The Relationship between Upright Postural Stability, Foot Mobility, and Plantar Tactile Sensitivity in Female Gymnasts

The study investigated the relationship between postural stability in an upright stance, foot mobility, and plantar tactile sensitivity in female athletes engaged in rhythmic and aesthetic gymnastics (n = 16) and non-gymnasts (n = 16). Postural stability was assessed during quiet standing on stable-platform (StP) and on a see-saw (SS) that was movable in the sagittal and frontal planes, with eyes open (EO) and eyes closed (EC). The maximum range of motion for plantar flexion (PF) and dorsiflexion was recorded using video and analyzed in the Kinovea software. The tactile sensitivity threshold of the sole was determined using Semmes–Weinstein monofilaments. The linear velocities (LV) of center-of-pressure fluctuations were higher in gymnasts on StP with EO and EC but were lower when standing on the sagittally moving SS with EO. The PF range of motion in both feet was greater in gymnasts (p < 0.001) and showed positive correlations (r = 0.39–0.46, p < 0.05–0.01) with LV in the StP stance. The mean tactile sensitivity thresholds of both feet were lower in gymnasts (p < 0.05–0.01) at the head of the fifth metatarsal bone, the midfoot, and the heel, and these values correlated positively (r = 0.36–0.72, p < 0.05–0.01) with LV in the SS conditions with EO. Tactile sensitivity was also correlated with the degree of increase in the confidence ellipse area and body sway velocity on the SS relative to StP, independent of PF. Thus, the higher body sway velocities in standard tests on a stable support observed in gymnasts, which indicate greater postural control effort, are associated with ankle hyperlaxity. This relationship is likely attributable to reduced proprioceptive sensitivity in the non-contractile structures of the ankle during routine body sway. Conversely, high plantar tactile sensitivity, as well as the effective use of visual information for postural control, underlies the high postural stability demonstrated by gymnasts when standing on unstable supports.