Intrinsic Foot Muscle Strengthening Interventions for Older Adults

Background: Falls are the leading cause of injury in adults 65 years and older. While causes of falls are multifactorial, foot function plays a vital role. The intrinsic foot muscles (IFM), those that originate and insert within the foot, provide stability and sensory input important for balance. Weakness or disuse of the IFM in older adults can contribute to faulty foot and toe alignment, which have been cited as independent predictors of falls. Wearing minimally cushioned footwear or performing strengthening exercises that target the IFM may improve these muscles' strength, endurance, proprioceptive qualities, and foot/toe structure, which may improve functional mobility and balance in older adults, and thus, prevent falls.

Purpose: The purpose of the proposed research is to analyze the effects of two IFM strengthening interventions (minimal footwear use or strengthening exercises) on IFM strength, proprioception, foot/toe structure, balance and functional mobility, and fall risk in older adults.

Design: Randomized control trial with an effectiveness-implementation hybrid design Type I

Methods: Adults ages > 65 years who can ambulate household distances with or without an assistive device who are determined to be at risk for falls will be invited to participate. Individuals with poor foot sensation, vestibular disorders, lower extremity amputation, injury or surgery to the lower extremities or lumbar spine in the previous 6 months, impaired cognitive ability to follow verbal and written instructions, and those who have participated in a fall prevention program in the past 6 months will be excluded. Following informed consent and initial screening, participants will be randomly allocated to one of three intervention groups (n=90, 30/group):

1. intrinsic foot muscle strengthening exercises
2. minimal footwear prescribed walking
3. control (will receive a fall prevention brochure and seated active motion exercises)

Participants will be encouraged to perform interventions 5 days/week for 16 weeks. After an initial in-person instruction session, participants will have 1 follow-up meeting to review instructions, after which they will receive bimonthly phone calls as a reminder to adhere to the intervention and to record any falls and related details. Participants will be asked to record intervention performance, daily step count (measured by pedometer), and falls in provided diaries. Balance, functional mobility, and fall risk will be measured using the Mini-BesTest, proprioception will be measured using the Lower Extremity Position Test, foot and toe structure will be measured using navicular drop and valgus angle of the 1st metatarsophalangeal joint. Cross sectional area (cm2) of the abductor hallucis, flexor hallucis brevis, flexor digitorum brevis, and quadratus plantae muscles will be measured using ultrasound imaging. Measures regarding balance and functional mobility, proprioception, foot/toe structure, and muscle cross sectional area will occur at baseline, 8 and 16 weeks, and 1 year. Following the 16-week intervention period, participants will be encouraged to continue their intervention twice per week. Ongoing falls diaries and bimonthly phone calls from researchers will occur for 12 months after baseline to record long-term fall rate (falls per person per year). In addition, a process evaluation will be performed regarding participant impressions of the interventions and other study activities to inform future research and clinical implementation.

Data Analysis: a 4 group x 4 time point repeated measures analysis of covariance (ANCOVA) will be used to assess changes in balance, and functional mobility, proprioception, foot/toe structure, and muscle cross sectional area. Falls data will be measured as the rate of falls per person in a 12-month period beginning with the date of the baseline measure, and change in fall risk status will be assessed using Mini-BesTest scores. Implementation data will undergo both quantitative and qualitative analyses.

Significance: Intrinsic foot muscle strengthening interventions have seldom been studied in older adults and their effects and mechanism are not established. This will be the first study to assess the effects of these interventions on proprioception in older adults, the first to use ultrasound imaging measurement following intrinsic foot muscle strengthening in older adults, and the first study to analyze the long-term effects on falls after the performance of these specific interventions. The interventions assessed in this research proposal are simple, safe, and affordable and may have a major impact on functional mobility and reduction of falls for older adults.