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 (<i>p</i> < 0.01), indicating faster responses, whereas relaxation time (Tr) increased and sustain time (Ts) decreased (<i>p</i> < 0.05), suggesting temporary fatigue. Maximal displacement (Dm) increased (<i>p</i> < 0.01), indicating reduced stiffness. In contrast, the GM showed greater responsiveness after stiffness jumps, characterized by shorter Tc and Td (<i>p</i> < 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.