The Impact of Jump Type on Muscle Contractile Behavior: Fatigue or Potentiation After Countermovement and Stiffness Jumps?

Jumping exercises are widely applied in sport performance and conditioning due to their crucial role in enhancing neuromuscular function and lower-limb power. Acute effects related to contractile properties measured by tensiomyography (TMG) remain insufficiently explored. This study aimed to examine the acute effects of two jump types—bilateral countermovement jumps (CMJs) and stiffness jumps (STs)—on the contractile properties of the vastus medialis (VM) and medial gastrocnemius (GM) muscles. Twenty-nine kinesiology students (fourteen males, fifteen females; age 19.4 ± 0.7 years) performed CMJ and ST protocols in a randomized order. Muscle contractile characteristics were measured before and immediately after each protocol and analyzed using a mixed-model repeated-measures ANOVA. Significant pre–post changes were found in both muscles. In the VM, contraction (Tc) and delay (Td) times decreased (p < 0.01), indicating faster responses, whereas relaxation time (Tr) increased and sustain time (Ts) decreased (p < 0.05), suggesting temporary fatigue. Maximal displacement (Dm) increased (p < 0.01), indicating reduced stiffness. In contrast, the GM showed greater responsiveness after stiffness jumps, characterized by shorter Tc and Td (p < 0.01), and reduced endurance after CMJs. These findings highlight muscle specific neuromuscular adaptations and provide practical insights for optimizing warm-up, training, and rehabilitation protocols through targeted jump selection.