We investigated whether there is a difference in body position and posture between young and elderly adults that may account for an increased risk of injury for elderly adults when performing the same tasks as their younger counterparts. We found that there was less stability and greater load on the back segment in the elderly male lift. We assessed stability by measuring the horizontal distance from the ankle joint to the body's center of mass. Stability decreases as the center of mass moves further from the ankle joint. The distance for the young male subject was only 0.06m, while the distance for the elderly male subject was 0.19m. This shows that the elderly subject was less stable. Not only did the stability decrease for the elderly male at the ankle joint, the amount of torque increased. Less torque is needed at the ankle joint for increased stability. We also found the torque of the hip joint for both subjects, and the elderly male had a torque at the hip joint of 139 Nm compared to a torque of 128 Nm for the young male. Greater torque indicates greater load on the lower back.
Studies have demonstrated that elderly people are less stable while performing shortening and lengthening contractions with the lightest loads (Graves, et al 2000). Our findings corroborated this finding. Because the elderly male was less stable at greatest hip flexion, he has a greater risk of falling forward at this point. This is especially important in analysis of elderly adults because falls are more prevalent and likely to injure. The elderly male also experienced greater load on the back segment due to the greater torque at the hip joint. This indicates that the elderly male was more likely to experience muscle injury to his back. We would suggest that both elderly and young adults bend more at the knee during lifting, increasing stability and decreasing loads on the back.
There are some limitations to our study. First, we only sampled two subjects, who may not be typical of the entire populations they are representing. This problem could be rectified by studying larger sample sizes for both age groups, as well as including female subjects. Second, even though we asked them to bend as they normally would, the movement we studied may not be the one they typically exhibit. Multiple samples from each subject should correct for any discrepancies between normal and studied movements.
Daubney, M.E., Calhoun, E.G. (2000) Lower-extremity muscle force and balance performance in adults aged 65 years and older. Physical Therapy 79: 1177-85.
Graves, A.E., Kornatz, K.W., Enoka, R.M. (2000) Older adults use a unique strategy to lift inertial loads with the elbow flexor muscles. Journal of Neurophysiology 83: 2030-9.