The Impact of Participant Instructions on Lumbopelvic Rhythm During Forward Spine Flexion and Return

Spine motion and outcome measures derived therein may be confounded by the motion instructions provided to participants during data collection. This observational analytical laboratory-controlled study explored the impact of instructions for forward flexion trials on the lumbopelvic ratio (LPR) and spine kinematics. Twenty-five participants (mean age: 25.68 [9.31] y) performed forward bending trials with general instructions and then specific instructions to avoid hip motion and follow pacing. Participants were equipped with triaxial accelerometers at the lumbar spine (first lumbar vertebra) and pelvis (second sacral vertebra) to measure lumbar and pelvic excursions and LPR across the movement phases. The Wilcoxon signed-rank test was used to compare outcome variables between conditions. Lumbar excursion did not differ significantly between conditions, whereas pelvic excursion was significantly reduced in the specific instructions condition (P < .05). LPR showed considerable variability in the specific instructions condition, but there was no significant difference from the general instruction condition. Thus, instructing participants to limit hip motion appears to reduce pelvic excursion during forward bending without statistically affecting lumbar motion or the LPR. Providing and reporting clear and precise movement instructions to participants is important as they can change kinematics. Further, it appears that verbal instructions alone are unlikely to achieve complete spine movement isolation in all participants.