Biomechanics of the threshold of balance recovery

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Falls are the leading causes of hospitalizations and permanent disabilities due to unintentional injuries in Canada. However, only recently has a critical mass of studies emerged on balance recovery in response to sufficiently large postural perturbations that avoiding a fall is not always possible. Unfortunately, these studies at the threshold of balance recovery have neglected middle-aged adults and sideways and backward losses of balance. They have also used a variety of postural perturbations which makes comparisons between studies difficult. OVER THE LAST 5 YEARS, we evaluated the decline in balance recovery ability across the whole spectrum of ages from 18 to 85yrs; provided further evidence that the choice of postural perturbation does not affect the threshold of balance recovery; and validated an inverted pendulum on a skid model at the threshold of balance recovery. Indeed, using healthy younger, middle-aged and older adults, we showed that balance recovery ability declines exponentially with age as early as 51, 61 and 70yrs for forward, sideways and backward leans, respectively. Moreover, using healthy younger and older adults, we developed a dimensionless method to compare results from different postural perturbations. In particular, this perturbation threshold line method separates falls from recoveries for lean releases, lean releases with waist pull, waist pulls while walking and surface translations. Finally, we showed that an inverted pendulum on a skid model could be used to theoretically predict if a given postural perturbation will lead to an unavoidable fall or if balance recovery is possible. IN THE NEXT 5 YEARS, I will answer some of the remaining questions regarding the effects of AGE and loss of balance DIRECTION on our dimensionless method to compare postural perturbations, as well as begin to explore the influence of PAIN, a risk factor for falls, on the threshold of balance recovery. OUR 1ST OBJECTIVE is to experimentally determine i) the maximum forward initial lean angles from which healthy YOUNGER, MIDDLE-AGED and OLDER adults can be suddenly released and still recover balance using a single step for 3 backward surface translation velocities, and ii) the maximum backward surface translation velocities from which the same participants can be suddenly pulled and still recover balance using a single step for 3 walking velocities. OUR 2ND OBJECTIVE is to experimentally determine the maximum FORWARD, SIDEWAYS and BACKWARD i) initial lean angles and ii) surface translation velocities from which healthy younger, middle-aged and older adults can be suddenly released or pulled, respectively, and still recover balance using a single step. We will also validate the inverted pendulum on a skid model for all of these combined postural perturbations and loss of balance directions. Finally, OUR 3RD OBJECTIVE is to experimentally i) determine the effect of INDUCED PAIN at 2 different sites on the maximum forward initial lean angles in healthy participants, and ii) evaluate one of the possible neurophysiological mechanisms responsible for this interaction. We will also explore possible intervention methods, if this protocol is deemed safe for individuals with CHRONIC PAIN. My engineering approach, using experiments and theoretical modeling as well as biomechanical and neurophysiological measures, will advance knowledge at the threshold of balance recovery. Long term, this proposal will reduce the need for time consuming and dangerous experiments, could help in designing equipment that detects or even prevents falls, and may even help in fall litigation cases. It could also lead to more efficient intervention programs to prevent that first injurious fall, thereby improving quality of life and functional autonomy.