Biomechanical Effects of Sandal Strap Design on Gait Kinematics and Electromyographic Activation Patterns: A Speed-Dependent Analysis

Abstract

Background: Sandals are widely favored for their comfort; however, their open design may reduce foot support and compromise gait stability. Objective: This study examined the effects of various sandal strap configurations and walking speeds on spatiotemporal gait parameters and the integrated electromyographic (iEMG) activity of lower limb muscles. Methods: Twenty-four healthy adult males (age: 25.00 ± 1.22 years; mass: 71.50 ± 11.84 kg; height: 173.50 ± 3.50 cm) participated in this study. A two-way repeated-measures ANOVA was performed to assess the effects of three footwear conditions (barefoot, Crocs strapped, and Crocs strapless) across three walking speeds (1.2, 1.6, and 2.0 m/s). Gait outcomes included step length, step width, step frequency, peak plantar loading duration, and iEMG activity of key lower limb muscles: gluteus maximus (GM), rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), and lateral gastrocnemius (LG). Results: Footwear condition significantly affected step width (p < 0.05) and step frequency (p < 0.001). A significant interaction between footwear and walking speed was observed for peak plantar loading duration in both the forefoot and heel regions (p < 0.05). Additionally, significant differences in RF and GM iEMG activity were found between barefoot and strapped conditions (p < 0.05). Conclusions: Strapped sandals improve plantar load distribution and gait stability by regulating step frequency and reducing lower limb muscle activation, with these effects being more pronounced at higher walking speeds, particularly during forefoot and heel loading phases.

Keywords: biomechanics; gait; iEMG; sandals; walking condition; walking speed.

Figure 1

(A) Schematic diagram of the gait cycle; (B) EMG marker placement location; (C) two wearing conditions of Crocs.

Figure 2

Proportion of iEMG for each muscle relative to total activation at three walking speeds.

Figure 3

The distribution of correlation coefficients between gait parameters and muscle activation characteristics under different footwear conditions and walking speeds is shown. In the lower left of the figure, each colored square in the matrix represents the Pearson correlation coefficient between variables, with colors ranging from dark red (positive correlation), through white (no correlation), to dark blue (negative correlation). The upper right of the matrix uses pie charts to present the strength and direction of these correlations intuitively. CD, cadence; FF, time to maximum force of the forefoot; HL, time to maximum force of the heel; LS, lateral symmetry; MF, time to maximum force of the midfoot; RF, TA, GM, MG, LG, BF, IEMG contribution rates of individual muscles; SL, stride length; SW, step width.