The Effects Of Incremental Loading On Center Of Pressure And Sagittal Plane Kinematics In Healthy Adults During Safety Bar Squat

PURPOSE: To determine if increasing load during a safety bar squat creates significant changes in ground reaction forces (GrF), medial-lateral (ML) center of pressure (CoP) distance, anterior-posterior (AP) CoP distance, and sagittal plane kinematics in healthy individuals. METHODS: Ten healthy subjects (5 males, 5 females; 157.55 lbs ± 33.15 lbs; 23.8 ± 1.23 years old). Participants completed a standardized 5-minute warm-up. APDM sensors were placed on each subject’s feet, lower legs, upper legs, lumbar spine, and sternum to record sagittal plane joint kinematics. Participants completed a maximum of three squats in the following sequence: body weight (BW), squat with the bar, adding 35%, 50%, 65%, and 80% of the participant’s BW. Participants performed a squat with self-selected foot positioning and squat depth based on comfort. Force plates were used to measure peak vertical force (PVF), combined ML CoP distance, and combined AP CoP distance. For statistical analysis, univariate linear regressions were utilized to determine the relationship between CoP distance and sagittal plane ranges of motion of lumbar flexion, hip flexion, knee flexion, and dorsiflexion with PVF for each squat condition. A between-group one-way ANOVA was utilized to compare changes in PVF, ML CoP distance, AP CoP distance, and segmental sagittal range of motion. RESULTS: ML CoP, AP CoP, and sagittal plane range of motion were not independent predictors of PVF at different weights (p= > .05). There is a significant difference between BW and PVF for loads of 50%, 65%, and 80% BW (p = <.05, eta squared = .324). There was no significant difference among PVF for 50%, 65%, and 80% BW (p= > .05). CONCLUSIONS: There is consistent PVF, sagittal kinematics, and CoP distance in healthy individuals’ squat performance with loads up to 80% of BW. The significant difference and large effect size between BW peak vertical force and PVF in loads of 50%, 65%, and 80% BW suggests that loads above 50% BW require greater force production demands. No significant difference between PVF for 50%, 65%, and 80% BW may suggest that healthy individuals' kinematic performance and capacity demands are the same for loads between 50-80% BW. These findings may be useful when comparing squat performance in an injured population.