Browse

Individuals with chronic ankle instability (CAI) have postural control deficits and appear to be more reliant on visual information to maintain balance. The underlying cause of this visual reliance remains unknown. Our purpose was to determine how sensory integration and visual performance influence postural control under different visual occlusion levels in those with CAI. Sensory integration ability, as measured by the Sensory Organization Test, was not associated with postural control in those with CAI. Visual performance variables, such as perception span, depth perception, and target capture explained between 13% and 45% of postural control variance across visual occlusion levels. The results suggest that improving visual performance in those with CAI may improve postural control across levels of visual occlusion.

Context: Advancements in portable load-cell technology have enabled high-quality assessment of shoulder internal (IR) and external rotation (ER) peak force (F_max) and rate of force development (RFD). This study’s purpose was to explore the reliability and differences between IR and ER F_max and RFD in different testing positions using a novel load-cell device. Design: A within-subjects repeated-measures design was employed to compare the intersession values and reliability of F_max and RFD for both shoulder IR and ER across 3 positions: seated-0°, supine-0° and supine-90°. Methods: National-level swimmers (n = 19; age = 16.8 [1.0] y) completed 3 testing occasions of each condition (combination of arm, rotation, and test position) separated by 7 to 14 days. Results: IR superseded ER in all testing positions. The association between these positions across IR and ER was typically strong for both F_max and RFD (r > .85, P < .001) except for IR RFD (r = .56–.73, P < .05). For sessions 2 to 3, F_max intraclass correlation coefficient and CV (intraclass correlation coefficient = .89–.96, CV = 5.2%–8.8%) were typically within acceptable ranges, whereas RFD (intraclass correlation coefficient = .74–.90, CV = 11.5%–18.1%) often exhibited inflated error. Conclusion: The supine (90°) position was the most consistent position across both measures. Load-cell technology can be confidently used to assess shoulder rotation F_max in 3 different positions, whereas RFD should be used with caution without protocol refinement.

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.

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.

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.

Sufficient muscle strength is suggested to reduce frontal plane knee loading during change of direction maneuvers. However, it is currently not thoroughly understood if lower extremity strength is associated with increased frontal plane knee biomechanics during change of direction in youth female team sport players. The objective of this cross-sectional study was to investigate the influence of maximal muscle strength on knee valgus angle and knee abduction moment during 180° pivot turn in 106 youth female team sport players. Lower hip abductor strength, lower knee extensor strength, and higher knee flexor strength were associated with increased knee valgus. Higher knee flexor and leg press strength were associated with increased knee abduction moment. The study found associations between both decreased and increased lower extremity muscle strength and frontal plane knee biomechanics. However, these associations could explain only 20% of the variance in frontal plane knee biomechanics at best.

Context: Interest in the effects of concurrently using neuromuscular electrical stimulation (NMES) and blood flow restriction (BFR) to improve muscle strength has risen, but limited studies and inconsistent findings have led to more questions. The 2 current projects aimed to systematically investigate how NMES waveform shape and BFR occlusion pressure acutely influence electrically elicited force (EEF) and tissue oxygen saturation (StO₂) of the knee extensors. Design: A single-session repeated-measures design was followed. Methods: EEF and StO₂ were measured in 2 different groups of 15 participants during 3 sets of NMES contractions. Ten NMES contractions per set were performed with 5 minutes of passive interset recovery. In the first project, different NMES waveforms (RUS, Russian burst-modulated alternating current; VMS, biphasic pulsed current; and VMS-Burst, burst-modulated biphasic pulsed current) were administered for each set, while BFR was applied at 60% limb occlusion pressure (LOP). During the second projet, VMS was administered, while a different BFR occlusion pressure (0% LOP, 40% LOP, and 80% LOP) was used during each set. Two-way repeated-measures analysis of variance examined if repetition and/or NMES waveform (first project) or BFR occlusion pressure (second project) significantly affected (P < .05) EEF or StO₂. Results: VMS (12% [7%] MVIF) and VMS-Burst (13% [10%] MVIF) led to higher EFF compared with RUS (6% [5%] MVIF) with 60% LOP; 80% LOP (20% [14%] MVIF) led to lower EEF compared with 0% LOP (29% [17%] MVIF) with VMS. No significant differences in StO₂ were observed between NMES waveforms or BFR occlusion pressures. Conclusions: If a clinician wanted to concurrently use NMES and BFR, the acute findings of the current projects would suggest the use of VMS or VMS-Burst with lower BFR occlusion pressure (40% LOP). However, further investigation into how these parameters would influence muscle strength subsequent to a training/rehabilitation intervention should be performed.

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 R ²] = .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.

Clinical Scenario: Ballet dancers exhibit a high risk of musculoskeletal injuries with around 75% of all injuries attributed to overuse injuries. The high prevalence of chronic injuries suggests contributions caused by abnormal biomechanics in combination with repetitive stress common to ballet. Traditional sports settings implement movement screening tools including the Movement Competency Screen (MCS) and functional movement screen (FMS) to identify factors predisposing athletes to injury. However, unique training demands and movement patterns of ballet and contemporary pose challenges for fundamental movement screenings. Identifying relationships between movement screening scores and injury incidence in dancers may allow for early injury risk factors detection and injury prevention programs implementation to reduce overall injury rate. Clinical Question: Does implementation of the MCS improve prediction of injury incidence compared with use of the FMS™ in collegiate, preprofessional, and professional ballet, and contemporary dancers? Summary of Key Findings: Three studies met the inclusion criteria for critical appraisal. One study utilized the MCS while the other 2 implemented the FMS™ to assess ballet and modern dancers. These studies concluded the MCS may predict injury when implemented as a preseason screening in ballet and contemporary. The FMS™ did not demonstrate predictive capability for injuries in ballet and contemporary dancers. Clinical Bottom Line: While the MCS shows injury prediction potential, a dance-specific movement screening more accurately representing dance-related movement patterns may improve validity in this population. Continuation and standardization of dance injury research is imperative to understand movement compensations predisposing individuals to injury and injury prevention measures. Recommendation: Grade B evidence suggests potential predictive ability of the MCS in identifying dance-related injury, while no association exists between the FMS™ and dance injuries. Additional research regarding dance-specific movement application to functional screenings shows potential for accurate and reliable injury prediction methods for ballet and modern dancers.

Context: Active management of modifiable factors during the early rehabilitation stage can help patients who have undergone anterior cruciate ligament (ACL) reconstruction successfully return to sports. This study aimed to determine predictors for performance on the single-leg hop test and Tegner activity score 12-month post-ACL reconstruction, based on knee function assessed 3-month postsurgery. Design: Prospective cohort study. Methods: Ninety-one patients who underwent ACL reconstruction were recruited. Multivariate logistic regression analysis was performed to identify predictors of the one hop test and Tegner activity score 12-month postsurgery, based on a knee examination performed 3 months after ACL reconstruction. Factors evaluated at 3 months included the Biodex balance system anteroposterior and mediolateral indexes; Y balance test anterior, posteromedial, and posterolateral reaches; knee extensors and flexors peak torque per body weight; and knee extensors and flexors average power per body weight. Results: The knee extensor peak torque per body weight (PT/BW) and Biodex balance system-mediolateral index with cutoff values of 132 N·m/kg and 0.45, respectively were identified as predictors for achieving a limb symmetric index within 10% on the hop test. Furthermore, achieving a Tegner activity score over 6 was predicted by Y balance test-posteromedial reach and knee flexors average power per body weight, with cutoff values of 92.5 cm and 122 W/kg, respectively. Conclusion: Three months following ACL reconstruction, knee extensor peak torque, and mediolateral balance predicted performance on the hop test, while dynamic posteromedial balance and knee flexors average power predicted rotational ability, at the 12-month assessment.