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To determine whether visually assessed performances of the single-leg squat (SLS) and vertical drop jump (VDJ) were associated with future noncontact anterior cruciate ligament (ACL) injury.Prognostic accuracy cohort study.Elite female handball and football (soccer) athletes (n = 880) were tested from 2007 to 2014 and tracked through 2015. Trained physical therapists visually rated each leg during a SLS and overall control during a VDJ. Receiver operating characteristic curve, Pearson chi-square, and logistic regression analyses were used to determine the prognostic accuracy of the 2 screening tests.Sixty-five noncontact ACL injuries occurred during the follow-up period. Fourteen percent of athletes who sustained an ACL injury had poor SLS performance, compared to 17% of the noninjured athletes (Neither SLS nor VDJ test performance distinguished between athletes who sustained a subsequent noncontact ACL injury and those who did not.

The aim of this study was to investigate if frontal plane knee and hip control in single-leg squats or vertical drop jumps with an overhead target were associated with future non-contact anterior cruciate ligament (ACL) injury in elite female athletes. Of the 429 handball and 451 football athletes (age 21.5 ± 4.0 years, height 169.6 ± 6.4 cm, body weight 67.1 ± 8.0 kg), 722 non-injured and 56 non-contact ACL injured participants were eligible for analysis. We calculated lateral pelvic tilt, frontal plane knee projection angle, medial knee position, and side-to-side asymmetry in these from 2D videos recorded at baseline, and recorded any new ACL injuries prospectively. None of the aforementioned variables in either screening task were different or could discriminate between injured and non-injured athletes (all

Dear editor,We appreciate the letter to the editor by Russo et al. (2021) on our recent paper ‘Kiss goodbye to the “kissing knees”: no association between frontal plane inward knee motion and risk ...

Classification algorithms determine the similarity of an observation to defined classes, e.g., injured or healthy athletes, and can highlight treatment targets or assess progress of a treatment. The primary aim was to cross-validate a previously developed classification algorithm using a different sample, while a secondary aim was to examine its ability to predict future ACL injuries. The examined outcome measure was 'healthy-limb' class membership probability, which was compared between a cohort of athletes without previous or future (No Injury) previous (PACL) and future ACL injury (FACL). The No Injury group had significantly higher probabilities than the PACL (p < 0.001; medium effect) and FACL group (p ≤ 0.045; small effect). The ability to predict group membership was poor for the PACL (area under curve [AUC]; 0.61

The novel coronavirus infection has substantially increased over the last year causing a global pandemic. The rate of infection is persistently rising which has forced many authorities to promote stay at home orders. Individuals may experience an increase in anxiety due to spending longer durations at home, working from home, lacking direct social interactions with friends and family, monetary losses, and potentially getting infected from the virus. Increased anxiety for prolonged periods is linked to elevated blood pressure, heart attacks, and strokes. To evaluate the influence of the pandemic on psychological health, we conducted a study on effects of mindfulness based stress reduction (MBSR) and stress management education (SME). To analyze the effects of the pandemic on mental health of our participants, we compared a group which was not affected by the pandemic (NPG) to a group that was affected by the pandemic (PG). The primary aim of this study was to compare the effects of 8‐weeks active intervention of MBSR and SME in NPG and PG on state‐trait anxiety and decentering. 36 adults participated in the study. All the participants were randomly enrolled in either 8‐weeks of MBSR or SME training. The NPG had 19 participants with 10 in MBSR and 9 in the SME group. The PG had 17 participants with 8 in MBSR and 9 in SME group. The MBSR group had weekly group sessions of ~2.5h on body scanning, meditation and light yoga while the SME group had concurrent sessions on nutrition, sleep, and stress management. Both the groups also did home practice daily for ~45 minutes. The NPG met in person for each of the 8 weeks, but the PG completed the last 4‐weeks of the course online due to a stay‐at‐home mandate at the time in Michigan. All the participants filled out a questionnaire on state anxiety, trait anxiety and decentering before and after the 8‐weeks. A ReANOVA was used to compare the differences across the 8 weeks, with condition (PG vs. NPG) as a between‐subjects factor. The results showed that there was a significant increase in decentering in PG after the 8‐weeks (treatment x condition and time x condition both p

Sports injuries have negative consequences on team performance, acute and long-term impact on individual well-being and quality of life, and cost implications for individuals and society. This chapter focuses on various Human Factors and Ergonomics (HFE) methods that can be used to facilitate the design of tools and methods to optimize and enhance injury prevention efforts. First, a basic overview of the epidemiology and historical frameworks for injury prevention research is presented. Second, we provide an example of how HFE methods have been applied to optimize observational risk analysis assessment and training. Third, we highlight the need, and strategies for, optimizing uptake and adherence to evidence-based injury prevention efforts. Finally, we comment briefly on opportunities for future work and integration of HFE methods to help reduce the risk of sport injuries.

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 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.

The purpose of the study was to assess the within-session and between-session reliability of knee kinematics and kinetics in a vertical drop jump task among elite female handball and football athletes. Specifically, we aimed to quantify the within-session waveform consistency and between-session consistency of the subject ranking for a variety of knee kinematics and kinetics. Forty-one elite female handball and football (soccer) athletes were tested in two sessions. The reliability of three-dimensional knee biomechanical measurements was quantified by the intra-class correlation, Spearman's rank correlation, and typical error. All the selected discrete variables achieved excellent within-session reliability (ICC > 0.87). The typical error of valgus angles, internal rotation angles, and internal rotation moment was constant throughout the whole stance phase. For between-session reliability, the selected discrete variables achieved good to excellent reliability (ICC > 0.69), except peak internal rotation moment (ICC = 0.40). All between-session rank correlation coefficients ranged from 0.56 to 0.90. Most of the discrete variables achieved good to excellent reliability in both within-session and between-session analysis. Moreover, moderate to strong between-session consistency of subject rankings was found, implying that the measurements assessed during the vertical drop jump demonstrate sufficient reliability to be used in both single-session and multiple-session studies.

Mentoring and coaching are effective and sometimes necessary strategies to foster the development of expertise. However, these learning enhancement methods are multifactorial and often ambiguously characterized. The goal of this chapter is to unpack this complex interactional relationship to more fully describe what it means to be an effective coach/mentor, and to better understand their role in developing expertise. Specifically, this chapter provides: (1) a detailed description of the different components and functions of mentoring, coaching, and preceptorship; (2) a summary of the meta-analytic evidence supporting the effectiveness of developmental support roles on a range of outcome measures (e.g., job performance); (3) a review of the empirical evidence supporting the development of expertise in mentoring-type roles; and (4) concluding remarks summarizing some of the major issues, and suggestions for how to advance this area of research.

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).

Quantifying countermovement jump (CMJ) and landing knee flexion angle is important for performance and injury risk assessment. The purpose of the study was to compare electrogoniometer (El-Gon)- and video-derived CMJ and landing knee flexion angle. Twenty-two adults performed three CMJs while knee flexion angle was simultaneously assessed using an El-Gon and video. The average systematic offset (RMSE) of the El-Gon-derived knee flexion angle throughout the entire movement was 7.03° ± 2.69°. Excellent reliability was demonstrated by the El-Gon (ICCavg = 0.92). Countermovement knee flexion angle, maximum landing knee flexion angle and flexion angle at maximum vertical ground reaction force were 12.0°, 10.9°, and 5.7° higher, respectively, when assessed using El-Gon (p < 0.001), compared to video. Errors between instruments are likely due to El-Gon crosstalk, misalignment and/or axis determination. The El-Gon is a cost-effective and time-efficient alternative to video analysis for the assessment of knee flexion angle if the error is accounted for and the sensor is precisely attached.

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.

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

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.

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 (por = 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 (p0.05). 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.

This study evaluated the effectiveness of a periodized plyometric training program and the impact of the duration of the post-training recovery period on countermovement jump performance. Fourteen women subjects participated in a 6-week periodized plyometric training program. Ten women subjects served as non-training controls. All subjects' countermovement jump height, peak power, and body mass were assessed before and 2, 4, 6, 8, and 10 days after training. Kinetic data were obtained via a force platform using the average of 3 repetitions of the countermovement jump for each testing session. Jump height was 25.0% greater (por = 0.05) after training with no difference (p0.05) between recovery periods of 2, 4, 6, 8, or 10 days, for the training group. Peak power was 11.6-14.3% (por = 0.001) greater after training for the training group with no difference (p0.05) between recovery periods of 2, 4, 6, 8, or 10 days. Analysis revealed no significant difference (p0.05) for jump height or peak power from pre- to posttest for the control group. Practitioners should prescribe periodized plyometric programs with decreasing volume and increasing intensity to improve jump performance without a need for a post-training recovery period.

This study evaluated impulse (I), peak ground reaction forces (GRF), and the rate of force development (RFD) of a variety of exercise modes for the purpose of estimating the magnitude and rate of mechanical loading as a measure of osteogenic potential. Twenty-three subjects participated in this study (mean +/- SD, age 21.2 +/- 1.4 years; body mass 77.8 +/- 16.2 kg). Kinetic data were obtained via a force platform for the test exercises modes, which included walking, jogging, depth jumps, loaded jump squats, and the back squat. Repeated measures analysis of variance revealed significant main effects for I, GRF, and RFD (p < or = 0.001). Bonferroni-adjusted post hoc analyses demonstrated that I and GRF were different between each exercise mode and that RFD was different between all exercise modes except for jogging and the back squat. The depth jump demonstrated the highest GRF and RFD, while the back squat produced the highest I. The jump squat produced the second highest value for all the variables assessed. Thus, the depth jump, jump squat, and back squat appear to offer the greatest potential as osteogenic stimuli and a mixed mode training strategy including exercises such as these is recommended. These results suggest that walking and jogging may have less osteogenic potential.

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.

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 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.

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.

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 (por= 0.001) but not for the interaction between plyometric exercise type and gender (p0.05). 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.

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.

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.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.Significant interactions between test condition and gender indicate differences in response to RVC during knee extension tests for power and work (Por = 0.05) and for knee flexion tests for peak torque and power (Por = 0.05). All subjects produced higher peak torque and power during knee extension in the RVC condition (Por = 0.05). Men produced a higher rate of torque development and work during knee extension (Por = 0.05) and a higher peak torque and power during knee flexion in the RVC condition (Por = 0.05). Prime mover activation was greater in the RVC condition for most tests (Por = 0.05). Women demonstrated lower bilateral flexor digitorum superficialis activation than men during all tests in the RVC condition (Por = 0.05).RVC increased the performance of several outcome variables assessed, which coincides with the concomitant increase in EMG of the prime movers.

Background Identifying individuals with a high risk for ACL injury is important for injury prevention. Current screening methods exist but rely on expensive and time consuming biomechanical analysis, limiting large scale application. Objective The aim of this experiment was to investigate observational ACL injury risk assessment performance. Design Individual raters viewed 25 frontal plane video clips of female high school athletes performing a drop vertical jump. Five video clips were repeated. The decision task was to rate the athletes risk for an ACL injury on a 10 point scale (1=very low, 10=very high). Concurrent 3D peak knee abduction moment (KAM) was calculated for the video-taped athletes and served as the criterion for ACL injury risk level. Setting Raters viewed the video clips and responded using a computer. Participants A convenience sample of 40 allied health professionals/students served as raters. Risk factor assessment In order to perform signal detection analysis on the judgments, ratings greater than 5 were considered high risk. Main outcome measurements To assess judgment performance, Spearman rho (ρ), sensitivity ( A9 ) and decision bias ( B D ) were calculated. Intra-rater consistency was assessed by calculating typical error between the 5 repeated video clips. Rater performance was also compared to the ACL Nomogram (KAM prediction model). Results Correlation between continuous KAM and subjective ratings ranged from −0.16 to 0.39 (Nomogram ρ=0.64). However, the best performer (M.S. Physiotherapist) displayed a sensitivity value of 0.85 ( B D =0.19) which was similar to the Nomogram measure of 0.97 ( B D =−0.48). In general, intra-rater consistency was sufficient with 83% of raters displaying typical error values less than 1. Conclusions Superior performance during visual assessment of ACL injury risk appears to be difficult but achievable. Research describing expertise mechanisms is warranted.