Association between changes in intrinsic foot muscle swelling and improvements in navicular drop height after toe flexor exercises

Background Exercise efficacy can be determined by muscle swelling confirmed through ultrasound, but this method has not been investigated for the intrinsic foot muscles (IFM). Objective To investigate changes over time in muscle swelling and navicular drop (ND) values after IFM exercises and evaluated the relationship between changes in muscle swelling and ND values. Methods In total, 40 feet (10 men; 10 women) were included. The navicular height (NVH) in sitting and standing positions and four IFM cross-sectional areas (CSAs) were measured. Measurements were taken pre-exercise, immediately, and 10 and 20 min after the toe flexor exercise (TFE) at 80% or greater intensity for 40 times. Changes over time in muscle swelling and ND values in men and women and their relationship were evaluated. Results Significant increases were observed in CSAs of all IFMs and improved navicular bone height in sitting and standing positions post-exercise. There was a moderate correlation between changes in CSAs of abductor hallucis (AbH) in women from pre-exercise and changes in ND values from pre-exercise up to 20 min post-exercise. Conclusion A positive correlation between AbH muscle swelling and ND values was observed in women, suggesting the importance of the AbH muscle in arch support.