# Acute Effects of Midsole Bending Stiffness on Lower Extremity Biomechanics during Layout Jumps
## 1 Introduction  
Vertical jumping is a critical individual competitive ability for basketball players [1]. Outstanding vertical jumping performance enables basketball players to obtain an advantage in terms of avoiding defenders and placing the ball through the basket [2; 3; 4]. When a player drives towards the basket, a common strategy is shooting with a layup for short contact time, which will likely disrupt the defense of the opposing team [2; 3; 4; 5]. Therefore, enhancing the layup jump (LJ) ability is essential for basketball players to improve their competitive ability.  
Based on existing literature, approaches to enhancing the LJ ability focus on developing training protocols. [PERSON] et al. [6] showed that speed and strength are related to LJ ability. However, existing studies have indicated that specific footwear can affect the biomechanical characteristics of the lower extremities and performance during LJs [7; 8]. [PERSON] et al. [8] demonstrated that a high collarheight would affect the partial kinetics of the ankle joint in the push-off phase of an LJ. Therefore, optimal footwear may change the lower extremity biomechanical characteristics and improve the player's performance.  
In recent studies, the optimization of shoe construction around the metatarsophalangeal (MTP) joint for improved performance has attracted considerable attention from researchers [9; 10]. From a biomechanical perspective, the MTP joint is primarily used to dorsiflex in the stance phase, in which the MTP joint absorbs large amounts of energy, while energy generation (EG) is close to zero [10]. The reduction in MTP joint energy loss can significantly improve the performance in the lower extremities. Several studies have proven that increasing the stiffness in the MTP joint can significantly reduce the energy loss in the MTP joint, modulate the pattern of the lower extremity kinetic chain, and improve running performance. [PERSON] et al. [11] proposed that the stiff structure around the MTP joint shifts the point-of-force application to the front edge of the shoe-ground contact plane and significantly reduces the negative work. Their results showed that a stiff midsole modulates the reaction force leverage and angular velocity, and subsequently, changes the work condition and power generation capability.  
Moreover, [PERSON] et al. [12] indicated that the increased bending stiffness of the MTP joint improves the angular impulse of the MTP, ankle, knee, and hip joints, and enhances the running energetics. In contrast, the influence of stiff midsole shoes (SS) on the lower extremity biomechanics in jumping is limited and inconsistent. [PERSON] et al. [13] investigated the effect of stiff midsoles on jumping performance, and stated that it is likely to enhance the jumping performance under fatigue conditions. However, [PERSON] et al. [14] stated that no significant difference existed between the performance of sprint and vertical jumping when 17 collegiate athletes performed 5 m sprints with medial plate shoes. Similarly, [PERSON] et al. [15] did not find significant changes in concentric squat jumping from a fixed position when three types of shoes with different stiffness levels were tested. Studies on the effect of shoes with a stiff midsole on the lower extremities while performing LJs are limited. Moreover, the effect of shoe midsole stiffness on the kinematics and kinetic energy of the lower extremity chain or performance of LJs remains unclear.  
Thus, the present study aimed to determine the effects of different levels of midsole bending stiffness on the performance and biomechanical characteristics of the lower extremities during specific basketball movements, such as LJs, by using basketball shoes with different stiffness levels. We tested the hypothesis that wearing SS reduces the range of motion (ROM) in the MTP joint, increases the ROM in the ankle, knee, and hip joints, correspondingly affects the joint energy of these joints and jump height, and enhances the muscular strength of lower extremities during LJs.