OBJECTIVES To compare mechanical and neuromuscular strategies between high- and low-pain subgroups of male athletes with chronic ankle instability (CAI) during single-leg drop landing. DESIGN Cross-sectional study. SETTING Biomechanics laboratory. PARTICIPANTS Eighty-four male Tier 2-3 athletes, stratified into high-pain CAI (n = 28), low-pain CAI (n = 28), and healthy control (n = 28) groups. MAIN OUTCOME MEASURES Lower-limb kinematics, impact loading, joint moments, eccentric work and energy contributions, surface electromyographic root mean square amplitude, and co-contraction index. RESULTS Significant group effects were observed for kinematic outcomes (p ≤ 0.042; ηp2 = 0.075-0.384), joint kinetics and energetics (p ≤ 0.042; ηp2 = 0.075-0.561), and neuromuscular outcomes (p = 0.005-0.017; ηp2 = 0.096-0.124). The high-pain CAI group exhibited lower ankle plantarflexor moment than both comparison groups (both p < 0.001; d = 1.192-1.210), lower ankle eccentric work (p ≤ 0.001; d = 1.030-1.853), lower ankle energy contribution (p ≤ 0.002; d = 0.983-2.133), and greater knee energy contribution (both p < 0.001; d = 1.209-1.818). The low-pain CAI group exhibited less hip flexion and greater ankle plantarflexion at initial contact and greater ankle dorsiflexion range of motion (p ≤ 0.024; d = 0.736-1.398). The high-pain CAI group showed greater tibialis anterior activation than the low-pain group (p = 0.004; d = 0.903) and greater rectus femoris-biceps femoris co-contraction than controls (p = 0.045; d = 0.672). External impact-loading measures did not differ among groups (p = 0.114-0.265; ηp2 = 0.032-0.058). CONCLUSIONS Pain-defined CAI subgroups differed in interjoint load sharing and selected neuromuscular measures despite comparable external impact loading.
