Longitudinal Bending Stiffness Research Articles

The effect of cycling shoe sole stiffness on sprint power output

Competitive and recreational cyclists use stiff-soled shoes that firmly attach to ‘clipless’ pedals. When compared to very flexible running shoes, very stiff cycling shoes with clipless pedals enhance power output during sprint cycling. However, a recent study showed no difference in power output or sprint performance between commercially available cycling shoes that span a range of longitudinal bending stiffnesses (∼200 to 500 N·m/rad). Thus, we sought to identify the likely range of sole stiffnesses below 200 N·m/rad over which reduced cycling shoe sole stiffness begins to decrease maximal power output. We measured the mechanical power outputs of 25 road cyclists during maximal sprints wearing shoes with identical uppers but with three different sole stiffnesses. Each participant completed nine 50 m sprints (three trials for each shoe) on a road with a steady, uphill grade of 9.1%. The three shoe sole conditions were: injected nylon (longitudinal bending stiffness 194 N·m/rad), moderate stiffness thermoplastic polyurethane (medium TPU) (43 N·m/rad), and low stiffness TPU (soft TPU) (9 N·m/rad) all ridden with the same clipless pedals. Stiffness was quantified using a simple testing apparatus. Power output decreased below the sole stiffness of ∼200 N·m/rad but only moderately. Maximal 1 s crank power (Pmax1) decreased −3.1% (ES = −0.59, p = 0.020) from Nylon to medium TPU and then further decreased −2.4% (ES 16 = −0.50, p = 0.054) from medium TPU to soft TPU. Interpolating our results suggests just a ∼1% loss in Pmax1 at a sole stiffness of 100 N·m/rad. Within reasonable limits, cycling shoe sole stiffness has only a small effect on power output.

Advances in longitudinal equivalent bending stiffness analysis-novel nonlinear characteristics in the assembly process of prefabricated subway stations

The longitudinal bending stiffness of quasi-rectangular prefabricated subway stations plays a great important role in studying their mechanical behavior and conducting safety assessments. To address the issue of immature stress assumptions for existing prefabricated subway stations, three stress assumptions and five bending modes are proposed while considering the coupling effect between axial force and bending moment. The study investigates novel nonlinear characteristics in the longitudinal equivalent bending stiffness and the influencing factors during the assembly of an existing subway station. An effective method for identifying the longitudinal bending modes suitable for the prefabricated subway station is established, the proposed solution has a good agreement with measured longitudinal bending stiffness efficiency. The study demonstrates that the longitudinal bending mode of the prefabricated subway station shifts from "upward convex" to "downward concave" due to the stepwise assembly method. The longitudinal bending stiffness efficiency displays a significant hysteresis curve, eventually stabilizing at approximately 1 %. Upon completion of the monitoring ring assembly, the concrete bears both longitudinal tensile and compressive stress. When assembling 10 rings from the monitoring ring, the longitudinal reinforcing bars bear tensile stress. The longitudinal bending stiffness of the prefabricated subway station exhibits significant time-variable characteristics throughout the assembly process. The research findings can provide effective references for the analysis of longitudinal mechanics and bending performance during the assembly process.

Numerical Study on the Mechanical Performance of a Flexible Arch Composite Bridge with Steel Truss Beams over Its Entire Lifespan

Steel truss–arch composite bridge systems are widely used in bridge engineering to provide sufficient space for double lanes. However, a lack of research exists on their mechanical performance throughout their lifespan, resulting in uncertainties regarding bearing capacity and the risk of bridge failure. This paper conducts a numerical study of the structural mechanical performance of a flexible arch composite bridge with steel truss beams throughout its lifespan to determine the critical components and their mechanical behavior. Critical vehicle loads are used to assess the bridge’s mechanical performance. The results show that the mechanical performance of the bridge changes significantly when the temporary piers and the bridge deck pavement are removed, substantially influencing the effects of the vehicle loads on the service life. The compressive axial force of the diagonal bar significantly increases to 33,101 kN near the supports during the two construction stages, and the axial force in the upper chord of the midspan increases by 4.1 times under a critical load. Moreover, the suspender tensions and maximum vertical displacement are probably larger than the limit of this bridge system in the service stage, and this is caused by the insufficient longitudinal bending stiffness of truss beams. Therefore, monitoring and inspection of critical members are necessary during the removal of temporary piers and bridge deck paving, and an appropriate design in steel truss beams is required to improve the life cycle assessment of this bridge system.

The influence of longitudinal bending stiffness on running economy and biomechanics in male and female runners

The purpose of this study was to evaluate the influence of different longitudinal bending stiffnesses (LBS) on running economy and lower extremity joint biomechanics in male and female runners. Thirty participants (15 F;15M) performed a treadmill protocol of five-minute randomised aerobic runs with four different footwear conditions varying in LBS: 16.1 N/mm; 32.7 N/mm; 46.1 N/mm; 90.1 N/mm. Biomechanical data was collected at the metatarsophalangeal (MTP) and ankle joints. Running economy was quantified via oxygen consumption data. Oxygen consumption observed no significant differences between footwear conditions (p = 0.960) or significant interaction between footwear and sex (p = 0.126). Stance time observed a significant difference between footwear conditions (p < 0.001), and a significant interaction of footwear and sex (p = 0.008), increasing in females as stiffness increased. At the MTP joint, a shoe effect was present for peak bending angle (p < 0.001), peak extension (p = 0.040) and flexion (p < 0.001) angular velocity, and energy generated at the joint (p = 0.010). There was also an interaction effect of peak MTP extension angular velocity (p = 0.044), with females slightly decreasing as stiffness increased, with no reaction from males. At the ankle joint, a shoe effect was present for peak dorsiflexion (p < 0.001) and plantarflexion (p < 0.001) angular velocity, peak negative power (p < 0.001) and energy absorbed at the joint (p < 0.001). Comparing the interaction between shoe condition and male/female runners, male and female runners reacted similarly to the increased LBS with no effect on running economy and subtle changes in the stance time and MTP angular velocity for female runners. While further research is needed in this area investigating aspects related to sex-specific optimal stiffness element location and geometry, it does not appear that the stiffness magnitude has a sex dependence.

Effects of the increase of longitudinal bending stiffness of advanced footwear technology on 3,000m performance, pacing strategy, and biomechanics

This study aimed to analyse the effects of shoes with increased longitudinal bending stiffness (LBS) on 3,000 m performance, pacing strategy, heart rate, and biomechanics in trained runners. Twelve male trained runners performed a 3,000 m time trial test in an experimental shoe with a carbon fibre plate to increase the LBS (LBS-increased) and a Control shoe (without carbon fibre plate). Running performance (total time), pacing, heart rate, and biomechanical variables were registered and analysed for each 1000 m split. An individual analysis of the responders was performed based on the smallest worthwhile change. The 3,000 m time trial performance improved by 0.74% (585.83 ± 33.39 vs. 590.17 ± 34.35 s, p < 0.001, large d = 0.829) in the LBS-increased condition compared to the Control condition with a high inter-individual variability. There were no significant differences for the split effect (p = 0.898, small ηp2 = 0.021). The performance improvement was accompanied by an increase in step length (p < 0.001, large ηp2 = 0.717) throughout the time trial test and an increase of flight time in the split 1 and 2 (p < 0.05, moderate d = 0.793, 0.686, respectively) and vertical oscillation in the split 2 and 3 (p < 0.05, moderate d = 0.727, 0.652). However, the heart rate remained unchanged between conditions. The increase of LBS in footwear can improve 3,000 m performance without causing changes in the pacing strategy. Small modifications in running kinematics accompanied the improvements in running performance but without changes in heart rate. Moreover, LBS-increased did not affect all runners equally highlighting the need for further understanding of individual responses.

Biomechanical Investigation of Lower Limbs during Slope Transformation Running with Different Longitudinal Bending Stiffness Shoes.

During city running or marathon races, shifts in level ground and up-and-down slopes are regularly encountered, resulting in changes in lower limb biomechanics. The longitudinal bending stiffness of the running shoe affects the running performance. This research aimed to investigate the biomechanical changes in the lower limbs when transitioning from level ground to an uphill slope under different longitudinal bending stiffness (LBS) levels in running shoes. Fifteen male amateur runners were recruited and tested while wearing three different LBS running shoes. The participants were asked to pass the force platform with their right foot at a speed of 3.3 m/s ± 0.2. Kinematics data and GRFs were collected synchronously. Each participant completed and recorded ten successful experiments per pair of shoes. The range of motion in the sagittal of the knee joint was reduced with the increase in the longitudinal bending stiffness. Positive work was increased in the sagittal plane of the ankle joint and reduced in the keen joint. The negative work of the knee joint increased in the sagittal plane. The positive work of the metatarsophalangeal joint in the sagittal plane increased. Transitioning from running on a level surface to running uphill, while wearing running shoes with high LBS, could lead to improved efficiency in lower limb function. However, the higher LBS of running shoes increases the energy absorption of the knee joint, potentially increasing the risk of knee injuries. Thus, amateurs should choose running shoes with optimal stiffness when running.

Relationship Between Advanced Footwear Technology Longitudinal Bending Stiffness and Energy Cost of Running.

Shoe longitudinal bending stiffness (LBS) is often considered to influence running economy (RE) and thus, running performance. However, previous results are mixed and LBS levels have not been studied in advanced footwear technology (AFT). The purpose of this study was to evaluate the effects of increased LBS from curved carbon fiber plates embedded within an AFT midsole compared to a traditional running shoe on RE and spatiotemporal parameters. Twenty-one male trained runners completed three times 4 min at 13 km/h with two experimental shoe models with a curved carbon fiber plate embedded in an AFT midsole with different LBS values (Stiff: 35.5 N/mm and Stiffest: 43.1 N/mm), and a Control condition (no carbon fiber plate: 20.1 N/mm). We measured energy cost of running (W/kg) and spatiotemporal parameters in one visit. RE improved for the Stiff shoe condition (15.71 ± 0.95 W/kg; p < 0.001; n2 = 0.374) compared to the Control condition (16.13 ± 1.08 W/kg; 2.56%) and Stiffest condition (16.03 ± 1.19 W/kg; 1.98%). However, we found no significant differences between the Stiffest and Control conditions. Moreover, there were no spatiotemporal differences between shoe conditions. Changes in LBS in AFT influences RE suggesting that moderately stiff shoes have the most effective LBS to improve RE in AFT compared to very stiff shoes and traditional, flexible shoe conditions while running at 13 km/h.

Effect of increased shoe longitudinal bending stiffness on ankle and foot biomechanics in jump-cut movements of low and high degrees

Lateral ankle sprains are the most common injuries in indoor and court sports, with ankle inversion being a primary injury driver. Stabilising the ankle during multidirectional changes is crucial for injury prevention. Conversely, increased shoe stiffness has been hypothesised to influence the magnitude of ankle inversion and may raise the risk for ankle injuries. Therefore, the purpose of this study was to investigate the influence of shoe longitudinal bending stiffness on ankle biomechanics during indoor and court sport-specific cutting movements. Biomechanical data from 19 participants were collected using a motion capture system and force plate. A jump-cut protocol with two different cutting directions after landing was performed in indoor shoes with and without carbon plate inserts of varying stiffness. Ankle kinematics and kinetics were analysed with statistical parametric mapping and repeated measures analysis of variance. A significant increase in ankle inversion during the 180° cut and a reduction in forefoot inversion (foot torsion) for stiffer footwear conditions during both the 45° and 180° cut were observed. While dorsiflexion moments differed during the last 10% of ground contact, ankle inversion moments did not significantly diverge between shoe conditions. Furthermore, a noteworthy correlation between footwear longitudinal bending stiffness and torsional stiffness was identified. In conclusion, increased bending stiffness significantly affected ankle and foot kinematics. The ankle compensated for restricted mobility and higher demands during high-degree jump-cuts, while foot torsion played a more prominent role in low-degree cuts. The heightened ankle inversion during high-degree cuts may induce an elevated risk for lateral ankle sprains. Further longitudinal studies are necessary to comprehensively understand injury incidence and the role of shoe stiffness in injury prevention.

The Impact of Running Experience and Shoe Longitudinal Bending Stiffness on Lower Extremity Biomechanics

Purpose The impacts of shoe stiffness on running biomechanics are well-documented, while the specific effects on the performance of biomechanically distinct groups such as novice runners and experienced runners are still largely unexplored. The study aimed to evaluate the biomechanical effects of different shoe longitudinal bending stiffness (adjusted by inserting carbon plate) on the lower limb during running in novice runners and experienced runners. Methods Twelve experienced runners and ten novice runners ran at a speed of 4.47 m/s while randomly wearing shoes with either low stiffness (5.9 Nm/rad) or high stiffness (8.6 Nm/rad). An Opensim musculoskeletal model was adopted for estimating lower limb joint angles, joint angular velocities, joint moment, joint work, peak joint reaction forces during running stance phase. Results Results showed that novice runners displayed greater lower limb joint mobility and less joint moment, while experienced runners exhibited less joint mobility but greater joint moment, and higher peak joint reaction forces were observed at the knee and ankle joints. Furthermore, increased shoe longitudinal bending stiffness resulted in higher peak joint reaction forces at the metatarsophalangeal joint for novice runners while lower for experienced runners. Conclusions Novice runners may face an increased risk of metatarsal pain or stress fractures when dealing with higher shoe stiffness. This nuanced understanding of joint dynamics underscores the need for tailored training and footwear recommendations to mitigate injury risks specific to different levels of running experience.

Influence of Running Shoe Longitudinal Bending Stiffness on Running Economy and Performance in Trained and National Level Runners.

Previous results about shoe longitudinal bending stiffness (LBS) and running economy (RE) show high variability. This study aimed to assess the effects of shoes with increased LBS on RE and performance in trained and national runners. Twenty-eight male runners were divided into two groups according to their 10-km performance times (trained, 38-45 min and national runners, <34 min). Subjects ran 2 × 3 min (at 9 and 13 km·h -1 for trained, and 13 and 17 km·h -1 for national runners) with an experimental shoe with carbon fiber plate to increase the LBS (Increased LBS) and a control shoe (without carbon fiber plate). We measured energy cost of running (W·kg -1 ) and spatiotemporal parameters in visit one and participants performed a 3000 m time trial (TT) in two successive visits. Increased LBS improved RE in the trained group at slow (11.41 ± 0.93 W·kg -1 vs 11.86 ± 0.93 W·kg -1 ) and fast velocity (15.89 ± 1.24 W·kg -1 vs 16.39 ± 1.24 W·kg -1 ) and only at the fast velocity in the national group (20.35 ± 1.45 W·kg -1 vs 20.78 ± 1.18 W·kg -1 ). The improvements in RE were accompanied by different changes in biomechanical variables between groups. There were a similar improvement in the 3000 m TT test in Increased LBS for trained (639 ± 59 vs 644 ± 61 s in control shoes) and national runners (569 ± 21 vs 574 ± 21 s in control shoes) with more constant pace in increased LBS compared with control shoes in both groups. Increasing shoe LBS improved RE at slow and fast velocities in trained runners and only at fast velocity in national runners. However, the 3000 m TT test improved similarly in both levels of runners with increased LBS. The improvements in RE are accompanied by small modifications in running kinematics that could explain the difference between the different levels of runners.

Effects of longitudinal bending stiffness and midsole foam on running energetics and biomechanics

Effects of longitudinal bending stiffness and midsole foam on running energetics and biomechanics

Peak plantar pressures in running footwear with increased longitudinal bending stiffness

Peak plantar pressures in running footwear with increased longitudinal bending stiffness

Model test investigation on the longitudinal mechanical property of shield tunnels considering internal structure

Reasonable evaluation of longitudinal mechanical property of shield tunnel is critical to the design and maintenance of tunnel structures. Traditionally, the internal structure has not been involved in the existing studies on the longitudinal mechanical properties of shield tunnels, of which the effect on the longitudinal mechanical properties of shield tunnels remains unknown. In this study, a series of physical similar model tests were conducted on homogeneous model (HM), non-homogeneous model (NHM) and non-homogeneous model with internal structure (NHMI), the effect of internal structure and longitudinal force on the longitudinal mechanical properties of road-metro shield tunnels were investigated. The longitudinal strain, displacement, curvature, and circumferential joint deformation of the tunnels were analyzed in depth. The experimental results show that the internal structure can reduce the longitudinal deformation of shield tunnels greatly, and the maximum displacement of tunnels with internal structure can be reduced by 70.58 %, the curvature radius can be increased by 1.73 to 2.36 times, the dislocation of the circumferential joint can be reduced by up to 70.4 %, and the opening of the circumferential joint can be reduced by up to 67.37 %. The longitudinal bending stiffness efficiency of tunnels ranges from 0.66 to 0.86 after taking into account the effect of internal structures. Increasing the longitudinal force from 0 MPa to 0.3 MPa significantly improves the longitudinal bending stiffness efficiency of tunnels, after which increasing the longitudinal force has no significant effect on the longitudinal mechanical properties of the tunnel.

Evaluation of Longitudinal Equivalent Bending Stiffness of Shield Tunnel with Residual Jacking Force

Existing tunnels are often subject to longitudinal bending when undercrossing tunnelling. It is of significance to more accurately evaluate the longitudinal equivalent bending stiffness (LEBS) of the existing tunnel within the influential zone. A new analytical method is proposed for the LEBS of tunnel segmental lining joints with consideration of incorporating combined action of residual jacking force and bending moment. The solution can degenerate into a special case with no residual jacking force, which agrees well with other classical solutions and validates the model and solutions. Sensitivity analyses are carried out for the bending moment, tunnel geometry, tensile stiffness of bolts and concrete grade on the LEBS, and effective ratio of the LEBS considering residual jacking force. The LEBS and the effective ratio of LEBS increase nonlinearly as an S-curve with the residual jacking force and decrease with an increasing bending moment. The results show that the LEBS of the shield tunnel is variable stiffness, which exhibits a significant nonlinearity. The maximum increment of the LEBS reaches 80.3% as the ring width increases from 1 m to 2 m, and the LEBS of the shield tunnel increases by approximately 1.3 × 107 kN·m2 for every 4-bolt added. The influential order on the LEBS of shield tunnels is the tunnel diameter &gt; lining thickness &gt; bolts diameter &gt; ring width &gt; the number of bolts &gt; elastic modulus of bolts. When the effective ratio of LEBS is more than 0.85, it does not change with the ring width, lining thickness, tensile stiffness of bolts, and concrete grade. The response characteristics of the tunnel parameters on the LEBS, considering the residual jacking force, could provide a theoretical basis for the design and deformation control of shield tunnels when undercrossing tunnelling.

Analytical algorithm of longitudinal bending stiffness of shield tunnel considering longitudinal residual jacking force

Longitudinal bending stiffness is a fundamental parameter of shield tunnels, and its value directly affects the analysis of their longitudinal response. Existing studies have not considered the tensile stiffness of segment ring joints and longitudinal residual jacking force when determining the value of the longitudinal bending stiffness of an existing shield tunnel. Therefore, through theoretical analysis, this study considered the longitudinal bending deformation under an external load action as two parts, namely the longitudinal bending deformation of the homogeneous pipe and the longitudinal bending deformation induced by the opening of the segment ring joints. An analytical algorithm of the longitudinal bending stiffness of the shield tunnel was obtained, considering that this longitudinal bending stiffness was related to various factors such as the elastic modulus of the material of the segment ring, outer diameter of the shield tunnel, width of the segment ring, number of the segment ring joints and tensile stiffness of the connecting bolt. A scaled shield tunnel model that considered tensile stiffness of the segment ring joints and longitudinal residual jacking force was designed, and longitudinal bending stiffness tests of the model were conducted accordingly. The tests were designed to measure the longitudinal bending deformation and opening of the segment ring joints. The validation of the theoretical analysis result based on the test data demonstrates that the longitudinal residual jacking force could only reduce the longitudinal bending deformation and the opening of the segment ring joints at small loads, it had almost no effect under larger loads. The measured longitudinal bending stiffness of the shield tunnel model was generally consistent with that obtained using the theoretical algorithm. Thus, in the longitudinal response analysis of the shield tunnel, the effect of the longitudinal residual jacking force on the enhancement of the longitudinal bending stiffness need not be considered.

Increasing Shoe Longitudinal Bending Stiffness Is Not Beneficial to Reduce Energy Cost During Graded Running

Carbon plates have been used to increase running shoes' longitudinal bending stiffness (LBS), leading to reductions in the energy cost of level running (Cr). However, whether or not this is true during uphill (UH) running remains unknown. The aim of our study was to identify the effect of LBS on Cr during UH running. Twenty well-trained male runners participated in this study. Cr was determined using gas exchange during nine 4-minute bouts performed using 3 different LBS shoe conditions at 2.22 and 4.44m/s on level and 2.22m/s UH (gradient: + 15%) running. All variables were compared using 2-way analyses of variance (LBS × speed/grade effects). There was no significant effect of LBS (F = 2.04; P = .14, ηp2=.11) and no significant LBS × grade interaction (F = 0.31; P = .87, ηp2=.02). Results were characterized by a very large interindividual variability in response to LBS changes. The current study contributes to a growing body of literature reporting no effect of LBS on Cr during level and UH running. Yet, the very large interindividual differences in response to changes in LBS suggest that increasing shoe LBS may be beneficial for some runners.

Theoretical analysis on the deformation of existing tunnel caused by under-crossing of large-diameter slurry shield considering construction factors

With the expansion of underground space networks, new tunnels especially large-diameter shields under-crossing existing tunnels have been commonly practiced. To obtain a better understanding of the effect of large-diameter slurry shield under-crossing on the existing tunnel and provide a quick and effective tool for evaluating the deformation behaviors of the existing tunnel before construction, in this study a simplified analytical method is proposed. Based on the two-stage method, and considering the characteristics of construction factors such as additional thrust on the shield excavation face of the slurry shield machine, friction force of the shield shell, and grouting pressure of the shield tail, deformation of the existing tunnel caused by the crossing of the large-diameter slurry shield in saturated soil is calculated. The proposed method is verified with field measurement data from a case study. A parametric analysis is conducted to study the influence of typical factors on tunnel responses, including longitudinal bending stiffness, elastic modulus, clearance between two tunnels, and shield crossing angle. The parametric study indicates a significant influence of the crossing angle on maximum settlement and the influence range of settlement of the existing tunnel. Recommendations for safe values of shield crossing clearance are given. The proposed analytical solution can be used as a reference to predict the potential risk of new large-diameter slurry shield crossing on the existing tunnel in engineering practices.

Influence of Footwear Features on Oxygen Consumption and Running Economy: A Review

It has been reported that the new technology applied to current racing shoes has increased the performance of runners who use this kind of footwear. This improvement has been proven in the scientific literature in relation to oxygen consumption. Nevertheless, as it is a novel topic, there is a lack of knowledge about which specific features achieve a decrease in oxygen consumption during running. Thus, the purpose of this study was to determine the influence of the features of footwear, specifically the shoe mass, the cushioning system, the longitudinal bending stiffness and the comfort feeling on running economy. This review was carried out from the bibliographic search in the main databases such as PubMed, Cochrane Plus and Medline and considering the PRISMA statement as a reference so that an analysis of the results has been obtained together with the methodological quality and risk of bias of the studies. Nineteen articles met the inclusion criteria, which presented a moderate/high methodological quality, and an analysis of their results was carried out. Footwear features such as the shoe mass, the cushioning system and the longitudinal bending stiffness produce advantages compared to other footwear that does not include this technology. Due to the lack of evidence, the influence of comfort feeling on oxygen consumption has not been proved.

Running Velocity and Longitudinal Bending Stiffness Influence the Asymmetry of Kinematic Variables of the Lower Limb Joints.

Running-related limb asymmetries suggest specific sports injuries and recovery circumstances. It is debatable if running speed affected asymmetry, and more research is required to determine how longitudinal bending stiffness (LBS) affected asymmetry. The purpose of this study was to investigate the influence of running velocity and LBS on kinematic characteristics of the hip, knee, ankle, metatarsophalangeal joint (MTP) and the corresponding asymmetry. Kinematic (200 Hz) running stance phase data were collected bilaterally for 16 healthy male recreational runners (age: 23.13 ± 1.17, height: 175.2 ± 1.6 cm, body mass: 75.7 ± 3.6 kg, BMI: 24.7 ± 1.3 kg/m2) running on a force plate at three different velocities (10, 12 and 14 km/h) and three increasing-LBS shoes in a randomized order. The symmetry angle (SA) was calculated to quantify gait asymmetry magnitude at each running velocity and LBS. Changes in running velocity and LBS led to differences in kinematic variables between the hip, knee, ankle and MTP (p &lt; 0.05). Significant changes in SA caused by running velocity were found in the knee flexion angle (p = 0.001) and flexion angle peak velocity (p &lt; 0.001), ankle plantarflexion angle (p = 0.001) and plantarflexion angle peak velocity (p = 0.043) and MTP dorsiflexion angle (p = 0.001) and dorsiflexion angle peak velocity (p = 0.019). A significant change in the SA caused by LBS was found in the MTP dorsiflexion peak angle velocity (p = 0.014). There were interaction effects between running velocity and LBS on the MTP plantarflexion angle (p = 0.033) and plantarflexion angle peak velocity (p = 0.038). These findings indicate the existence of bilateral lower limb asymmetry. Meanwhile, it was proved that running velocity and LBS can influence the asymmetry of lower limb joints. Additionally, there was an interaction between running velocity and LBS on the asymmetry of the lower limb. These findings can provide some information for sports injuries, such as metatarsal stress fractures and anterior cruciate ligament injuries. They can also provide some useful information for running velocities and running shoes.

Individual physiological responses to changes in shoe bending stiffness: a cluster analysis study on 96 runners.

Shoe longitudinal bending stiffness is known to influence running economy (RE). Recent studies showed divergent results ranging from 3% deterioration to 3% improvement in RE when bending stiffness increases. The variability of these results highlights inter-individual differences. Thus, our purpose was to study the runner-specific metabolic responses to changes in shoe bending stiffness. After assessing their maximal oxygen consumption ([Formula: see text] max) and aerobic speed (MAS) during a first visit, 96 heterogeneous runners performed two treadmill 5min runs at 75% [Formula: see text] max with two different prototypes of shoes on a second day. Prototypes differed only by their forefoot bending stiffness (17N/mm vs. 10.4N/mm). RE and stride kinematics were recorded during each trial. A clustering analysis was computed by comparing the measured RE and the technical measurement error of our gas exchange analyzer to identify functional groups of runners, i.e., responding similarly to footwear interventions. ANOVAs were then computed on biomechanical and morphological variables to compare the functional groups. Considering the whole sample (n = 96), there was no significant difference in RE between the two conditions. Cluster 1 (n = 29) improves RE in the stiffest condition (2.7 ± 2.1%). Cluster 2 (n = 26) impairs RE in the stiffest condition (2.7 ± 1.3%). Cluster 3 (n = 41) demonstrated no change in RE (0.28 ± 0.65%). Cluster 1 demonstrated 1.7km·h-1 greater MAS compared to cluster 2 (p = 0.014). The present study highlights that the effect of shoe bending stiffness on RE is runner-specific. High-level runners took advantage of increased bending stiffness, whereas medium-level runners did not. Finally, this study emphasizes the importance of individual response examination to understand the effect of footwear on runner's performance.