Bryan L. Riemann

Gender differences in strength and lower extremity kinematics during landing.

This study evaluated kinematic, vertical ground reaction forces, and strength variables in healthy collegiate female basketball, volleyball, and soccer players compared with matched male subjects. Thirty athletes did single-leg landing and forward hop tasks. An electromagnetic tracking device synchronized with a force plate provided kinematic data and vertical ground reaction force data, respectively. Maximum angular displacement and time to maximum angular displacement kinematic variables were calculated for hip flexion, abduction, rotation, knee flexion, and lower leg rotation. Vertical ground reaction force data normalized to body mass provided impulse, maximum force, time to maximum force, and stabilization time variables. An isokinetic device measured quadriceps and hamstring peak torque to body mass at 60°/second. With both tasks, females had significantly less knee flexion and lower leg internal rotation maximum angular displacement, and less knee flexion time to maximum angular displacement than males. For the single-leg land, females had significantly more hip internal rotation maximum angular displacement, and less lower leg internal rotation time to maximum angular displacement than males. For the forward hop, females had significantly more hip rotation time to maximum angular displacement than males. Females also had significantly less peak torque to body mass for the quadriceps and hamstrings than males. Weaker thigh musculature may be related to the abrupt stiffening of the knee and lower leg on landing in females.

Effect of Peripheral Afferent Alteration of the Lateral Ankle Ligaments on Dynamic Stability

Background The sensorimotor influence of the lateral ankle ligaments in muscle activation is unclear. Hypothesis The lateral ankle ligaments have significant sensorimotor influence on muscle activation. Study Design Controlled laboratory study. Methods Muscle-firing characteristics in response to a high-speed inversion perturbation and during gait were assessed in 13 normal subjects. Solutions (1.5% lidocaine or a placebo of saline) were injected bilaterally into the anterior talofibular and calcaneofibular ligaments (1.5 ml per ligament) to alter peripheral afferent influence. Subjects were again tested with the same protocol. Results The protective response of the anterior tibialis and peroneal muscles during inversion perturbation and mean muscle activation amplitude decreased during running after both injections. After injection, no significant differences were seen for muscle reflex latencies, maximum amplitude, time to maximum amplitude during inversion perturbation, or mean amplitude during walking. Conclusion The lateral ankle ligaments have a sensorimotor influence on muscle activation. Clinical Relevance Induced edema from the injected solutions may have altered the sensorimotor influence of the lateral ankle ligaments, thereby inhibiting the dynamic ankle stabilizers. This finding suggests that dynamic stability may be compromised because of swelling after joint injury.

Kinematic analysis of the hip and trunk during bilateral stance on firm, foam, and multiaxial support surfaces

OBJECTIVE To differentiate hip and trunk motion during double-leg stance. DESIGN Trunk and hip angular position variances were measured on different support surfaces with and without vision. BACKGROUND Postural control results from motion about the hips and trunk during bilateral stance. While the hip joint has been studied extensively, information concerning relative amounts of hip and trunk motions during postural control is limited. METHODS Trunk flexion/extension, trunk lateral flexion, right and left hip flexion/extension and abduction/adduction angular position variances were assessed in 14 normal subjects using an electromagnetic tracking system during bilateral stance on firm, foam, and multiaxial support surfaces with and without vision. RESULTS Significantly greater amounts of motion occurred at all joints for the multiaxial-eyes closed condition compared to all other surface-vision conditions. No significant differences were found between any other surface-vision conditions. Within the multiaxial-eyes closed condition, right and left hip flexion/extension and abduction/adduction magnitudes were significantly greater than those of trunk flexion and lateral flexion, and left hip flexion/extension motion was significantly greater than that of the right hip. CONCLUSIONS Postural control mechanisms involve similar amounts of motion at the hips and trunk, except for conditions under which a rigid base of support becomes unstable and vision is eliminated. RELEVANCE These results suggest that the trunk and hips should be considered separately during kinematic analysis of postural control. This information may be useful in providing a more sensitive assessment of postural control to identify balance-related pathologies associated with stroke, concussion, and somatosensory deficits.

Effect of lateral ankle ligament anesthesia on single-leg stance stability

PURPOSE This study was designed to determine, in isolation, the contribution of lateral ankle ligament mechanoreceptors to postural stability during single leg static (eyes open, eyes closed) and landing tasks. METHODS Fourteen healthy subjects (nine males, five females) underwent two different treatment conditions (control, anesthesia) in a counterbalanced order (48-h interval). During the anesthetic treatment, lidocaine was injected into the anterior talofibular and calcaneofibular ligament (1.5 cc each) regions. Postural stability was measured using forceplate and kinematic variables. The average of each variable across multiple trials under each treatment for the three tasks was analyzed statistically. RESULTS Results of all statistical analyses failed to demonstrate significant alterations (P > 0.05) in postural control attributable to the treatment condition. CONCLUSION These results suggest that lateral ankle ligament mechanoreceptors either do not make a significant contribution to single leg stance stability, do not have a unique, irreplaceable role, or have a role that is too subtle to be detected given the measurement techniques used. Thus, the idea that single leg stability becomes altered after ankle joint injury because of proprioceptive disruption was not supported. This would suggest that reported postural control alterations in persons after repetitive ankle injury more likely occur as a result of alterations in mechanical stability, motor components, and/or central motor programming.

Shoulder muscle reflex latencies under various levels of muscle contraction.

Previous research in relaxed muscles shows that muscle reflex latencies are too slow to protect the shoulder. However, during athletic activity when injury occurs, some level of shoulder muscle contraction typically exists. The purpose of the current study was to assess shoulder muscle reflex latencies under various levels of muscle contraction. Seventeen healthy subjects participated. A perturbation consisting of an external rotation collision force to the anterior forearm in a position of apprehension under various levels of muscle contraction (0%, 20%, and 50% of a maximum voluntary muscle contraction) was applied. Muscle reflex latencies were measured as the time from perturbation application to onset of muscle activity. Electromyography measured activity onset of the rotator cuff muscles and the primary humeral movers. During 0%, the latissimus dorsi muscle reflex latency was significantly slower than most other muscles. No difference existed between muscles in the 20% and 50% conditions. For the rotator cuff muscles, the reflex latencies significantly quickened for 20% and 50% compared with the relaxed state (0%). Overall, introducing muscle contraction significantly quickened muscle reflex latencies. These results provide clinicians with a better understanding of the role that these reflexes play in joint stability in a position of injury vulnerability like a position of apprehension.

Role of Isokinetic Testing and Training After ACL Injury and Reconstruction

This chapter focuses on the role of isokinetics with regard to testing and training after ACL injury and reconstruction. This includes the use of isokinetics for screening, evaluation, treatment, rehabilitation, and criteria for discharge to return to sports. Specific considerations for testing after ACL reconstruction are detailed. Testing and training protocols are provided.

Statistical Primer for Athletic Trainers: Understanding the Role of Statistical Power in Comparative Athletic Training Research

OBJECTIVE   To describe the concept of statistical power as related to comparative interventions and how various factors, including sample size, affect statistical power. BACKGROUND   Having a sufficiently sized sample for a study is necessary for an investigation to demonstrate that an effective treatment is statistically superior. Many researchers fail to conduct and report a priori sample-size estimates, which then makes it difficult to interpret nonsignificant results and causes the clinician to question the planning of the research design. DESCRIPTION   Statistical power is the probability of statistically detecting a treatment effect when one truly exists. The α level, a measure of differences between groups, the variability of the data, and the sample size all affect statistical power. RECOMMENDATIONS   Authors should conduct and provide the results of a priori sample-size estimations in the literature. This will assist clinicians in determining whether the lack of a statistically significant treatment effect is due to an underpowered study or to a treatments actually having no effect.

A Bilateral Comparison of the Underlying Mechanics Contributing to the Seated Single-Arm Shot-Put Functional Performance Test

CONTEXT Functional performance tests (FPTs) are tools used to assess dynamic muscle strength and power. In contrast to the lower extremity, fewer FPTs are available for the upper extremity. The seated single-arm shot put test has the potential to fill the void in upper extremity FPTs; however, the underlying mechanics have not been examined and, therefore, the validity of bilateral comparisons is unknown. OBJECTIVE To examine the effects of upper extremity dominance and medicine-ball mass on the underlying mechanics of the seated single-arm shot put. DESIGN Crossover study. SETTING Biomechanics laboratory. PATIENTS OR OTHER PARTICIPANTS Fifteen women (age = 23.6 ± 2.1 years, height = 1.65 ± .07 m, mass = 68.1 ± 11.7 kg) and 15 men (age = 24.3 ± 4.0 years, height = 1.80 ± 0.06 m, mass = 88.1 ± 16.4 kg), all healthy and physically active. INTERVENTION(S) Seated single-arm shot-put trials using the dominant and nondominant limbs were completed using three 0.114-m-diameter medicine-ball loads (1 kg, 2 kg, 3 kg). MAIN OUTCOME MEASURE(S) Customized touch-sensitive gloves, synchronized with kinematic data of the hands, signaled ball release, so that release height, release angle, and peak anterior and vertical velocity could be quantified for each trial. In addition, the horizontal range from release to first floor impact was recorded. RESULTS The dominant-limb horizontal ranges were 7% to 11% greater ( P < .001) than for the nondominant limb for each of the 3 ball masses. No bilateral release-height or -angle differences were revealed ( P ≥ .063). Release velocities were 7.6% greater for the dominant limb than the nondominant limb ( P = .001). CONCLUSIONS Our results support the use of the seated single-arm shot put test as a way to compare bilateral upper extremity functional performance. The near-identical release heights and angles between the dominant and nondominant limbs support the interpretation of measured bilateral horizontal-range differences as reflecting underlying strength and power differences.