Coordinate activity of the quadratus lumborum posterior layer, lumbar multifidus, erector spinae, and gluteus medius during single-leg forward landing

This study aimed to clarify the differences in electromyographic activity between the quadratus lumborum anterior (QL-a) and posterior layers (QL-p), and the relationship among trunk muscles and gluteus medius (GMed) activities during forward landing. Thirteen healthy men performed double-leg and single-leg (ipsilateral or contralateral sides as the electromyography measurement of trunk muscles) forward landings from a 30 cm-height-box. The onset of electromyographic activity in pre-landing and the electromyographic amplitude of the unilateral QL-a, QL-p, abdominal muscles, lumbar multifidus (LMF), erector spinae (LES), and bilateral GMed were recorded. Two-way ANOVA was used to compare the onset of electromyographic activity (3 landing leg conditions × 10 muscles) and electromyographic amplitude among (3 landing leg conditions × 2 phases). The onset of QL-p was significantly earlier in contralateral-leg landing than in the double-leg and ipsilateral-leg landings. The onset of LMF and LES was significantly earlier than that of the abdominal muscles in contralateral-leg landing. QL-p activity and GMed activity on the contralateral leg side in the pre-landing were significantly higher in contralateral-leg landing than in the other leg landings. To prepare for pelvic and trunk movements after ground contact, LMF, LES, QL-p on non-support leg side, and GMed on support leg side showed early or high feedforward activation before ground contact during single-leg forward landing.