Journal of biomechanics最新文献

People with multiple sclerosis (PwMS) experience elevated fall risk, yet traditional gait measures such as step variability provide limited insight into underlying control mechanisms. We examined step-to-step regulation of foot placement in PwMS versus age-matched controls during treadmill walking with and without anteroposterior (AP) and mediolateral (ML) optical flow perturbations. Fifteen PwMS and fifteen matched controls completed three-minute walking trials while kinematics were recorded. Detrended fluctuation analysis (DFA) assessed the temporal organization of step width (SW) and step length (SL) time series, and direct control analysis (DCA) quantified stride-to-stride corrections. DFA showed lesser SW persistence during ML perturbations compared to other conditions, indicating tighter regulation under lateral balance challenges. A group × condition interaction revealed that PwMS, but not controls, exhibited reduced SL persistence during both AP and ML perturbations. These results highlight broader disruptions in temporal organization of stepping in PwMS. DCA revealed that both groups increased corrective responses to SW deviations under ML perturbations, but model fit (R²) values were lower, indicating reduced consistency than unperturbed walking. Additionally, PwMS showed reduced SW corrections during AP perturbations. In contrast, neither SL regression coefficients nor R² values differed by group or condition. Together, DFA and DCA suggest that PwMS exhibit disrupted temporal structure of foot placement regulation, particularly for SL under visually destabilizing conditions, and that stronger but less consistent SW corrections emerge under ML challenges. These complementary analyses provide novel insight into mechanisms of walking instability in PwMS and may inform interventions targeting reliable step-to-step control.

Muscle force sharing is typically resolved by minimizing a specific objective function to approximate neural control strategies. An inverse optimal control approach was applied to identify the "best" objective function, among a positive linear combination of basis objective functions, associated with the gait of two post-stroke males, one high-functioning and one low-functioning. By comparing objective-function-predicted muscle forces to those of a reference EMG-driven model, using Root-Mean-Squared-Errors (RMSE) and Pearson Correlation Coefficients (CC), it was found that the "best" objective function is subject- and leg-specific. No single function works universally well, yet the best options are usually differently weighted combinations of muscle activation- and power-minimization. Subject-specific inverse optimal control models performed best on their respective limbs (RMSE 178/213 N, CC 0.71/0.61 for respective legs of subject 1; RMSE 205/165 N, CC 0.88/0.85 for respective legs of subject 2), but cross-subject generalization was poor, particularly for paretic legs. Moreover, minimizing the root mean square of muscle power emerged as important for paretic limbs, while minimizing activation-based functions dominated for non-paretic limbs. This may suggest different neural control strategies between affected and unaffected sides, possibly altered by the presence of spasticity. Among the 15 considered objective functions commonly used in inverse dynamics-based computations, the root mean square of muscle power was the only one explicitly incorporating muscle velocity, leading to a possible model for spasticity in the paretic limbs. Although this objective function has been rarely used, it may be relevant for modeling pathological gait, such as post-stroke gait.

Scapular dyskinesis (SD) is prevalent among overhead athletes and associated with dysfunctions of the rotator cuff. Although the musculotendinous architecture of the supraspinatus changes with arm elevation, the influence of scapular kinematics remains unclear. Thus, this study aimed to investigate the dynamic changes in the supraspinatus's musculotendinous architecture and its association with scapular kinematics during scaption in participants with SD. Twenty-one asymptomatic male college volleyball players with type I SD were recruited. Participants were asked to perform scaption from 0° to 60° while the pennation angle (PA) and fiber bundle length (FBL) of supraspinatus were measured using real-time sonography synchronized with a motion capture system to record scapular kinematics. Paired t-tests were used to compare the scapular kinematics, PA, and FBL between 0° and 60° of scaption. Multivariable regression analysis examined the relationship between the scapular kinematics and the FBL or PA. At 60° of scaption, participants demonstrated greater scapular upward rotation and posterior tilting (p < 0.001), along with shorter FBL and larger PA (p < 0.05), compared with 0°. Scapular kinematics significantly explained the variance in FBL, but not in PA. At 60°, scapular upward rotation was significantly associated with FBL lengthening (β = -0.56, p = 0.02). Scapular upward rotation facilitates lengthening of the supraspinatus during arm elevation. These findings suggest that impaired scapular control in SD may compromise rotator cuff performance. Rehabilitation for supraspinatus dysfunction should incorporate scapular motion training.

While bone mechanical properties during adulthood are well-documented, the mechanical properties of immature bone during infancy and adolescence remain poorly characterized. In this study, nanoindentation mapping was performed to measure the indentation modulus (E) and hardness (H) across four anatomical quadrants (anterior, posterior, medial, and lateral) in the tibial cortical bone of female C57BL/6J mice at postnatal ages of 3, 7, 14, 21, and 56 days (6 mice per age group). Two-way ANOVA revealed no significant interaction between age and anatomical location for E (p = 0.946) or H (p = 0.769), whereas age demonstrated a significant main effect on both E (p < 0.001, η² = 0.528) and H (p < 0.001, η² = 0.111). Results demonstrated a significant age-dependent increase in E across all anatomical quadrants (p < 0.001), while H showed no consistent developmental trend. Linear regression models revealed differential growth trajectories in E among quadrants, with medial and lateral quadrants exhibiting slightly faster increases. These findings may provide some insights into the developmental biomechanics of immature bone and establish a foundation for multiscale modeling of skeletal growth.

The purpose of this study was to assess whether initial pre-activation muscle length alters stretch-shortening cycle (SSC) performance enhancement in permeabilized single muscle fibres. Single fibres (n = 16) from the psoas major of Sprague Dawley rats (n = 6, 13-14 weeks) were dissected and chemically permeabilized. Fibres were maximally activated (pCa 4.5) while mounted between a force transducer and length controller. For pre-activation at a long length, the fibre was passively stretched from 2.5 to an average sarcomere length of 3.0 µm. After passive force stabilized, the fibre was activated before being rapidly shortened to 2.5 µm at 10 Lo/s to detach all cross-bridges. Activation was maintained and once active force recovered the fibre underwent the SSC protocol. For pre-activation at optimal length, the fibre passively underwent the same protocol as the long length condition. However, activation only began once the fibre was returned to a sarcomere length of 2.5 µm. For SSCs, fibres were stretched from sarcomere lengths of 2.5 to 3.0 µm and immediately shortened back to 2.5 µm at a speed of 0.6 Lo/s for both phases. The SSC effect was calculated by comparing work and power during shortening to an active shortening contraction not preceded by active lengthening. The SSC enhancement (∼55% increase; all P < 0.003) was not significantly different between the two initial pre-activation muscle lengths (P > 0.14). Therefore, initial pre-activation muscle length does not significantly alter the SSC effect of permeabilized single fibres as non-cross-bridges structures, such as titin, were unlikely to be differently modified by the pre-activation starting lengths.

Single-leg lateral jumps are a complex, multi-joint and multi-planar task with distinct biomechanical demands compared to vertical and forward jumps, yet they remain relatively under-researched. Their unique demands provide an opportunity to ask mechanistic questions regarding multi-joint control and assess key aspects of athletic performance, but detailed biomechanical descriptions of task performance are lacking. The purpose of this study was to quantify joint contributions to whole-body dynamics and jump distance, and to examine hip muscle recruitment during maximal-distance single-leg lateral jumps. Eighteen female athletes performed three maximal-distance single-leg lateral jumps from each limb while full-body kinematics, kinetics, and hip muscle activation were recorded. Whole-body (WB) centre-of-mass (COM) power and work were computed as the dot product of the ground reaction force and WB-COM velocity. Inverse dynamics analysis on linked segment models were used to calculate joint power and work. Work done on the WB-COM explained 68% of the variance observed in normalized jump distances across participants. Total joint power underestimated whole-body centre-of mass power by 23%. The ankle joint was the primary contributor (p < 0.001) though only hip (R² = 0.33, p = 0.01) and knee (R² = 0.55, p = 0.0004) joint work scaled with jump distance. Large variability in individuals' hip muscle recruitment strategy and relative hip joint contributions to task performance highlight limitations in relating muscle activation to joint, whole-body, and task performance at the group-level. These findings suggest quantifying segmental power flow and muscle power contributions might provide greater insight into how individuals coordinate and control multiple muscles and joints to perform single-leg lateral jumps.

Ankle-foot deformities, such as clubfoot, pose treatment challenges due to complex and patient-specific biomechanics. Accurate assessment of muscle force behavior is essential for tailoring interventions, yet conventional gait analysis is limited in isolating muscle-specific function. Intraoperative force measurements via the muscle's tendon offer a unique opportunity to directly quantify muscle mechanics. This study aimed to characterize the passive and active force-angle relationship of the tibialis anterior (TA) muscle, intraoperatively. Ten patients (ages 3-62) undergoing corrective foot surgery were enrolled, including five with idiopathic deformities and five with neurogenic conditions (hereditary motor and sensory neuropathy, n = 3; cerebral palsy, n = 2). Isometric TA forces were recorded at multiple ankle angles. Patients with neurogenic deformities exhibited greater ankle range of motion compared to those with idiopathic deformities (by 30.1%, p = 0.006). Passive forces were near 0 N in dorsiflexion and increased toward plantar flexion (PF), with a maximum of 50.3 N at 55° PF; no significant group differences were observed (p = 0.42). Active force-ankle angle profiles showed high inter-individual variability, with peak values ranging from 31.1 N to 431.6 N and no significant differences between groups (p = 0.81). Substantial variability in curve shape remained after normalization, indicating distinct functional profiles across patients. This study demonstrates the feasibility of directly quantifying the patient-specific force-generating capacity of the TA muscle. From a forward-looking perspective, incorporating such patient-specific force data into musculoskeletal models may improve force estimations and support more personalized surgical strategies for ankle-foot deformities.

Recent studies show the relevance of using sEMG signals and extracted features in powered prosthesis control. However, amputation technique determines the availability of residual muscles, and minimizing sensor number is to be preferred. Therefore, (i) limiting the total number of sEMG muscle inputs, (ii) minimizing the inputs from the lower leg muscles, and (iii) completely excluding the lower leg muscles will make the control algorithm economical, flexible, and practical, respectively. Using healthy population data, the aim was to conduct a systematic analysis for ranking possible muscle combinations based on prediction success for ankle kinematics and kinetics during stair ascending motion. We used eight muscle inputs in a long short-term memory (LSTM): rectus femoris (RF), vastus medialis (VM), tibialis anterior (TA), peroneus longus (PL), gluteus maximus (Gmax), biceps femoris (BF), medial gastrocnemius (MG), and soleus (SOL). sEMG feature and muscle combinations were ranked based on Pearson's correlation coefficient (r > 0.90 indicates successful correlation) and root-mean-square-error. The best-performing involved several muscles: TA + SOL + MG + PL + VM + BF + Gmax (r_position = 0.93, r_moment = 0.95). However, a single muscle also performed successfully: SOL (r_position = 0.91, r_moment = 0.94) economical variation. SOL + BF (r_position = 0.92, r_moment = 0.94) was the flexible variation. The results confirm the successful use of sEMG also for a highly demanding motion but eliminate a practical variation.

Synthetic polymer scaffolds with aligned fibers permit engineered tendon development and the formation of an aligned, collagen rich matrix. However, many tissue engineered constructs cannot withstand physiologically relevant loads. Both tendon development and normal homeostasis require loading, and tendons adapt to loading. In vitro loading of tissue engineered constructs further promotes engineered tendon development, but results vary by cell type, strain applied, and frequency of the loading. However, both under- and overloading of tendon is detrimental and disrupts stiffness and collagen organization in vivo, and levels of loading comparable to that which occurs during fetal development are generally unexplored for engineered tendon development. The objective of this study was to determine the optimal number of daily cycles of dynamic tensile loading for in vitro human adipose stem cell (hASC) cultured on poly(ε-caprolactone) 3D meltblown scaffolds. hASC-seeded scaffolds were loaded for 0 (control), 1,000 (low), 5,000 (moderate), 10,000 (high) cycles 3 times/week to 6% strain at 1 Hz. Loading at 5,000-cycles/session led to increased dsDNA, collagen, and collagen/dsDNA compared to unloaded control, and 1,000-cycles/session was intermediate in response. Loading up to 10,000-cycles/session increased dsDNA compared to unloaded control and the 5,000-cycle group but did not increase collagen content or collagen/dsDNA. Dynamic loading had no effect on glycosaminoglycan expression or collagen alignment. Loading at 5,000-cycles/session increased linear region modulus, yield stress, phase shift, and hysteresis and secant stiffness at high strains compared to the unloaded control but did not affect yield stretch or stress relaxation. However, the 10,000-cycle group was detrimental to mechanical properties, suggesting an overload phenotype.