A Six-Week Neuromuscular and Performance Training Program Improves Speed, Agility, Dynamic Balance, and Core Endurance in Junior Tennis Players

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Abstract

Objective: Tennis requires speed, agility, and explosive power.

Few studies have assessed the effects of a training program in junior players who are not on an elite or national level. We evaluated the impact of a program that combined components of a knee ligament injury prevention program with other exercises to improve athletic performance indicators. We hypothesized that this program would significantly improve dynamic single-leg balance and function, correct lower limb asymmetry, enhance speed and agility, and improve core endurance.

Methods: Forty-two players (31 females, 11 males; mean age, 14 Å} 2 years) participated in the 6-week program conducted by a tennis professional and certified trainers. Each training session included a dynamic warm-up, jump training, strength training, and tennis specific agility and hitting drills. Two single-leg hop tests, baseline and service box speed and agility tests, a 1-court suicide run, and an abdominal endurance test were conducted at baseline and 3 days after the last session. Fifteen athletes participated in more than one training program a mean of 9 months apart.

Results: In all 42 players, statistically significant improvements and large-moderate effect sizes were measured for speed, agility, dynamic single-leg balance, and abdominal endurance. Players who participated in multiple programs continued to improve, although the magnitude of the improvements was smaller than those obtained from the first training program. There were no differences in the percent of improvement in any of the tests between genders.

Conclusions: The program improved neuromuscular and athletic

performance indicators in junior tennis players. Repeated training

for continued improvements is justified as required or desired by the

player. The program is appropriate for pre-season training for high

school players or before the initiation of seasonal tournament play.

Reducing the Risk of Noncontact Anterior Cruciate Ligament Injuries in the Female Athlete

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Abstract: High school and collegiate female athletes have a significantly increased risk of sustaining a noncontact anterior cruciate ligament injury compared with male athletes participating in the same sport. This review summarizes the current knowledge of the risk factors hypothesized to influence this problem, and the neuromuscular training programs designed to correct certain biomechanics problems noted in female athletes. The risk factors include a genetic predisposition for sustaining a knee ligament injury, environmental factors, anatomical indices, hormonal influences, and neuromuscular factors. The greatest amount of research in this area has studied differences between female and male athletes in movement patterns during athletic tasks; muscle strength, activation, and recruitment patterns; and knee joint stiffness under controlled, preplanned, and reactive conditions in the laboratory. Neuromuscular retraining programs have been developed in an attempt to reduce these differences. The successful programs teach athletes to control the upper body, trunk, and lower body position; lower the center of gravity by increasing hip and knee flexion during activities; and develop muscular strength and techniques to land with decreased ground reaction forces. In addition, athletes are taught to preposition the body and lower extremity prior to initial ground contact to obtain the position of greatest knee joint stability and stiffness. Two published programs have significantly reduced the incidence of noncontact anterior cruciate ligament injuries in female athletes participating in basketball, soccer, and volleyball. Other programs were ineffective, had a poor study design, or had an insufficient number of participants, which precluded a true reduction in the risk of this injury. In order to determine which risk factors for non contact anterior cruciate ligament ruptures are significant, future investigations should include larger cohorts of athletes in multiple sports, analyze factors from all of the major risk categories, and follow athletes for at least one full athletic season. Future risk assessment studies should incorporate reactive tasks under more realistic sports conditions.

Assessment of Lower Limb Neuromuscular Control in Prepubescent Athletes

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Background: Although neuromuscular indices have been extensively studied in adolescents and adults, limited data exist for prepubescent children.

Hypothesis: No differences exist between prepubescent boys and girls in lower limb strength, symmetry on single-legged hop testing, and limb alignment during drop-jump testing.

Study Design: Cross-sectional study (prevalence); Level of evidence, 1.

Methods: The authors tested 27 female and 25 male athletes who were aged 9 to 10 years and matched for both body mass index and years of organized sports participation. In a drop-jump screening test, the distance between the right and left hips, knees, and ankles was measured as an indicator of lower limb axial alignment in the coronal plane. The distance between the knees and ankles was normalized by the hip separation distance. Quadriceps and hamstrings strengths were measured isokinetically at 180 deg/s. Lower limb symmetry was determined from 2 single-legged hop function tests.

Results: Boys demonstrated greater mean absolute and normalized knee and ankle separation distances on the drop-jump test. Even so, 76% of boys had a normalized knee separation distance of 60% or less of the hip separation distance, as did 93% of girls, indicating a distinctly valgus alignment. There were no differences between the sexes in quadriceps and hamstrings peak torques, hamstrings/quadriceps ratio, time to peak torque, total work, or lower limb symmetry values.

Conclusions: A high percentage of the prepubescent athletes studied had a distinctly valgus lower limb alignment during the drop-jump test and a lack of lower limb symmetry during the hop tests. These same indices have been hypothesized to increase the risk for knee ligament injuries in older athletes. Neuromuscular training may be needed to address these issues in children.

Neuromuscular Retraining in Female Adolescent Athletes: Effect on Athletic Performance Indices and Noncontact Anterior Cruciate Ligament Injury Rates

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Abstract: While many anterior cruciate ligament (ACL) prevention programs have been

published, few have achieved significant reductions in injury rates and improvements in

athletic performance indices; both of which may increase compliance and motivation of

athletes to participate. A supervised neuromuscular retraining program (18 sessions) was

developed, aimed at achieving both of these objectives. The changes in neuromuscular indices

were measured after training in 1000 female athletes aged 13–18 years, and the noncontact

ACL injury rate in 700 of these trained athletes was compared with that of 1120 control

athletes. There were significant improvements in the drop-jump test, (p < 0.0001, effect size

[ES] 0.97), the single-leg triple crossover hop (p < 0.0001, ES 0.47), the t-test

(p < 0.0001, ES 0.64), the multi-stage fitness test (p < 0.0001, ES 0.57), hamstring strength

(p < 0.0001), and quadriceps strength (p < 0.01). The trained athletes had a significant

reduction in the noncontact ACL injury incidence rate compared with the controls (1 ACL

injury in 36,724 athlete-exposures [0.03] and 13 ACL injuries in 61,244 exposures [0.21],

respectively, p = 0.03). The neuromuscular retraining program was effective in reducing

noncontact ACL injury rate and improving athletic performance indicators.

Factors Used to Determine Return to Unrestricted Sports Activity After ACL Reconstruction

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Purpose: Anterior cruciate ligament (ACL) reconstruction is commonly performed in athletes, with

the goal of return to sports activities. Unfortunately, this operation may fail, and the rates of either

reinjuring an ACL-reconstructed knee or sustaining an ACL rupture to the contralateral knee range

from 3% to 49%. One problem that exists is a lack of information and consensus regarding the

appropriate criteria for releasing patients to unrestricted sports activities postoperatively. The purpose

of this study was to determine the published criteria used to allow athletes to return to unrestricted

sports activities after ACL reconstruction. Methods: A systematic search was performed to identify

the factors investigators used to determine when return to athletics was allowed after primary ACL

reconstruction. Inclusion criteria were English language, publication within the last 10 years, clinical

trial, all adult patients, primary ACL reconstruction, original research investigation, and minimum 12

months’ follow-up. Results: Of 716 studies identified, 264 met the inclusion criteria. Of these, 105

(40%) failed to provide any criteria for return to sports after ACL reconstruction. In 84 studies (32%)

the amount of time postoperatively was the only criterion provided. In 40 studies (15%) the amount

of time along with subjective criteria were given. Only 35 studies (13%) noted objective criteria

required for return to athletics. These criteria included muscle strength or thigh circumference (28

studies), general knee examination (15 studies), single-leg hop tests (10 studies), Lachman rating (1

study), and validated questionnaires (1 study). Conclusions: The results of this systematic review

show noteworthy problems and a lack of objective assessment before release to unrestricted sports

activities. General recommendations are made for quantification of muscle strength, stability,

neuromuscular control, and function in patients who desire to return to athletics after ACL reconstruction,

with acknowledgment of the need for continued research in this area. Level of Evidence:

Level IV, systematic review of Level I to IV studies.

The Drop-Jump Screening Test

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Background: A valgus lower limb alignment has been noted during noncontact anterior cruciate ligament injuries. A video drop jump test can indicate an athlete’s ability to control lower limb axial alignment in the coronal plane.

Hypotheses: Female athletes have decreased knee separation distances on landing and acceleration; male athletes have a neutrally aligned lower limb position. A neuromuscular training program will significantly increase knee separation distance in female athletes.

Study Design: Cohort study; Level of evidence, 2.

Methods: The authors tested 325 female and 130 male athletes aged 11 to 19 years. The distance between the hips, knees, and ankles was measured during a drop-jump test. The separation distance between the knees and ankles was normalized by the hip separation distance. A neuromuscular training program (Sportsmetrics) was completed by 62 female athletes, and their jump-landing characteristics were reexamined.

Results: A marked decrease in knee separation distance was found on takeoff in 80% of female athletes and in 72% of male athletes. There was no difference between male and female athletes in the normalized knee and ankle separation distance during the landing and takeoff phases. The knee separation distance on landing was 23 ± 9 cm in the female athletes and 22 ± 8 cm in the male athletes. The normalized knee separation distance was 51% ± 19% in the female athletes and 51% ± 15% in the male athletes. After training, statistically significant increases were found in the female athletes in the knee separation distance on landing (29 ± 8 cm, P < .0001) and in the normalized knee separation distance (68% ± 18%, P < .0001). The trained female athletes had significantly greater knee separation distance and normalized knee separation distance than did the males (P < .0001).

Conclusions: The majority of untrained female and male athletes demonstrated a valgus alignment appearance on the video test. After neuromuscular training, female athletes had improved knee separation distances and a more neutral lower limb alignment on landing and takeoff.

Effect of Fatigue Protocols on Lower Limb Neuromuscular Function and Implications for Anterior Cruciate Ligament Injury Prevention Training

Fatigue AJSM 2017

Background: Approximately two-thirds of anterior cruciate ligament (ACL) tears are sustained during noncontact situations when an athlete is cutting, pivoting, decelerating, or landing from a jump. Some investigators have postulated that fatigue may result in deleterious alterations in lower limb biomechanics during these activities that could increase the risk of noncontact ACL injuries.  However, prior studies have noted a wide variation in fatigue protocols, athletic tasks studied, and effects of fatigue on lower limb kinetics and kinematics.

Purpose: First, to determine if fatigue uniformly alters lower limb biomechanics during athletic tasks that are associated with non contact ACL injuries. Second, to determine if changes should be made in ACL injury prevention training programs to alter the deleterious effects of fatigue on lower limb kinetics and kinematics.

Study Design: Systematic review; Level of evidence, 4.

Methods: A systematic review of the literature using MEDLINE was performed. Key terms were fatigue, neuromuscular, exercise, hop test, and single-legged function tests. Inclusion criteria were original research studies involving healthy participants, use of a fatigue protocol, study of at least 1 lower limb task that involved landing from a hop or jump or cutting, and analysis of at least 1 biomechanical variable.

Results: Thirty-seven studies involving 806 athletes (485 female, 321 male; mean age, 22.7 years) met the inclusion criteria. General fatigue protocols were used in 20 investigations, peripheral protocols were used in 17 studies, and 21 different athletic tasks were studied (13 single-legged, 8 double-legged). There was no consistency among investigations regarding the effects of fatigue on hip, knee, or ankle joint angles and moments or surface electromyography muscle activation patterns. The fatigue protocols typically did not produce statistically significant changes in ground-reaction forces.

Conclusion: Published fatigue protocols did not uniformly produce alterations in lower limb neuromuscular factors that heighten the risk of noncontact ACL injuries. Therefore, justification does not currently exist for major changes in ACL injury prevention training programs to account for potential fatigue effects. However, the effect of fatigue related to ACL injuries is worthy of further investigation, including the refinement of protocols and methods of analysis.

Neuromuscular Retraining Intervention Programs Systematic Review

Neuro Train Arthr 2014

Purpose: The purpose of this study was to identify neuromuscular training intervention programs that significantly reduced the incidence of noncontact anterior cruciate ligament (ACL) injury rates in female adolescent athletes.

Methods: A systematic search of PubMed was conducted to determine the outcome of ACL neuromuscular retrainingprograms in a specific population. The inclusion criteria were English language, published from 1994-2013, original clinical trials, all evidence levels, female athletes aged 19 years or younger, and noncontact ACL injury incidence rates determined by athlete-exposures.

Results: Of 694 articles identified, 8 met the inclusion criteria. Three training programs significantly reduced noncontact ACL injury incidence rates in female adolescent athletes. These were the Sportsmetrics, Prevent Injury and Enhance Performance, and Knee Injury Prevention programs. The estimated number of athletes who needed to train to prevent 1 ACL injury in these 3 studies ranged from 70 to 98, and the relative risk reduction ranged from 75% to 100%. Five programs did not significantly reduce noncontact ACL injury incidence rates. The ACL injury incidence rates for control subjects were lower in these studies (0.03 to 0.08 per 1,000 athlete-exposures) than in those investigations that had a significant effect (0.21 to 0.49 per 1,000 athlete-exposures). There was wide variability among all programs in the frequency, duration, and timing of training; how training was conducted, supervised, or controlled; the components of the program; how exposure data were calculated; noncontact ACL injury incidence rates in the control
groups; and compliance with training. Conclusions: Three ACL intervention programs successfully reduced noncontact ACL injury incidence rates in female adolescent athletes. Pooling of data of all ACL intervention programs is not recommended because of numerous methodologic differences among studies.

Level of Evidence: Level II, systematic review of Level I and II studies.

Sportsmetrics Soccer Program Results

Noyes, FR, Barber-Westin, SD, Smith, ST, and Campbell, T.

A training program to improve neuromuscular and performance indices in female high school soccer players. J Strength Cond Res 27(2): 340–351, 2013

Sportsmetrics Soccer Paper, JSCR 2013

The purpose of this study was to determine if a sports-specific anterior cruciate ligament injury prevention training program could improve neuromuscular and performance indices in female high school soccer players. We combined components from a published knee ligament intervention program for jump and strength training with other exercises and drills to improve speed, agility, overall strength, and aerobic fitness. We hypothesized that this program would significantly improve neuromuscular and athletic performance indices in high school female soccer players. The supervised 6-week program was done 3 d·wk for 90–120 minutes per session on the soccer fields and weight room facilities in area high schools. In phase 1, 62 athletes underwent a video drop jump test, t-test, 2 vertical jump tests, and a 37-m sprint test before and upon completion of the training program. In phase 2, 62 other athletes underwent a multistage fitness test before and after training. There were significant improvements in the mean absolute knee separation distance (p , 0.0001), mean absolute ankle separation distance (p , 0.0001), and mean normalized knee separation distance (p , 0.0001) on the drop-jump, indicating a more neutral lower limb alignment on landing. Significant improvements were found in the t-test (p , 0.0001), estimated maximal aerobic power (p , 0.0001), 37-m sprint test (p = 0.02), and in the 2-step approach vertical jump test (p = 0.04). This is the first study we are aware of that demonstrated the effectiveness of a knee ligament injuryprevention training program in improving athletic performance indices in high school female soccer players. Future studies will determine if these findings improve athlete compliance and team participation in knee ligament injury intervention training.

Objective Criteria for Return to Athletics

Sue D. Barber-Westin, BS and Frank R. Noyes, MD

Obj Criteria Return to Athletics, PhysSM 2011

Abstract

Objective: To review anterior cruciate ligament (ACL) clinical studies to assess the objective functional criteria used to determine when patients can return to athletics postoperatively, and to determine the rates of reinjury to either knee when these criteria are applied. Methods: A literature search was conducted using the Medline database. The inclusionary criteria were the English language, publication between April 2001 and April 2011, original clinical trials, all levels of evidence, primary ACL reconstruction, skeletal maturity, minimum 2 years of follow-up, and >1 objective test used to allow release to sports activities. The exclusionary criteria were revision ACL reconstructions or dislocated knees; studies that specifically excluded patients with ACL graft failure or reinjuries; major concomitant procedures such as high tibial osteotomy, meniscus allograft, other knee ligament reconstructions; and case reports, abstracts, review articles, and technical notes. Results: Three objective criteria were used to allow release to sports activities. The most common were lower extremity muscle strength, followed by lower limb symmetry and knee examination parameters of range of knee motion and effusion. Twelve studies listed 1 criterion for release to sports, 8 studies listed 2 criteria, and 1 study recommended 3 criteria. Failure rates of the ACL reconstructions raged from 0% to 3% in 7 studies, from 4% to 6% in 6 studies, from 7% to 10% in 4 studies, and from 14% to 24 % in 4 studies. There were no injuries in the contralateral ACL in 14 studies (67%); in the other 7 studies, contralateral injury was reported in 2% to 15% of patients. Conclusions: Few objective functional criteria are used to determine when patients return to unrestricted sports activities. Clinically feasible recommendations are made for measurement of muscle strength, lower limb symmetry, lower limb neuromuscular control, and ligament function in patients who desire to return to athletics after ACL reconstruction. Future studies are required to determine whether the demonstration of normal lower limb function before return to sports is effective in reducing reinjury rates.