Lindsay J. DiStefano

Integrated Injury Prevention Program Improves Balance and Vertical Jump Height in Children

DiStefano, LJ, Padua, DA, Blackburn, JT, Garrett, WE, Guskiewicz, KM, and Marshall, SW. Integrated injury prevention program improves balance and vertical jump height in children. J Strength Cond Res 24(2): 332-342, 2010-Implementing an injury prevention program to athletes under age 12 years may reduce injury rates. There is limited knowledge regarding whether these young athletes will be able to modify balance and performance measures after completing a traditional program that has been effective with older athletes or whether they require a specialized program for their age. The purpose of this study was to compare the effects of a pediatric program, which was designed specifically for young athletes, and a traditional program with no program in the ability to change balance and performance measures in youth athletes. We used a cluster-randomized controlled trial to evaluate the effects of the programs before and after a 9-week intervention period. Sixty-five youth soccer athletes (males: n = 37 mass = 34.16 ± 5.36 kg, height = 143.07 ± 6.27 cm, age = 10 ± 1 yr; females: n = 28 mass = 33.82 ± 5.37 kg, height = 141.02 ± 6.59 cm) volunteered to participate and attended 2 testing sessions in a research laboratory. Teams were cluster-randomized to either a pediatric or traditional injury prevention program or a control group. Change scores for anterior-posterior and medial-lateral time-to-stabilization measures and maximum vertical jump height and power were calculated from pretest and post-test sessions. Contrary with our original hypotheses, the traditional program resulted in positive changes, whereas the pediatric program did not result in any improvements. Anterior-posterior time-to-stabilization decreased after the traditional program (mean change ± SD = −0.92 ± 0.49 s) compared with the control group (−0.49 ± 0.59 s) (p = 0.003). The traditional program also increased vertical jump height (1.70 ± 2.80 cm) compared with the control group (0.20 ± 0.20 cm) (p = 0.04). There were no significant differences between control and pediatric programs. Youth athletes can improve balance ability and vertical jump height after completing an injury prevention program. Training specificity appears to affect improvements and should be considered with future program design.

Evidence Supporting Balance Training in Healthy Individuals: A Systemic Review

DiStefano, LJ, Clark, MA, and Padua, DA. Evidence supporting balance training in healthy individuals: a brief review. J Strength Cond Res 23(9): 2718-2731, 2009-Balance is considered a risk factor for several injuries and consequently a focus of many strengthening, injury prevention, and rehabilitation programs. There are several studies that have evaluated the ability of balance training to improve balance ability in a healthy population with no general consensus. We conducted a systematic review to evaluate the body of evidence regarding the effectiveness of balance training on improving various forms of balance ability in a healthy population. Three electronic databases and the reference lists of selected articles were searched. Studies were included that evaluated balance ability before and after healthy subjects performed a multisession balance training program. Two individuals reviewed all articles and agreed upon the selection criteria. Sixteen articles were selected, abstracted, and reviewed. Means and measures of variability were recorded to calculate effect sizes, and study quality was assessed using the PEDro instrument. There is strong evidence to suggest that balance training can improve static balance ability on stable and unstable surfaces, as well as dynamic balance ability. Elite athletes have the potential to improve static balance on an unstable surface and dynamic balance ability, but a ceiling effect appears to occur with stable balance ability on a stable surface. Balance training programs performed at least 10 minutes per day, 3 days per week, for 4 weeks that incorporate various methods of balance training appear to improve balance ability. Types of balance training included the use of tilt boards, unstable surfaces, and dynamic body movements while maintaining a static stance.

Retention of Movement Pattern Changes After a Lower Extremity Injury Prevention Program Is Affected by Program Duration

Background: Changes in movement patterns have been repeatedly observed immediately after completing a lower extremity injury prevention program. However, it is not known if movement pattern changes are maintained after discontinuing the training program. Hypothesis: The ability to maintain movement pattern changes after training has ceased may be influenced by the program’s duration. The authors hypothesized that among individuals who completed either a 3-month or 9-month training program and who demonstrated immediate movement pattern changes, only those who completed the 9-month training program would maintain movement pattern changes after a 3-month period of no longer performing the exercises. Study Design: Cohort study; Level of evidence, 2. Methods: A total of 140 youth soccer athletes from 15 separate teams volunteered to participate. Athletes’ movement patterns were assessed using the Landing Error Scoring System (LESS) at pretest, posttest, and 3 months after ceasing the program (retention test). Eighty-four of the original 140 participants demonstrated improvements in their LESS scores between pretest and posttest (change in LESS score >0) and were included in the final analyses for this study (n = 84; 20 boys and 64 girls; mean age, 14 ± 2 years; age range, 11-17 years). Teams performed 3-month (short-duration group) and 9-month (extended-duration group) injury prevention programs. The exercises performed were identical for both groups. Teams performed the programs as part of their normal warm-up routine. Results: Although both groups improved their total LESS scores from pretest to posttest, only the extended-duration training group retained their improvements 3 months after ceasing the injury prevention program (F2,137 = 3.38; P = .04). Conclusion: Results suggest that training duration may be an important factor to consider when designing injury prevention programs that facilitate long-term changes in movement control.

Effects of an Age-Specific Anterior Cruciate Ligament Injury Prevention Program on Lower Extremity Biomechanics in Children

Background: Implementing an anterior cruciate ligament injury prevention program to athletes before the age at which the greatest injury risk occurs (15-17 years) is important from a prevention standpoint. However, it is unknown whether standard programs can modify lower extremity biomechanics in pediatric populations or if specialized training is required. Hypothesis/Purpose: To compare the effects of traditional and age-specific pediatric anterior cruciate ligament injury prevention programs on lower extremity biomechanics during a cutting task in youth athletes. The authors hypothesized that the age-specific pediatric program would result in greater sagittal plane motion (ie, hip and knee flexion) and less motion in the transverse and frontal plane (ie, knee valgus, knee and hip rotation) as compared with the traditional program. Study Design: Randomized controlled trial; Level of evidence, 1. Methods: Sixty-five youth soccer athletes (38 boys, 27 girls) volunteered to participate. The mean age of participants was 10 ± 1 years. Teams (n, 7) were cluster randomized to a pediatric injury prevention program, a traditional injury prevention program, or a control group. The pediatric program was modified from the traditional program to include more feedback, progressions, and variety. Teams performed their programs as part of their normal warm-up routine. Three-dimensional lower extremity biomechanics were assessed during a sidestep cutting task before and after completion of the 9-week intervention period. Results: The pediatric program reduced the amount of knee external rotation at initial ground contact during the cutting task, F (2,62) = 3.79, P = .03 (change: pediatric, 7.73° ± 10.71°; control, –0.35° ± 7.76°), as compared with the control group after the intervention period. No other changes were observed. Conclusion: The injury prevention program designed for a pediatric population modified only knee rotation during the cutting task, whereas the traditional program did not result in any changes in cutting biomechanics. These findings suggest limited effectiveness of both programs for athletes younger than 12 years of age in terms of biomechanics during a cutting task.

Seven Steps for Developing and Implementing a Preventive Training Program: Lessons Learned from JUMP-ACL and Beyond

Musculoskeletal injuries during military and sport-related training are common, costly and potentially debilitating. Thus, there is a great need to develop and implement evidence-based injury prevention strategies to reduce the burden of musculoskeletal injury. The lack of attention to implementation issues is a major factor limiting the ability to successfully reduce musculoskeletal injury rates using evidence-based injury prevention programs. We propose 7 steps that can be used to facilitate successful design and implementation of evidence-based injury prevention programs within the logical constraints of a real-world setting by identifying implementation barriers and associated solutions. Incorporating these 7 steps along with other models for behavioral health interventions may improve the overall efficacy of military and sport-related injury prevention programs.

Quadriceps and Hamstrings Coactivation During Common Therapeutic Exercises

CONTEXT Anterior tibial shear force and knee valgus moment increase anterior cruciate ligament (ACL) loading. Muscle coactivation of the quadriceps and hamstrings influences anterior tibial shear force and knee valgus moment, thus potentially influencing ACL loading and injury risk. Therefore, identifying exercises that facilitate balanced activation of the quadriceps and hamstrings might be beneficial in ACL injury rehabilitation and prevention. OBJECTIVE To quantify and compare quadriceps with hamstrings coactivation electromyographic (EMG) ratios during commonly used closed kinetic chain exercises. DESIGN Cross-sectional study. SETTING Research laboratory. PATIENTS OR OTHER PARTICIPANTS Twenty-seven healthy, physically active volunteers (12 men, 15 women; age = 22.1 ± 3.1 years, height = 171.4 ± 10 cm, mass = 72.4 ± 16.7 kg). INTERVENTION(S) Participants completed 9 separate closed chain therapeutic exercises in a randomized order. MAIN OUTCOME MEASURE(S) Surface electromyography quantified the activity level of the vastus medialis (VM), vastus lateralis (VL), medial hamstrings (MH), and biceps femoris (BF) muscles. The quadriceps-to-hamstrings (Q:H) coactivation ratio was computed as the sum of average quadriceps (VM, VL) EMG amplitude divided by the sum of average hamstrings (MH, BF) EMG amplitude for each trial. We used repeated-measures analyses of variance to compare Q:H ratios and individual muscle contributions across exercises (α = .05), then used post hoc Tukey analyses. RESULTS We observed a main effect for exercise (F(3,79) = 22.6, P< .001). The post hoc Tukey analyses revealed smaller Q:H ratios during the single-limb dead lift (2.87 ± 1.77) than the single-limb squat (5.52 ± 2.89) exercise. The largest Q:H ratios were observed during the transverse-lunge (7.78 ± 5.51, P< .001), lateral-lunge (9.30 ± 5.53, P< .001), and forward-lunge (9.70 ± 5.90, P< .001) exercises. CONCLUSIONS The most balanced (smallest) coactivation ratios were observed during the single-limb dead-lift, lateral-hop, transverse-hop, and lateral band-walk exercises. These exercises potentially could facilitate balanced activation in ACL rehabilitation and injury-prevention programs. They also could be used in postinjury rehabilitation programs in a safe and progressive manner.

Hypohydration and hyperthermia impair neuromuscular control after exercise.

PURPOSE This study aimed to evaluate the effects of hypohydration and hyperthermia during exercise on movement technique and postural control. METHODS Twelve healthy men (age = 20 ± 2 yr, height = 182 ± 8 cm, mass = 74.0 ± 8.2 kg, V˙O2max = 57.0 ± 6.0 mL·kg·min; mean ± SD) completed four randomized test sessions: euhydrated temperate (EUT), euhydrated hot (EUH), hypohydrated temperate (HYT), and hypohydrated hot (HYH). Temperate and hot conditions were performed in 18.0°C ± 0.2°C, 50.0% ± 3.5% relative humidity, and 34.0°C ± 0.3°C, 45.0% ± 4.5% relative humidity, respectively. Movement technique and postural control were assessed before exercise (PRE), after exercise (POST), and after recovery (REC). Movement technique was evaluated using the Landing Error Scoring System (LESS). Postural control was assessed using the Balance Error Scoring System (BESS) and center-of-pressure sway velocity (SV) and elliptical sway area (ESA) during a dynamic balance test. The 90-min treadmill exercise protocol (1.34-1.78 m·s; 5% grade) required subjects to walk carrying a 20.5-kg rucksack. Subjects sat quietly in the test environment during a 60-min recovery period after exercise. Repeated-measures ANOVAs with a Tukey-HSD post hoc test evaluated differences between time and condition for dependent variables. RESULTS Exercise during HYH significantly increased LESS scores (PRE = 3.72 ± 1.73, POST = 4.42 ± 1.75) compared with HYT (3.75 ± 1.76) and EUH (3.61 ± 1.71) (P < 0.05). LESS scores remained elevated during REC for HYH compared with EUT (4.39 ± 1.47 vs 3.47 ± 2.05, P < 0.05). The HYH condition caused the greatest number of BESS errors (P = 0.02), largest ESA (P < 0.05), and highest SV (P = 0.02). Regardless of the condition, participants had the most BESS errors (P = 0.002) and highest SV (P = 0.003) during POST compared with the PRE and REC. CONCLUSIONS Hypohydration during exercise in the heat impairs neuromuscular control. These findings suggest that physical activity in the heat while dehydrated may affect parameters associated with a higher risk of injury.

A dynamic warm-up model increases quadriceps strength and hamstring flexibility.

Abstract Aguilar, AJ, DiStefano, LJ, Brown, CN, Herman, DC, Guskiewicz, KM, and Padua, DA. A dynamic warm-up model increases quadriceps strength and hamstring flexibility. J Strength Cond Res 26(4): 1130–1141, 2012—Research suggests that static stretching can negatively influence muscle strength and power and may result in decreased functional performance. The dynamic warm-up (DWU) is a common alternative to static stretching before physical activity, but there is limited research investigating the effects of a DWU. The purpose of this study was to compare the acute effects of a DWU and static stretching warm-up (SWU) on muscle flexibility, strength, and vertical jump using a randomized controlled trial design. Forty-five volunteers were randomly assigned into a control (CON), SWU, or DWU group. All participants rode a stationary bicycle for 5 minutes and completed a 10-minute warm-up protocol. During this protocol, the DWU group performed dynamic stretching and running, the SWU group performed static stretching, and the CON group rested. Dependent variables were measured immediately before and after the warm-up protocol. A digital inclinometer measured flexibility (degrees) for the hamstrings, quadriceps, and hip flexor muscles. An isokinetic dynamometer measured concentric and eccentric peak torque (N·m/kg) for the hamstrings and quadriceps. A force plate was used to measure vertical jump height (meters) and power (watts). In the DWU group, there was a significant increase in hamstring flexibility (pretest: 26.4 ± 13.5°, posttest: 16.9 ± 9.4°; p < .0001) and eccentric quadriceps peak torque (pretest: 2.49 ± 0.83 N·m/kg, posttest: 2.78 ± 0.69 N·m/kg; p = 0.04). The CON and SWU did not significantly affect any flexibility, strength, or vertical jump measures (p > 0.05). The DWU significantly improved eccentric quadriceps strength and hamstrings flexibility, whereas the SWU did not facilitate any positive or negative changes in muscle flexibility, strength, power, or vertical jump. Therefore, the DWU may be a better preactivity warm-up choice than an SWU.

Effects of resistance training fatigue on joint biomechanics.

Abstract Hooper, DR, Szivak, TK, DiStefano, LJ, Comstock, BA, Dunn-Lewis, C, Apicella, JM, Kelly, NA, Creighton, BC, Volek, JS, Maresh, CM, and Kraemer, WJ. Effects of resistance training fatigue on joint biomechanics. J Strength Cond Res 27(1): 146–153, 2013—Resistance training has been found to have a multitude of benefits. However, when performed with short rest, resistance training can result in substantial fatigue, which may have a negative impact on exercise technique. The purpose of this study is to examine the effects of fatigue from resistance exercise on joint biomechanics to determine what residual movement effects may exist after the workout. Twelve men with at least 6 months of resistance training experience (age 24 ± 4.2 years, height 173.1 ± 3.6 cm, weight 76.9 ± 7.8 kg) performed 5 body weight squats before (pretest) and after (posttest) a highly fatiguing resistance training workout. Lower extremity biomechanics were assessed using a 3-dimensional motion analysis system during these squats. Peak angle, total displacement, and rate were assessed for knee flexion, trunk flexion, hip flexion, hip rotation, and hip adduction. Results showed a significant decrease in peak angle for knee flexion (Pre: 120.28 ± 11.93°, Post: 104.46 ± 9.85°), hip flexion (Pre: −109.42 ± 12.49°, Post: −95.8 ± 12.30°), and hip adduction (Pre: −23.32 ± 7.04°, Post: −17.30 ± 8.79°). There was a significant reduction in angular displacement for knee flexion (Pre: 115.56 ± 10.55°, Post: 103.35 ± 10.49°), hip flexion (Pre: 97.94 ± 10.69°, Post: 90.51 ± 13.22°), hip adduction (Pre: 17.79 ± 7.36°, Post: 11.89 ± 4.34°), and hip rotation (Pre: 30.72 ± 12.28, Post: 20.48 ± 10.12). There was also a significant reduction in displacement rate for knee flexion (Pre: 2.20 ± 0.20, Post: 1.98 ± 0.20), hip flexion (Pre: 1.92 ± 0.20, Post: 1.76 ± 0.27), hip adduction (Pre: −0.44 ± 0.17, Post: −0.31 ± 0.17), and hip rotation (Pre: 0.59 ± 0.23, Post: 0.38 ± 0.21). This study demonstrated that there are lasting residual effects on movement capabilities after a high-intensity short rest protocol. Thus, strength and conditioning coaches must be careful to monitor movements and exercise techniques after such workouts to prevent injury and optimize subsequent exercise protocols that might be sequenced in order.

COMPARISON OF INTEGRATED AND ISOLATED TRAINING ON PERFORMANCE MEASURES AND NEUROMUSCULAR CONTROL

Abstract DiStefano, LJ, DiStefano, MJ, Frank, BS, Clark, MA, and Padua, DA. Comparison of integrated and isolated training on performance measures and neuromuscular control. J Strength Cond Res 27(4): 1083–1090, 2013—Traditional weight training programs use an exercise prescription strategy that emphasizes improving muscle strength through resistance exercises. Other factors, such as stability, endurance, movement quality, power, flexibility, speed, and agility are also essential elements to improving overall functional performance. Therefore, exercises that incorporate these additional elements may be beneficial additions to traditional resistance training programs. The purpose of the study was to compare the effects of an isolated resistance training program (ISO) and an integrated training program (INT) on movement quality, vertical jump height, agility, muscle strength and endurance, and flexibility. The ISO program consisted of primarily upper and lower extremity progressive resistance exercises. The INT program involved progressive resistance exercises, and core stability, power, and agility exercises. Thirty subjects were cluster randomized to either the ISO (n = 15) or INT (n = 15) training program. Each training group performed their respective programs 2 times per week for 8 weeks. The subjects were assessed before (pretest) and after (posttest) the intervention period using the following assessments: a jump-landing task graded using the Landing Error Scoring System (LESS), vertical jump height, T-test time, push-up and sit-up performance, and the sit-and-reach test. The INT group performed better on the LESS test (pretest: 3.90 ± 1.02, posttest: 3.03 ± 1.02; p = 0.02), faster on the T-test (pretest: 10.35 ± 1.20 seconds, posttest: 9.58 ± 1.02 seconds; p = 0.01), and completed more sit-ups (pretest: 40.20 ± 15.01, posttest: 46.73 ± 14.03; p = 0.045) and push-ups (pretest: 40.67 ± 13.85, posttest: 48.93 ± 15.17; p = 0.05) at posttest compared with pretest, and compared with the ISO group at posttest. Both groups performed more push-ups (p = 0.002), jumped higher (p < 0.001), and reached further (p = 0.008) at posttest compared with that at pretest. Performance enhancement programs should use an integrated approach to exercise selection to optimize performance and movement technique benefits.