Abstract Title Isolating abductor hallucis and tibialis posterior activation for targeted foot arch strengthening Jadah Eshenaur D.O.’28, Jackson Watson D.O.’28, Shane McClinton P.T., D.P.T., Ph.D. OCS, FAAOMPT, CSCS Background The abductor hallucis (AbdH) and tibialis posterior (TP) contribute to foot arch strength(1,3) and are often the target of foot strengthening programs.(2,4,5) However, strategies to isolate AbdH and TP while minimizing activation of compensatory muscles such as the flexor hallucis longus, flexor digitorum longus, and tibialis anterior have not been identified. This preliminary study aims to provide clinical guidance for isolating and strengthening the AbdH and TP. Methods Surface and fine-wire electromyography (EMG) measured muscle activity in 10 subjects during different foot strengthening exercises. EMG data was normalized to each muscle’s peak dynamic activity across all exercise conditions. Radar plots were constructed to identify exercises with optimal TP and AbdH activation. Results AbdH demonstrated its highest activation during the unilateral heel raise while TP had its highest activation with the plantar flexion inversion exercise. Exercises that yielded the highest activation for both AbdH and TP with minimal compensatory muscle activation included the plantar flexion inversion towel sweep (PITS), short foot (SF) in sitting, and walking. Exercises with the highest overall activation of both AbdH and TP, regardless of compensation, included the unilateral heel raise, SF hop, and unilateral stance SF. Conclusion When initiating foot training, seated PITS and SF exercises, and walking will optimize AbdH and TP recruitment while minimizing compensatory muscle activation. The next logical progression would be the unilateral stance SF before progressing to the unilateral heel raise and hopping exercises which demonstrated the highest activation, but with more compensatory muscle recruitment. References 1. Fiolkowski, P., Brunt, D., Bishop, M., Woo, R., & Horodyski, M. (2003). Intrinsic pedal musculature support of the medial longitudinal arch: an electromyography study. The Journal of Foot and Ankle Surgery, 42(6), 327–333. https://doi.org/10.1053/j.jfas.2003.10.003 2. Osborne, J., Menz, H. B., Whittaker, G. A., & Landorf, K. B. (2023). Development of a foot and ankle strengthening program for the treatment of plantar heel pain: a Delphi consensus study. Journal of Foot and Ankle Research, 16(1). https://doi.org/10.1186/s13047-023-00668-2 3. Jung, D.-Y., Koh, E.-K., & Kwon, O.-Y. (2011). Effect of foot orthoses and short-foot exercise on the cross-sectional area of the abductor hallucis muscle in subjects with pes planus: A randomized controlled trial1. Journal of Back and Musculoskeletal Rehabilitation, 24(4), 225–231. https://doi.org/10.3233/bmr-2011-0299 Ridge, S. T., Myrer, J. W., Olsen, M. T., Jurgensmeier, K., & Johnson, A. W. (2017). Reliability of doming and toe flexion testing to quantify foot muscle strength. Journal of Foot and Ankle Research, 10(1). https://doi.org/10.1186/s13047-017-0237-y 4. Ridge, S. T., Olsen, M. T., Bruening, D. A., Jurgensmeier, K., Griffin, D., Davis, I. S., & Wayne Johnson, A. (2018). Walking in Minimalist Shoes Is Effective for Strengthening Foot Muscles. Medicine & Science in Sports & Exercise, 51(1), 1. https://doi.org/10.1249/mss.0000000000001751