Principal Component Analysis of Lifting Kinematics and Kinetics in Pregnant Subjects

Abstract

Low back pain (LBP) is estimated to affect 50- 90% of women during pregnancy with more than a third of women reporting it as a severe problem compromising their ability to work during pregnancy and affecting normal daily life and sleep patterns. The aim of this study was to investigate the differences in kinematics and kinetics of lifting in pregnant subjects. Methodology Fifteen maternal subjects (age: 32.0±2.3 yrs; height: 165.3±5.5cm; weight: 71.7±6.4kg) were tested at the third trimester of pregnancy (32-38 weeks). Twenty-seven retro reflective markers were placed on the various bony landmarks of the subjects. An eight-camera motion analysis system (VICON 512, VICON, Oxford, UK) was used to record movements of the body segment and synchronised force plate (AMTI, Watertown, MA, USA) parameters in three dimensions. Eight non-pregnant subjects (age: 29.6±3.1yrs; height:167.3±5.6cm; weight:65.4±8.4kg) were used as controls. Each subject lifted a 4 kg plastic box (dimension: 31.5x25x20 cm), which is representative of commonly lifted items. Motion of the ankle, knee and hip joints and pelvic segments were investigated. Principal component (PC) analysis was applied to 23 kinematic and kinetic variables from each group. The total PC score for each subject was calculated, and a one-tail student-t test was used to test for significant differences between the groups. Results Significant group differences (p<0.05) were found for three of the PC scores. Parameters found to be major contributors to these differences included minimum hip flexion extension moment; maximum knee flexion moment; maximum ankle plantar flexion and knee flexion angles and average hip flexion extension angles. Discussion PCA was able to identify different lifting kinematics and kinetics in pregnant subjects and important biomechanical differences when compared with the control group. This is the first study to identify such lifting differences during pregnancy. © 2009 International Federation of Medical and Biological Engineering.