Effects of 4-Week Intervention Combining High-Definition Transcranial Direct Current Stimulation and Foot Core Exercise on Lower-Limb Joint Coordination Patterns and Variability.

Coordination patterns and variability are key components of motor control. This study aimed to examine the effects of a 4-week high-definition transcranial direct current stimulation (HD-tDCS) combined with foot core exercise (FCE) on lower limb coordination patterns and variability during Y-balance test (YBT). Fifty-five healthy male participants were allocated to four groups by using randomization procedure (i.e., HD-tDCS + FCE, sham-tDCS + FCE, HD-tDCS, and FCE). Participants performed three YBT trials on the non-dominant (left) limb before and after a 4-week intervention (3 sessions/week, 20 min/session). The post-test reaching distance was matched to baseline performance to minimize the effect of variations in reaching distance on movement kinematics. A modified vector coding technique was used to characterize hip-ankle (H-A), hip-knee (H-K), and knee-ankle (K-A) coordination. In the posteromedial direction of YBT, the sagittal-plane H-K coupling demonstrated an increase in in-phase coordination (10.89%, p = 0.013) and a reduction in proximal-dominant coordination (13.86%, p = 0.015) following the HD-tDCS + FCE intervention relative to baseline and the FCE group. Sagittal-plane K-A coordination variability increased (p = 0.001) and frontal-plane K-A coordination variability (p = 0.021) and transverse-plane H-K coordination variability decreased (p = 0.004) following the combined intervention. These changes were significantly greater than those observed after sham stimulation and single interventions. A 4-week intervention combining HD-tDCS and FCE modulated coordination patterns and induced plane-related changes in coordination variability, suggesting a synergistic effect and a potential neuromechanical basis for enhanced postural stability.