John P. Abt

Neuromuscular and biomechanical characteristic changes in high school athletes: a plyometric versus basic resistance program

Background: In order to improve neuromuscular and biomechanical characteristic deficits in female athletes, numerous injury prevention programs have been developed and have successfully reduced the number of knee ligament injuries. However, few have investigated the neuromuscular and biomechanical changes following these training programs. It is also largely unknown what type of program is better for improving the landing mechanics of female athletes. Objectives: To investigate the effects of an 8 week plyometric and basic resistance training program on neuromuscular and biomechanical characteristics in female athletes. Methods: Twenty seven high school female athletes participated either in a plyometric or a basic resistance training program. Knee and hip strength, landing mechanics, and muscle activity were recorded before and after the intervention programs. In the jump-landing task, subjects jumped as high as they could and landed on both feet. Electromyography (EMG) peak activation time and integrated EMG of thigh and hip muscles were recorded prior to (preactive) and subsequent to (reactive) foot contact. Results: Both groups improved knee extensor isokinetic strength and increased initial and peak knee and hip flexion, and time to peak knee flexion during the task. The peak preactive EMG of the gluteus medius and integrated EMG for the gluteus medius during the preactive and reactive time periods were significantly greater for both groups. Conclusions: Basic training alone induced favourable neuromuscular and biomechanical changes in high school female athletes. The plyometric program may further be utilised to improve muscular activation patterns.

The Effect of Direction and Reaction on the Neuromuscular and Biomechanical Characteristics of the Knee during Tasks that Simulate the Noncontact Anterior Cruciate Ligament Injury Mechanism

Background Jumping and landing tasks that have a change in direction have been implicated as a mechanism of noncontact anterior cruciate ligament injury. Yet, to date, neuromuscular and biomechanical research has focused primarily on straight landing tasks during planned jumps. Hypothesis Lateral and reactive jumps increase the neuromuscular and biomechanical demands placed on the anterior cruciate ligament, and women perform these tasks differently from men. Study Design Controlled laboratory study. Methods A total of 18 male and 17 female healthy high school basketball players underwent an analysis of the knee during planned and reactive 2-legged stop-jump tasks in 3 different directions that included novel methodology to incorporate a reactive component. Ground-reaction forces, joint kinematics, joint kinetics, and electromyographic activity were assessed during the tasks. Results Jump direction and task (planned or reactive) significantly affected joint angles, ground-reaction forces, knee joint moments, and proximal anterior tibia shear forces; female players demonstrated different kinematic, kinetic, and electromyographic characteristics during these tasks. Conclusion and Clinical Relevance Jump direction significantly influenced knee biomechanics, suggesting that lateral jumps are the most dangerous of the stop-jumps. Reactive jumps were also significantly different, suggesting differences between planned laboratory experiments and actual athletic competition. The results of this study indicate that directional and reactive jumps should be included in research methodology and injury-prevention programs.

Reliability, Precision, Accuracy, and Validity of Posterior Shoulder Tightness Assessment in Overhead Athletes

Background Posterior shoulder tightness with subsequent loss of humeral internal rotation range of motion has been linked to upper extremity lesions in overhead athletes. A valid clinical assessment is necessary to accurately identify posterior shoulder tightness as a contributor to injury. Purpose To describe a modified supine assessment of posterior shoulder tightness by establishing the reliability, precision, clinical accuracy, and validity of the assessment. Study Design Cohort study (diagnosis); Level of evidence, 2. Methods Intrasession, intersession, and intertester reliability and precision were established by comparing the commonly used side-lying assessment of posterior shoulder tightness and the described modified supine assessment. Clinical accuracy of both methods was obtained using an electromagnetic tracking device to track humeral and scapular motion. Construct validity was established by identifying posterior shoulder tightness in a group of overhead athletes (baseball pitchers and tennis players) reported in the literature to have limited humeral internal rotation and posterior shoulder tightness. Results The side-lying intrasession intraclass correlation coeffecient (standard error of measurement), intersession intraclass correlation coeffecient (standard error of measurement), and intertester intraclass correlation coeffecient (standard error of measurement) were 0.83 cm (0.9), 0.42 cm (1.7), and 0.69 cm (1.4), respectively. The supine intrasession intraclass correlation coeffecient (standard error of measurement), intersession intraclass correlation coeffecient (standard error of measurement), and intertester intraclass correlation coeffecient (standard error of measurement) were 0.91° (1.1°), 0.75° (1.8°), and 0.94° (1.8°), respectively. In side-lying, the clinical accuracy expected was 0.9 ± 0.6 cm of error while, when measured supine, it was 3.5° ± 2.8° of error. Both assessments resulted in minimal scapular protraction (~3.5°). Between groups, baseball pitchers and tennis players had significantly less internal rotation range of motion (P < .0001) and greater posterior shoulder tightness (P = .004) when measured in supine, but not in side-lying (P = .312). Conclusion Both methods resulted in good clinician accuracy and precision, suggesting that both can be performed accurately. The supine method can be assessed more reliably than side-lying between both sessions and testers. Clinical Relevance Clinicians may want to consider use of the supine method given the higher reliability, validity, and similar precision and clinical accuracy.

Neuromuscular contributions to anterior cruciate ligament injuries in females.

Although anterior cruciate ligament (ACL) injuries are not gender specific, they do occur at a significantly greater rate in females. Biomechanical and neuromuscular deficits in females have been documented as factors contributing to ACL injuries, however little research has been conducted in the area of preventative training programs to improve these deficits. This article will describe the biomechanical and neuromuscular factors that contribute to ACL injuries in females, and provide a foundation from which preventative training programs should be designed.

RELATIONSHIP BETWEEN CYCLING MECHANICS AND CORE STABILITY

Core stability has received considerable attention with regards to functional training in sports. Core stability provides the foundation from which power is generated in cycling. No research has described the relationship between core stability and cycling mechanics of the lower extremity. The purpose of this study was to determine the relationship between cycling mechanics and core stability. Hip, knee, and ankle joint kinematic and pedal force data were collected on 15 competitive cyclists while cycling untethered on a high-speed treadmill. The exhaustive cycling protocol consisted of cycling at 25.8 km·h−1 while the grade was increased 1% every 3 minutes. A core fatigue workout was performed before the second treadmill test. Total frontal plane knee motion (test 1: 15.1 ± 6.0°; test 2: 23.3 ± 12.5°), sagittal plane knee motion (test 1: 69.9 ± 4.9°; test 2: 79.3 ± 10.1°), and sagittal plane ankle motion (test 1: 29.0 ± 8.5°; test 2: 43.0 ± 22.9°) increased after the core fatigue protocol. No significant differences were demonstrated for pedaling forces. Core fatigue resulted in altered cycling mechanics that might increase the risk of injury because the knee joint is potentially exposed to greater stress. Improved core stability and endurance could promote greater alignment of the lower extremity when riding for extended durations as the core is more resistant to fatigue.

Running Kinematics and Shock Absorption Do Not Change After Brief Exhaustive Running

Abt, JP, Sell, TC, Chu, Y, Lovalekar, M, Burdett, RG, and Lephart, SM. Running kinematics and shock absorption do not change after brief exhaustive running. J Strength Cond Res 25(6): 1479-1485, 2011—Because of the nature of running, the forces encountered require a proper coordination of joint action of the lower extremity to dissipate the ground reaction forces and accelerations through the kinetic chain. Running-related muscle fatigue may reduce the shock absorbing capacity of the lower extremity and alter running kinematics. The purpose of this study was to determine if a bout of exhaustive running at a physiologically determined high intensity, changes running kinematics, impact accelerations, and alters shock attenuating capabilities. It was hypothesized that as a result of fatigue induced by an exhaustive run, running kinematics, impact accelerations at the head and shank, acceleration reduction, and shock attenuation would change. A within-subject, repeated-measures design was used for this study. Twelve healthy, competitive male and female distance runners participated. Subjects performed 2 testing sessions consisting of a &OV0312;O2max treadmill protocol to determine the heart rate at ventilatory threshold and a fatigue-inducing running bout at the identified ventilatory threshold heart rate. Kinematic data included knee flexion, pronation, time to maximum knee flexion, and time to maximum pronation. Acceleration data included shank acceleration, head acceleration, and shock attenuation. No significant differences resulted for the kinematic or acceleration variables. Although the results of this study do not support the original hypotheses, the influence of running fatigue on kinematics and accelerations remains inconclusive. Future research is necessary to examine fatigue-induced changes in running kinematics and accelerations and to determine the threshold at which point the changes may occur.

Less Body Fat Improves Physical and Physiological Performance in Army Soldiers

The purpose of this study was to compare physical and physiological fitness test performance between Soldiers meeting the Department of Defense (DoD) body fat standard (< or = 18%) and those exceeding the standard (> 18%). Ninety-nine male 101st Airborne (Air Assault) Soldiers were assigned to group 1: < or = 18% body fat (BF) or group 2: > 18% BE. Groups 1 and 2 had similar amounts of fat-free mass (FFM) (66.8 +/- 8.2 vs. 64.6 +/- 8.0, p = 177). Each subject performed a Wingate cycle protocol to test anaerobic power and capacity, an incremental treadmill maximal oxygen uptake test for aerobic capacity, isokinetic tests for knee flexion/extension and shoulder internal/external rotation strength, and the Army Physical Fitness Test. Results showed group 1: < 18% BF performed significantly better on 7 of the 10 fitness tests. In Soldiers with similar amounts of FFM, Soldiers with less body fat had improved aerobic and anaerobic capacity and increased muscular strength.

Reliability, precision, and gender differences in knee internal/external rotation proprioception measurements

OBJECTIVE To develop and assess the reliability and precision of knee internal/external rotation (IR/ER) threshold to detect passive motion (TTDPM) and determine if gender differences exist. DESIGN Test-retest for the reliability/precision and cross-sectional for gender comparisons. SETTING University neuromuscular and human performance research laboratory. PARTICIPANTS Ten subjects for the reliability and precision aim. Twenty subjects (10 males and 10 females) for gender comparisons. INTERVENTION All TTDPM tests were performed using a multi-mode dynamometer. Subjects performed TTDPM at two knee positions (near IR or ER end-range). Intraclass correlation coefficient (ICC (3,k)) and standard error of measurement (SEM) were used to evaluate the reliability and precision. Independent t-tests were used to compare genders. MAIN OUTCOME MEASUREMENTS TTDPM toward IR and ER at two knee positions. RESULTS Intrasession and intersession reliability and precision were good (ICC=0.68-0.86; SEM=0.22°-0.37°). Females had significantly diminished TTDPM toward IR at IR-test position (males: 0.77°±0.14°, females: 1.18°±0.46°, p=0.021) and TTDPM toward IR at the ER-test position (males: 0.87°±0.13°, females: 1.36°±0.58°, p=0.026). No other significant gender differences were found (p>0.05). CONCLUSIONS The current IR/ER TTDPM methods are reliable and accurate for the test-retest or cross-section research design. Gender differences were found toward IR where the ACL acts as the secondary restraint.

Injury Epidemiology of U.S. Army Special Operations Forces

Musculoskeletal injuries have long been a problem in general purpose forces, yet anecdotal evidence provided by medical, human performance, and training leadership suggests musculoskeletal injuries are also a readiness impediment to Special Operations Forces (SOF). The purpose of this study was to describe the injury epidemiology of SOF utilizing self-reported injury histories. Data were collected on 106 SOF (age: 31.7 ± 5.3 years, height: 179.0 ± 5.5 cm, mass: 85.9 ± 10.9 kg) for 1 year before the date of laboratory testing and filtered for total injuries and those with the potential to be preventable based on injury type, activity, and mechanism. The frequency of musculoskeletal injuries was 24.5 injuries per 100 subjects per year for total injuries and 18.9 injuries per 100 subjects per year for preventable injuries. The incidence of musculoskeletal injuries was 20.8 injured subjects per 100 subjects per year for total injuries and 16.0 injured subjects per 100 subjects per year for preventable injuries. Preventable musculoskeletal injuries comprised 76.9% of total injuries. Physical training (PT) was the most reported activity for total/preventable injuries (PT Command Organized: 46.2%/60.0%, PT Noncommand Organized: 7.7%/10.0%, PT Unknown: 3.8%/5.0%). Musculoskeletal injuries impede optimal physical readiness/tactical training in the SOF community. The data suggest a significant proportion of injuries are classified as preventable and may be mitigated with human performance programs.

Knee Proprioception and Strength and Landing Kinematics During a Single-Leg Stop-Jump Task

CONTEXT The importance of the sensorimotor system in maintaining a stable knee joint has been recognized. As individual entities, knee-joint proprioception, landing kinematics, and knee muscles play important roles in functional joint stability. Preventing knee injuries during dynamic tasks requires accurate proprioceptive information and adequate muscular strength. Few investigators have evaluated the relationship between knee proprioception and strength and landing kinematics. OBJECTIVE To examine the relationship between knee proprioception and strength and landing kinematics. DESIGN Cross-sectional study. SETTING University research laboratory. PATIENTS OR OTHER PARTICIPANTS Fifty physically active men (age = 26.4 ± 5.8 years, height = 176.5 ± 8.0 cm, mass = 79.8 ± 16.6 kg). INTERVENTION(S) Three tests were performed. Knee conscious proprioception was evaluated via threshold to detect passive motion (TTDPM). Knee strength was evaluated with a dynamometer. A 3-dimensional biomechanical analysis of a single-legged stop-jump task was used to calculate initial contact (IC) knee-flexion angle and knee-flexion excursion. MAIN OUTCOME MEASURE(S) The TTDPM toward knee flexion and extension, peak knee flexion and extension torque, and IC knee-flexion angle and knee flexion excursion. Linear correlation and stepwise multiple linear regression analyses were used to evaluate the relationships of both proprioception and strength against landing kinematics. The α level was set a priori at .05. RESULTS Enhanced TTDPM and greater knee strength were positively correlated with greater IC knee-flexion angle (r range = 0.281-0.479, P range = .001-.048). The regression analysis revealed that 27.4% of the variance in IC knee-flexion angle could be accounted for by knee-flexion peak torque and TTDPM toward flexion (P = .001). CONCLUSIONS The current research highlighted the relationship between knee proprioception and strength and landing kinematics. Individuals with enhanced proprioception and muscular strength had better control of IC knee-flexion angle during a dynamic task.