The influence of gender on spine, hip, knee, and ankle motions during a reaching task

In the present study, the motions of the different postural joints involved in reaching tasks starting from an upright posture were examined and the influence of gender on the movement pattern used was determined. Specifically, motion about the ankle, knee, and hip joints as well as angular motion of the thoracic segment with respect to the sacrum (lumbar motion) were measured. Ten healthy subjects (5 men, 5 women) reached for targets at 2 locations normalized to the subject's trunk length, arm length, and hip height. To reach each target, subjects had to bend the trunk forward. Joint motion was measured with a Selspot motion analysis system. The change in joint angle (measured in the sagittal plane from an upright standing position to the final posture adopted at target contact) was calculated for each joint. In addition, the ratio of the changes in joint angle of the lumbar spine and the hip (spine/hip ratio) was determined. Compared with female subjects, male subjects exhibited, on average, greater rotation about the lumbar spine and less rotation about the hips and knees. The spine/hip ratios for men and women were dramatically different. Men had, on average, a spine/hip ratio of 1.20 and women an average of 0.20. Those data reveal that 2 vastly different movement patterns are employed during reaching tasks that necessitate some forward bending of the trunk. Men tend to flex equally about the hips and spine, with minimal flexion about the knees, whereas women flex primarily about the hips and knees, with minimal flexion about the spine. Thus, the kinematic redundancy is resolved differently depending on gender.