Alterations in dynamic balance control over time following botulinum toxin injection for calf hypertrophy.

[BACKGROUND] Botulinum toxin type A (BoNT-A) injection into the gastrocnemius muscle is widely used to reduce calf hypertrophy, particularly for aesthetic purposes. However, given the essential role of the gastrocnemius muscle in propulsion and postural control during walking, weakening this muscle may subtly affect dynamic balance.

[RESEARCH QUESTION] Does gastrocnemius BoNT-A injection alter whole-body balance control during level walking over time?

[METHODS] Fifteen healthy female adults received BoNT-A injections to bilateral gastrocnemius. Participants were assessed at baseline, 1 month, and 3 months post-injection. Measurements included shank circumferences and volume, temporospatial gait parameters, COM-COP inclination angles (IA), and their rate of change (RCIA) in both sagittal and frontal planes.

[RESULTS] Shank volume showed a statistically significant reduction at one month and three months post-injection. Temporospatial parameters, including step length, cadence, and speed, remained statistically unchanged. While COM-COP IA in both planes was preserved, RCIA increased significantly in the sagittal plane during the first and second half of double limb support (p = 0.033 and 0.050) and in the frontal plane during early single limb support (p = 0.038). These findings suggest subtle changes in dynamic balance control, even without observable gait temporospatial deviations.

[SIGNIFICANCE] This study highlights that gastrocnemius BoNT-A injections, although preserving basic gait performance, can compromise fine-tuned balance regulation during walking. Clinicians should consider the implications for postural stability, particularly in populations at risk of falls. Future studies should assess the combined effects of footwear (e.g., high-heels) and uneven terrains on post-injection gait balance control.