Longitudinal Changes in Hip Strength and Range of Motion in Female Youth Soccer Players: Implications for ACL Injury, A Pilot Study.

CONTEXT: Risk of anterior cruciate ligament (ACL) injuries in young female athletes increases with age, appearing to peak during maturation. Changes in hip muscle strength and range of motion (ROM) during this time may contribute to altered dynamic movement patterns that are known to increase risk of ACL injuries. Understanding the longitudinal changes in hip strength and ROM is needed to develop appropriate interventions to reduce the risk of ACL injuries. OBJECTIVE: To examine the longitudinal changes in hip strength and ROM in female youth soccer players. DESIGN: Longitudinal descriptive study. SETTING: Field setting. PARTICIPANTS: 14 female youth soccer athletes (14.1 ± 1.1 y, 165.8 ± 5.3 cm, 57.5 ± 9.9 kg) volunteered as part of a multiyear risk factor screening project. MAIN OUTCOME MEASURES: Clinical measures of hip strength and ROM were collected annually over 3 consecutive years. Passive hip internal rotation (IR), external rotation (ER), abduction (ABD), and adduction (ADD) ROM were measured with a digital inclinometer. Isometric hip ABD and extension (EXT) strength were evaluated using a hand-held dynamometer. Separate repeated-measures ANOVAs compared hip strength and ROM values across 3 consecutive years (P < .05). RESULTS: As youth female soccer players increased in age, there were no changes in normalized hip ABD (P = .830) or EXT strength (P = .062) across 3 consecutive years. Longitudinal changes in hip ROM were observed with increases in hip IR (P = .001) and ABD (P < .001), while hip ADD (P = .009) and ER (P < .001) decreased. CONCLUSIONS: Anatomical changes at the hip occur as youth female soccer players increase in age. While there are no changes in hip strength, there is an increase in hip IR and ABD ROM with a concomitant decrease in hip ER and ADD ROM. The resulting asymmetries in hip ROM may decrease the activation and force producing capabilities of the hip muscles during dynamic activities, contributing to altered lower extremity mechanics known to increase the risk of ACL injuries.

Sustained Improvements in Dynamic Balance and Landing Mechanics After a 6-Week Neuromuscular Training Program in College Women's Basketball Players.

CONTEXT: Epidemiological data demonstrate the need for lower-extremity injury-prevention training. Neuromuscular-control (NMC) programs are immediately effective at minimizing lower-extremity injury risk and improving sport-related performance measures. Research investigating lasting effects after an injury-prevention program is limited. OBJECTIVE: To determine whether dynamic balance, landing mechanics, and hamstring and quadriceps strength could be improved after a 6-wk NMC intervention and maintained for a season. DESIGN: Prospective case series. SETTING: Controlled laboratory. PARTICIPANTS: 11 Division I women's basketball players (age 19.40 ± 1.35 y, height 178.05 ± 7.52 cm, mass 72.86 ± 10.70 kg). INTERVENTIONS: Subjects underwent testing 3 times, completing the Star Excursion Balance Test (SEBT), Landing Error Scoring System (LESS), and isometric strength testing for the hamstrings and quadriceps muscles. Pretest and posttest 1 occurred immediately before and after the intervention, respectively, and posttest 2 at the end of the competitive season, 9 mo after posttest 1. Subjects participated in eighteen 30-min plyometric and NMC-training sessions over a 6-wk period. MAIN OUTCOME MEASURES: The normalized SEBT composite score, normalized peak isometric hamstrings:quadriceps (H:Q) ratio, and the LESS total score. RESULTS: The mean composite reach significantly improved over time (F2,10 = 6.96, P = .005) where both posttest scores were significantly higher than pretest (70.41% ± 4.08%) (posttest 1 73.48% ± 4.19%, t10 = -3.11, P = .011) and posttest 2 (74.2% ± 4.77%, t10 = -3.78, P = .004). LESS scores significantly improved over time (F2,10 = 6.29, P = .009). The pretest LESS score (7.30 ± 3.40) was higher than posttest 1 (4.9 ± 1.20, t10 = 2.71, P = .024) and posttest 2 (5.44 ± 1.83, t10 = 2.58, P = .030). There were no statistically significant differences (P > .05) over time for the H:Q ratio when averaging both legs (F2,10 = 0.83, P = .45). CONCLUSIONS: A 6-wk NMC program improved landing mechanics and dynamic balance over a 9-mo period in women's basketball players. NMC adaptations can be retained without an in-season maintenance program.

Intrarater reliability of the functional movement screen.

The Functional Movement Screen (FMS) is a tool that quantifies movement patterns as a way to detect performance asymmetries. Although previous study has investigated the reliability of FMS, no current research has examined intrarater reliability or how clinical experience plays a role in the reliability of this tool. In this controlled laboratory study design, repeated measures were used to investigate how experience using the FMS and clinical experience as an athletic trainer (AT) affects the intrarater reliability of FMS testing. Before the data collection, 3 individuals recruited from the university community provided signed informed consent to serve as videotaped models performing the FMS test. The participants (raters) in the study, with different levels of FMS and clinical experience, viewed each of the 3 videotaped models and rated the video models on each exercise of the FMS according to the script that was presented by one of the study investigators. A week later, the participants watched the same videos again, in a different randomized order, and rated each video model on each exercise. After the scores from the participants were collected from both sessions, the intersession scores of the FMS were examined to establish intrarater reliability of all the participants. Additionally, the intrarater reliability of different groups of clinicians and students was compared to make inferences about the influence of clinical experience as an AT along with previous experience using the FMS. The ATs with at least 6 months of experience using the FMS (ATExp group) had the strongest intrarater reliability [intraclass correlation coefficients, ICC (2,1): 0.946], followed by the AT group with moderate reliability [ICC (2,1): 0.771]. This study indicates that intrarater reliability is strong and seems to strengthen when the individuals have experience using the FMS in addition to clinical experience.

Relationship between gluteal muscle strength, corticospinal excitability, and jump-landing biomechanics in healthy women.

CONTEXT: Components of gluteal neuromuscular function, such as strength and corticospinal excitability, could potentially influence alterations in lower extremity biomechanics during jump landing. OBJECTIVE: To determine the relationship between gluteal muscle strength, gluteal corticospinal excitability, and jump-landing biomechanics in healthy women. SETTING: University laboratory. DESIGN: Descriptive laboratory study. PARTICIPANTS: 37 healthy women (21.08 ± 2.15 y, 164.8 ± 5.9 cm, 65.4 ± 12.0 kg). INTERVENTIONS: Bilateral gluteal strength was assessed through maximal voluntary isometric contractions (MVIC) using an isokinetic dynamometer. Strength was tested in the open chain in prone and side-lying positions for the gluteus maximus and gluteus medius muscles, respectively. Transcranial magnetic stimulation was used to elicit measures of corticospinal excitability. Participants then performed 3 trials of jump landing from a 30-cm box to a distance of 50% of their height, with an immediate rebound to a maximal vertical jump. Each jump-landing trial was video recorded (2-D) and later scored for errors. MAIN OUTCOME MEASURES: MVICs normalized to body mass were used to assess strength in the gluteal muscles of the dominant and nondominant limbs. Corticospinal excitability was assessed by means of active motor threshold (AMT) and motor-evoked potentials (MEP) elicited at 120% of AMT. The Landing Error Scoring System (LESS) was used to evaluate jump-landing biomechanics. RESULTS: A moderate, positive correlation was found between dominant gluteus maximus MEP and LESS scores (r = .562, P = .029). No other significant correlations were observed for MVIC, AMT, or MEP for the gluteus maximus and gluteus medius, regardless of limb. CONCLUSIONS: The findings suggest a moderate relationship between dominant gluteus maximus corticospinal excitability and a clinical measure of jump-landing biomechanics. Further research is required to substantiate the findings and expand our understanding of the central nervous system's role in athletic movement.

Inter-limb differences in quadriceps strength and volitional activation.

In this crossover study, we wished to determine if normalized inter-limb differences in strength differed from inter-limb differences in voluntary activation at 30°, 70°, and 90° of knee flexion. We also assessed the relationship between inter-limb differences in torque with the inter-limb differences in activation. Twenty-five healthy volunteers were used for final data analyses; the order of leg tested, joint angle, and measurement technique (isokinetic strength, voluntary activation) were randomly assigned. Quadriceps strength was measured isokinetically at 1.05 rad · s(-1), while quadriceps voluntary activation was assessed via the central activation ratio. Absolute values of inter-limb differences for both measures were calculated by subtracting the non-dominant leg values from those of the dominant leg. Inter-limb isokinetic strength differences were greater than inter-limb central activation ratio differences at all joint angles (P = 0.003). Interestingly, inter-limb deficits between measures were not strongly correlated, suggesting that these measurements may be evaluating completely different phenomena within the neuromuscular system. These measurement techniques may provide unique information regarding neuromuscular function, suggesting that researchers and clinicians must utilize information from both techniques to determine the true clinical nature of inter-limb deficits.

Effects of arthroscopic partial meniscectomy on quadriceps strength: a systematic review.

CONTEXT: Arthroscopic partial meniscectomy (APM) after meniscal tear has been widely accepted and associated with quick return to activity. Unfortunately, meniscectomy is associated with risk for knee osteoarthritis, which may be attributed to postsurgical quadriceps weakness. This has important implications, as the quadriceps play a prominent role in knee stabilization and energy attenuation in the lower extremity. OBJECTIVE: To determine the magnitude of interlimb quadriceps strength deficits in people with unilateral APM by systematically reviewing the current literature. EVIDENCE ACQUISITION: The Web of Knowledge databases were searched on September 22, 2010, using terms meniscus OR meniscectomy AND quadriceps strength OR quadriceps weakness. Included articles were written in English, reporting means and SDs of isokinetic peak torque at 60° and 180°/s for both limbs. EVIDENCE SYNTHESIS: Four articles were included in the final analysis. Effect sizes and 95% confidence intervals (CI) were calculated between limbs for periods less than 1 mo, 1-3 mo, 3-6 mo, and more than 6 mo. CONCLUSION: Homogeneous effect sizes indicate quadriceps weakness in the involved limb. Effects were strong at less than 1 mo (d = -1.01 to -1.62), while weak to strong effects were found for 1-3 mo (d = -0.40 to -8.04) and 3-6 mo (d = -0.40 to -5.11). Weak effects were found at more than 6 mo (d = -0.30 to -0.37). Definitive effects with a CI not crossing zero were found in 65% of the data. Although APM patients return to function within weeks after surgery, prolonged quadriceps strength deficits may increase the risk of knee-joint degeneration. Furthermore, evidence of bilateral dysfunction after unilateral injury may suggest that neuromuscular deficits post-APM are greater than the interlimb differences found in this review. Further research should be conducted to determine the nature of strength deficits and the best methods for restoring strength after APM.

Different modes of feedback and peak vertical ground reaction force during jump landing: a systematic review.

CONTEXT: Excessive ground reaction force when landing from a jump may result in lower extremity injuries. It is important to better understand how feedback can influence ground reaction force (GRF) and potentially reduce injury risk. OBJECTIVE: To determine the effect of expert-provided (EP), self-analysis (SA), and combination EP and SA (combo) feedback on reducing peak vertical GRF during a jump-landing task. DATA SOURCES: We searched the Web of Science database on July 1, 2011; using the search terms ground reaction force, landing biomechanics, and feedback elicited 731 initial hits. STUDY SELECTION: Of the 731 initial hits, our final analysis included 7 studies that incorporated 32 separate data comparisons. DATA EXTRACTION: Standardized effect sizes and 95% confidence intervals (CIs) were calculated between pretest and posttest scores for each feedback condition. DATA SYNTHESIS: We found a homogeneous beneficial effect for combo feedback, indicating a reduction in GRF with no CIs crossing zero. We also found a homogeneous beneficial effect for EP feedback, but the CIs from 4 of the 10 data comparisons crossed zero. The SA feedback showed strong, definitive effects when the intervention included a videotape SA, with no CIs crossing zero. CONCLUSIONS: Of the 7 studies reviewed, combo feedback seemed to produce the greatest decrease in peak vertical GRF during a jump-landing task.

Effects of chronic ankle instability on energy dissipation in the lower extremity.

PURPOSE: This study aimed to investigate the influence of chronic ankle instability (CAI) on lower extremity joint energy dissipation patterns during a stop-jump task. METHODS: Nineteen participants with self-reported CAI and 19 healthy control participants volunteered. Participants performed five double-leg vertical stop-jump tasks onto a force plate. Lower extremity kinetics and kinematics were examined with an electromagnetic tracking system interfaced with a nonconductive force plate. Lower extremity joint energy dissipations were calculated for the hip, knee, and ankle in the sagittal plane during 50, 100, 150, and 200 ms after initial contact with the force plate. Energy dissipation values were normalized to the product of body mass and height [J · (N · m)(-1)]. Individual joint contribution to total lower extremity energy dissipation by the ankle, knee, and hip was reported as the percentage of energy dissipation by each joint over the total energy dissipation of all three joints. Independent t-tests and standard mean differences were conducted to assess differences in each dependent variable between the CAI and the control groups. Significance was set a priori at P < 0.05. RESULTS: The CAI group demonstrated significantly less percentage of knee energy dissipation (P = 0.04) and higher percentage of ankle energy dissipation (P = 0.035) of the total energy dissipation during the 100 ms immediately after initial contact compared with the control group. CONCLUSIONS: We found altered energy dissipation patterns at the knee and ankle during a stop-jump task in the CAI group. These findings may provide insight into kinetic alterations that may be associated with CAI. Future research should consider this information as it may be used to develop more effective interventions to target these potentially modifiable energy dissipation patterns in those with CAI.

Different exercise training interventions and drop-landing biomechanics in high school female athletes.

CONTEXT: Anterior cruciate ligament (ACL) injuries are common in female athletes and are related to poor neuromuscular control. Comprehensive neuromuscular training has been shown to improve biomechanics; however, we do not know which component of neuromuscular training is most responsible for the changes. OBJECTIVE: To assess the efficacy of either a 4-week core stability program or plyometric program in altering lower extremity and trunk biomechanics during a drop vertical jump (DVJ). DESIGN: Cohort study. SETTING: High school athletic fields and motion analysis laboratory. PATIENTS OR OTHER PARTICIPANTS: Twenty-three high school female athletes (age = 14.8 ± 0.8 years, height = 1.7 ± 0.07 m, mass = 57.7 ± 8.5 kg). INTERVENTION(S): Independent variables were group (core stability, plyometric, control) and time (pretest, posttest). Participants performed 5 DVJs at pretest and posttest. Intervention participants engaged in a 4-week core stability or plyometric program. MAIN OUTCOME MEASURE(S): Dependent variables were 3-dimensional hip, knee, and trunk kinetics and kinematics during the landing phase of a DVJ. We calculated the group means and associated 95% confidence intervals for the first 25% of landing. Cohen d effect sizes with 95% confidence intervals were calculated for all differences. RESULTS: We found within-group differences for lower extremity biomechanics for both intervention groups (P ≤ .05). The plyometric group decreased the knee-flexion and knee internal-rotation angles and the knee-flexion and knee-abduction moments. The core stability group decreased the knee-flexion and knee internal-rotation angles and the hip-flexion and hip internal-rotation moments. The control group decreased the knee external-rotation moment. All kinetic changes had a strong effect size (Cohen d > 0.80). CONCLUSIONS: Both programs resulted in biomechanical changes, suggesting that both types of exercises are warranted for ACL injury prevention and should be implemented by trained professionals.

Neuromuscular changes after aerobic exercise in people with anterior cruciate ligament-reconstructed knees.

CONTEXT: Anterior cruciate ligament (ACL) reconstructions are common, especially in young, active people. The lower extremity neuromuscular adaptations seen after aerobic exercise provide information about how previously injured patients perform and highlight deficits and, hence, areas for focused treatment. Little information is available about neuromuscular performance after aerobic exercise in people with ACL reconstructions. OBJECTIVE: To compare dynamic balance, gluteus medius muscle activation, vertical jump height, and hip muscle strength after aerobic exercise in people with ACL-reconstructed knees. DESIGN: Case-control study. SETTING: Research laboratory. PATIENTS OR OTHER PARTICIPANTS: Of 34 recreationally active volunteers, 17 had a unilateral primary ACL reconstruction at least 2 years earlier and 17 were matched controls. INTERVENTION(S): All participants performed 20 minutes of aerobic exercise on a treadmill. MAIN OUTCOME MEASURE(S): We recorded dynamic, single-legged balance electromyographic gluteus medius muscle activation, single-legged vertical jump height, and maximum isometric strength for hip abduction, extension, and external rotation preexercise and postexercise. RESULTS: Participants with ACL reconstructions exhibited shorter reach distances during dynamic balance tasks, indicating poorer dynamic balance, and less gluteus medius muscle electromyographic activation. Reductions in hip abduction and extension strength after exercise were noted in all participants; however, those with ACL reconstructions displayed greater hip extensor strength loss after aerobic exercise than did the control group. CONCLUSIONS: Neuromuscular changes after aerobic exercise exist in both patients with ACL reconstructions and controls. The former group may experience greater deficits in hip extensor strength after aerobic exercise. Reduced reach distances in people with ACL reconstructions may represent a protective mechanism against excessive tibiofemoral rotation during dynamic balance. Clinicians should identify weaknesses in the resting state and after aerobic exercise in recreationally active patients and those with ACL reconstructions.