Journal of Applied Biomechanics最新文献

Rock climbing is a growing sport at both professional and recreational levels. Rock climbing requires specific hand positions with high force outputs to adapt to changing terrain requirements. The purpose of this study was to explore associations between years of climbing experience, the frequency of training, and skill level on force production in 2 different climbing-specific hand positions. A secondary purpose was to investigate sex differences in force output across climbing skill levels. Forty-nine participants ranging from Beginner to Expert skill participated. Maximum isometric pull force was tested in half-crimp and open-hand positions. Force output was larger in half-crimp versus open-hand positions. Higher skill, years of experience, and training frequency were all significantly correlated to greater force output in both hand positions. There were no force differences between males and females for Beginner/Intermediate and Advanced levels; however, males had higher force than females for Expert groups. These findings provide insight for athletes, coaches, and clinicians working with climbers regarding tissue adaptations specific to climbing grip. These findings have implications for climbing-specific training, expectations for force output, injury prevention, and reliance on hand force versus climbing technique for females climbing at high levels.

Shoes or insoles embedded with carbon fiber materials to increase longitudinal stiffness have been shown to enhance running and walking performance in elite runners, and younger adults, respectively. It is unclear, however, if such stiffness modifications can translate to enhanced mobility in older adults who typically walk with greater metabolic cost of transport compared to younger adults. Here, we sought to test whether adding footwear stiffness via carbon fiber insoles could improve walking outcomes (eg, distance traveled and metabolic cost of transport) in older adults during the 6-minute walk test. 20 older adults (10 M/10 F; 75.95 [6.01] y) performed 6-minute walk tests in 3 different shoe/insole stiffnesses (low, medium, and high) and their own footwear (4 total conditions). We also evaluated participants' toe flexor strength and passive foot compliance to identify subject-specific factors that influence performance from added shoe/insole stiffnesses. We found no significant group differences in distance traveled or net metabolic cost of transport (P ≥ .171). However, weaker toe flexors were associated with greater improvement in distance traveled between the medium and low stiffness conditions (P = .033, r = -.478), indicating that individual foot characteristics may help identify potential candidates for interventions involving footwear stiffness modifications.

Knee osteoarthritis (KOA) can have more pronounced effects on joint position sense (JPS) accuracy and gait characteristics. The aim of this study is to investigate the association between lower limb JPS and different aspects of gait pattern including gait asymmetry and variability and spatiotemporal coordination in individuals with bilateral KOA. In this cross-sectional study, lower limb JPS of 43 individuals with bilateral KOA (mild and moderate) were measured. Participants' gait patterns during treadmill walking with self-selected comfortable speed were assessed. The correlations between JPS errors and gait parameters of limb with moderate KOA were analyzed. Positive relationships were found between stance time symmetry index and JPS errors of hip abduction (r = .46, P = .003), ankle plantar flexion (r = .33, P = .03), and ankle dorsiflexion (r = .33, P = .03). Positive relationship was found between single limb support time symmetry index and hip abduction JPS error (r = .41, P = .008). Significant negative associations were found between coefficient of variation of step length and JPS errors of knee extension (r = .47, P = .002) and ankle plantar flexion (r = .33, P = .003). Results did not show any significant relationship between lower limb JPS errors and walk ratio. It is likely that lower limb JPS deficits are partially responsible for some changes in gait patterns observed in individuals with bilateral KOA.

The purpose of this study was to determine the role of antiphase trunk motion during quiet stance while maintaining constant visual and support surface conditions. Eyes-open quiet stance trials were performed on a firm support surface while wearing a rigid hip-knee orthotic brace that reduced antiphase trunk motion. Amplitude spectral density, coherence, and cophase were compared for hip-locked, hip-unlocked, and no-brace conditions. Amplitude spectral density calculations showed that trunk and leg sway velocities, and ankle torque (AT) decreased when antiphase trunk sway was allowed. Coherence and cophase estimates identified in-phase trunk-legs sway below 1 Hz and antiphase at higher frequencies. Legs-AT cophase calculations showed that the legs lagged the application of AT at all frequencies, while trunk-AT cophase showed the trunk lagged AT below 1 Hz and led AT at higher frequencies. The results demonstrate that antiphase trunk sway helps reduce sway velocity and AT. Furthermore, the trunk-leading cophase relationship with AT showed that antiphase trunk motion occurred before AT was applied. This implies that antiphase trunk motion facilitates changes in sway direction and helps regulate sway velocity. The results have significant implications for predicting postural control deficiencies due to injury, disease, and aging.

Advanced footwear technologies contain thicker, lightweight, and more resilient midsoles and are associated with improved running economy (RE) compared with traditional footwear. This effect is highly variable with some individuals gaining a greater RE benefit, indicating that biomechanics plays a mediating role with respect to the total effect. Indeed, the energy generated by contractile elements and the elastic energy recovered from stretched tendons and ligaments in the legs and feet are likely to change with footwear. Therefore, if RE is to be maximized according to individual characteristics, an individualized approach to footwear selection is required. However, current theoretical frameworks hinder this approach. Here, we introduce a framework that describes causal relationships between footwear properties, biomechanics, and RE. The framework proposes that RE changes with footwear due to (1) a direct effect of footwear properties-for example, increased or decreased energy return-and (2) a mediating effect of footwear on ankle and foot biomechanics and the spring-mass system. By describing the total effect as 2 complementary pathways, the framework facilitates research that aims to separately quantify direct and mediating effects of footwear. This may permit the development of footwear materials that can separately target the direct and individual mediating effects.

Reaching is a common daily activity requiring a range of humeral elevation that contributes to rotator cuff compression. The purpose of this study was to estimate supraspinatus and infraspinatus tendon compression risk relative to the acromion and coracoacromial ligament during reaching by manual wheelchair users with spinal cord injury. A cross-sectional design was used to evaluate 8 participants (7 males, median [range] age 36 y [23-61]). Electromagnetic motion capture recorded shoulder kinematics while participants reached for a can at 2 heights: low (0.91 m) and high (1.37 m). Using 1 set of computed tomographic-based bone models and individual glenohumeral kinematics, compression risk was evaluated as the percentage of the reach activity and number of seconds that tendon insertions were less than 5 mm from scapular landmarks. Reach conditions were compared using a Wilcoxon signed-rank test (α = .05). Although not statistically significant, the supraspinatus and infraspinatus relative to the acromion had approximately 40% of the activity duration or 0.8 seconds more time under 5 mm in low versus high reach, indicating increased risk of compression. Compression risk estimates were consistent with prior publications on planar arm movements. Estimating the risk of tendon compression using absolute time may help with understanding cumulative exposure during day-to-day activity.

Foot position during landing directly influences knee mechanics. Thus, the purpose of this study was to determine success in practicing, repeating, and transferring a desired foot progression angle (FPA) during landing, as well as changes in knee mechanics. Twenty females were randomly assigned to a control or verbal instruction group. On day 1, each group performed 40 drop landings. The verbal instruction group was instructed to "Land with 30 degrees of external rotation" before every trial. Feedback was provided on a terminal schedule in the form of knowledge of FPA error. On day 2, retention was assessed with 5 drop landings, while transfer was assessed during a 2-step stop-jump landing. Repeated-measures analyses of variance (2 × 4 [group × time]) were used to assess the influence of verbal instruction on knee mechanics. Participants who received verbal instruction exhibited increased FPA. They also demonstrated increased initial contact knee abduction during acquisition and retention. For all participants, initial contact knee flexion increased, while peak knee adduction moment decreased during acquisition. While the verbal instruction cue was effective in promoting an increase in FPA and reducing some ACL injury risk factors during practice and retention, this cue may only be effective to tasks similar to what was practiced.

Intramuscular (iEMG) and surface electromyographic (sEMG) signals have been compared previously using predictive regression equations, finite element modeling, and correlation and cross-correlation analyses. Although subcutaneous fat thickness (SCFT) has been identified as a primary source of sEMG signal amplitude attenuation and low-pass filter equivalence, few studies have explored the potential effect of SCFT on sEMG and iEMG signal characteristics. The purpose of this study was to investigate the relationship between normalized submaximal iEMG and sEMG signal amplitudes collected from 4 muscles (rectus femoris, vastus lateralis, infraspinatus, and erector spinae) and determine whether SCFT explains more variance in this relationship. The effect of sex was also explored. Linear regression models demonstrated that the relationship between sEMG and iEMG was highly variable across the muscles examined (adjusted coefficient of determination [Adj R2] = .02-.74). SCFT improved the model fit for vastus lateralis, although this relationship only emerged with the inclusion of sex as a covariate. Thus, this research suggests that SCFT is not a prominent factor affecting the linearity between sEMG and iEMG. Researchers should investigate other parameters that may affect the linearity between sEMG and iEMG signals.

Jones fracture is a common injury in soccer players, caused by overload on the fifth metatarsal (M5) that can occur during crossover cutting. This study aimed to investigate the effects of the hip internal rotation (HIR) range in passive and dynamic conditions and foot progression angle (FPA) on the forces applied to the M5 during crossover cutting. The study included 20 men with experience playing soccer. The passive HIR was measured in the prone position. A 3-dimensional motion analysis system, force plates, and Footscan were used to measure the angle of the lower limb, including dynamic HIR, FPA, and plantar pressure to the M5, during crossover cutting in the 45° direction. Pearson correlation coefficient was measured to examine the relationship between variables. Passive and dynamic HIR were not related to the plantar pressure on the M5 (P > .05). However, increased FPA in movement direction correlated with a reduction in plantar pressure on the M5 (r = -.56, P < .01). Minimizing the FPA with respect to the new direction during crossover cutting reduced plantar pressure on the M5 and thus could prevent Jones fracture.