Objective This study systematically investigates the effects of key midsole characteristics (including hardness, thickness, and longitudinal bending stiffness (LBS)) on lower limb biomechanics during running, with particular emphasis on their impact on biomechanical parameters such as impact force, loading rate, ground reaction force, contact time, and plantar pressure distribution. This work aims to establish a theoretical foundation for optimizing running shoe midsole design and guiding future research directions, ultimately contributing to enhanced athletic performance and reduced injury risks.

Methods This study employed the PRISMA framework for literature screening. A comprehensive search was conducted across both Chinese (CNKI) and English (Web of Science) academic databases, yielding an initial pool of 872 relevant publications. Following rigorous quality assessment using the PEDro scale, 19 high-quality articles meeting the inclusion criteria were selected for final analysis. The selected literature was systematically reviewed to examine the biomechanical effects of running shoe midsole characteristics - including hardness, thickness, and longitudinal bending stiffness - on key biomechanical indicators such as impact force, loading rate, ground reaction forces, contact time, and plantar pressure distribution. Through comparative analysis of these studies, we synthesized the current evidence regarding midsole design parameters and their influence on lower limb biomechanics during running.

Results In terms of hardness, a midsole hardness ranging from Asker C 45 to 50 can effectively reduce the maximum loading rate. The zoned design with higher hardness on the medial side and lower hardness on the lateral side contributes to improved pressure distribution across the forefoot. When the hardness is lower than Shore A 20 or higher than Shore A 80, it will lead to an imbalance in energy return and an increase in impact force. In terms of thickness, runners for short-distance races may opt for running shoes with a midsole thickness of 20-25 mm, while marathon runners are better suited for thick-soled running shoes with a midsole thickness of 30-40 mm. The degree of longitudinal bending stiffness is associated with midsole hardness, thickness, and carbon plate technology. A full-length carbon fiber plate restricts metatarsophalangeal dorsiflexion, facilitates the forward shift of the center of plantar pressure, and reduces the peak value of anteroposterior ground reaction force. However, locally increasing the LBS in the midfoot region does not induce changes in impact characteristics.

Conclusion The design of midsole hardness, thickness, and longitudinal bending stiffness can exert a positive impact on running biomechanics. Full-length carbon fiber plates are particularly suitable for elite runners. Future research requires a systematic analysis of the interaction between midsole features, refining the adaptation threshold between individual biomechanical characteristics and midsole configurations, and paying attention to the long-term impact of midsole features on running biomechanics.