction forces.
OBJECTIVE
To develop a predictive model of the lift-off event during chair rise in healthy subjects, using foot-floor reaction forces.


BACKGROUND
An important event during chair rise is lift-off from the seat: the transition from the inherently stable three-point contact to the unstable two-point contact. There is no consistent or generally agreed upon method for estimating the time of lift-off when an instrumented seat is unavailable.


METHODS
Twenty healthy volunteers were divided into a testing set and training set. Each subject performed repeated chair rise trials at different speeds. Seat-floor and foot-floor forces, recorded with two force platforms, were used to develop a model of the lift-off event.


RESULTS
The magnitude of the vertical foot-floor reaction at lift-off (F0VF) was linearly related (R2 = 0.71, P < 0.001) to the peak vertical foot-floor reaction force (FMVF). A linear model was developed for the training group, which enabled prediction of lift-off time for the testing group with an absolute average error of 6 ms (about 1 data frame at 150 Hz). The linear model derived for the entire sample was: F0VF = 28.14 + FMVF * (0.6434).


CONCLUSIONS
The lift-off event for healthy subjects performing chair rise can be accurately predicted from foot-floor reaction forces, without requiring an instrumented seat.
Massachusetts General Hospital, Biomotion Laboratory, 40 Parkman St. RSL 010, Boston 02114, USA. cmcgibbon@partners.org
Chris A
CA
McGibbon
Dov
D
Goldvasser
David E
DE
Krebs
Donna
D
Moxley Scarborough
D001835:Body Weight; D005260:Female; D006801:Humans; D008297:Male; D008960:Models, Psychological; D011187:Posture; D011930:Reaction Time