Comparison of three strategies of trunk support during asymmetric two-handed reach in standing.

No trunk support (NTS) was compared to a lower trunk support (LTS) of leaning against a worktable and a dynamic upper trunk support (UTS) using postural kinematics, trunk extensor muscle activity and subjective rating of both comfort and effort. Ten females completed 3 repetitions where they lifted 0 and 5 kg load from a symmetrical position at hip-height to a 45° asymmetric position at: i) hip-height and ii) shoulder-height. Human motion capture showed trunk flexion decreased by 12° ± 10 with trunk support with hip-height reach. The table blocked axial rotation of the pelvis which was compensated by an additional 8° ± 6 rotation of the thoracic segment. Surface EMG of the lumbar erector spinae, contralateral to reach, showed the UTS to be almost twice as effective as the LTS with shoulder-height reach with a 30% ± 18 reduction. With hip-height reach, UTS resulted in a smaller reduction equal to 23% ± 27 while the LTS had no effect. Further investigation is needed to determine optimal performance parameters for trunk support with complex, dynamic trunk postures and whether altered kinematics arising from LTS have higher risk of upper back discomfort.