APPROACH
1\) The main study The main study to investigate the difference between BT and PBT is a parallel-group randomized controlled trial with 6 months follow-up from baseline to determine the effect of PBT program on stepping behavior and fall incidence in community-dwelling older people. The study has been designed in accordance with the Consolidated Standards of Reporting Trials (CONSORT) statement48.
Participants, recruitment and screening Participants will consist of community-dwelling adults aged over 65 years without a recent history of falls (one or more falls in the past 12 months). All participants will be required to obtain medical clearance from their general practitioner prior to participation in the study. Exclusion criteria will be neurological, cardiovascular or musculoskeletal impairment that adversely affect balance or limit involvement in the intervention, diagnosis of dementia, cognitive impairment (score\<24 on Mini Mental State Examination after adjustment for age and years of education49), functional disability/limitation in activities of daily living (Score\>3 on Bayer Activities of Daily Living Scale50), osteoporosis, use of medication that affects balance or causes dizziness (e.g. psychotropics) and participation in supervised exercise one or more times per week.
Random allocation and concealment Randomization will be performed following baseline assessment by personnel not involved in recruitment, training or assessments. Participants will be informed that they will receive one of two treatments. Due to the nature of the intervention, research personnel administering the treatments cannot be blinded to group allocation. However, the personnel that perform the prospective falls evaluation will be blinded to group allocation.
Intervention BT group. This group will undertake 12 weeks of twice weekly BT in accordance with ACSM guidelines. Training will be conducted in small groups under the supervision of a trainer. Training will involve mobility, resistance and balance training components.
PBT group. The PBT protocol uses multi-directional surface translations to provoke rapid compensatory stepping responses to recover balance. The protocol is a modified version of the stepping (but not grasping) component of the PBT program described by Mansfield et al., which was designed to improve rapid stepping reactions and minimize foot collisions in accordance with well-established principles of motor learning including individualization, specificity, progressive overload, and variability of training. At each session the PBT group will experience multi- directional disturbances to standing posture (forwards, backwards, left, right) delivered via translations of a motorized treadmill. 24 perturbations will be administered in a random sequence (with variation in timing, magnitude and direction) and interspersed with 30 s treadmill walking. Successful recoveries during training will be followed by an increase in the degree of difficulty, whereas consecutive failures will result in a return to the perturbation intensity that had previously been performed successfully. Our pilot testing indicates that the prescribed peak accelerations on our motorized treadmill to within ±3% can be achieved. The occurrence of actual falls will be prevented via the use of a custom safety harness attached to an overhead cable instrumented with a force transducer used previously. One familiarization trial in each perturbation direction will be performed at 50% intensity at the beginning of the first training session. Training sessions will be terminated when the participant completes the planned number of trials or if the participant elects not to continue (e.g. feels tired, uncomfortable or unwell).
Primary outcome measures The tether-release54 test will be used to determine whether training effects generalize to balance recovery reactions that are not part of the intervention. Loss of balance will be induced by releasing participants from static forward lean postures corresponding to 15%, 20% and 25% of their body weight on a horizontal restraining tether in accordance with the PI's previous work groups published procedures. Participants will be instructed to attempt to regain balance by taking a single, rapid step. Full body kinematics and ground reaction forces will be recorded during all balance recovery tasks using a 3D motion capture system (12-camera Motion Analysis) and force platforms embedded in the ground (AMTI, Watertown, USA). Outcome measures will be margin of stability at touchdown of the stepping leg, step leg kinematics (step length and velocity) and trunk kinematics (trunk angle and trunk angular velocity). All analysis will be performed using OpenSim57 in accordance with the PI's and his previous research units published methods.
Secondary outcomes measures Falls frequency will be monitored over the 3 months of the intervention and following 3 months of follow up with monthly falls diaries. Participants will return monthly falls diaries (daily entries) to determine frequency, time, location and cause of falls and related injuries as per consensus recommendations for falls trials52.
OVERALL SUMMARY
The proposed investigation forms the basis of improved understanding of balance recovery training methods and are important steps for ongoing research into the efficacy of balance recovery training modes relative to reducing the incidence of falls. In particular, the proposed study is the necessary precursor to a large prospective study to evaluate the effect of balance recovery training on health and wellbeing of rural Montanans.
