Effects of hip and knee isokinetic strengths on lower extremity acceleration during roundhouse kicks to the head and chest in taekwondo

Background In taekwondo, sufficient kicking force is required to score valid points on electronic protectors. Impact force varies with kicking speed, and lower extremity strength is crucial for optimal scoring. Objective To investigate the relationship between isokinetic strength and segmental acceleration in the striking leg during roundhouse kicks (RHKs). Methods Seventeen female taekwondo athletes (age: 208 ± 1.81 years) participated. Lower limb isokinetic strength was assessed with a dynamometer, and segmental accelerations were measured using inertial sensors. Correlations between isokinetic moments and accelerations during mid-level and high-level RHKs were analyzed using Fisher's Z transformation. Results During mid-level RHKs, knee flexion moments correlated with ankle accelerations, while high-level RHKs showed additional correlations between hip flexion moments and segmental accelerations. Joint accelerations were driven by flexor moments (hip and knee flexion). No bilateral differences were found in isokinetic strength or segmental accelerations, except for ankle acceleration during high-level RHKs (p = 0.039). Significant increases in segmental accelerations (p < 0.05) strengthened by Fisher Z transformation, particularly for knee flexion and ankle acceleration (p < 0.05). Conclusions Mid-level RHKs are knee-dominant, while head-level kicks require greater contributions from both knee and hip flexion. Strengthening both extensor and flexor muscles is vital for optimizing kicking performance