The sample entropy (SEn) was used to explore standing balance ability and balance control characteristics of the human body under different time scales, in order to reveal the influence of different support conditions and standing tasks on balance control mechanisms.

Twenty-two young adults (11 males, 11 females) performed standing tasks on hard and soft support surfaces using both legs, the left leg, and the right leg. Each task lasted 30 seconds. Center of pressure (COP) data in the anterior-posterior (AP) and medial-lateral (ML) directions were collected, and sample entropy (SEn), entropic half-life (EnHL), and entropy change rate were calculated.

When males stood on their left leg on a soft support surface, significant differences in EnHL were observed in both the AP and ML directions (P<0.05). Significant differences in EnHL in the AP direction were also found for both males and females standing on their right leg on a soft support surface (P<0.05). Under all standing conditions, EnHL values for both males and females exceeded 100 ms. During one-legged standing on a soft support surface, males exhibited significantly higher SEn values in both the AP and ML directions compared to females (P<0.05). During double-legged standing on a hard support surface, males showed an entropy change rate of -0.005, indicating a backward movement trend and fewer posture adjustments. Additionally, during double-legged standing on a soft support surface, the time to reach EnHL in the ML direction was 194 ms for males and 192 ms for females, while females had a shorter EnHL time in the AP direction (168 ms). Changes in the support surface had a minor impact on EnHL.

Reduced proprioception may lead to variations in balance control strategies between genders and limbs. Males tended to adjust forward, whereas females tended to adjust backward. Gender did not significantly affect the stability of balance control during double-leg standing. Males may require more intervention and adjustment to maintain balance under specific disruptive conditions.