Practicing with Weighted Vests Induces Neuromechanical Changes in Countermovement Jump

Abstract

Jumping with preloaded vest is proposed as a method of warm up that leads to an increase in the height of subsequent jumps. However, the biomechanical adaptations during loaded jumps are still unknown. PURPOSE: The aim of this study was to explore the adaptive changes in the biomechanics of the lower limb joints during loaded maximal jumping. METHODS: Following a full set of warm-up jumps, healthy college students (10 male, 8 female, 64.4±16.3 kg, 1.7±0.809 m) were asked to perform 2 pre-test jumps with a loaded vest equal to 15% of their body mass. Following which, they performed 3 sets of 5 consecutive countermovement jumps (exercise set). This was followed by a post-test where the subject again jumped twice. The jumps of pre and post exercise set were compared. Kinetic and kinematic data were collected for 12 defined body segments. Subjects would be excluded from the study if they had any history of ankle sprain or any type of neuromuscular disorder. RESULTS: A significant increase in weighted jump height in males was observed during the post-test (28.45 vs. 26.48 cm, p-value <.01), an effect not seen in the females (18.9 vs. 18.5 cm, p-value <.01). This is consistent with the findings of Komi et al. (1977), who observed that during both drop jumps and counter movement jumps, males have better performances than women. Males also demonstrated significant increases in peak hip and knee angle, while females showed no significant changes in joint kinematics and kinetics. We also observed a significant increase in hip joint power and a decrease in ankle joint power. CONCLUSION: Increased range of motion in the knee and hip as well as a shift in joint power from distal to proximal joints may be the underlying strategy that resulted in increased post-test jump height. Perhaps, the lack of change in joint power and range of motion in females prevented them from increasing the jump height. One possible mechanistic explanation is a difference in joint and tendon stiffness between genders, which Komi et al. (1978) have suggested previously. From a practical perspective, these findings suggested that gender should play a role in the use of loaded jumping as a training procedure.