A validation test of using shoulder joint moment in evaluation of load in wheelchair propulsion

Manual wheelchair is an effective device for assisting independent life of motor disabled subjects. However, many users of manual wheelchair have been suffered from shoulder pain because propelling the wheelchair needs repetitive movement of upper extremities. The purpose of this study was to examine a validity of using shoulder joint moment in evaluation of load on the users in wheelchair propulsion. Since shoulder joint moment can evaluate mechanical load on the shoulder, the indexes are expected to provide information to help wheelchair propulsion in decreasing of shoulder pain. Two evaluation indexes derived from shoulder joint moment were tested in this paper: F
_t
/M
_s
and F
_r
/M
_s
, which showed contribution of shoulder joint moment (M
_S
) to wheelchair propulsion (tangential force on handrim F
_T
) and to the resultant force on handrim (F
_R
). These indexes were compared to the index F
_T
/F
_R
which was based on previous studies. Measurements of movements during wheelchair propulsion were performed with 3 healthy subjects on stationary wheelchair ergometer under the different conditions of propulsion speed and resistance of ergometer. Correlation coefficient between the proposed indexes and F
_T
/F
_R
were low (-0.51 to 0.10), which suggested that the proposed indexes had different information from the index F
_T
/F
_R
. Change of the index values between low and high propulsion load conditions were different between subjects. These results suggest that using indexes derived from shoulder joint moment would be effective in evaluation of load in wheelchair propulsion.