Background: 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. Purpose: 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. Methods: 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. Results: 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. Conclusion: 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.

Background: The lunge exercise is commonly adopted in public fitness programs. However, inadequate training experience and knowledge may result in improper actions, resulting in lowering training efficacy and possibly causing exercise-related diseases. Methods: Twenty-four male fitness trainees (12 novices and 12 experienced seniors) were recruited. Kinematics, kinetics, and muscle activation were measured during forward and backward lunges with different loading positions. Two-way repeated measures ANOVA and one-dimensional statistical parametric mapping (SPM1D) were employed to explore various between training experience across different loading positions and lunge directions. Results: Hip, knee, and ankle ROM and angle peaks were significantly greater in novices than in seniors (P < 0.001). During forward lunges, dumbbells reduced hip moments and stiffness in novices (P < 0.001), while barbells increased ankle moments in seniors (P = 0.022). In the backward lunges, novices showed increased negative power and significant joint instability with dumbbells. Conclusions: Training experience is the significant influence during male lunge exercises. Novices show more stability when using dumbbells instead of barbells for forward lunges. Novices are less stable during backward lunges than more experienced seniors. Overall, novices get a greater benefit of training with dumbbells, while seniors are less likely to hurt their knees and ankles when they use barbells.

(1) Background: Changes in midsole hardness may affect lower-limb impact loading during forefoot strike (FFS) running in children, yet the biomechanical basis for discriminating elevated VALR-related loading remains unclear. (2) Methods: Fourteen school-aged boys performed FFS running tests in experimental shoes with four midsole hardness levels (37, 42, 47, and 52 Shore C). Lower-limb kinematics and surface electromyography (sEMG) data were collected during the dominant leg stance phase. After preprocessing, VALR was calculated from 336 valid trials, and 28 stance-phase biomechanical features were extracted, yielding a final machine-learning dataset of 324 trials after excluding incomplete feature data. VALR was used to compare loading changes and define trial-level elevated-loading labels based on the median VALR value. Classification models were evaluated under participant-level GroupKFold validation, and XGBoost was retained for exploratory SHAP analysis. (3) Results: VALR showed an upward trend with increasing hardness, but no statistically supported change point was identified. XGBoost achieved an accuracy of 75.93%, precision of 74.14%, recall of 79.63%, F1-value of 0.768, and pooled out-of-fold AUC of 0.738. SHAP analysis indicated that distal and non-sagittal kinematic features contributed most to model classification. (4) Conclusions: Elevated VALR-related loading during children’s FFS running may be characterized by a multi-feature model-based pattern rather than a fixed midsole hardness threshold.