Dr. Brodie adjusting the accelerometers that were recently used to capture head jerk in the walking elderly.
Up to one in three people over 65 fall each year (Masud & Morris, 2001) and many older people have impaired dynamic stability. However, a cause and effect relationship between gait speed, step variability, dynamic stability, and falls is complex. For example, older people may walk more slowly to compensate for reduced capabilities (Menz et al, 2003), yet walking slower may increase walking variability (Beauchet et al, 2009). Also, changes in motor control may be ‘camouflaged by preferred walking speed’ (Helbostad & Moe-Nilssen, 2003).
This is the first investigation of head jerk in walking. Jerk is the time derivative of acceleration and in this study we measured it with accelerometers, similar to those found in mobile phones. Because head stability is important for vision and vestibular feedback, we hypothesized measuring head jerk while walking might reveal subtle changes in motor control associated with aging.
WHAT DID WE FIND?
Older people really do have jerkier head movements! An increased ratio of lateral to vertical head jerk was superior at distinguishing older from younger people (89% accuracy), and was much better than traditional measures such as step length. A principal component analysis revealed that this new measure of ‘head stability’ was distinct from ‘gait vigour’ and walking speed. Therefore head jerk provides new insights into how motor control strategies change as we age.
Images from two falls research volunteers as they walked down a hallway wearing head (green) and waist (blue) accelerometers. The image on the left is from a healthy 82 year old volunteer, whereas the image on the right is from an 82 year old volunteer with a history of falls.
SIGNIFICANCE AND IMPLICATIONS:
These findings suggest older people rely less on their dynamic (pendulum-like) stability, are more cautious, and may sacrifice economy of movement for perceived increases in safety. Measuring head jerk provides valuable information that can be used to further unravel the complex problem of predicting which people are likely to fall. This new measure can also inform possible fall prevention strategies for people at risk of falling. We are currently evaluating whether head jerk is also valuable in understanding how medication effects movement quality and falls risk in people with Parkinson’s disease.
PUBLICATION:
Brodie, M. A., Menz, H. B., & Lord, S. R. (2014). Age-associated changes in head jerk while walking reveal altered dynamic stability in older people. Exp Brain Res 232, 51-60.
KEY REFERENCES:
Beauchet O, Annweiler C, Lecordroch Y, Allali G, Dubost V, Herrmann FR, et al (2009). Walking speed-related changes in stride time variability: effects of decreased speed. J Neuroeng Rehabil 6, 32.
Helbostad JL, Moe-Nilssen R (2003). The effect of gait speed on lateral balance control during walking in healthy elderly. Gait Posture 18, 27-36.
Masud T, Morris RO (2001). Epidemiology of falls. Age Ageing 30, Suppl 4:3-7.
Menz HB, Lord SR, Fitzpatrick RC (2003). Age-related differences in walking stability. Age Ageing 32,137-142.