Instruction in reliability and magnitude of evaluation parameters at each phase of a sit-to-stand movement

The sit-to-stand movement strategy of each subject is different depending on whether the subjects perform voluntary movements or have concrete instructions (i.e., stand quickly), which is strongly reflected in the performance of each sit-to-stand movement phase. Thirty young-adult male subjects participated in this study (M age=20.7 yr; SD=2.6). Subjects performed the two movements from a chair height adjusted to the subject's lower thigh length. In the self-administered (SA) condition, subjects voluntarily stood up from the chair without instruction, and in the assigned-ordered (AO) condition subjects stood up from the chair as fast as possible. Vertical floor reaction force and electromyograms of the rectus femoris and tibialis anterior muscles were measured, and 15 parameters were selected. The parameters in the phase between the peak value of the floor reaction force and completion of the movement was highly reliable regardless of instruction. However, other parameters had different reliabilities between the instruction conditions. In particular, the parameters in the phase between starting the movement and the peak value of the floor reaction force under the assigned-order were higher than those of the self-administered condition. Moreover, the sit-to-stand movement was conducted faster in the assigned-order condition during the phase between starting the movement and buttocks-syneresis, and the peak value of the floor reaction force and completion of the movement. From the above, in the assigned-order condition "as fast as possible," the anteflexion bending movement and extension of knee and trunk joints were faster, and anteflexion movement was repeated more similarly under a concrete instruction such as moving as fast as possible.