Event standardization of sit-to-stand movements

Unlike gait analysis, no commonly accepted method for studying sit-to-stand (STS) movements exists. Most previous studies describing STS events used various methods to identify movement events while restricting sitting positions and movements. The present study observed natural rising from a sitting position using a simple method for measuring this common task. The purposes of this study were to compare commonly performed STS movements and to propose a standard system for defining identifiable sequential events.

Ground reaction forces of 100 adults who were healthy (50 male, 50 female) were recorded using a force platform as each participant performed 4 methods of rising from sitting on a standard chair. The 4 STS conditions were: with arms free, with hands on knees, using armrests, and with arms crossed.

For each subject, 11 recorded events from the vertical, fore-aft, and lateral dimensions were identified for all arm-use conditions. The only significant and clinically relevant force difference among arm-use conditions was that the armrests condition produced less average force than the other 3 conditions during the seat-off and vertical peak force events. Among average event times, the armrests condition showed significantly longer time to the vertical peak force event than the other conditions.

Because these events occurred invariably in sequential order for every individual for all arm-use conditions in a relatively large sample of observations during natural STS movements, this method may be useful for establishing a standard method to assess and compare patient functionality and allow comparisons among STS research studies.