The effect of footwear longitudinal bending stiffness on jumping performance and lower limb joint biomechanics

It remains unknown if shoes with increased longitudinal bending stiffness (LBS) can affect jump performance during stationary countermovement jumps with and without the use of arms, and whether a different amount of footwear LBS is optimal for each jump type. In this study, ten healthy male participants performed maximal countermovement jumps with and without free arm movement in four LBS conditions, accomplished by adding carbon fibre plates of varying thickness underneath the insole. Compared to the control LBS condition, significant decreases in metatarsophalangeal (MTP) joint range of motion (p = 0.043, d = 0.80) and negative work (p = 0.017, d = 0.68) were observed in the very stiff condition. A significant increase was also found for MTP joint positive work (p < 0.001, d = 1.18) in the very stiff LBS compared to the control condition; however, no change in maximum jump height was observed (p = 0.755, d = 0.03). Torsional spring energy at the MTP joint significantly increased in the very stiff LBS compared to the control condition (p = 0.017, d = 0.66). An interaction between jump type and footwear LBS was not observed (p = 0.630, ηp2 = 0.061); however, jumping with free arm movement redistributed positive work from the ankle and hip to the knee. The observed differences in joint biomechanics did not propagate to changes in maximal jump height, potentially due to the athletes not being able to properly translate energetic savings into jump performance. These findings suggest that performing stationary jumps in increased LBS footwear redistributes lower limb work but does not necessarily lead to changes in jump performance, regardless of arm movement.