Usefulness of Current Patient-Reported Outcome Scales for ACL Injury: A Mixed-Methods Evaluation of Stakeholder-Perceived Utility of Specific Constructs and Items Across the Rehabilitation Timeline.

Background: Numerous patient-reported outcome measures (PROMs) have been used in patients with anterior cruciate ligament reconstruction (ACLR), often with overlapping constructs of interest and limited content validity. Inefficient scale application increases burden and diminishes overall usefulness for both the patient and practitioner. Purpose: To isolate specific PROM items across a diverse set of constructs that patients and practitioners perceive as having the greatest value at various stages of recovery and return to sport (RTS) in patients after ACLR. Study Design: Cross-sectional study. Methods: A combined 77 stakeholders participated in this 2-phase mixed-methods investigation. In phase 1, a total of 27 patients and 21 practitioners selected individual PROM items from various constructs that had the greatest utility or importance. In phase 2, the highest rated items were further tested in a head-to-head comparison with 29 stakeholders who attended the 2022 ACL Injury Research Retreat. In addition to the utility assessment, practitioners answered other questions related to importance and timing of PROM assessments. Results: In phase 1, both patients and practitioners shared the same top item in 6 of the 8 (75%) constructs assessed. In phase 2, the construct of psychological burden was rated as "extremely important" by 59% of respondents, followed by physical function (54%), symptoms (35%), and donor site issues (10%). The PROM items of confidence, perceived likelihood of reinjury, and difficulty stopping quickly were rated by a respective 93%, 89%, and 86% of the sample as either "very useful" or "extremely useful." All constructs except donor site issues were rated by most stakeholders to be absolutely necessary to evaluate treatment progress and RTS readiness at the 6-month postoperative time and at RTS. Conclusion: Overall, psychological burden, with specific items related to confidence and reinjury likelihood, were rated as most important and useful by both patients and practitioners. The second most important and useful PROM item was related to higher intensity function (eg, decelerating or jumping/landing activities during sports).

Development of a prediction equation to estimate lower-limb arterial occlusion pressure with a thigh sphygmomanometer.

INTRODUCTION: Previous investigators have developed prediction equations to estimate arterial occlusion pressure (AOP) for blood flow restriction (BFR) exercise. Most equations have not been validated and are designed for use with expensive cuff systems. Thus, their implementation is limited for practitioners. PURPOSE: To develop and validate an equation to predict AOP in the lower limbs when applying an 18 cm wide thigh sphygmomanometer (SPHYG18cm). METHODS: Healthy adults (n = 143) underwent measures of thigh circumference (TC), skinfold thickness (ST), and estimated muscle cross-sectional area (CSA) along with brachial and femoral systolic (SBP) and diastolic (DBP) blood pressure. Lower-limb AOP was assessed in a seated position at the posterior tibial artery (Doppler ultrasound) using a SPHYG18cm. Hierarchical linear regression models were used to determine predictors of AOP. The best set of predictors was used to construct a prediction equation to estimate AOP. Performance of the equation was evaluated and internally validated using bootstrap resampling. RESULTS: Models containing measures of either TC or thigh composition (ST and CSA) paired with brachial blood pressures explained the most variability in AOP (54%) with brachial SBP accounting for majority of explained variability. A prediction equation including TC, brachial SBP, and age showed good predictability (R2 = 0.54, RMSE = 7.18 mmHg) and excellent calibration. Mean difference between observed and predicted values was 0.0 mmHg and 95% Limits of Agreement were ± 18.35 mmHg. Internal validation revealed small differences between apparent and optimism adjusted performance measures, suggesting good generalizability. CONCLUSION: This prediction equation for use with a SPHYG18cm provided a valid way to estimate lower-limb AOP without expensive equipment.

Allograft Anterior Cruciate Ligament Reconstruction Fails at a Greater Rate in Patients Younger Than 34 Years.

Purpose: To characterize the secondary anterior cruciate ligament (ACL) injury rates after primary allograft anterior cruciate ligament reconstruction (ACLR) and to identify the age cut-score at which the risk of allograft failure decreases. Methods: All patients who underwent primary ACLR within a single orthopaedic department between January 2005 and April 2020 were contacted at a minimum of 2 years post-ACLR to complete a survey regarding complications experienced post-surgery, activity level, and perceptions of knee health. Patients were excluded for incidence of previous ACLR (ipsilateral or contralateral) and/or age younger than 14 years. Relative proportions were calculated, binary regression analysis was performed, and receiver operating characteristic analysis was used to identify the threshold age for maximal sensitivity and specificity to predict high risk of allograft failure, defined as undergoing revision ACLR. Results: Of the 939 surveys completed, 398 patients underwent primary allograft ACLR (mean age 39.5 years; range 16.0-66.1 years; 54.3% female). The secondary ACL injury rate was 11.6% (5.8% ipsilateral revision ACLR, 5.8% contralateral ACL injury). Male and female patients had similar revision (5.5% male, 6.0% female, P = .82) and contralateral ACL injury rates (6.6% male, 5.1% female, P = .52). Receiver operating characteristic analysis indicated that age ≤34 years was threshold for differentiating high risk of allograft failure (area under the curve 0.65, 95% confidence interval 0.55-0.76; P = .014). Patients aged ≤34 years had a greater secondary injury rate than patients >34 years (20.4% (10.2% revision ACLR, 10.2% contralateral ACL injury) versus 6.9% (3.5% revision ACLR, 3.5% contralateral ACL injury; P < .001). Binary regression analysis demonstrated that decreasing age was associated with increased risk of graft failure (χ2 = 7.9, P = .02.). Conclusions: Allograft ACLR showed similar failure rates between sexes but displayed suboptimal graft failure outcomes in younger and active patients. By age 34 years, the increased revision risk for younger patients diminished. Level of Evidence: Level IV, therapeutic case series.

Determining independence and associations among various cardiovascular disease risk factors in 9-12 years old school-children: a cross sectional study.

BACKGROUND: Cardiovascular disease (CVD) risk assessment of children typically includes evaluating multiple CVD risk factors some of which tend to correlate each other. However, in older children and young adolescents, there are little data on the level of independence of CVD risk factors. The purpose of this study was to examine the relationships among various CVD risk factors to determine the level of independence of each risk factor in a sample of 5th-grade public school students. METHOD: A cross-sectional analysis of 1525 children (856 girls and 669 boys; age: 9-12 years) who participated in baseline CVD risk assessment for the (S)Partners for Heart Health program from 2010 - 2018. Thirteen CVD risk factor variables were used in the analysis and included blood lipids [low-density lipoprotein (LDL), high-density lipoprotein (HDL), total cholesterol (TC), and triglycerides], resting systolic and diastolic blood pressure (BP); anthropometrics [height, weight, body mass index (BMI), % body fat, waist circumference (WC)]. Additionally, acanthosis nigricans (a marker insulin resistance and diabetes), and cardiorespiratory fitness (VO2 ml/kg) was estimated using the PACER. Descriptive statistics, bivariate Pearson correlations, and principal component analysis were used to determine the relationships among these variables and the independence. RESULTS: Parallel analysis indicated two components should be extracted. Among the two components extracted, WC, % body fat, and BMI loaded highest on component 1, which explained 34% of the total variance. Systolic BP and diastolic BP loaded predominantly on component 2 and accounted for 17% of the variance. Cardiorespiratory fitness, acanthosis nigricans, HDL, and triglycerides loaded highest on the first component (loadings between 0.42 and 0.57) but still suggest some non-shared variance with this component. Low-density lipoprotein had low loadings on each component. Factor loadings were stable across sex. CONCLUSION: Among the various CVD risk indicators, measures of adiposity loaded highest on the component that explained the largest proportion of variability in the data reinforcing the importance of assessing adiposity in CVD risk assessment. In addition, blood pressure loaded highest on the second component, suggesting their relative independence when assessing CVD risk. The data also provide support and rationale for determining what CVD risk factors to include- based on resource needs. For example, researchers or public health programs may choose to assess WC instead of lipid profile for cardiovascular related problems if ease of assessment and cost are considerations.

The Effect of a Brief, Web-Based Animated Video for Improving Comprehension and Implementation Feasibility for Reducing Anterior Cruciate Ligament Injury: A Three-Arm Randomized Controlled Trial.

Neuromuscular injury prevention training (IPT) has been shown to reduce anterior cruciate ligament (ACL) injury risk by approximately 50%, but the implementation rate is low. One of the most important modifiable barriers for implementation is coaches' comprehension of risk and intervention strategies. This study aimed to evaluate the effect of a brief, web-based, animated video on ACL injury prevention comprehension and IPT implementation feasibility. Coaches in landing and cutting sports were recruited and randomized into three groups. (1) Intervention: brief multimedia animated video about ACL injury and prevention. (2) Active control: commonly accessed, text-based web resource about ACL injury and prevention. (3) Placebo control: brief multimedia video about concussions. Overall ACL comprehension-composed of basic ACL knowledge, risk knowledge, prevention knowledge, and severity knowledge-as well as implementation feasibility were all measured prior to and immediately following the interventions. Overall ACL comprehension improved the most in the animated video group (Cohen's d = 0.86) and, to a lesser degree, in the active control web-based article group (Cohen's d = 0.39). Both video and web-based article groups had greater implementation feasibility compared to the control group (p = 0.01). Overall, these initial results suggest that a brief, web-based, animated video has the potential to be a superior method for informing stakeholders in order to reduce traumatic injuries in sport.

Evidence-Based Best-Practice Guidelines for Preventing Anterior Cruciate Ligament Injuries in Young Female Athletes: A Systematic Review and Meta-analysis.

BACKGROUND: Injury prevention neuromuscular training (NMT) programs reduce the risk for anterior cruciate ligament (ACL) injury. However, variation in program characteristics limits the potential to delineate the most effective practices to optimize injury risk reduction. PURPOSE: To evaluate the common and effective components included in ACL NMT programs and develop an efficient, user-friendly tool to assess the quality of ACL NMT programs. STUDY DESIGN: Systematic review and meta-analysis. METHODS: Study inclusion required (1) a prospective controlled trial study design, (2) an NMT intervention aimed to reduce incidence of ACL injury, (3) a comparison group, (4) ACL injury incidence, and (5) female participants. The following data were extracted: year of publication, study design, sample size and characteristics, and NMT characteristics including exercise type and number per session, volume, duration, training time, and implementer training. Analysis entailed both univariate subgroup and meta-regression techniques using random-effects models. RESULTS: Eighteen studies were included in the meta-analyses, with a total of 27,231 participants, 347 sustaining an ACL injury. NMT reduced the risk for ACL injury from 1 in 54 to 1 in 111 (odds ratio [OR], 0.51; 95% CI, 0.37-0.69]). The overall mean training volume was 18.17 hours for the entire NMT (24.1 minutes per session, 2.51 times per week). Interventions targeting middle school or high school-aged athletes reduced injury risk (OR, 0.38; 95% CI, 0.24-0.60) to a greater degree than did interventions for college- or professional-aged athletes (OR, 0.65; 95% CI, 0.48-0.89). All interventions included some form of implementer training. Increased landing stabilization and lower body strength exercises during each session improved prophylactic benefits. A meta-regression model and simple checklist based on the aforementioned effective components (slope = -0.15, P = .0008; intercept = 0.04, P = .51) were developed to allow practitioners to evaluate the potential efficacy of their ACL NMT and optimize injury prevention effects. CONCLUSION: Considering the aggregated evidence, we recommend that ACL NMT programs target younger athletes and use trained implementers who incorporate lower body strength exercises (ie, Nordic hamstrings, lunges, and heel-calf raises) with a specific focus on landing stabilization (jump/hop and hold) throughout their sport seasons. CLINICAL RELEVANCE: Clinicians, coaches, athletes, parents, and practitioners can use the developed checklist to gain insight into the quality of their current ACL NMT practices and can use the tool to optimize programming for future ACL NMT to reduce ACL injury risk.

Neuromuscular Adaptations to Multimodal Injury Prevention Programs in Youth Sports: A Systematic Review with Meta-Analysis of Randomized Controlled Trials.

Objective: Neuromuscular injury prevention programs (IPP) can reduce injury rate by about 40% in youth sport. Multimodal IPP include, for instance, balance, strength, power, and agility exercises. Our systematic review and meta-analysis aimed to evaluate the effects of multimodal IPP on neuromuscular performance in youth sports. Methods: We conducted a systematic literature search including selected search terms related to youth sports, injury prevention, and neuromuscular performance. Inclusion criteria were: (i) the study was a (cluster-)randomized controlled trial (RCT), and (ii) investigated healthy participants, up to 20 years of age and involved in organized sport, (iii) an intervention arm performing a multimodal IPP was compared to a control arm following a common training regime, and (iv) neuromuscular performance parameters (e.g., balance, power, strength, sprint) were assessed. Furthermore, we evaluated IPP effects on sport-specific skills. Results: Fourteen RCTs (comprising 704 participants) were analyzed. Eight studies included only males, and five only females. Seventy-one percent of all studies investigated soccer players with basketball, field hockey, futsal, Gaelic football, and hurling being the remaining sports. The average age of the participants ranged from 10 years up to 19 years and the level of play from recreational to professional. Intervention durations ranged from 4 weeks to 4.5 months with a total of 12 to 57 training sessions. We observed a small overall effect in favor of IPP for balance/stability (Hedges' g = 0.37; 95%CI 0.17, 0.58), leg power (g = 0.22; 95%CI 0.07, 0.38), and isokinetic hamstring and quadriceps strength as well as hamstrings-to-quadriceps ratio (g = 0.38; 95%CI 0.21, 0.55). We found a large overall effect for sprint abilities (g = 0.80; 95%CI 0.50, 1.09) and sport-specific skills (g = 0.83; 95%CI 0.34, 1.32). Subgroup analyses revealed larger effects in high-level (g = 0.34-1.18) compared to low-level athletes (g = 0.22-0.75), in boys (g = 0.27-1.02) compared to girls (g = 0.09-0.38), in older (g = 0.32-1.16) compared to younger athletes (g = 0.18-0.51), and in studies with high (g = 0.35-1.16) compared to low (g = 0.12-0.38) overall number of training sessions. Conclusion: Multimodal IPP beneficially affect neuromuscular performance. These improvements may substantiate the preventative efficacy of IPP and may support the wide-spread implementation and dissemination of IPP. The study has been a priori registered in PROSPERO (CRD42016053407).

Injury Risk Estimation Expertise: Cognitive-Perceptual Mechanisms of ACL-IQ.

Instrument-based biomechanical movement analysis is an effective injury screening method but relies on expensive equipment and time-consuming analysis. Screening methods that rely on visual inspection and perceptual skill for prognosticating injury risk provide an alternative approach that can significantly reduce cost and time. However, substantial individual differences exist in skill when estimating injury risk performance via observation. The underlying perceptual-cognitive mechanisms of injury risk identification were explored to better understand the nature of this skill and provide a foundation for improving performance. Quantitative structural and process modeling of risk estimation indicated that superior performance was largely mediated by specific strategies and skills (e.g., irrelevant information reduction), and independent of domain-general cognitive abilities (e.g., mental rotation, general decision skill). These cognitive models suggest that injury prediction expertise (i.e., ACL-IQ) is a trainable skill, and provide a foundation for future research and applications in training, decision support, and ultimately clinical screening investigations.

Injury Risk Estimation Expertise: Assessing the ACL Injury Risk Estimation Quiz.

BACKGROUND: Available methods for screening anterior cruciate ligament (ACL) injury risk are effective but limited in application as they generally rely on expensive and time-consuming biomechanical movement analysis. A potentially efficient alternative to biomechanical screening is skilled movement analysis via visual inspection (ie, having experts estimate injury risk factors based on observations of athletes' movements). PURPOSE: To develop a brief, valid psychometric assessment of ACL injury risk factor estimation skill: the ACL Injury Risk Estimation Quiz (ACL-IQ). STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 3. METHODS: A total of 660 individuals participated in various stages of the study, including athletes, physicians, physical therapists, athletic trainers, exercise science researchers/students, and members of the general public in the United States. The ACL-IQ was fully computerized and made available online (www.ACL-IQ.org). Item sampling/reduction, reliability analysis, cross-validation, and convergent/discriminant validity analyses were conducted to refine the efficiency and validity of the assessment. RESULTS: Psychometric optimization techniques identified a short (mean time, 2 min 24 s), robust, 5-item assessment with high reliability (test-retest: r = 0.90) and high test sensitivity (average difference of exercise science professionals vs general population: Cohen d = 2). Exercise science professionals and individuals from the general population scored 74% and 53% correct, respectively. Convergent and discriminant validity was demonstrated. Scores on the ACL-IQ were best predicted by ACL knowledge and specific judgment strategies (ie, cue use) and were largely unrelated to domain-general spatial/decision-making ability, personality, or other demographic variables. Overall, 23% of the total sample (40% of exercise science professionals; 6% of general population) performed better than or equal to the ACL nomogram. CONCLUSION: This study presents the results of a systematic approach to assess individual differences in ACL injury risk factor estimation skill; the assessment approach is efficient (ie, it can be completed in <3 min) and psychometrically robust. The results provide evidence that some individuals have the ability to visually estimate ACL injury risk factors more accurately than other instrument-based ACL risk estimation methods (ie, ACL nomogram). The ACL-IQ provides the foundation for assessing the efficacy of observational ACL injury risk factor assessment (ie, does simple skilled visual inspection reduce ACL injuries?). The ACL-IQ can also be used to increase our understanding of the perceptual-cognitive mechanisms underlying injury risk assessment expertise, which can be leveraged to accelerate learning and improve performance.

Injury Risk Estimation Expertise: Interdisciplinary Differences in Performance on the ACL Injury Risk Estimation Quiz.

BACKGROUND: Simple observational assessment of movement is a potentially low-cost method for anterior cruciate ligament (ACL) injury screening and prevention. Although many individuals utilize some form of observational assessment of movement, there are currently no substantial data on group skill differences in observational screening of ACL injury risk. PURPOSE/HYPOTHESIS: The purpose of this study was to compare various groups' abilities to visually assess ACL injury risk as well as the associated strategies and ACL knowledge levels. The hypothesis was that sports medicine professionals would perform better than coaches and exercise science academics/students and that these subgroups would all perform better than parents and other general population members. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: A total of 428 individuals, including physicians, physical therapists, athletic trainers, strength and conditioning coaches, exercise science researchers/students, athletes, parents, and members of the general public participated in the study. Participants completed the ACL Injury Risk Estimation Quiz (ACL-IQ) and answered questions related to assessment strategy and ACL knowledge. RESULTS: Strength and conditioning coaches, athletic trainers, physical therapists, and exercise science students exhibited consistently superior ACL injury risk estimation ability (+2 SD) as compared with sport coaches, parents of athletes, and members of the general public. The performance of a substantial number of individuals in the exercise sciences/sports medicines (approximately 40%) was similar to or exceeded clinical instrument-based biomechanical assessment methods (eg, ACL nomogram). Parents, sport coaches, and the general public had lower ACL-IQ, likely due to their lower ACL knowledge and to rating the importance of knee/thigh motion lower and weight and jump height higher. CONCLUSION: Substantial cross-professional/group differences in visual ACL injury risk estimation exist. The relatively profound differences in injury risk estimation accuracy and their potential implications for risk screening suggest the need for additional training and outreach (see http://www.ACL-IQ.org). CLINICAL RELEVANCE: Parents and sport coaches would likely benefit from training or use of decision support tools such as the ACL nomogram to assess ACL injury risk. In addition, physicians and other sports medicine professionals may also benefit from improving risk estimation performance to reach clinical biomechanical standards.

The optimal back squat load for potential osteogenesis.

The osteogenic potential of exercise is reported to be partially a function of the magnitude of training loads. This study evaluated the ground reaction force (GRF) and rate of force development (RFD) of the eccentric and concentric phases of the back squat at 3 different loads. Twelve subjects performed the back squat on a force platform with loading conditions of 80, 100, and 120% of their 1 repetition maximum (RM). Back squats performed at 120% of the 1RM produced the highest GRF in both the eccentric and concentric conditions. No significant differences were found between RFD for any of the loading conditions. Performing the back squat at loads of 120% of the estimated 1RM, accomplished with reduced range of motion, results in higher GRF than the back squat performed at 80 or 100% of the 1RM. Thus, supermaximal back squat loads in excess of the 1RM, with decreased range of motion, may be a useful part of a resistance training program designed to maximize osteogenic potential.

Kinetic quantification of plyometric exercise intensity.

Ebben, WP, Fauth, ML, Garceau, LR, and Petushek, EJ. Kinetic quantification of plyometric exercise intensity. J Strength Cond Res 25(12): 3288-3298, 2011-Quantification of plyometric exercise intensity is necessary to understand the characteristics of these exercises and the proper progression of this mode of exercise. The purpose of this study was to assess the kinetic characteristics of a variety of plyometric exercises. This study also sought to assess gender differences in these variables. Twenty-six men and 23 women with previous experience in performing plyometric training served as subjects. The subjects performed a variety of plyometric exercises including line hops, 15.24-cm cone hops, squat jumps, tuck jumps, countermovement jumps (CMJs), loaded CMJs equal to 30% of 1 repetition maximum squat, depth jumps normalized to the subject's jump height (JH), and single leg jumps. All plyometric exercises were assessed with a force platform. Outcome variables associated with the takeoff, airborne, and landing phase of each plyometric exercise were evaluated. These variables included the peak vertical ground reaction force (GRF) during takeoff, the time to takeoff, flight time, JH, peak power, landing rate of force development, and peak vertical GRF during landing. A 2-way mixed analysis of variance with repeated measures for plyometric exercise type demonstrated main effects for exercise type and all outcome variables (p ≤ 0.05) and for the interaction between gender and peak vertical GRF during takeoff (p ≤ 0.05). Bonferroni-adjusted pairwise comparisons identified a number of differences between the plyometric exercises for the outcome variables assessed (p ≤ 0.05). These findings can be used to guide the progression of plyometric training by incorporating exercises of increasing intensity over the course of a program.

Kinetic analysis of several variations of push-ups.

Push-ups are a common and practical exercise that is used to enhance fitness, including upper body strength or endurance. The kinetic characteristics of push-ups and its variations are yet to be quantified. Kinetic quantification is necessary to accurately evaluate the training load, and thus the nature of the training stimulus, for these exercise variations. This study assessed the peak vertical ground reaction forces (GRFs) of push-up variations including the regular push-up and those performed with flexed knee, feet elevated on a 30.48-cm box, and a 60.96-cm box, and hands elevated on a 30.48-cm box and a 60.96-cm box. Twenty-three recreationally fit individuals (14 men, 9 women) performed each of the 6 push-up variations in a randomized order. Peak GRF and peak GRF expressed as a coefficient of subject body mass were obtained with a force platform. Push-ups with the feet elevated produced a higher GRF than all other push-up variations (p ≤ 0.05). Push-ups with hands elevated and push-ups from the flexed knee position produced a lower GRF than all other push-up variations (p ≤ 0.05). No gender differences in response to these push-up variations were found (p > 0.05). Additionally, subject height was not related to the GRF for any of the push-up conditions (p > 0.05) other than the condition where hands were elevated on a 60.96-cm box (p ≤ 0.05; r = 0.63). These data can be used to progress the intensity of push-ups in a program and to quantify the training load as a percentage of body mass.

Using the reactive strength index modified to evaluate plyometric performance.

The ability to develop force quickly is a requisite ability in most sports. The reactive strength index (RSI) has been developed as a measure of explosive strength and is derived by evaluating jump height divided by ground contact time during the depth jump (DJ). At present, the RSI is typically used to evaluate DJ performance, because it is the only plyometric exercise with an identifiable ground contact time. The purpose of this study was to introduce a modification of the RSI (RSImod) that can be used to evaluate the explosive power of any vertical plyometric exercise. This study will also assess the reliability of the RSImod, evaluate the RSImod of a variety of plyometric exercises, and examine gender differences. Twenty-six men and 23 women served as subjects. Subjects performed 3 repetitions for each of 5 plyometric exercises including the countermovement jump (CMJ), tuck jump, single-leg jump, squat jump, and dumbbell CMJ. Data were analyzed using a 2-way analysis of variance to evaluate differences in RSImod between the plyometric exercise and the interaction between plyometric exercise RSImod and gender. The analysis of RSImod revealed significant main effects for plyometric exercise type (p 0.05). Results of pairwise comparisons indicate that the RSImod is statistically different between all plyometric exercises studied. Intraclass correlation coefficients indicate that RSImod is highly reliable for all of the exercises studied. The RSImod offers a highly reliable method of assessing the explosiveness developed during a variety of plyometric exercises.

Kinetic analysis of concurrent activation potentiation during back squats and jump squats.

Concurrent activation potentiation enhances muscular force during open kinetic chain isometric and isokinetic exercises via remote voluntary contractions (RVCs). The purpose of this study was to evaluate the effect of RVCs on the performance of closed kinetic chain ground-based exercises. Subjects included 13 men (21.4+/-1.5 years) who performed the back squat and jump squat in 2 test conditions. The RVC condition included performing the test exercises while clenching the jaw on a mouth guard, forcefully gripping and pulling the barbell down into the trapezius, and performing a Valsalva maneuver. The normal condition (NO-RVC) included performing the test exercises without RVCs. Exercises were assessed with a force platform. Peak ground reaction force (GRF), rate of force development (RFD) during the first 100 milliseconds (RFD-100), RFD to peak GRF (RFD-P), and jump squat height (JH) were calculated from the force-time records. Data were analyzed using an analysis of variance. Results reveal that GRF and RFD-100 were higher in the RVC compared with the NO-RVC condition for both the back squat and jump squat (p

Gender-based analysis of hamstring and quadriceps muscle activation during jump landings and cutting.

This study evaluated gender differences in the magnitude and timing of hamstring and quadriceps activation during activities that are believed to cause anterior cruciate ligament (ACL) injuries. Twelve men (age = 21.0 +/- 1.2 years; body mass = 81.61 +/- 13.3 kg; and jump height = 57.61 +/- 10.15 cm) and 12 women (age = 19.91 +/- 0.9 years; body mass = 64.36 +/- 6.14 kg; and jump height = 43.28 +/- 7.5) performed 3 repetitions each of the drop jump (jump) normalized to the subject's vertical jump height, and a sprint and cut at a 45-degree angle (cut). Electromyography (EMG) was used to quantify rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), lateral hamstring (LH), and medial hamstrings (MH) activation, timing, activation ratios, and timing ratios before and after foot contact for the jump and cut and normalized to each subject's hamstring and quadriceps maximum voluntary isometric contraction. Data were analyzed using an analysis of variance with results demonstrating that during the postcontact phase of the cut, men demonstrated greater LH and MH activation than women. In the precontact phase of the jump, men showed earlier activation of the VL and VM, than women. Women produced longer RF and VM muscle bursts during the postcontact phase of the cut. Additionally, men showed a trend toward higher hamstring to quadriceps activation ratio than women for the postcontact phase of the cut. This study provides evidence that men are LH dominant during the postcontact phase of the cut compared with women, whereas women sustain RF activation longer than men during this phase. Men activate quadriceps muscles earlier than women in the precontact phase of the jump. Training interventions may offer the potential for increasing the rate and magnitude of hamstring muscle activation. These outcomes should be evaluated using EMG during movements that are similar to those that cause ACL injuries to determine if gender differences in muscle activation can be reduced.

Reliability of surface electromyography during maximal voluntary isometric contractions, jump landings, and cutting.

The reliability of electromyographic (EMG) data has been examined for isometric and slow dynamic tasks, but little is known about the repeatability of this data for ballistic movements. The purpose of this study was to examine the within-session, trial-to-trial reliability of a variety of quadriceps and hamstrings muscles during isometric and ballistic activities. Data were analyzed by way of intraclass correlation coefficients (ICC), intersubject coefficients of variation (CVinter), and intrasubject coefficients of variation (CVintra). Twenty-four subjects performed 3 repetitions each of 2 randomly ordered test exercises, including landing from a depth jump (J) and cutting after a 10-m sprint (C). Data were acquired and processed with root mean square EMG for the muscles assessed, and data were analyzed for each exercise using a repeated measures analysis of variance. Results revealed that all ICC values were greater than 0.80, with most values greater than 0.90, CVinter values ranged from 5.4% to 148.7%, and CVintra values ranged from 11.5% to 49.3%. This study indicates that EMG is a reliable method for assessing the reproducibility of both the quadriceps and hamstrings muscle activation during either isometric or ballistic exercises.

Evaluating plyometric exercises using time to stabilization.

Plyometric exercises are frequently used in strength and conditioning and rehabilitation programs because the landing phase of these exercises requires dynamic stabilization. This study examined the differences in landing stability of a variety of plyometric exercises by assessing time to stabilization (TTS), its reliability, and sex differences therein. Forty-nine men and women performed a variety of plyometric exercises thought to represent a continuum of difficulty of dynamic stabilization during landing. Plyometric exercises included line hops, cone hops, squat jumps, tuck jumps, countermovement jumps, dumbbell countermovement jumps, and single leg countermovement jumps, each performed for 3 repetitions on a force platform. A 2-way mixed analysis of covariance with repeated measures for plyometric exercise type was used to evaluate the main effects for plyometric exercise type and the interaction between plyometric exercise type and sex for TTS. Subject jumping ability was evaluated as a covariate. Results revealed significant main effects for plyometric exercise type (p < or = 0.001) and for the interaction between plyometric exercise type and sex (p = 0.002). Bonferroni adjusted post hoc analysis demonstrated differences in TTS between a number of plyometric exercises for men and women. Reliability analysis revealed intraclass correlation coefficients ranging from 0.51 to 0.86 with no significant difference between trials (p > 0.05). Practitioners who use plyometrics to train dynamic stability should create programs that progress the intensity of the exercises based on the results of this study. This study also demonstrated that TTS is moderately to highly reliable for a variety of jumping conditions for both men and women.

EMG analysis of concurrent activation potentiation.

PURPOSE: This study evaluated the effect of remote voluntary contractions(RVC) on concentric isokinetic knee extensor and flexor peak torque, rate of torque development, power, and work, the activation of the affected muscles, and gender differences therein. METHODS: Eleven men and 12 women were evaluated with EMG and isokinetic dynamometry during knee extension and flexion tests in RVC and baseline (NO-RVC) test conditions. The RVC condition included jaw clenching, hand gripping, and the Valsalva maneuver. A two-way mixed ANOVA with repeated measures for test condition was used to evaluate the main effects for each isokinetic measure, as well as the EMG of the prime movers, their antagonist,and the muscles involved in the RVC, and the interaction between test condition and gender. RESULTS: Significant interactions between test condition and gender indicate differences in response to RVC during knee extension tests for power and work (P < or = 0.05) and for knee flexion tests for peak torque and power (P < or = 0.05). All subjects produced higher peak torque and power during knee extension in the RVC condition (P < or = 0.05). Men produced a higher rate of torque development and work during knee extension (P < or = 0.05) and a higher peak torque and power during knee flexion in the RVC condition (P < or = 0.05). Prime mover activation was greater in the RVC condition for most tests (P < or = 0.05). Women demonstrated lower bilateral flexor digitorum superficialis activation than men during all tests in the RVC condition (P < or = 0.05). CONCLUSIONS: RVC increased the performance of several outcome variables assessed, which coincides with the concomitant increase in EMG of the prime movers.