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Date of Graduation
5-15-2025
Semester of Graduation
Spring
Degree Name
Master of Science (MS)
Department
Department of Biology
First Advisor
Dr. Roshna Wunderlich
Second Advisor
Dr. Corey Cleland
Third Advisor
Dr. Emily Naylor
Abstract
Cross-sloped surfaces create an asymmetrical substrate for foot contact, introducing a slip force within the transverse plane and a gravitational pull within the coronal plane that increases the tendency to topple downslope. To maintain stability, the foot must make structural adjustments across the hindfoot, midfoot, forefoot, and hallux. In chapter 1, I investigated how IFMs respond to varying substrate conditions and balance demands, providing insight into their functional role in maintaining stability and adapting foot structure in static and dynamic locomotor tasks. Twenty-four healthy adults participated in a series of dynamic walking trials on flat, cross-sloped and sandy substrates and also static balance trials. We used surface electromyography (EMG) to record the activity of six intrinsic foot muscles including muscles that both flex/extend and abduct/adduct the forefoot relative to the hindfoot, plantar pressure to assess foot-loading patterns during walking, and movement of the center of pressure (COPM) during static balance trials. IFM activity varied significantly across substrate conditions. Abductor hallucis (ABDH) and the first dorsal interosseus (PDIO1), on the medial side of the foot, were significantly more active (p < 0.05) when the foot was in the upslope position, while the third dorsal interosseous (PDIO3) and abductor digiti minini (ABDM), on the lateral side of the foot, showed significantly increased activation (p < 0.05) when the foot was in the downslope position compared to the flat and upslope. Peak plantar pressures under the first and fifth metatarsals were significantly higher in the downslope (p < 0.05) and upslope (p < 0.05) conditions, respectively. These asymmetrical activation patterns and load distribution suggest IFMs assist in decoupling foot segments to accommodate increased movement and asymmetrical load distribution and therefore increased stability and postural control while moving on cross-sloped surfaces. Contrary to expectations, IFM activation in sand walking did not differ from flat terrain. During balance tasks, all IFMs exhibited significantly greater activation (p < 0.05) in the eyes-closed compared to eyes-opened balance conditions. Given the natural decline of IFM strength with age and its association with fall risk and multiple foot pathologies, targeted IFM training, specifically the muscles responsible for mediolateral manipulation of foot elements, may enhance postural control and mobility in both every day and complex locomotor scenarios. While traditional strengthening programs primarily focus on flexion/extension-based exercises, the IFM that abduct/adduct the foot are likely critical for mediolateral stability and movement on uneven surfaces (chapter 1). In chapter 2, I compared the effects of targeted strengthening interventions on IFM cross-sectional area (CSA), neuromuscular activation patterns, and balance. This randomized control trial assigned participants to either an abduction/adduction (AA) exercise group, or a flexion/extension (FE) exercise group. The intervention lasted 12 weeks and included progressive resistance training specific to each exercise type. CSA of 6 individual IFM was assessed using musculoskeletal ultrasonography, and muscle activation during the exercises was measured via surface electromyography (EMG). Balance was assessed via single legged balance tasks while subjects had their eyes opened and their eyes closed. The specific IFMs analyzed included abductor hallucis (ABDH), abductor digiti minimi (ABDM), first and third dorsal interosseous (PDIO1, PDIO3), flexor digitorum brevis (FDB), and extensor digitorum brevis (EDB). The AA exercise group demonstrated significant increases in multiple IFMs CSA including ABDH and PDIO3 (p < 0.05), while both the FE exercise and control groups showed no significant changes. EMG analysis revealed that the AA exercises elicited significantly greater (p < 0.05) activation of ABDM, PDIO1, and PDIO3 compared to traditional flexion-based exercises. The interossei muscles also exhibited activation patterns similar to FDB during exercises requiring metatarsophalangeal (MTP) stabilization. Abduction/adduction exercises were more effective than traditional flexion/extension exercises in promoting both neuromuscular activation and hypertrophy of the IFMs responsible for mediolaterally modulating foot shape. These findings suggest that incorporating abduction/adduction exercises into rehabilitation and performance training programs may improve foot stability, balance, and mobility.
Included in
Biomechanics Commons, Exercise Physiology Commons, Musculoskeletal System Commons, Physical Therapy Commons
