Jensen L. Brent

The effects of plyometric vs. dynamic stabilization and balance training on power, balance, and landing force in female athletes.

Neuromuscular training protocols that include both plyometrics and dynamic balance exercises can significantly improve biomechanics and neuromuscular performance and reduce anterior cruciate ligament injury risk in female athletes. The purpose of this study was to compare the effects of plyometrics (PLYO) versus dynamic stabilization and balance training (BAL) on power, balance, strength, and landing force in female athletes. Either PLYO or BAL were included as a component of a dynamic neuromuscular training regimen that reduced measures related to ACL injury and increased measures of performance. Nineteen high school female athletes participated in training 3 times a week for 7 weeks. The PLYO (n = 8) group did not receive any dynamic balance exercises and the BAL (n = 11) group did not receive any maximum effort jumps during training. Pretraining vs. post-training measures of impact force and standard deviation of center of pressure (COP) were recorded during a single leg hop and hold. Subjects were also tested for training effects in strength (isokinetic and isoinertial) and power (vertical jump). The percent change from pretest to posttest in vertical ground reaction force was significantly different between the BAL and PLYO groups on the dominant side (p < 0.05). Both groups decreased their standard deviation of center of pressure (COP) during hop landings in the medial/lateral direction on their dominant side, which equalized pretested side to side differences. Both groups increased hamstrings strength and vertical jump. The results of this study suggest that both PLYO and BAL training are effective at increasing measures of neuromuscular power and control. A combination of PLYO and BAL training may further maximize the effectiveness of preseason training for female athletes.

Utilization of Modified NFL Combine Testing to Identify Functional Deficits in Athletes Following ACL Reconstruction

STUDY DESIGN Case control. OBJECTIVES To use modified NFL Combine testing methodology to test for functional deficits in athletes following anterior cruciate ligament (ACL) reconstruction following return to sport. BACKGROUND There is a need to develop objective, performance-based, on-field assessment methods designed to identify potential lower extremity performance deficits and related impairments in this population. METHODS Eighteen patients (mean ± SD age, 16.9 ± 2.1 years; height, 170.0 ± 8.7 cm; body mass, 71.9 ± 21.8 kg) who returned to their sport within a year following ACL reconstruction (95% CI: 7.8 to 11.9 months from surgery) participated (ACLR group). These individuals were asked to bring 1 or 2 teammates to serve as control participants, who were matched for sex, sport, and age (n = 20; mean ± SD age, 16.9 ± 1.1 years; height, 169.7 ± 8.4 cm; body mass, 70.1 ± 20.7 kg). Functional performance was tested using the broad jump, vertical jump, modified long shuttle, modified pro shuttle, modified agility T-test, timed hop, triple hop, single hop, and crossover hop tests. A 1-way multivariate analysis of variance (MANOVA) was used to evaluate group differences for dependent performance variables. RESULTS The functional performance measurements of skills requiring bilateral involvement of both lower extremities showed no group differences between the ACLR and control groups (P>.05). An overall group difference (P = .006) was observed for the combined limb symmetry index (LSI) measures. However, the modified double-limb performance tasks (long shuttle, modified agility T-test, and pro shuttle) were not, independently, sufficiently sensitive to detect limb deficits in individuals with ACL reconstruction. Conversely, the LSI on the distance measures of the single-limb performance tasks all provided moderate to large effect sizes to differentiate between the ACLR and control groups, as the individuals who had ACL reconstruction demonstrated involved limb deficits on all measures (P<.05). Finally, the LSI for the timed hop test was not different between groups (P>.05). CONCLUSIONS These findings indicate that, while unilateral deficits are present in individuals following ACL reconstruction, they may not be evident during bipedal performance or during modified versions of double-limb performance activities. Isolation of the involved limb with unilateral hopping tasks should be used to identify deficits in performance.

A pilot study to determine the effect of trunk and hip focused neuromuscular training on hip and knee isokinetic strength

Objective: The objective was to determine the effect of trunk focused neuromuscular training (TNMT) on hip and knee strength. The hypothesis was that TNMT would increase standing isokinetic hip abduction, but not knee flexion/extension, strength. Methods: 21 high-school female volleyball players (14 TMNT, mean age 15.4 (1.4) years, weight 170.5 (5.0) cm, height 64.1 (8.5) kg and 7 controls, mean age 16.0 (1.7) years, height 173.4 (10.0) cm, weight 63.9 (5.3) kg; p>0.05) were recruited to participate in this study. The 14 TNMT subjects participated in a TNMT protocol (twice weekly) over a 10 week period in addition to their standard once-weekly off-season strength training. Standing isokinetic hip abduction strength and seated knee flexion/extension strength were measured before and after TNMT. Results: A significant interaction of group and time was observed. The TNMT group increased isokinetic hip abduction strength approximately 15% (13.5% in the dominant leg: mean (SD) 46.6 (10.1) to 52.9 (11.4) foot-pounds and 17.1% in the non-dominant leg: 46.1 (10.4) to 54.0 (10.7) foot-pounds; p = 0.01). There was no difference in the control group in pre-test versus post-test measures. Post-test results also indicated no effect of TNMT on isokinetic knee extension (p = 0.57) or knee flexion (p = 0.57) strength. Conclusions: Ten weeks of TNMT increased standing hip abduction strength in female athletes. Increased hip abduction strength and recruitment may improve the ability of female athletes to increase control of lower limb alignment and decrease knee loads resulting from increased trunk displacement during sports activities.

Real-time assessment and neuromuscular training feedback techniques to prevent ACL injury in female athletes.

SOME ATHLETES MAY BE MORE SUSCEPTIBLE TO AT-RISK KNEE POSITIONS DURING SPORTS ACTIVITIES, BUT THE UNDERLYING CAUSES ARE NOT CLEARLY DEFINED. THIS ARTICLE SYNTHESIZES IN VIVO, IN VITRO, AND IN SILICO (COMPUTER-SIMULATED) DATA TO DELINEATE LIKELY RISK FACTORS TO THE MECHANISM(S) OF NONCONTACT ANTERIOR CRUCIATE LIGAMENT (ACL) INJURIES. FROM THESE IDENTIFIED RISK FACTORS, WE WILL DISCUSS NEWLY DEVELOPED REAL-TIME SCREENING TECHNIQUES THAT CAN BE USED IN TRAINING SESSIONS TO IDENTIFY MODIFIABLE RISK FACTORS. TECHNIQUES PROVIDED WILL TARGET AND CORRECT ALTERED MECHANICS THAT MAY REDUCE OR ELIMINATE RISK FACTORS AND AID IN THE PREVENTION OF NONCONTACT ACL INJURIES IN HIGH-RISK ATHLETES.

Augmented Feedback Supports Skill Transfer and Reduces High-Risk Injury Landing Mechanics A Double-Blind, Randomized Controlled Laboratory Study

Background: There is a current need to produce a simple, yet effective method for screening and targeting possible deficiencies related to increased anterior cruciate ligament (ACL) injury risk. Hypothesis: Frontal plane knee angle (FPKA) during a drop vertical jump will decrease upon implementing augmented feedback into a standardized sport training program. Study Design: Controlled laboratory study. Methods: Thirty-seven female participants (mean ± SD: age, 14.7 ± 1.5 years; height, 160.9 ± 6.8 cm; weight, 54.5 ± 7.2 kg) were trained over 8 weeks. During each session, each participant received standardized training consisting of strength training, plyometrics, and conditioning. They were also videotaped running on a treadmill at a standardized speed and performing a repeated tuck jump for 10 seconds. Study participants were randomized into 2 groups and received augmented feedback on either their jumping (AF) or sprinting (CTRL) form. Average (mean of 3 trials) and most extreme (trial with greatest knee abduction) FPKA were calculated from 2-dimensional video captured during performance of the drop vertical jump. Results: After testing, a main effect of time was noted, with the AF group reducing their FPKA average by 37.9% over the 3 trials while the CTRL group demonstrated a 26.7% reduction average across the 3 trials (P < .05). Conversely, in the most extreme drop vertical jump trial, a significant time-by-group interaction was noted (P < .05). The AF group reduced their most extreme FPKA by 6.9° (pretest, 18.4° ± 12.3°; posttest, 11.4° ± 10.1°) on their right leg and 6.5° (pretest, 16.3° ± 14.5°; posttest, 9.8° ± 10.7°) on their left leg, which represented a 37.7% and 40.1% reduction in FPKA, respectively. In the CTRL group, no similar changes were noted in the right (pretest, 16.9° ± 14.3°; posttest, 14.0° ± 12.3°) or left leg (pretest, 9.8° ± 11.1°; posttest, 7.2° ± 9.2°) after training. Conclusion: Providing athletes with augmented feedback on deficits identified by the tuck jump assessment has a positive effect on their biomechanics during a different drop vertical jump task that is related to increased ACL injury risk. The ability of the augmented feedback to support the transfer of skills and injury risk factor reductions across different tasks provides exciting new evidence related to how neuromuscular training may ultimately cross over into retained biomechanics that reduce ACL injuries during sport. Clinical Relevance: The tuck jump assessment’s ease of use makes it a timely and economically favorable method to support ACL prevention strategies in young girls.

PREDICTORS OF SPRINT START SPEED: THE EFFECTS OF RESISTIVE GROUND-BASED VS. INCLINED TREADMILL TRAINING

There is currently no consensus with regard to the most effective method to train for improved acceleration, or with regard to which kinematic variable provides the greatest opportunity for improvement in this important performance characteristic. The purpose of this study was to determine the effects of resistive ground-based speed training and incline treadmill speed training on speed-related kinematic measures and sprint start speed. The hypothesis tested was that incline treadmill training would improve sprint start time, while the ground-based resistive training would not. Corollary hypotheses were that treadmill training would increase stride frequency and ground-based training would not affect kinematics during the sprint start. Thirty-one high school female soccer players (15.7 ± 0.5 years) were assigned to either treadmill (n = 17) or ground-based (n = 14) training groups and trained 2 times a week for 6 weeks. The treadmill group utilized incline speed training on a treadmill, while the ground-based group utilized partner band resistance ground-based techniques. Three-dimensional motion analysis was used (4.5 m mark) before and after training to quantify kinematics during the fastest of 3 recorded sprint starts (9.1 m). Both groups decreased average sprint start time from 1.75 ± 0.12 to 1.68 ± 0.08 seconds (p > 0.001). Training increased stride frequency (p = 0.030) but not stride length. After training, total vertical pelvic displacement and stride length predicted 62% of the variance in sprint start time for the resistive ground-based group, while stride length and stride frequency accounted for 67% prediction of the variance in sprint start time for the treadmill group. The results of this study indicate that both incline treadmill and resistive ground-based training are effective at improving sprint start speed, although they potentially do so through differing mechanisms.

The back squat: A proposed assessment of functional deficits and technical factors that limit performance

ABSTRACT FUNDAMENTAL MOVEMENT COMPETENCY IS ESSENTIAL FOR PHYSICAL ACTIVITY PARTICIPATION AND FOR REDUCING INJURY RISK, WHICH ARE BOTH KEY ELEMENTS OF HEALTH PROMOTION. THE SQUAT MOVEMENT PATTERN IS ARGUABLY ONE OF THE MOST CRITICAL FUNDAMENTAL MOVEMENTS NECESSARY TO IMPROVE SPORT PERFORMANCE, TO REDUCE INJURY RISK, AND TO SUPPORT LIFELONG PHYSICAL ACTIVITY. BASED ON CURRENT EVIDENCE, THIS FIRST (1 OF 2) REPORT DECONSTRUCTS THE TECHNICAL PERFORMANCE OF THE BACK SQUAT AND PRESENTS A NOVEL DYNAMIC SCREENING TOOL THAT INCORPORATES IDENTIFICATION TECHNIQUES FOR KNOWN FUNCTIONAL DEFICITS. THE FOLLOW-UP REPORT WILL OUTLINE TARGETED CORRECTIVE METHODOLOGY FOR EACH OF THESE FUNCTIONAL DEFICITS.

How Young is "Too Young" to Start Training?

LEARNING OBJECTIVESTo introduce an integrative neuromuscular training model that can be used to enhance the health, fitness, and wellness of all children and adolescents.To understand the potential benefits associated with strength and conditioning programs implemented with youth to reduce injury risk and enhance motor skill development that will support a physically active lifestyle.To comprehend the concept of “training age” and the implications associated with systematic training beginning during early childhood.

Does an in-season only neuromuscular training protocol reduce deficits quantified by the tuck jump assessment?

BACKGROUND Female athletes are 4–6 times more likely to suffer an ACL injury than males in comparable sports. A link between landing biomechanics and ACL injury has led to the development of injury prevention focused training protocols. It is often difficult to measure the protocols’ efficacy of different protocols on reduction of ACL injury-related factors.

Hip and knee extensor moments predict vertical jump height in adolescent girls.

Ford, KR, Myer, GD, Brent, JL, and Hewett, TE. Hip and knee extensor moments predict vertical jump height in adolescent girls. J Strength Cond Res 23(4): 1327-1331, 2009-Biomechanical factors, such as hip and knee extensor moments, related to drop jump (DJ) performance have not been investigated in adolescent girls. The purpose of this study was to determine the key independent biomechanical variables that predict overall vertical jump performance in adolescent girls. Sixteen high school adolescent girls from club-sponsored and high school-sponsored volleyball teams performed DJ at 3 different drop heights (15, 30, and 45 cm). A motion analysis system consisting of 10 digital cameras and a force platform was used to calculate vertical jump height, joint angles, and joint moments during the tasks. A multiple linear regression was used to determine the biomechanical parameters that were best predictive of vertical jump height at each box drop distance. The 2 predictor variables in all 3 models were knee and hip extensor moments. The models predicted 82.9, 81.9, and 88% of the vertical jump height variance in the 15, 30, and 45 cm trials, respectively. The results of the investigation indicate that knee and hip joint moments are the main contributors to vertical jump height during the DJ in adolescent girls. Strength and conditioning specialists attempting to improve vertical jump performance should target power and strength training to the hip and knee extensors in their athletes.