Application of Principal Component Analysis to Forward Reactive Stepping: Whole-body Movement Strategy Differs as a Function of Age and Sex

Background: Differences in reactive stepping strategy to recover balance have been investigated as a function of age and sex, but to date have been measured using discrete step or joint specific measures. It is unknown how whole-body strategy or underlying motor control objectives differ between age and sex groups in forward reactive stepping.

Research question: Does whole-body movement and/or motor control strategy differ as a function of age or sex in a forward reactive step to maintain balance?

Methods: Forty young and older adults (45 females, 35 males) participated in this study. All participants performed five reactive stepping trials in response to a forward balance perturbation while whole-body kinematics and ground reaction forces were collected. Features of whole-body movement strategy were determined using a principal component analysis model. Average principal component (PC) scores were compared between groups as a measure of whole-body movement strategy and within participant relative standard deviation of PC scores were compared to determine if motor control objectives differed across groups.

Results: Significant differences in reactive stepping strategy were observed both as a function of age and sex. Older adults had a greater step length and width, greater anterior trunk and pelvis translation, greater knee flexion angles and anterior translation of the hip joint on the stepping leg compared to young participants. Males had lesser step length and width, as well as greater trunk flexion compared to females. No differences in relative standard deviation of PC scores were observed between age or sex-based groups suggesting that motor control objectives were similar between groups.

Significance: This study demonstrates how whole-body movement strategy differs as a function of age and sex, which explains why previously reported discrete outcomes occur. Additionally, it does not seem that motor control strategy objectives differ between age or sex groups in forward reactive stepping.