Arthrogenic Muscle Inhibition Following Anterior Cruciate Ligament Injury.

Arthrogenic muscle inhibition (AMI) is a common impairment in individuals who sustain an anterior cruciate ligament (ACL) injury. The AMI causes decreased muscle activation, which impairs muscle strength, leading to aberrant movement biomechanics. The AMI is often resistant to traditional rehabilitation techniques, which leads to persistent neuromuscular deficits following ACL reconstruction. To better treat AMI following ACL injury and ACL reconstruction, it is important to understand the specific neural pathways involved in AMI pathogenesis, as well as the changes in muscle function that may impact movement biomechanics and long-term structural alterations to joint tissue. Overall, AMI is a critical factor that limits optimal rehabilitation outcomes following ACL injury and ACL reconstruction. This review discusses the current understanding of the: (1) neural pathways involved in the AMI pathogenesis following ACL injury; (2) consequence of AMI on muscle function, joint biomechanics, and patient function; and (3) development of posttraumatic osteoarthritis. Finally, the authors review the evidence for interventions specifically used to target AMI following ACL injury.

Assessing Step Count-Dependent Changes in Femoral Articular Cartilage Using Ultrasound.

OBJECTIVES: To evaluate changes in the femoral cartilage cross-sectional area (CSA) measured with ultrasound (US) between baseline and 1000, 2000, 3000, 4000, and 5000 steps of walking on a treadmill. METHODS: Forty-one healthy individuals completed a single testing session. Participants rested with their knees extended on a plinth for 45 minutes to unload the femoral cartilage. Ultrasound was used to acquire images of the femoral cartilage before the treadmill-walking protocol. After the baseline US acquisition, participants walked on a treadmill at their preferred overground walking speed for 1000 steps, after which additional US images of the femoral cartilage were acquired. This process was repeated after 2000, 3000, 4000, and 5000 steps. A 1-way repeated-measures analysis of variance compared the CSA across the 6 step counts. An analysis of variance with repeated measures on time and Bonferroni corrected planned comparisons (.05/5) were used to evaluate differences in the femoral cartilage at each step count compared to baseline. RESULTS: The study included 20 male and 21 female participants (mean age ± SD, 21.5 ± 2.8 years; mean body mass index, 24.3 ± 3.4 kg/m 2 ). The CSAs were significantly greater at the 2000-step (1.27 ± 1.75 mm 2 ; P < .001), 4000-step (0.89 ± 1.17 mm2; P < .001), and 5000-step (2.10 ± 1.73 mm 2 ; P < .001) points compared to baseline. The CSA was significantly less at the 3000-step point (1.05 ± 1.29 mm 2 ; P < .001) compared to baseline. CONCLUSIONS: Changes in the CSA after walking may be dependent on the number of steps. The participants had a significant decrease in the CSA after 3000 steps of normal walking and a significant increase in the CSA after 2000, 4000, and 5000 steps of normal walking.

Quadriceps weakness associates with greater T1ρ relaxation time in the medial femoral articular cartilage 6 months following anterior cruciate ligament reconstruction.

PURPOSE: Quadriceps weakness following anterior cruciate ligament reconstruction (ACLR) is linked to decreased patient-reported function, altered lower extremity biomechanics and tibiofemoral joint space narrowing. It remains unknown if quadriceps weakness is associated with early deleterious changes to femoral cartilage composition that are suggestive of posttraumatic osteoarthritis development. The purpose of the cross-sectional study was to determine if quadriceps strength was associated with T1ρ relaxation times, a marker of proteoglycan density, of the articular cartilage in the medial and lateral femoral condyles 6 months following ACLR. It is hypothesized that individuals with weaker quadriceps would demonstrate lesser proteoglycan density. METHODS: Twenty-seven individuals (15 females, 12 males) with a patellar tendon autograft ACLR underwent isometric quadriceps strength assessments in 90°of knee flexion during a 6-month follow-up exam. Magnetic resonance images (MRI) were collected bilaterally and voxel by voxel T1ρ relaxation times were calculated using a five-image sequence and a monoexponential equation. Following image registration, the articular cartilage for the weight-bearing surfaces of the medial and lateral femoral condyles (MFC and LFC) were manually segmented and further sub-sectioned into posterior, central and anterior regions of interest (ROI) based on the corresponding meniscal anatomy viewed in the sagittal plane. Univariate linear regression models were used to determine the association between quadriceps strength and T1ρ relaxation times in the entire weight-bearing MFC and LFC, as well as the ROI in each respective limb. RESULTS: Lesser quadriceps strength was significantly associated with greater T1ρ relaxation times in the entire weight-bearing MFC (R2 = 0.14, P = 0.05) and the anterior-MFC ROI (R2 = 0.22, P = 0.02) of the ACLR limb. A post hoc analysis found lesser strength and greater T1ρ relaxation times were significantly associated in a subsection of participants (n = 18) without a concomitant medial tibiofemoral compartment meniscal or chondral injury in the entire weight-bearing MFC, as well as anterior-MFC and central-MFC ROI of the ACLR and uninjured limb. CONCLUSIONS: The association between weaker quadriceps and greater T1ρ relaxation times in the MFC suggests deficits in lower extremity muscle strength may be related to cartilage composition as early as 6 months following ACLR. Maximizing quadriceps strength in the first 6 months following ACLR may be critical for promoting cartilage health early following ACLR. LEVEL OF EVIDENCE: Prognostic level 1.

Medial Unloader Braces and Lateral Heel Wedges Do not Alter Gait Biomechanics in Healthy Young Adults.

Context: Orthotic devices such as medial unloader knee braces and lateral heel wedges may limit cartilage loading following trauma or surgical repair. However, little is known regarding their effects on gait biomechanics in young, healthy individuals who are at risk of cartilage injury during physical activity due to greater athletic exposure compared with older adults. Objective: Determine the effect of medial unloader braces and lateral heel wedges on lower-extremity kinematics and kinetics in healthy, young adults. Design: Cross-sectional crossover design. Setting: Laboratory setting. Patients: Healthy, young adults who were recreationally active (30 min/d for 3 d/wk) between 18 and 35 years of age, who were free from orthopedic injury for at least 6 months, and with no history of lower-extremity orthopedic surgery. Interventions: All subjects completed normal over ground walking with a medial unloader brace at 2 different tension settings and a lateral heel wedge for a total of 4 separate walking conditions. Main Outcome Measures: Frontal plane knee angle at heel strike, peak varus angle, peak internal knee valgus moment, and frontal plane angular impulse were compared across conditions. Results: The medial unloader brace at 50% (-2.04° [3.53°]) and 100% (-1.80° [3.63°]) maximum load placed the knee in a significantly more valgus orientation at heel strike compared with the lateral heel wedge condition (-0.05° [2.85°]). However, this difference has minimal clinical relevance. Neither of the orthotic devices altered knee kinematics or kinetics relative to the control condition. Conclusions: Although effective in older adults and individuals with varus knee alignment, medial unloader braces and lateral heel wedges do not influence gait biomechanics in young, healthy individuals.

Ankle Dorsiflexion displacement is associated with hip and knee kinematics in females following anterior cruciate ligament reconstruction.

The purpose of this study was to examine associations between ankle dorsiflexion (ankle-DF) displacement and knee and hip kinematics and kinetics during a jump-landing task in females following anterior cruciate ligament reconstruction (ACLR). Females (n = 23) with a history of unilateral ACLR (≥ 6-months post-ACLR) underwent a three-dimensional lower extremity biomechanical evaluation. Pearson Product Moment (r) correlations assessed associations between ankle-DF displacement and knee and hip kinematic and kinetic variables. On the involved-limb, individuals with lesser ankle-DF displacement demonstrated greater knee abduction displacement during the loading phase (r = -0.645, p = 0.001). On the uninvolved-limb, individuals with greater ankle-DF displacement demonstrated greater hip flexion displacement (r = 0.599, p = 0.003) and knee flexion displacement (r = -0.545, p = 0.007). There were no other significant associations between ankle-DF displacement and ankle, knee, or hip biomechanical variables on either limb (p > 0.05). Our findings demonstrate that reduced ankle-DF motion appears to share a different relationship between the involved- and uninvolved-limbs in females post-ACLR.

Reaction Time and Joint Kinematics During Functional Movement in Recently Concussed Individuals.

OBJECTIVE: To compare movement reaction time and joint kinematics between athletes with recent concussion and matched control recreational athletes during 3 functional tasks. DESIGN: Cross-sectional. SETTING: Laboratory. PARTICIPANTS: College-aged recreational athletes (N=30) comprising 2 groups (15 participants each): (1) recent concussion group (median time since concussion, 126d; range, 28-432d) and (2) age- and sex-matched control group with no recent concussions. INTERVENTIONS: We investigated movement reaction time and joint kinematics during 3 tasks: (1) jump landing, (2) anticipated cut, and (3) unanticipated cut. MAIN OUTCOME MEASURES: Reaction time and reaction time cost (jump landing reaction time-cut reaction time/jump landing reaction time×100%), along with trunk, hip, and knee joint angles in the sagittal and frontal planes at initial ground contact. RESULTS: There were no reaction time between-group differences, but the control group displayed improved reaction time cost (10.7%) during anticipated cutting compared with the concussed group (0.8%; P=.030). The control group displayed less trunk flexion than the concussed group during the nondominant anticipated cut (5.1° difference; P=.022). There were no other kinematic between-group differences (P≥.079). CONCLUSIONS: We observed subtle reaction time and kinematic differences between individuals with recent concussion and those without concussion more than a month after return to activity after concussion. The clinical interpretation of these findings remains unclear, but may have future implications for postconcussion management and rehabilitation.

Weak associations between body mass index and self-reported disability in people with unilateral anterior cruciate ligament reconstruction.

PURPOSE AND HYPOTHESIS: Individuals with an anterior cruciate ligament reconstruction (ACLR) are susceptible to persistent disability, weight gain and the development of knee osteoarthritis. It remains unclear whether body mass index (BMI) is a factor that influences disability following ACLR. The purpose of this study was to determine the association between BMI and self-reported disability [International Knee Documentation Committee (IKDC) Index] in individuals with a unilateral ACLR. We hypothesized that lower BMI would associate with higher IKDC. METHODS: BMI and IKDC were measured in 668 individuals with a unilateral ACLR (60.9% female, BMI 24.4 ± 3.7 kg/m2, IKDC 84.7 ± 11.9%). Bivariate associations were conducted between BMI and IKDC for the entire sample and selected subsets (gender, ACLR graft type and history of meniscal injury). Multiple regression analyses were used to determine the impact of potential covariates (Tegner score, age and months since ACLR) for significant bivariate associations. After accounting for covariates, there were no significant associations between BMI and IKDC when separately evaluating the cohort based on either gender or history of a concomitant meniscal injury. The odds of achieving age- and gender-matched healthy population average IKDC scores for those with low (<25) and high (≥25) BMI were determined. RESULTS: Lower BMI associated with higher IKDC (r = -0.08, P = 0.04). For the entire sample, BMI did not uniquely predict variance in IKDC (ΔR 2 > 0.001, n.s.) after accounting for covariates. BMI uniquely predicted a significant but negligible amount of variance in IKDC in individuals with a patellar tendon autograft (ΔR 2 = 0.015, n.s.). Individuals with low BMI demonstrated higher odds (odds ratio = 1.45; 1.05-1.99) of achieving population average IKDC scores compared to participants with high BMI. CONCLUSIONS: There was a significant but negligible correlation between lower BMI and lesser disability in individuals with unilateral ACLR and individuals who are underweight or of normal BMI demonstrated higher odds of achieving population average IKDC scores compared to overweight or obese individuals. While an overall association was found between lower BMI and lesser disability, the magnitude of the association remains negligible; therefore, BMI was not a strong clinical predictor of successful ACLR outcomes in this cohort of patients with unilateral ACLR. LEVEL OF EVIDENCE: Cross-sectional prognostic study, Level II.

Correction to: Estrogen and muscle stiffness have a negative relationship in females.

In the original publication the name of the fourth reviewer was incorrectly published.

The Influence of Verbal and Tactile Feedback on Electromyographic Amplitude of the Shoulder Musculature During Common Therapeutic Exercises.

CONTEXT: Verbal and tactile feedback (VTF) during rehabilitation exercises can increase muscle activation, thus improving the therapeutic benefits. However, it is unclear which feedback method elicits the greatest electromyographic (EMG) amplitude. OBJECTIVE: To determine if the addition of tactile to verbal feedback (VF) increases EMG amplitude of selected shoulder musculature during scapular plane elevation (Ys), shoulder horizontal abduction with external rotation (Ts), and scapular retraction with external rotation (Ws). DESIGN: Repeated-measures cross-over design. SETTING: Biomechanics laboratory. PARTICIPANTS: A total of 30 physically active adults volunteered for this study-age = 20.23 (1.25) years; height = 1.71 (0.073) m; and mass = 70.11 (15.14) kg. INTERVENTIONS: Electromyography of the serratus anterior; upper, middle, and lower trapezii; and anterior and posterior deltoids was recorded during Ys, Ts, and Ws with VTF and VF alone during separate testing sessions. Participants completed baseline trials without feedback, then received VTF and VF across 2 counterbalanced sessions. MAIN OUTCOME MEASURES: Difference scores were calculated between prefeedback and postfeedback interventions, and the difference score between baseline measurements was used as a control. One-way analysis of variance of the difference scores was used to evaluate the influence of VTF and VF on EMG amplitude during Ys, Ts, and Ws. RESULTS: There was a significant difference between conditions for EMG amplitude of the middle trapezius (F2,28 = 4.09, P = .02) and serratus anterior (F2,28 = 3.91, P = .03) during Ys, the middle trapezius (F2,28 = 7.82, P = .001) during Ws, and the upper (F2,28 = 3.61, P = .03) and middle trapezii (F2,28 = 5.81, P = .01) during Ts. Post hoc testing revealed that both feedback conditions elicited greater EMG amplitude compared with no feedback, but there were no significant differences between the feedback conditions. CONCLUSIONS: The addition of tactile feedback to VF does not increase EMG amplitude compared with VF alone. This study indicates that feedback, regardless of type, is more beneficial than providing no feedback, for increasing EMG amplitude.

Greater intracortical inhibition associates with lower quadriceps voluntary activation in individuals with ACL reconstruction.

Decreased voluntary activation contributes to quadriceps weakness following anterior cruciate ligament reconstruction (ACLR). Alterations in neural excitability are likely responsible for reductions in quadriceps voluntary activation, and may be due to specific alterations in intracortical inhibition and facilitation. Therefore, we sought to determine if intracortical inhibition (SICI) and intracortical facilitation (ICF) associate with quadriceps voluntary activation in individuals with ACLR. Twenty-seven participants with a primary, unilateral ACLR were enrolled in this study. Bilateral central activation ratio (CAR) and paired-pulse transcranial magnetic stimulation were used to assess quadriceps voluntary activation, as well as SICI and ICF in the vastus medalis, respectively. Pearson Product Moment correlations were used to determine the association between CAR and (1) SICI, and (2) ICF in each limb. Lesser CAR associated with lesser SICI amplitude (r = 0.502, P = 0.008) in the ACLR limb. No associations in the contralateral limb were significant. Our results suggest greater intracortical inhibition associates with lesser voluntary activation in individuals with ACL. Implementing interventions that target intracortical inhibition may aid in restoring quadriceps voluntary activation following ACLR.

Visual Utilization During Postural Control in Anterior Cruciate Ligament- Deficient and -Reconstructed Patients: Systematic Reviews and Meta-Analyses.

OBJECTIVE: To determine whether anterior cruciate ligament-deficient (ACL-D) individuals and individuals with a reconstructed anterior cruciate ligament (ACL-R) rely more heavily on visual information to maintain postural control. DATA SOURCES: PubMed, CINAHL, and SPORTDiscus databases were searched from their earliest available date to May 24, 2016, using a combination of keywords. STUDY SELECTION: Articles were included if they reported any instrumented static single-leg balance outcome in both a patient and control sample. The means and SDs of these outcomes must have been reported with both eyes open and eyes closed. DATA EXTRACTION: Sample sizes, means, and SDs of single-leg balance measures for each group's eyes open and eyes closed testing conditions were extracted. The methodological quality of included studies was independently evaluated by multiple authors using an adapted version of the Quality Index. DATA SYNTHESIS: Effect sizes were calculated by dividing the differences in change between eyes closed and eyes open in the ACL-D and control group and the ACL-R and control group by the pooled SD from the eyes closed trials for each analysis. Significant differences between the ACL-D and control group (effect size, -1.66; 95% confidence interval [CI], -2.90 to -.41) were noted. The ACL-R and control group were not different (effect size, -.61; 95% CI, -2.17 to .95). CONCLUSIONS: ACL-D individuals but not individuals with ACL-R demonstrate a greater reliance on visual information during single-leg stance compared with healthy individuals.

Whole-Body Vibration Improves Early Rate of Torque Development in Individuals With Anterior Cruciate Ligament Reconstruction.

Pamukoff, DN, Pietrosimone, B, Ryan, ED, Lee, DR, Brown, LE, and Blackburn, JT. Whole body vibration improves early rate of torque development in individuals with anterior cruciate ligament reconstruction. J Strength Cond Res 31(11): 2992-3000, 2017-The purpose of this study was to compare the effect of whole-body vibration (WBV) and local muscle vibration (LMV) on early and late quadriceps rate of torque development (RTD), and electromechanical delay (EMD) in individuals with anterior cruciate ligament reconstruction (ACLR). Twenty individuals with ACLR were recruited for this study. Participants performed isometric squats while being exposed to WBV, LMV, or no vibration (control) in a randomized order during separate visits. Early and late quadriceps RTD and EMD were assessed during a maximal voluntary isometric knee extension before and immediately after WBV, LMV, or control. There was a significant condition by time interaction for early RTD (p = 0.045) but not for late RTD (p = 0.11) or EMD of the vastus medialis (p = 0.15), vastus lateralis (p = 0.17), or rectus femoris (p = 0.39). Post hoc analyses indicated a significant increase in early RTD after WBV (+5.59 N·m·s·kg; 95% confidence interval, 1.47-12.72; p = 0.007). No differences were observed in the LMV or control conditions, and no difference was observed between conditions at posttest. The ability to rapidly produce knee extension torque is essential to physical function, and WBV may be appropriate to aid in the restoration of RTD after ACLR.

Immediate effect of vibratory stimuli on quadriceps function in healthy adults.

INTRODUCTION: The purpose of this study was to compare the effect of whole body vibration (WBV) and local muscle vibration (LMV) on quadriceps function. METHODS: Sixty adults were randomized to WBV, LMV, or control groups. Quadriceps function [Hoffmann (H)-reflex, active motor threshold (AMT), motor evoked potential (MEP) and electromyographic amplitude, peak torque (PT), rate of torque development (RTD), and central activation ratio (CAR)] was assessed before and immediately after and 10 and 20 minutes after interventions. RESULTS: WBV improved PT, CAR, AMT, EMG, and MEP amplitude, and EMG amplitude and CAR were greater than control after application. LMV improved EMG amplitude and AMT, and EMG amplitude was greater than control after application. AMT remained lower 10 and 20 minutes after WBV and LMV. No differences were noted between LMV and WBV. Vibration did not influence H-reflex or RTD. CONCLUSIONS: WBV and LMV increased quadriceps function and may be used to enhance the efficacy of strengthening protocols. Muscle Nerve 54: 469-478, 2016.

Whole-Body and Local Muscle Vibration Immediately Improve Quadriceps Function in Individuals With Anterior Cruciate Ligament Reconstruction.

OBJECTIVE: To determine the immediate effects of a single session of whole-body vibration (WBV) and local muscle vibration (LMV) on quadriceps function in individuals with anterior cruciate ligament reconstruction (ACLR). DESIGN: Singe-blind, randomized crossover trial. SETTING: Research laboratory. PARTICIPANTS: Population-based sample of individuals with ACLR (N=20; mean age ± SD, 21.1±1.2y; mean mass ± SD, 68.3±14.9kg; mean time ± SD since ACLR, 50.7±21.3mo; 14 women; 16 patellar tendon autografts, 3 hamstring autografts, 1 allograft). INTERVENTIONS: Participants performed isometric squats while being exposed to WBV, LMV, or no vibration (control). Interventions were delivered in a randomized order during separate visits separated by 1 week. MAIN OUTCOME MEASURES: Quadriceps active motor threshold (AMT), motor-evoked potential (MEP) amplitude, Hoffmann reflex (H-reflex) amplitude, peak torque (PT), rate of torque development (RTD), electromyographic amplitude, and central activation ratio (CAR) were assessed before and immediately after a WBV, LMV, or control intervention. RESULTS: There was an increase in CAR (+4.9%, P=.001) and electromyographic amplitude (+16.2%, P=.002), and a reduction in AMT (-3.1%, P<.001) after WBV, and an increase in CAR (+2.7%, P=.001) and a reduction in AMT (-2.9%, P<.001) after LMV. No effect was observed after WBV or LMV in H-reflex, RTD, or MEP amplitude. AMT (-3.7%, P<.001), CAR (+5.7%, P=.005), PT (+.31Nm/kg, P=.004), and electromyographic amplitude (P=.002) in the WBV condition differed from the control condition postapplication. AMT (-3.0% P=.002), CAR (+3.6%, P=.005), and PT (+.30Nm/kg, P=.002) in the LMV condition differed from the control condition postapplication. No differences were observed between WBV and LMV postapplication in any measurement. CONCLUSIONS: WBV and LMV acutely improved quadriceps function and could be useful modalities for restoring quadriceps strength in individuals with knee pathologies.

The Myotonometer: Not a Valid Measurement Tool for Active Hamstring Musculotendinous Stiffness.

CONTEXT: Hamstring musculotendinous stiffness (MTS) is associated with lower-extremity injury risk (ie, hamstring strain, anterior cruciate ligament injury) and is commonly assessed using the damped oscillatory technique. However, despite a preponderance of studies that measure MTS reliably in laboratory settings, there are no valid clinical measurement tools. A valid clinical measurement technique is needed to assess MTS and permit identification of individuals at heightened risk of injury and track rehabilitation progress. OBJECTIVE: To determine the validity and reliability of the Myotonometer for measuring active hamstring MTS. DESIGN: Descriptive laboratory study. SETTING: Laboratory. PARTICIPANTS: 33 healthy participants (15 men, age 21.33 ± 2.94 y, height 172.03 ± 16.36 cm, mass 74.21 ± 16.36 kg). MAIN OUTCOME MEASURES: Hamstring MTS was assessed using the damped oscillatory technique and the Myotonometer. Intraclass correlations were used to determine the intrasession, intersession, and interrater reliability of the Myotonometer. Criterion validity was assessed via Pearson product-moment correlation between MTS measures obtained from the Myotonometer and from the damped oscillatory technique. RESULTS: The Myotonometer demonstrated good intrasession (ICC3,1 = .807) and interrater reliability (ICC2,k = .830) and moderate intersession reliability (ICC2,k = .693). However, it did not provide a valid measurement of MTS compared with the damped oscillatory technique (r = .346, P = .061). CONCLUSIONS: The Myotonometer does not provide a valid measure of active hamstring MTS. Although the Myotonometer does not measure active MTS, it possesses good reliability and portability and could be used clinically to measure tissue compliance, muscle tone, or spasticity associated with multiple musculoskeletal disorders. Future research should focus on portable and clinically applicable tools to measure active hamstring MTS in efforts to prevent and monitor injuries.

Anterior cruciate ligament injury alters preinjury lower extremity biomechanics in the injured and uninjured leg: the JUMP-ACL study.

BACKGROUND: Information as to how anterior cruciate ligament (ACL) injury and reconstructive surgery (ACLR) alter lower extremity biomechanics may improve rehabilitation and return to play guidelines, reducing the risk for repeat ACL injury. AIM: To compare lower extremity biomechanics before ACL injury and after subsequent ACLR for the injured and uninjured leg. METHODS: Baseline unilateral lower extremity biomechanics were collected on the dominant leg of participants without ACL injury when they entered the Joint Undertaking to Monitor and Prevent ACL (JUMP-ACL) study. Thirty-one participants with subsequent ACL injury, reconstructive surgery and full return to physical activity completed repeat, follow-up biomechanical testing, as did 39 uninjured, matched controls. Not all injured participants suffered injury to the dominant leg, requiring separation of those with ACL injury into two groups: ACLR-injured leg group (n=12) and ACLR-uninjured leg group (n=19). We compared the landing biomechanics of these three groups (ACLR-injured leg, ACLR-uninjured leg, control) before ACL injury (baseline) with biomechanics after ACL injury, surgery and return to physical activity (follow-up). RESULTS: ACL injury and ACLR altered lower extremity biomechanics, as both ACLR groups demonstrated increases in frontal plane movement (increased hip adduction and knee valgus). The ACLR-injured leg group also exhibited decreased sagittal plane loading (decreased anterior tibial shear force, knee extension moment and hip flexion moment). No high-risk biomechanical changes were observed in control group participants. CONCLUSIONS: ACL injury and ACLR caused movement pattern alterations of the injured and uninjured leg that have previously shown to increase the risk for future non-contact ACL injury.

Does Visual Performance Influence Head Impact Severity Among High School Football Athletes?

OBJECTIVE: To compare the odds of sustaining moderate and severe head impacts, rather than mild, between high school football players with high and low visual performance. DESIGN: Prospective quasi-experimental. SETTING: Clinical Research Center/On-field. PARTICIPANTS: Thirty-seven high school varsity football players. INTERVENTIONS: Athletes completed the Nike SPARQ Sensory Station visual assessment before the season. Head impact biomechanics were captured at all practices and games using the Head Impact Telemetry System. MAIN OUTCOME MEASURES: Each player was classified as either a high or low performer using a median split for each of the following visual performance measures: visual clarity, contrast sensitivity, depth perception, near-far quickness, target capture, perception span, eye-hand coordination, go/no go, and reaction time. We computed the odds of sustaining moderate and severe head impacts against the reference odds of sustaining mild head impacts across groups of high and low performers for each of the visual performance measures. RESULTS: Players with better near-far quickness had increased odds of sustaining moderate [odds ratios (ORs), 1.27; 95% confidence intervals (CIs), 1.04-1.56] and severe head impacts (OR, 1.45; 95% CI, 1.05-2.01) as measured by Head Impact Technology severity profile. High and low performers were at equal odds on all other measures. CONCLUSIONS: Better visual performance did not reduce the odds of sustaining higher magnitude head impacts. Visual performance may play less of a role than expected for protecting against higher magnitude head impacts among high school football players. Further research is needed to determine whether visual performance influences concussion risk. CLINICAL RELEVANCE: Based on our results, we do not recommend using visual training programs at the high school level for the purpose of reducing the odds of sustaining higher magnitude head impacts.

Comparison of plantar flexor musculotendinous stiffness, geometry, and architecture in male runners with and without a history of tibial stress fracture.

Greater lower extremity joint stiffness may be related to the development of tibial stress fractures in runners. Musculotendinous stiffness is the largest contributor to joint stiffness, but it is unclear what factors contribute to musculotendinous stiffness. The purpose of this study was to compare plantar flexor musculotendinous stiffness, architecture, geometry, and Achilles tendon stiffness between male runners with and without a history of tibial stress fracture. Nineteen healthy runners (age = 21 ± 2.7 years; mass = 68.2 ± 9.3 kg; height = 177.3 ± 6.0 cm) and 19 runners with a history of tibial stress fracture (age = 21 ± 2.9 years; mass = 65.3 ± 6.0 kg; height = 177.2 ± 5.2 cm) were recruited from community running groups and the university's varsity and club cross-country teams. Plantar flexor musculotendinous stiffness was estimated from the damped frequency of oscillatory motion about the ankle follow perturbation. Ultrasound imaging was used to measure architecture and geometry of the medial gastrocnemius. Dependent variables were compared between groups via one-way ANOVAs. Previously injured runners had greater plantar flexor musculotendinous stiffness (P < .001), greater Achilles tendon stiffness (P = .004), and lesser Achilles tendon elongation (P = .003) during maximal isometric contraction compared with healthy runners. No differences were found in muscle thickness, pennation angle, or fascicle length.

Ankle Dorsiflexion Displacement During Landing is Associated With Initial Contact Kinematics but not Joint Displacement.

The ankle, knee, and hip joints work together in the sagittal plane to absorb landing forces. Reduced sagittal plane motion at the ankle may alter landing strategies at the knee and hip, potentially increasing injury risk; however, no studies have examined the kinematic relationships between the joints during jump landings. Healthy adults (N = 30; 15 male, 15 female) performed jump landings onto a force plate while three-dimensional kinematic data were collected. Joint displacement values were calculated during the loading phase as the difference between peak and initial contact angles. No relationship existed between ankle dorsiflexion displacement during landing and three-dimensional knee and hip displacements. However, less ankle dorsiflexion displacement was associated with landing at initial ground contact with larger hip flexion, hip internal rotation, knee flexion, knee varus, and smaller plantar flexion angles. Findings of the current study suggest that restrictions in ankle motion during landing may contribute to contacting the ground in a more flexed position but continuing through little additional motion to absorb the landing. Transverse plane hip and frontal plane knee positioning may also occur, which are known to increase the risk of lower extremity injury.

Whole body and local muscle vibration reduce artificially induced quadriceps arthrogenic inhibition.

OBJECTIVE: To evaluate the effects of whole body vibration (WBV) and local muscle vibration (LMV) on quadriceps function after experimental knee effusion (ie, simulated pathology). DESIGN: Randomized controlled trial. SETTING: Research laboratory. PARTICIPANTS: Healthy volunteers (N=43) were randomized to WBV (n=14), LMV (n=16), or control (n=13) groups. INTERVENTIONS: Saline was injected into the knee to induce quadriceps arthrogenic muscle inhibition (AMI). All groups then performed isometric squats while being exposed to WBV, LMV, or no vibration (control). MAIN OUTCOME MEASURES: Quadriceps function was assessed at baseline, immediately after effusion, and immediately and 5 minutes after each intervention (WBV, LMV, control) via voluntary peak torque (VPT) and the central activation ratio (CAR) during maximal isometric knee extension on a multifunction dynamometer. RESULTS: The CAR improved in the WBV (11.4%, P=.021) and LMV (7.3%, P<.001) groups immediately postintervention, but they did not improve in the control group. Similarly, VPT increased by 16.5% (P=.021) in the WBV group and 23% (P=.078) in the LMV group immediately postintervention, but it did not increase in the control group. The magnitudes of improvements in the CAR and VPT did not differ between the WBV and LMV groups. CONCLUSIONS: Quadriceps AMI is a common complication following knee pathology that produces quadriceps dysfunction and increases the risk of posttraumatic osteoarthritis. Quadriceps strengthening after knee pathology is often ineffective because of AMI. WBV and LMV improve quadriceps function equivocally after simulated knee pathology, effectively minimizing quadriceps AMI. Therefore, these stimuli may be used to enhance quadriceps strengthening, therefore improving the efficacy of rehabilitation and reducing the risk of osteoarthritis.