Effects of anterior–posterior center of pressure position on knee and hip joint biomechanics, external load variables, and muscle activation during the conventional deadlift

The conventional deadlift (CDL) is a closed kinetic chain, multi-joint resistance exercise involving lower-limb joint extension against a heavy external load. The anterior–posterior (AP) center of pressure (COP) position may alter joint moment arms and redistribute mechanical demands across the lower-limb joints. However, whether deliberate COP manipulation affects joint kinematics, kinetics, and muscle activation during the CDL remains unclear. This study investigated the effects of AP COP position on knee and hip kinematics and kinetics, barbell-related external moment variables, and muscle activation during the CDL. Twenty-eight resistance-trained men performed the CDL under three COP conditions (anterior, neutral, and posterior) in a counterbalanced order. Three-dimensional kinematic, ground reaction force, and surface electromyographic data were collected synchronously. Peak net knee and hip joint moments, knee and hip joint angles, the barbell-related external moments and moment arms at the respective peak net joint moments, and the mean normalized muscle activation (%MVIC) of seven muscles were calculated during the upward and downward phases. One-way repeated-measures analysis of variance and the Friedman test were used to compare variables among conditions. In both phases, the peak knee flexion moment and biceps femoris long-head activation were greatest in the anterior condition. In the posterior condition, the barbell-related hip external moment, moment arm, and quadriceps activation were greatest in both phases, whereas the peak hip extension moment and gluteus maximus activation were greatest during the upward phase. The knee and hip joint angles did not differ significantly among conditions in either phase. Activation of the rectus abdominis and erector spinae did not differ significantly among the conditions. The AP COP position was associated with a redistribution of net joint moments between the knee and hip and with changes in lower-limb muscle activation during the CDL. An anterior COP was associated with greater knee flexion moment and biceps femoris activation, whereas a posterior COP was associated with greater hip extension moment and greater quadriceps and gluteus maximus activation. Deliberately adjusting the COP position may help tailor the biomechanical demands of the CDL to specific training goals. Not applicable. Not applicable.