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Context Return-to-activity (RTA) assessments are commonly administered after anterior cruciate ligament reconstruction (ACLR) to manage the patient's postoperative progressions back to activity. To date, few data are available on the clinical utility of these assessments to predict patient outcomes such as secondary anterior cruciate ligament (ACL) injury once the athlete has returned to activity. Objective To identify the measures of patient function at 6 months post-ACLR that best predict RTA and second ACL injury at a minimum of 2 years after ACLR. Design Prospective cohort study. Setting Laboratory. Patients or Other Participants A total of 234 patients with primary, unilateral ACLR completed functional assessments at approximately 6 months post-ACLR. Of these, 192 (82.1%) completed follow-up at ≥2 years post-ACLR. Main Outcome Measure(s) The 6-month functional assessments consisted of patient-reported outcomes, isokinetic knee-flexor and -extensor strength, and single-legged hopping. We collected RTA and secondary ACL injury data at ≥2 years after ACLR. Results Of the patients who were able to RTA (n = 155), 44 (28.4%) had a subsequent ACL injury, 24 (15.5%) to the ipsilateral graft ACL and 20 (12.9%) to the contralateral ACL. A greater proportion of females had a secondary injury to the contralateral ACL (15/24, 62.5%), whereas a greater proportion of males reinjured the ipsilateral ACL graft (15/20, 75.0%; P = .017). Greater knee-extension symmetry at 6 months increased the probability of reinjury (B = 0.016, P = .048). Among patients with RTA at 8 months, every month that RTA was delayed reduced the risk of reinjury by 28.4% (B = –0.284, P = .042). Descriptive statistics of patient function stratified between the early and delayed RTA groups can be found in the Supplemental Table (available online at http://dx.doi.org/10.4085/1062-6050-0407.20.S1). Conclusions Patients with more symmetric quadriceps strength at 6 months post-ACLR were more likely to experience another ACL rupture, especially those who returned to sport at

Context: Isometric quadriceps strength metrics and patient-reported outcomes are commonly used in return to sport assessments in those with anterior cruciate ligament reconstruction (ACLR). Patients may be experiencing clinical knee-related symptoms aggravating enough to seek additional medical care following ACLR. In addition to seeking additional medical care, these patient-reported clinical knee-related symptoms may, also, be influencing function in individuals following ACLR. However, it is unknown if there is an association between these common quadriceps metrics and patient-reported clinical knee-related symptom state. Objective: To determine if meeting isometric quadriceps strength and symmetry criteria is associated with acceptable clinical knee-related symptoms 5–7 months post-ACLR. Design: Cross-sectional study Setting: Laboratories Patients or Other Participants: We classified individuals 5–7 months post-ACLR based on their isometric ACLR and uninvolved limb quadriceps strength and/or quadriceps strength symmetry. We, also, dichotomized participants based the Englund et al. criteria for unacceptable clinical knee-related symptoms. Main Outcome Measure(s): Quadriceps strength variables were compared between groups using ANCOVAs and the relative risk of a participant in each quadriceps strength group reporting acceptable clinical knee-related symptoms were determined using binary logistic regression. Results: One hundred and seventy-three individuals participated in the current study. Isometric quadriceps strength and LSI were significantly different (p Conclusions: The majority (85.0%) of individuals recovering from ACLR fail to meet either the clinical quadriceps strength or symmetry criteria 5–7 months post-ACLR. Quadriceps strength and quadriceps strength symmetry are clinically important but may not be a primary determinant of clinical knee-related symptom state within the first 6-months post-ACLR.

Context The International Knee Documentation Committee Subjective Knee Evaluation Form (IKDC) is the most frequently used patient-reported measure of subjective knee function among individuals with anterior cruciate ligament reconstruction (ACLR). Yet, due to the limitations of traditional validation approaches, whether the IKDC measures knee function as intended is unclear. Rasch analysis offers a robust validation approach, which may enhance the clinical interpretation of the IKDC. Objective To assess the psychometric properties, ability to classify health status, and relationships between the IKDC and objective measures of strength and functional performance relative to a newly proposed reduced-item instrument. Design Cross-sectional study. Setting Laboratory. Patients or Other Participants A total of 77 individuals with primary unilateral ACLR (age = 21.9 ± 7.8 years, time postsurgery = 6.2 ± 1.0 months) and 76 age-matched control individuals (age = 22.0 ± 4.2 years). Main Outcome Measure(s) Rasch analysis was used to assess the psychometric properties of the IKDC. Receiver operator characteristic curves and logistic regression were calculated to assess the accuracy of classifying participants with ACLR versus control participants. Pearson product moment and Spearman rank order correlation analyses were conducted to evaluate relationships among subjective knee function, quadriceps torque, and single-limb hop performance. Results Rasch analysis aided the development of a reduced 8-item instrument (IKDC-8), which yielded improved psychometric properties in the rating scale performance (IKDC-8 = 0, IKDC = 3 nonmonotonic “misbehaving” items), percentage of variance accounted for by 1 dimension (IKDC-8 = 71.5%, IKDC = 56.7%), and precision in item separation (IKDC-8 = 9.79, IKDC = 5.02). The IKDC was an outstanding diagnostic tool, and the IKDC-8 was excellent, correctly classifying 87.2% and 82.7% of cases, respectively. Using the Hanley-McNeil formula, we found no difference in the areas under the respective receiver operator characteristic curves. Equivalent associations between subjective and objective knee function were observed regardless of the instrument used. Conclusions We demonstrated evidence of enhanced reliability and validity for a parsimonious measure of subjective knee function. The proposed instrument reduces the number of items, increases the score interpretability as measuring a single construct, and improves the rating scale functioning while not diminishing its ability to classify participants with ACLR versus control participants or changing existing relationships with objective measures of recovery. We suggest the IKDC-8 may enhance clinical use by reducing administration time, improving the interpretation of the subjective knee function score, and clarifying functional ability.

ContextThe causes of persistent muscle weakness after anterior cruciate ligament reconstruction (ACLR) are not well known. Changes in muscle oxygenation have been proposed as a possible mechanism.ObjectiveTo investigate changes in quadriceps muscle oxygenation during knee extension in ACLR-involved and ACLR-uninvolved limbs.DesignCase-control study.SettingLaboratory.Patients or Other ParticipantsA total of 20 individuals: 10 patients with primary, unilateral ACLR (7 women, 3 men; age = 22.90 ± 3.45 years, height = 170.81 ± 7.93 cm, mass = 73.7 ± 15.1 kg) and 10 matched control individuals (7 women, 3 men; age = 21.50 ± 2.99 years, height = 170.4 ± 10.7 cm, mass = 68.86 ± 9.51 kg).Intervention(s)Each participant completed a single data-collection session consisting of 5-second isometric contractions at 25%, 50%, and 75% of the volitional maximum followed by a 30-second maximal isometric knee-extension contraction.Main Outcome Measure(s)Oxygenated hemoglobin (O2Hb) measures in the reconstructed thigh were continuously recorded (versus the uninvolved contralateral limb as well as the nondominant thigh of healthy control individuals) using 3 wearable, wireless near-infrared spectroscopy units placed superficially to the vastus medialis, vastus lateralis, and rectus femoris muscles. Relative changes in oxygenation were ensemble averaged and plotted for each contraction intensity with associated 90% CIs. Statistical significance occurred where portions of the exercise trials with CIs on the O2Hb graph did not overlap. Effect sizes (Cohen d, 90% CI) were determined for statistical significance.ResultsWe observed less relative change in O2Hb in patients with ACLR than in healthy control participants in the rectus femoris at 25% (d = 2.1; 90% CI = 1.5, 2.7), 50% (d = 2.8; 90% CI = 2.6, 2.9), and 75% (d = 2.0; 90% CI = 1.9, 2.2) and for the vastus medialis at 75% (d = 1.5; 90% CI = 1.4, 1.5) and 100% (d = 2.6; 90% CI = 2.5, 2.7). Less relative change in O2Hb was also noted for the vastus medialis in ACLR-involved versus ACLR-uninvolved limbs at 100% (d = 2.62; 90% CI = 2.54, 2.70).ConclusionsQuadriceps muscle oxygenation during exercise differed between patients with ACLR and healthy control individuals. However, not all portions of the quadriceps were affected uniformly across contraction intensities.

The International Knee Documentation Committee (IKDC) Subjective Knee Evaluation is the most frequently used patient-reported measure of subjective knee function among individuals with ACL reconstruction (ACLR). Yet, limitations with traditional validation approaches leave it unclear whether the IKDC measures knee function as intended. Rasch analysis offers a robust validation approach, which may enhance clinical interpretation of the IKDC.1) To assess the psychometric properties, 2) ability to classify health status, and 3) relationships between the IKDC and objective measures of strength and functional performance relative to a newly proposed reduced-item instrument.Cross-sectional.Laboratory.Seventy-seven individuals with primary, unilateral ACLR (21.9±7.8 years, 6.2±1.0 months post-surgery), and seventy-six age-matched controls.Rasch analysis was used to assess the psychometric properties of the IKDC. Receiver-operator-characteristic curves and logistic regression were used to assess the accuracy of classifying ACLR versus control participants. Correlations (Pearson and Spearman) were used to assess relationships between subjective knee function, quadriceps torque, and single-limb hop performance.Rasch analysis aided the development of a reduced 8-item instrument (IKDC-8), which yielded improved psychometric properties in misfit analysis, percent of variance accounted for by one dimension (IKDC-8=71.5%; IKDC=56.7%), and item reliability. The IKDC was an outstanding diagnostic tool and the IKDC-8 was excellent, correctly classifying 87.2% and 82.7% of cases, respectively. The Hanley-McNeil formula found that there was no significant difference in the areas under the respective ROC curves. Equivalent associations between subjective and objective knee function were observed regardless of instrument used.We observed evidence of enhanced reliability and validity for a parsimonious measure of subjective knee function. The proposed instrument reduces the number of items, increases score interpretability as measuring a single construct, and improves the rating scale functioning, while not significantly diminishing its ability to classify ACLR versus control participants or changing existing relationships with objective measures of recovery. We suggest the IKDC-8 may enhance clinical use by reducing administration time, improving the interpretation of the subjective knee function score, and clarifying functional ability.

Context Relationships between quadriceps function and patient-reported outcomes after anterior cruciate ligament reconstruction (ACLR) are variable and may be confounded by including patients at widely different time points after surgery. Understanding these relationships during the clinically relevant phases of recovery may improve our knowledge of specific factors that influence clinical outcomes. Objective To identify the relationships between quadriceps function and patient-reported outcomes in patients 2 years (late) after ACLR, including those with posttraumatic knee osteoarthritis. Design Cross-sectional study. Setting Laboratory. Patients or Other Participants A total of 72 patients after ACLR: early (n = 34, time from surgery = 9.0 ± 4.3 months), late (n = 30, time from surgery = 70.5 ± 41.6 months), or osteoarthritis (n = 8, time from surgery = 115.9 ± 110.0 months). Main Outcome Measure(s) The total Knee Injury and Osteoarthritis Outcome Score (KOOS) and Veterans RAND 12-Item Health Survey (VR-12) were used to quantify knee function and global health. Predictors of patient-reported outcomes were involved-limb and symmetry indices of quadriceps function (isokinetic strength [peak torque, total work, average power], maximum voluntary isometric contraction torque, fatigue index, central activation ratio, Hoffmann reflex, active motor threshold) and demographics (age, activity level, pain, kinesiophobia, time since surgery). Multiple linear regression analyses were used to predict KOOS and VR-12 scores in each group. Results In the early patients, knee-extensor work, active motor threshold symmetry, pain, and activity level explained 67.8% of the variance in the KOOS score (P < .001); knee-extensor work, activity level, and pain explained 53.0% of the variance in the VR-12 score (P < .001). In the late patients, age and isokinetic torque symmetry explained 28.9% of the variance in the KOOS score (P = .004). In the osteoarthritis patients, kinesiophobia and isokinetic torque explained 77.8% of the variance in the KOOS score (P = .010); activity level explained 86.4% of the variance in the VR-12 score (P = .001). Conclusions Factors of muscle function and demographics that explain patient-reported outcomes were different in patients early and late after ACLR and in those with knee osteoarthritis.

Context: Injury-prediction models have identified trunk muscle function as an identifiable factor for future injury. A history of low back pain (HxLBP) may also place athletes at increased risk for future low back pain. Reduced muscle thickness of the lumbar multifidus (LM) and transversus abdominis (TrA) has been reported among populations with clinical low back pain via ultrasound imaging in multiple positions. However, the roles of the LM and TrA in a more functional cohort and for injury prediction are still unknown.Objectives: To (1) assess the reliability of LM and TrA ultrasound measures, (2) compare changes in muscle thickness across positions between persons reporting or not reporting HxLBP, and (3) determine the ability to distinguish between groups.Design: Cross-sectional study.Setting: Research laboratory.Patients or Other Participants: Participants were 34 people who did not report HxLBP (age = 22 ± 7 years, body mass index = 23.7 ± 2.7) and 25 people who reported HxLBP (age = 25 ± 10 years, body mass index = 24.0 ± 3.2).Main Outcome Measure(s): Muscle thickness and changes in muscle thickness of the LM and TrA as shown on ultrasound imaging.Results: Intraclass correlation coefficients ranged from 0.641 to 0.943 for all thickness measures and from 0 to 0.693 for all averaged thickness modulations bilaterally. Participants who reported HxLBP had voluntarily reduced TrA thickness modulations compared with those not reporting HxLBP (P = .03), and the testing position influenced TrA thickness modulations (P < .01). No differences were observed for LM thickness modulations between groups or positions (P > .05). A tabletop cutoff value of 1.32 had a sensitivity of 0.640 and a specificity of 0.706, whereas a seated cutoff value of 1.18 had a sensitivity of 0.600 and a specificity of 0.647.Conclusions: In participants reporting HxLBP, TrA thickness modulations were lower and both tabletop and seated thickness modulations were able to distinguish reported HxLBP status. These findings suggest that TrA muscle function may be altered by HxLBP.

Context When returning to physical activity, patients with a history of anterior cruciate ligament reconstruction (ACL-R) often experience limitations in knee-joint function that may be due to chronic impairments in quadriceps motor control. Assessment of knee-extension torque variability may demonstrate underlying impairments in quadriceps motor control in patients with a history of ACL-R.Objective To identify differences in maximal isometric knee-extension torque variability between knees that have undergone ACL-R and healthy knees and to determine the relationship between knee-extension torque variability and self-reported knee function in patients with a history of ACL-R.Design Descriptive laboratory study.Setting Laboratory.Patients or Other Participants A total of 53 individuals with primary, unilateral ACL-R (age = 23.4 ± 4.9 years, height = 1.7 ± 0.1 m, mass = 74.6 ± 14.8 kg) and 50 individuals with no history of substantial lower extremity injury or surgery who served as controls (age = 23.3 ± 4.4 years, height = 1.7 ± 0.1 m, mass = 67.4 ± 13.2 kg).Main Outcome Measure(s) Torque variability, strength, and central activation ratio (CAR) were calculated from 3-second maximal knee-extension contraction trials (90° of flexion) with a superimposed electrical stimulus. All participants completed the International Knee Documentation Committee (IKDC) Subjective Knee Evaluation Form, and we determined the number of months after surgery. Group differences were assessed using independent-samples t tests. Correlation coefficients were calculated among torque variability, strength, CAR, months after surgery, and IKDC scores. Torque variability, strength, CAR, and months after surgery were regressed on IKDC scores using stepwise, multiple linear regression.Results Torque variability was greater and strength, CAR, and IKDC scores were lower in the ACL-R group than in the control group (P < .05). Torque variability and strength were correlated with IKDC scores (P < .05). Torque variability, strength, and CAR were correlated with each other (P < .05). Torque variability alone accounted for 14.3% of the variance in IKDC scores. The combination of torque variability and number of months after surgery accounted for 21% of the variance in IKDC scores. Strength and CAR were excluded from the regression model.Conclusions Knee-extension torque variability was moderately associated with IKDC scores in patients with a history of ACL-R. Torque variability combined with months after surgery predicted 21% of the variance in IKDC scores in these patients.

Context Individuals with a history of anterior cruciate ligament reconstruction (ACLR) are at greater risk of reinjury and developing early-onset osteoarthritis due to persistent abnormal joint loading. Real-time clinical assessment tools may help identify patients experiencing abnormal movement patterns after ACLR. Objective To compare performance on the Landing Error Scoring System (LESS) between participants with ACLR and uninjured control participants and to determine the relationship between LESS score and knee-extension strength in these participants. Design Controlled laboratory study. Setting Research laboratory. Patients or Other Participants Forty-six recreationally active participants, consisting of 22 with ACLR (12 men, 10 women; age = 22.5 ± 5.0 years, height = 172.8 ± 7.2 cm, mass = 74.2 ± 15.6 kg, body mass index = 24.6 ± 4.0) and 24 healthy control participants (12 men, 12 women; age = 21.7 ± 3.6 years, height = 168.0 ± 8.8 cm, mass = 69.2 ± 13.6 kg, body mass index = 24.3 ± 3.2) were enrolled. Main Outcome Measure(s) Bilateral normalized knee-extension maximal voluntary isometric contraction (MVIC) torque (Nm/kg) and LESS scores were measured during a single testing session. We compared LESS scores between groups using a Mann-Whitney U test and the relationships between LESS scores and normalized knee-extension MVIC torque using Spearman ρ bivariate correlations. Results The ACLR participants had a greater number of LESS errors (6.0 ± 3.6) than healthy control participants (2.8 ± 2.2; t44 = −3.73, P = .002). In ACLR participants, lower normalized knee-extension MVIC torque in the injured limb (ρ = −0.455, P = .03) was associated with a greater number of landing errors. Conclusions Participants with ACLR displayed more errors while landing. The occurrence of landing errors was negatively correlated with knee-extension strength, suggesting that weaker participants had more landing errors. Persistent quadriceps weakness commonly associated with ACLR may be related to a reduced quality of lower extremity movement during dynamic tasks.

Context The most common modality used to address acute inflammation is cryotherapy. Whereas pain decreases with cryotherapy, evidence that changes occur in perfusion of skeletal muscle is limited. We do not know whether ice attenuates the increases in perfusion associated with acute inflammation. Objective To examine the effects of repeated applications of ice bags on perfusion of the gastrocnemius muscle after an eccentric exercise protocol. Design Controlled laboratory study. Setting Laboratory. Patients or Other Participants Eighteen healthy participants (3 men, 15 women; age = 22.2 ± 2.2 years, height = 166.0 ± 11.9 cm, mass = 69.4 ± 25.0 kg). Intervention(s) To induce eccentric muscle damage, participants performed 100 unilateral heel-lowering exercises off a step to the beat of a metronome. A randomized intervention (cryotherapy, sham, control) was applied to the exercised lower extremity immediately after the protocol and again at 10, 24, and 34 hours after the protocol. Main Outcome Measure(s) Baseline perfusion measurements (blood volume, blood flow, and blood flow velocity) were taken using contrast-enhanced ultrasound of the exercised leg. Perfusion was reassessed after the first intervention and 48 hours after the protocol as percentage change scores. Pain was measured with a visual analog scale at baseline and at 10, 24, 34, and 48 hours after the protocol. Separate repeated-measures analyses of variance were used to assess each dependent variable. Results We found no interactions among interventions for microvascular perfusion. Blood volume and blood flow, however, increased in all conditions at 48 hours after exercise (P < .001), and blood flow velocity decreased postintervention from baseline (P = .041). We found a time-by-intervention interaction for pain (P = .009). Visual analog scale scores were lower for the cryotherapy group than for the control group at 34 and 48 hours after exercise. Conclusions Whereas eccentric muscle damage resulted in increased blood flow, ice did not decrease muscle perfusion 48 hours after exercise. Therefore, ice does not seem to decrease muscle perfusion when blood flow is elevated, as it would be during inflammation.

Context: Anterior cruciate ligament (ACL) injury and ACL reconstruction (ACLR) result in persistent alterations in lower extremity movement patterns. The progression of lower extremity biomechanics from the time of injury has not been described. Objective: To compare the 3-dimensional (3D) lower extremity kinematics and kinetics of walking among individuals with ACL deficiency (ACLD), individuals with ACLR, and healthy control participants from 3 to 64 months after ACLR. Data Sources: We searched PubMed and Web of Science from 1970 through 2013. Study Selection and Data Extraction: We selected only articles that provided peak kinematic and kinetic values during walking in individuals with ACLD or ACLR and comparison with a healthy control group or the contralateral uninjured limb. Data Synthesis: A total of 27 of 511 identified studies were included. Weighted means, pooled standard deviations, and 95% confidence intervals were calculated for the healthy control, ACLD, and ACLR groups at each reported time since surgery. The magnitude of between-groups (ACLR versus ACLD, control, or contralateral limb) differences at each time point was evaluated using Cohen d effect sizes and associated 95% confidence intervals. Peak knee-flexion angle (Cohen d = −0.41) and external knee-extensor moment (Cohen d = −0.68) were smaller in the ACLD than in the healthy control group. Peak knee-flexion angle (Cohen d range = −0.78 to −1.23) and external knee-extensor moment (Cohen d range = −1.39 to −2.16) were smaller in the ACLR group from 10 to 40 months after ACLR. Reductions in external knee-adduction moment (Cohen d range = −0.50 to −1.23) were present from 9 to 42 months after ACLR. Conclusions: Reductions in peak knee-flexion angle, external knee-flexion moment, and external knee-adduction moment were present in the ACLD and ACLR groups. This movement profile during the loading phase of gait has been linked to knee-cartilage degeneration and may contribute to the development of osteoarthritis after ACLR.

Context: Patient-reported outcomes (PROs) evaluate how patients describe symptoms as well as level of physical function or quality of life. The Western Ontario and McMaster Universities Osteoarthritis (WOMAC) Index is one of the most common PROs used to assess disability in patients with knee osteoarthritis (OA), yet the Single Assessment Numeric Evaluation (SANE) is a single-question instrument that may improve the efficiency associated with the measurement of patient function. Objective: To determine the associations between (1) SANEFunction and the physical dysfunction subsection of the WOMAC index (WOMACDysfunction) before rehabilitation and after a 4-week therapeutic exercise intervention as well as (2) the percentage change in SANEFunction and WOMACDysfunction in people with knee OA after 4 weeks of therapeutic exercise. Design: Cross-sectional study. Setting: Research laboratory. Patients or Other Participants: Thirty-six participants (15 men, 21 women) with radiographic knee OA. Intervention(s): Participants completed 12 sessions (over a 4-week period) of therapeutic exercise to strengthen the lower extremity. Main Outcome Measure(s): The SANEFunction and WOMACDysfunction (WOMACDysfunction normalized to 100%) scores were collected before and after the 4-week intervention. Percentage change scores over the 4-week intervention were calculated for both measures. Results: Participants with a higher SANEFunction score demonstrated a lower WOMACDysfunction score at baseline (rs = –0.44, P = .007) and at the 4-week time point (rs = –0.69, P < .001). There was a nonsignificant and weak association between the changes in the SANEFunction and WOMACDysfunction scores over the 4 weeks of therapeutic exercise (rs = –0.17, P < .43). Conclusions: The SANEFunction and WOMACDysfunction scores demonstrated moderate to weak associations before and after a 4-week exercise program, respectively, whereas the changes in SANEFunction and WOMACDysfunction scores were not associated. These PROs may be measuring different aspects of self-reported function and therefore should not be used interchangeably to determine a therapeutic response.

Context : Sex differences in lower extremity neuromuscular function have been reported after anterior cruciate ligament reconstruction (ACLR). Research evidence supports different levels of fatigability in men and women and between patients with ACLR and healthy controls. The influence of sex on the response to continuous exercise in patients with ACLR is not clear. Objective : To compare quadriceps neuromuscular function after exercise between men and women with ACLR. Design : Descriptive laboratory study. Setting : Laboratory. Patients or Other Participants : Twenty-six active volunteers (13 men [50%]: age = 24.1 ± 4.4 years, height = 179.1 ± 9.8 cm, mass = 80.1 ± 9.4 kg, months since surgery = 43.5 ± 37.0; 13 women [50%]: age = 24.2 ± 5.6 years, height = 163.0 ± 5.9 cm, mass = 62.3 ± 8.3 kg, months since surgery = 45.8 ± 42.7) with a history of unilateral primary ACLR at least 6 months earlier. Intervention(s) : Thirty minutes of continuous exercise comprising 5 separate 6-minute cycles, including 5 minutes of uphill walking and 1 minute of body-weight squatting and step-ups. Main Outcome Measure(s) : Normalized knee-extension maximal voluntary isometric contraction torque, quadriceps superimposed-burst torque, and quadriceps central activation ratio before and after exercise. We performed separate 2 (sex: men, women) × 2 (time: preexercise, postexercise) repeated-measures analyses of variance for the 3 variables. Separate, independent-samples t tests were calculated to compare preexercise with postexercise change in all dependent variables between sexes. Results : A significant group-by-time interaction was present for knee-extension torque (P = .04). The percentage reduction in knee-extension maximal voluntary isometric contraction torque (men = 1.94%, women = −10.32%; P = .02) and quadriceps central activation ratio (men = −1.45%, women = −8.69%; P = .03) experienced by men was less than that observed in women. Conclusions : In the presence of quadriceps dysfunction, female participants experienced greater-magnitude reductions in quadriceps function after 30 minutes of exercise than male participants. This indicates a reduced ability to absorb knee-joint loads, which may have significant implications for reinjury and joint osteoarthritis in women after ACLR.

Context: Individuals with chronic ankle instability (CAI) present with decreased modulation of the Hoffmann reflex (H-reflex) from a simple to a more challenging task. The neural alteration is associated with impaired postural control, but the relationship has not been investigated in individuals with CAI. Objective: To determine differences in H-reflex modulation and postural control between individuals with or without CAI and to identify if they are correlated in individuals with CAI. Design: Descriptive laboratory study. Setting: Laboratory. Patients or Other Participants: A total of 15 volunteers with CAI (9 males, 6 females; age = 22.6 ± 5.8 years, height = 174.7 ± 8.1 cm, mass = 74.9 ± 12.8 kg) and 15 healthy sex-matched volunteers serving as controls (9 males, 6 females; age = 23.8 ± 5.8 years, height = 171.9 ± 9.9 cm, mass = 68.9 ± 15.5 kg) participated. Intervention(s): Maximum H-reflex (Hmax) and motor wave (Mmax) from the soleus and fibularis longus were recorded while participants lay prone and then stood in unipedal stance. We assessed postural tasks of unipedal stance with participants' eyes closed for 10 seconds using a forceplate. Main Outcome Measure(s): We normalized Hmax to Mmax to obtain Hmax : Mmax ratios for the 2 positions. For each muscle, H-reflex modulation was quantified using the percentage change scores in Hmax : Mmax ratios calculated from prone position to unipedal stance. Center-of-pressure data were used to compute 4 time-to-boundary variables. Separate independent-samples t tests were performed to determine group differences. Pearson product moment correlation coefficients were calculated between the modulation and balance measures in the CAI group. Results: The CAI group presented less H-reflex modulation in the soleus (t26 = −3.77, P = .001) and fibularis longus (t25 = −2.59, P = .02). The mean of the time-to-boundary minima in the anteroposterior direction was lower in the CAI group (t28 = −2.06, P = .048). We observed a correlation (r = 0.578, P = .049) between the fibular longus modulation and mean of time-to-boundary minima in the anteroposterior direction. Conclusions: The strong relationship indicated that, as H-reflex amplitude in unipedal stance was less down modulated, unipedal postural control was more impaired. Given the deficits in H-reflex modulation and postural control in the CAI group, the relationship may provide insights into the neurophysiologic mechanism of postural instability.

Context: Fatigue of the gluteus medius (GMed) muscle might be associated with decreases in postural control due to insufficient pelvic stabilization. Men and women might have different muscular recruitment patterns in response to GMed fatigue. Objective: To compare postural control and quality of movement between men and women after a fatiguing hip-abduction exercise. Design: Descriptive laboratory study. Setting: Controlled laboratory. Patients or Other Participants: Eighteen men (age = 22 ± 3.64 years, height = 183.37 ± 8.30 cm, mass = 87.02 ±12.53 kg) and 18 women (age = 22 ± 3.14, height = 167.65 ± 5.80 cm, mass = 66.64 ± 10.49 kg) with no history of low back or lower extremity injury participated in our study. Intervention(s): Participants followed a fatiguing protocol that involved a side-lying hip-abduction exercise performed until a 15% shift in electromyographic median frequency of the GMed was reached. Main Outcome Measure(s): Baseline and postfatigue measurements of single-leg static balance, dynamic balance, and quality of movement assessed with center-of-pressure measurements, the Star Excursion Balance Test, and lateral step-down test, respectively, were recorded for the dominant lower extremity (as identified by the participant). Results: We observed no differences in balance deficits between sexes (P > .05); however, we found main effects for time with all of our postfatigue outcome measures (P ≤ .05). Conclusions: Our findings suggest that postural control and quality of movement were affected negatively after a GMed-fatiguing exercise. At similar levels of local muscle fatigue, men and women had similar measurements of postural control.

Context: Knee braces and neoprene sleeves are commonly worn by people with anterior cruciate ligament reconstructions (ACLRs) during athletic activity. How knee braces and sleeves affect muscle activation in people with ACLRs is unclear.Purpose: To determine the effects of knee braces and neoprene knee sleeves on the quadriceps central activation ratio (CAR) before and after aerobic exercise in people with ACLRs.Design: Crossover study.Patients or Other Participants: Fourteen people with a history of ACLR (9 women, 5 men: age = 23.61 ± 4.44 years, height = 174.09 ± 9.82 cm, mass = 75.35 ± 17.48 kg, months since ACLR = 40.62 ± 20.41).Intervention(s): During each of 3 sessions, participants performed a standardized aerobic exercise protocol on a treadmill. The independent variables were condition (brace, sleeve, or control) and time (baseline, pre-exercise with brace, postexercise with brace, postexercise without brace).Main Outcome Measure(s): Normalized torque measured during a maximal voluntary isometric contraction (TMVIC) and CAR were measured by a blinded assessor using the superimposed burst technique. The CAR was expressed as a percentage of full muscle activation. The quadriceps CAR and TMVIC were measured 4 times during each session: baseline, pre-exercise with brace, postexercise with brace, and postexercise without brace.Results: Immediately after the application of the knee brace, TMVIC decreased (P = .01), but no differences between bracing conditions were observed. We noted reduced TMVIC and CAR (P < .001) after exercise, both with and without the brace. No differences were seen between bracing conditions after aerobic exercise.Conclusions: The decrease in TMVIC immediately after brace application was not accompanied by differences between bracing conditions. Wearing a knee brace or neoprene sleeve did not seem to affect the deterioration of quadriceps function after aerobic exercise.

Context: The ability to accurately estimate quadriceps voluntary activation is an important tool for assessing neuromuscular function after a variety of knee injuries. Different techniques have been used to assess quadriceps volitional activation, including various stimulating electrode types and electrode configurations, yet the optimal electrode types and configurations for depolarizing motor units in the attempt to assess muscle activation are unknown. Objective: To determine whether stimulating electrode type and configuration affect quadriceps central activation ratio (CAR) and percentage-of-activation measurements in healthy participants. Design: Crossover study. Setting: Research laboratory. Patients and Other Participants: Twenty participants (13 men, 7 women; age = 26 ± 5.3 years, height = 173.85 ± 7.3 cm, mass = 77.37 ± 16 kg) volunteered. Intervention(s): All participants performed 4 counter-balanced muscle activation tests incorporating 2 different electrode types (self-adhesive, carbon-impregnated) and 2 electrode configurations (vastus, rectus). Main Outcome Measure(s): Quadriceps activation was calculated with the CAR and percentage-of-activation equations, which were derived from superimposed burst and resting torque measurements. Results: No differences were found between conditions for CAR and percentage-of-activation measurements, whereas resting twitch torque was higher in the rectus configuration for both self-adhesive (216 ± 66.98 Nm) and carbon-impregnated (209.1 ± 68.22 Nm) electrodes than in the vastus configuration (209.5 ± 65.5 Nm and 204 ± 62.7 Nm, respectively) for these electrode types (F1,19 = 4.87, P = .04). In addition, resting twitch torque was greater for both electrode configurations with self-adhesive electrodes than with carbon-impregnated electrodes (F1,19 = 9.33, P = .007). Bland-Altman plots revealed acceptable mean differences for agreement between electrode type and configuration for CAR and percentage of activation, but limits of agreement were wide. Conclusions: Although these electrode configurations and types might not necessarily be able to be used interchangeably, differences in electrode type and configuration did not seem to affect CAR and percentage-of-activation outcome measures.

Context: Anterior cruciate ligament (ACL) reconstructions are common, especially in young, active people. The lower extremity neuromuscular adaptations seen after aerobic exercise provide information about how previously injured patients perform and highlight deficits and, hence, areas for focused treatment. Little information is available about neuromuscular performance after aerobic exercise in people with ACL reconstructions. Objective: To compare dynamic balance, gluteus medius muscle activation, vertical jump height, and hip muscle strength after aerobic exercise in people with ACL-reconstructed knees. Design: Case-control study. Setting: Research laboratory. Patients or Other Participants: Of 34 recreationally active volunteers, 17 had a unilateral primary ACL reconstruction at least 2 years earlier and 17 were matched controls. Intervention(s): All participants performed 20 minutes of aerobic exercise on a treadmill. Main Outcome Measure(s): We recorded dynamic, single-legged balance electromyographic gluteus medius muscle activation, single-legged vertical jump height, and maximum isometric strength for hip abduction, extension, and external rotation preexercise and postexercise. Results: Participants with ACL reconstructions exhibited shorter reach distances during dynamic balance tasks, indicating poorer dynamic balance, and less gluteus medius muscle electromyographic activation. Reductions in hip abduction and extension strength after exercise were noted in all participants; however, those with ACL reconstructions displayed greater hip extensor strength loss after aerobic exercise than did the control group. Conclusions: Neuromuscular changes after aerobic exercise exist in both patients with ACL reconstructions and controls. The former group may experience greater deficits in hip extensor strength after aerobic exercise. Reduced reach distances in people with ACL reconstructions may represent a protective mechanism against excessive tibiofemoral rotation during dynamic balance. Clinicians should identify weaknesses in the resting state and after aerobic exercise in recreationally active patients and those with ACL reconstructions.

Context: Arthrogenic muscle inhibition is an important underlying factor in persistent quadriceps muscle weakness after knee injury or surgery. Objective: To determine the magnitude and prevalence of volitional quadriceps activation deficits after knee injury. Data Sources: Web of Science database. Study Selection: Eligible studies involved human participants and measured quadriceps activation using either twitch interpolation or burst superimposition on patients with knee injuries or surgeries such as anterior cruciate ligament deficiency (ACLd), anterior cruciate ligament reconstruction (ACLr), and anterior knee pain (AKP). Data Extraction: Means, measures of variability, and prevalence of quadriceps activation (QA) failure ( Data Synthesis: A total of 21 data sets from 18 studies were initially identified. Data from 3 studies (1 paper reporting data for both ACLd and ACLr, 1 on AKP, and the postarthroscopy paper) were excluded from the primary analyses because only graphical data were reported. Of the remaining 17 data sets (from 15 studies), weighted mean QA in 352 ACLd patients was 87.3% on the involved side, 89.1% on the uninvolved side, and 91% in control participants. The QA failure prevalence ranged from 0% to 100%. Weighted mean QA in 99 total ACLr patients was 89.2% on the involved side, 84% on the uninvolved side, and 98.5% for the control group, with prevalence ranging from 0% to 71%. Thirty-eight patients with AKP averaged 78.6% on the involved side and 77.7% on the contralateral side. Bilateral QA failure was commonly reported in patients. Conclusions: Quadriceps activation failure is common in patients with ACLd, ACLr, and AKP and is often observed bilaterally.

Context The superimposed-burst (SIB) technique is commonly used to quantify central activation failure after knee-joint injury, but its reliability has not been established in pathologic cohorts. Objective To assess within-session and between-sessions reliability of the SIB technique in patients with patellofemoral pain. Design Descriptive laboratory study. Setting University laboratory. Patients or Other Participants A total of 10 patients with self-reported patellofemoral pain (1 man, 9 women; age = 24.1 ± 3.8 years, height = 167.8 ± 15.2 cm, mass = 71.6 ± 17.5 kg) and 10 healthy control participants (3 men, 7 women; age = 27.4 ± 5.0 years, height = 173.5 ± 9.9 cm, mass = 78.2 ± 16.5 kg) volunteered. Intervention(s) Participants were assessed at 6 intervals spanning 21 days. Intraclass correlation coefficients (ICCs [3,3]) were used to assess reliability. Main Outcome Measure(s) Quadriceps central activation ratio, knee-extension maximal voluntary isometric contraction force, and SIB force. Results The quadriceps central activation ratio was highly reliable within session (ICC [3,3] = 0.97) and between sessions through day 21 (ICC [3,3] = 0.90–0.95). Acceptable reliability of knee extension (ICC [3,3] = 0.75–0.91) and SIB force (ICC [3,3] = 0.77–0.89) was observed through day 21. Conclusions The SIB technique was reliable for clinical research up to 21 days in patients with patellofemoral pain.

Context: Return to activity in the presence of quadriceps dysfunction may predispose individuals with anterior cruciate ligament reconstruction (ACLR) to long-term joint degeneration. Asymmetry may manifest during movement and result in altered knee-joint–loading patterns; however, the underlying neurophysiologic mechanisms remain unclear. Objective: To compare limb symmetry of quadriceps neuromuscular function between participants with ACLR and participants serving as healthy controls. Design: Descriptive laboratory study. Setting: Research laboratory. Patients or Other Participants: A total of 22 individuals with ACLR (12 men, 10 women) and 24 individuals serving as healthy controls (12 men, 12 women). Main Outcome Measure(s): Normalized knee-extension maximal voluntary isometric contraction (MVIC) torque (Nm/kg), quadriceps central activation ratio (CAR) (%), quadriceps motor-neuron–pool excitability (Hoffmann reflex to motor wave ratio), and quadriceps active motor threshold (AMT) (% 2.0 T) were measured bilaterally and used to calculate limb symmetry indices for comparison between groups. We used analyses of variance to compare quadriceps Hoffmann reflex to motor wave ratio, normalized knee-extension MVIC torque, quadriceps CAR, and quadriceps AMT between groups and limbs. Results: The ACLR group exhibited greater asymmetry in knee-extension MVIC torque (ACLR group = 0.85 ± 0.21, healthy group = 0.97 ± 0.14; t44 = 2.26, P = .03), quadriceps CAR (ACLR group = 0.94 ± 0.11, healthy group = 1.00 ± 0.08; t44 = 2.22, P = .04), and quadriceps AMT (ACLR group = 1.13 ± 0.18, healthy group = 1.02 ± 0.11; t34 = −2.46, P = .04) than the healthy control group. Conclusions: Asymmetries in measures of quadriceps function and cortical excitability were present in patients with ACLR. Asymmetry in quadriceps strength, activation, and cortical excitability persisted in individuals with ACLR beyond return to recreational activity. Measuring the magnitude of asymmetry after ACLR represents an important step in understanding long-term reductions in self-reported function and increased rate of subsequent joint injury in otherwise healthy, active individuals after ACLR.

Context: Persistent muscle weakness after anterior cruciate ligament (ACL) reconstruction may be due to underlying activation failure and arthrogenic muscle inhibition (AMI). Knee-joint cryotherapy has been shown to improve quadriceps function transiently in those with AMI, thereby providing an opportunity to improve quadriceps muscle activation and strength in patients with a reconstructed ACL. Objective: To compare quadriceps muscle function in patients with a reconstructed ACL who completed a 2-week intervention including daily cryotherapy (ice bag), daily exercises, or both. Design: Cross-sectional study. Setting: Laboratory. Patients or Other Participants: A total of 30 patients with reconstructed ACLs who were at least 6 months post-index surgery and had measurable quadriceps AMI. Intervention(s): The patients attended 4 supervised visits over a 2-week period. They were randomly assigned to receive 20 minutes of knee-joint cryotherapy, 1 hour of therapeutic rehabilitation exercises, or cryotherapy followed by exercises. Main Outcome Measure(s): We measured quadriceps Hoffmann reflex, normalized maximal voluntary isometric contraction torque, central activation ratio using the superimposed-burst technique, and patient-reported outcomes before and after the intervention period. Results: After the 2-week intervention period, patients who performed rehabilitation exercises immediately after cryotherapy had higher normalized maximal voluntary isometric contraction torques (P = .002, Cohen d effect size = 1.4) compared with those who received cryotherapy alone (P = .16, d = 0.58) or performed exercise alone (P = .16, d = 0.30). Conclusions: After ACL reconstruction, patients with AMI who performed rehabilitation exercises immediately after cryotherapy experienced greater strength gains than those who performed cryotherapy or exercises alone.

Context:Chronic ankle instability is characterized by repetitive lateral ankle sprains. Prophylactic ankle taping is a common intervention used to reduce the risk of ankle sprains. However, little research has been conducted to evaluate the effect ankle taping has on gait kinematics.Objective:To investigate the effect of taping on ankle and knee kinematics during walking and jogging in participants with chronic ankle instability.Design:Controlled laboratory study.Setting:Motion analysis laboratory.Patients or Participants:A total of 15 individuals (8 men, 7 women; age = 26.9 ± 6.8 years, height = 171.7 ± 6.3 cm, mass = 73.5 ± 10.7 kg) with self-reported chronic ankle instability volunteered. They had an average of 5.3 ± 3.1 incidences of ankle sprain.Intervention(s):Participants walked and jogged in shoes on a treadmill while untaped and taped. The tape technique was a traditional preventive taping procedure. Conditions were randomized.Main Outcome Measure(s):Frontal-plane and sagittal-plane ankle and sagittal-plane knee kinematics were recorded throughout the entire gait cycle. Group means and 90% confidence intervals were calculated, plotted, and inspected for percentages of the gait cycle in which the confidence intervals did not overlap.Results:During walking, participants were less plantar flexed from 64% to 69% of the gait cycle (mean difference = 5.73° ± 0.54°) and less inverted from 51% to 61% (mean difference = 4.34° ± 0.65°) and 76% to 81% (mean difference = 5.55° ± 0.54°) of the gait cycle when taped. During jogging, participants were less dorsiflexed from 12% to 21% (mean difference = 4.91° ± 0.18°) and less inverted from 47% to 58% (mean difference = 6.52° ± 0.12°) of the gait cycle when taped. No sagittal-plane knee kinematic differences were found.Conclusions:In those with chronic ankle instability, taping resulted in a more neutral ankle position during walking and jogging in shoes on a treadmill. This change in foot positioning and the mechanical properties of the tape may explain the protective aspect of taping in preventing lateral ankle sprains.

Context: Isolated lumbar paraspinal muscle fatigue causes lower extremity and postural control deficits. Objective: To describe the change in body position during gait after fatiguing lumbar extension exercises in persons with recurrent episodes of low back pain compared with healthy controls. Design: Case-control study. Setting: Motion analysis laboratory. Patients or Other Participants: Twenty-five recreationally active participants with a history of recurrent episodes of low back pain, matched by sex, height, and mass with 25 healthy controls. Intervention(s): We measured 3-dimensional lower extremity and trunk kinematics before and after fatiguing isometric lumbar paraspinal exercise. Main Outcome Measure(s): Measurements were taken while participants jogged on a custom-built treadmill surrounded by a 10-camera motion analysis system. Results: Group-by-time interactions were observed for lumbar lordosis and trunk angles (P < .05). A reduced lumbar spine extension angle was noted, reflecting a loss of lordosis and an increase in trunk flexion angle, indicating increased forward trunk lean, in healthy controls after fatiguing lumbar extension exercise. In contrast, persons with a history of recurrent low back pain exhibited a slight increase in spine extension, indicating a slightly more lordotic position of the lumbar spine, and a decrease in trunk flexion angles after fatiguing exercise. Regardless of group, participants experienced, on average, greater peak hip extension after lumbar paraspinal fatigue. Conclusions: Small differences in response may represent a necessary adaptation used by persons with recurrent low back pain to preserve gait function by stabilizing the spine and preventing inappropriate trunk and lumbar spine positioning.

A neuromuscular relationship exists between the lumbar extensor and quadriceps muscles during fatiguing exercise. However, this relationship may be different for persons with low back pain (LBP).To compare quadriceps inhibition after isometric, fatiguing lumbar extension exercise between persons with a history of LBP and control subjects.A 2 x 3 factorial, repeated-measures, time-series design with independent variables of group (persons with a history of LBP, controls) and time (baseline, postexercise set 1, postexercise set 2).University research laboratory.Twenty-five subjects with a history of LBP were matched by sex, height, and mass to 25 healthy control subjects.Electromyography median frequency indexed lumbar paraspinal muscular fatigue while subjects performed 2 sets of isometric lumbar extension exercise. Subjects exercised until a 15% downward shift in median frequency for the first set and a 25% shift for the second set were demonstrated.Knee extension force was measured while subjects performed an isometric maximal quadriceps contraction. During this maximal effort, a percutaneous electric stimulus was applied to the quadriceps, causing a transient, supramaximal increase in force output. We used the ratio between the 2 forces to estimate quadriceps inhibition. Quadriceps electromyographic activity was recorded during the maximal contractions to compare median frequencies over time.Both groups exhibited significantly increased quadriceps inhibition after the first (12.6% +/- 10.0%, P.001) and second (15.2% +/- 9.7%, P.001) exercise sets compared with baseline (9.6% +/- 9.3%). However, quadriceps inhibition was not different between groups.Persons with a history of LBP do not appear to be any more or less vulnerable to quadriceps inhibition after fatiguing lumbar extension exercise.

Muscular fatigue impedes sensorimotor function and may increase the risk of shoulder injury during activity. The effects of fatigue on the sensorimotor system of the shoulder have been studied with various results. Deceleration times have been used to study neuromuscular control of the shoulder; however, no studies involving the effects of fatigue on deceleration times have been reported.To compare shoulder deceleration times after a shoulder internal rotation perturbation before and after a repetitive throwing exercise protocol.A 2 x 2 repeated-measures design.Exercise and sport injury laboratory.Twenty healthy, recreationally active men (age = 24.76 +/- 4.03 years, height = 178.41 +/- 8.36 cm, mass = 80.16 +/- 15.20 kg) volunteered to participate in the study. To ensure familiarity with the overhead motion, all subjects chosen had previously participated in an overhead throwing sport.The independent variables were time (preintervention and postintervention) and session (experimental and control). The intervention consisted of continuous overhead throwing. The subjects were considered fatigued when a 10% decrease in velocity was noted on 3 consecutive pitches.Time necessary to decelerate from an internal rotation perturbation.Deceleration time was significantly increased by the fatiguing intervention ( P = .001).The decreased ability to decelerate may be an adaptive response by the subjects to dissipate a lower percentage of force per second.

Although poor paraspinal muscle endurance has been associated with less quadriceps activation (QA) in persons with a history of low back pain, no authors have addressed the acute neuromuscular response after lumbar paraspinal fatiguing exercise.To compare QA after lumbar paraspinal fatiguing exercise in healthy individuals and those with a history of low back pain.A 2 x 4 repeated-measures, time-series design.Exercise and Sport Injury Laboratory.Sixteen volunteers participated (9 males, 7 females; 8 controls and 8 with a history of low back pain; age = 24.1 +/- 3.1 years, height = 173.4 +/- 7.1 cm, mass = 72.4 +/- 12.1 kg).Subjects performed 3 sets of isometric lumbar paraspinal fatiguing muscle contractions. Exercise sets continued until the desired shift in lumbar paraspinal electromyographic median power frequency was observed. Baseline QA was compared with QA after each exercise set.An electric burst was superimposed while subjects performed a maximal quadriceps contraction. We used the central activation ratio to calculate QA = (F(MVIC)/[F(MVIC) + F(Burst)])* 100, where F = force and MVIC = maximal voluntary isometric contractions. Quadriceps electromyographic activity was collected at the same time as QA measurements to permit calculation of median frequency during MVIC.Average QA decreased from baseline (87.4% +/- 8.2%) after the first (84.5% +/- 10.5%), second (81.4% +/- 11.0%), and third (78.2% +/- 12.7%) fatiguing exercise sets. On average, the group with a history of low back pain showed significantly more QA than controls. No significant change in quadriceps median frequency was noted during the quadriceps MVICs.The quadriceps muscle group was inhibited after lumbar paraspinal fatiguing exercise in the absence of quadriceps fatigue. This effect may be different for people with a history of low back pain compared with healthy controls.