Charles B. Swanik

Sex differences in baseline neuropsychological function and concussion symptoms of collegiate athletes

Objective: To investigate sex differences in baseline neuropsychological function and concussion symptoms between male and female collegiate athletes. Methods: A post-test only design was used to examine baseline neuropsychological test scores and concussion symptoms. A total of 1209 NCAA Division I collegiate athletes from five northeastern universities in the USA completed a baseline ImPACT test. ImPACT, a computerised neuropsychological test battery, was administered during an athlete’s pre-season. Results: Female athletes performed significantly better than male athletes on baseline verbal memory scores (p = 0.001), while male athletes performed significantly better than female athletes on baseline visual memory scores (p = 0.001). Female athletes endorsed a significant number of mild baseline symptoms as compared to male athletes. Conclusions: Male and female athletes exhibit differences on baseline neuropsychological test performance and concussion symptoms.

A bilateral comparison of posterior capsule thickness and its correlation with glenohumeral range of motion and scapular upward rotation in collegiate baseball players

HYPOTHESIS We hypothesized that posterior capsule thickness (PCT) would be greater on the dominant arm compared to the non-dominant arm. We also hypothesized that PCT would negatively correlate with glenohumeral internal rotation and scapular upward rotation. In addition, PCT would positively correlate with glenohumeral external rotation. However, currently PCT has not been measured nor have correlations been identified to exist with glenohumeral and scapular motion. Therefore, the purpose of the study was to determine if the posterior capsule was hypertrophied on the dominant arm and to identify if relationships exist with glenohumeral internal rotation (IR), external rotation (ER), and scapular upward rotation (SUR). MATERIALS AND METHODS PCT was measured using a 10-MHz transducer. Glenohumeral IR and ER was measured supine using a digital inclinometer. SUR was measure at 0°, 60°, 90°, and 120° of glenohumeral abduction using a modified digital inclinometer. RESULTS PCT was greater on the dominant compared with the nondominant arm (P = .001). A negative correlation was found between PCT and IR (-0.498, P = .0001). A positive correlation was found between PCT and ER (0.450, P = .002) and between PCT and SUR at 60°, 90°, and 120° of glenohumeral abduction (0.388, P = .006; 0.327, P = .023; 0.304, P = .036, respectively). DISCUSSION This in vivo study demonstrated a hypertrophied posterior capsule and its association with GIRD, ER, and SUR. These observations suggest that PCT does occur on the throwing arm of baseball players and is linked with glenohumeral and scapular alterations. CONCLUSIONS This methodology could be used as a noninvasive screening evaluation for overhead athletes to identify those who may be at risk for shoulder injuries due to excessive capsular thickening.

Glenohumeral rotation and scapular position adaptations after a single high school female sports season.

CONTEXT Anterior instability and impingement are common in overhead athletes and have been associated with decreases in internal rotation (IR) and increases in external rotation (ER) motion. However, the chronology and the effect of different female sports on these conditions have yet to be determined. OBJECTIVE To measure glenohumeral IR and ER rotation, total range of motion, and scapular position in female overhead athletes over a single competitive season. DESIGN Multiple group pretest-posttest study. SETTING High school. PATIENTS OR OTHER PARTICIPANTS Thirty-six female overhead athletes (age = 15.29 +/- 1.18 years, height = 164.16 +/- 7.14 cm, mass = 58.24 +/- 9.54 kg) with no history of shoulder or elbow surgery participating in high school swimming, volleyball, or tennis. INTERVENTION(S) Participants were measured for all dependent variables at preseason and postseason. MAIN OUTCOME MEASURE(S) Participants were measured for glenohumeral IR and ER with the scapula stabilized. Total glenohumeral range of motion was calculated as the sum of IR and ER. Scapular upward rotation was measured at 0 degrees , 60 degrees , 90 degrees , and 120 degrees of glenohumeral abduction in the scapular plane, and scapular protraction was measured at 0 degrees , 45 degrees (hands on hips), and 90 degrees of glenohumeral abduction. RESULTS Internal rotation decreased from preseason to postseason (P = .012). Swimmers had less IR than both volleyball and tennis players (P = .001). External rotation also decreased in the swimmers (P = .001). Overall, preseason to postseason total motion decreased for athletes participating in swimming (P = .001) and tennis (P = .019). For all participants, preseason to postseason scapular protraction at 45 degrees glenohumeral abduction decreased (P = .007). CONCLUSIONS Female overhead athletes demonstrated decreases in IR after only one competitive season. Clinically, our results indicate that overhead athletes should be monitored for motion changes throughout their competitive seasons.

Examining Neuromuscular Control During Landings on a Supinating Platform in Persons With and Without Ankle Instability

Background: Ankle instability is a costly public health concern because of the associated recurrent sprains. It is evident there are neuromuscular control deficits predisposing these individuals to their ankle “giving way.” Individuals with a history of lateral ankle sprain, who did not develop instability, may hold the key to understanding proper neuromuscular control after injury. Hypotheses: On the basis of previous research, the authors hypothesized that individuals with ankle instability would demonstrate reduced peroneal activation, causing a more inverted position of the ankle, before and after landing. Study Design: Controlled laboratory study. Methods: This study aimed to evaluate preparatory and reactive neuromuscular control when landing on a custom-designed ankle supinating device in individuals with ankle instability (AI), individuals with a history of lateral ankle sprains without instability (LAS), and uninjured controls (CON). Forty-five participants (15 per group) were asked to land on a device built to simulate the mechanism of a lateral ankle sprain (supination) while kinematics and muscle activity of the lower extremity were monitored. Results: Contrary to our hypotheses, the AI group displayed significantly increased preparatory (P = .01) and reactive (P = .02) peroneal activation, while the LAS group demonstrated a trend toward increased preparatory tibialis anterior muscle activation (P = .07), leading to a decreased plantar flexion of the ankle at landing. Conclusion: The AI group was likely acting in a protective fashion to a potentially injurious situation, indicating these individuals can activate the peroneals if needed. The LAS group’s strategy may be a safer strategy in that a less plantar-flexed position of the ankle is more close-packed and stable. Further, it appears the long-latency response of the peroneals may be enhanced in these individuals, which indicates motor learning at the supraspinal level to promote dynamic restraint. Clinical Relevance: Individuals with AI can increase peroneal activation when necessary to dynamically stabilize the ankle, indicating the potential for training/rehabilitation. Further, the LAS group may deploy a different control strategy after injury to protect the ankle from subsequent sprains, which deserves investigation during activities of daily living. A greater understanding of these strategies will lead to the development of more appropriate treatment paradigms after injury to minimize the incidence of instability.

Neuromuscular dynamic restraint in women with anterior cruciate ligament injuries.

The purpose of this study was to identify neuromuscular characteristics related to dynamic restraint in the knee. Observing compensatory changes to these characteristics in women with anterior cruciate ligament injuries provides important information for understanding functional knee stability, injury prevention, and performance. Twelve female subjects with anterior cruciate ligament injuries and 17 female control subjects participated in this study to assess electromyographic activity during landing from a hop and knee perturbation; hamstring muscle stiffness and flexibility; and isokinetic strength. Females with anterior cruciate ligament deficiencies had significantly increased preparatory muscle activity in the lateral hamstring before landing, but no differences in reactive muscle activity during landing or reflex latency after joint perturbation. Females with anterior cruciate ligament deficiencies had significantly less hamstring muscle stiffness and flexibility, but also had greater peak torque and torque development for knee flexion. Lower Lysholm scores were observed in females with anterior cruciate ligament deficiencies but no difference was found in functional performance of the single leg hop test. These neuromuscular characteristics provide a foundation for future research investigating injury prevention and rehabilitation techniques that maximize dynamic restraint through stiffness regulation and the timing of specific muscle activation strategies.

Gender comparisons of dynamic restraint and motor skill in children.

Objectives:To assess differences in neuromuscular dynamic restraint between high-skilled and low-skilled prepubescent girls and boys. To determine the contribution of sport experience and physical characteristics to motor skill. Subjects:Nineteen girls and 17 boys (8.89-9.40 y) participated. Intervention:Isometric hamstring and quadriceps muscle strength was assessed. Subjects performed 3 landing trials for measurement of preparatory EMG and vertical leg stiffness. Motor skill was assessed through analysis of 12 fundamental tasks. Sport experience was reported as hours per week and total years in organized and nonorganized activity. Outcome Measures:Dynamic restraint variables of isometric strength, preparatory EMG activity, and vertical leg stiffness were measured between groups. The contributions of time in sport, type of sport, and physical characteristics on skill were analyzed. Results:No significant gender or skill differences were found in quadriceps strength (P = 0.73), hamstring strength (P = 0.96), hamstring-to-quadriceps ratio (P = 0.71), or vertical leg stiffness (P = 0.38). Low-skilled children exhibited significantly greater (47.8%) preparatory hamstring-quadriceps coactivation than high-skilled subjects (P = 0.03). Participation in organized and nonorganized sport accounted for 29% of the variance in motor skill. Conclusions:Neuromuscular differences between genders were not observed, but dynamic restraint EMG measures differed between skill levels. The factors predisposing females to noncontact injuries may develop prepuberty to postpuberty from a combination of variables. Greater coactivation in the low-skilled group appears consistent with immature feedforward neuromuscular control strategies. These unrefined motor skills are less economical, may compromise dynamic restraint, and appear partially determined by sport experience.

Humeral retroversion and its association with posterior capsule thickness in collegiate baseball players

HYPOTHESIS AND BACKGROUND Baseball players commonly present with decreases in internal rotation (IR) and concurrent increases in external rotation (ER) motion. Several glenohumeral (GH) adaptations have been theorized to cause these changes in motion, including humeral retroversion (HR) and posterior capsule thickness (PCT). However, limited data exist examining the inter-relationship between HR and PCT. Therefore, the purpose of this study was to measure HR, GH IR and ER rotation, and PCT. MATERIALS AND METHODS HR and PCT were measured with an ultrasound system (Sonosite Titan; Sonosite, Bothell, WA, USA), and GH IR and ER were measured with a digital inclinometer. RESULTS The dominant arm had significantly more HR (15.6°, P = .0001) than the nondominant arm. Pearson correlation coefficients showed a significant negative relationship between HR and GH IR (-0.472, P = .001) and a significant positive relationship between HR and GH ER (0.295, P = .042). A significant positive correlation was also found between HR and PCT (0.427, P = .003). DISCUSSION This was the first study to identify a relationship between HR and PCT in addition to GH IR and ER. The identification of these multiple correlations appears to suggest that the loss of IR caused by HR may be placing additional stress on the posterior capsule during the deceleration phase of the throw, thereby causing a fibroblastic healing response. CONCLUSIONS HR has previously been identified as a positive adaptation because of the increase in ER without anterior capsule attenuation. However, this study suggests that HR may be contributing to the negative adaptation of PCT.

Muscle Spindle Traffic in Functionally Unstable Ankles During Ligamentous Stress

CONTEXT Ankle sprains are common in athletes, with functional ankle instability (FAI) developing in approximately half of cases. The relationship between laxity and FAI has been inconclusive, suggesting that instability may be caused by insufficient sensorimotor function and dynamic restraint. Research has suggested that deafferentation of peripheral mechanoreceptors potentially causes FAI; however, direct evidence confirming peripheral sensory deficits has been elusive because previous investigators relied upon subjective proprioceptive tests. OBJECTIVE To develop a method for simultaneously recording peripheral sensory traffic, joint forces, and laxity and to quantify differences between healthy ankles and those with reported instability. DESIGN Case-control study. SETTING University laboratory. PATIENTS OR OTHER PARTICIPANTS A total of 29 participants (age = 20.9 ± 2.2 years, height = 173.1 ± 8.9 cm, mass = 74.5 ± 12.7 kg) stratified as having healthy (HA, n = 19) or unstable ankles (UA, n = 10). INTERVENTION(S) Sensory traffic from muscle spindle afferents in the peroneal nerve was recorded with microneurography while anterior (AP) and inversion (IE) stress was applied to ligamentous structures using an ankle arthrometer under test and sham conditions. MAIN OUTCOME MEASURE(S) Laxity (millimeters or degrees) and amplitude of sensory traffic (percentage) were determined at 0, 30, 60, 90, and 125 N of AP force and at 0, 1, 2, 3, and 4 Nm of IE torque. Two-factor repeated-measures analyses of variance were used to determine differences between groups and conditions. RESULTS No differences in laxity were observed between groups (P > .05). Afferent traffic increased with increased force and torque in test trials (P < .001). The UA group displayed decreased afferent activity at 30 N of AP force compared with the HA group (HA: 30.2% ± 9.9%, UA: 17.1% ± 16.1%, P < .05). CONCLUSIONS The amplitude of sensory traffic increased simultaneously with greater ankle motion and loading, providing evidence of the integrated role of capsuloligamentous and musculotendinous mechanoreceptors in maintaining joint sensation. Unstable ankles demonstrated diminished afferent traffic at low levels of force, suggesting the early detection of joint loading may be compromised.

Effect of elastic taping on postural control deficits in subjects with healthy ankles, copers, and individuals with functional ankle instability.

Background: Ankle sprains are the most common injury among physically active people, with common sequelae including repeated episodes of giving way, termed functional ankle instability. Copers are a cohort in ankle research comprised of those who have sprained their ankle but have not suffered any further dysfunction. The use of an elastic tape, Kinesio Tape, in sports medicine practice has recently gained popularity and may help improve postural control deficits related to functional ankle instability. The purpose of this study was to examine the immediate and prolonged effects of Kinesio Taping on postural control in healthy, coper, and unstable ankles as measured through single-limb balance on a force plate. Methods: Sixty physically active, college-aged participants (72.5 ± 9.7 cm, 74.2 ± 16.2 kg, 21.5 ± 2.6 years) were stratified into healthy, coper, or unstable groups using the Cumberland Ankle Instability Tool (CAIT) combined with their history of ankle injury. Dependent variables included time-to-boundary (TTB) measures and traditional center of pressure (COP) measures in both the mediolateral (frontal) and anteroposterior (sagittal) planes. Testing was performed prior to tape application, immediately after application of the tape, 24 hours following tape application, and immediately after tape removal. Results: Significant differences between groups were observed for COP standard deviation and range in the sagittal plane. Significant differences between tape conditions for TTB absolute minima and standard deviation were also noted. Post hoc testing revealed large to medium effect sizes for the group differences and very small effect sizes for the differences between conditions. Conclusions: Our study did not reveal decisively relevant changes following application of Kinesio Tape to the ankle. However, we did observe sagittal plane postural control deficits in subjects with ankle instability measured through summary COP variables over 20-second trials. Clinical Relevance: Ankle instability is a concern for many clinicians. Kinesio Taping, although a popular form of clinical intervention, remains understudied. Evidence from this study does not support the use of Kinesio Taping for improving postural control deficits in those with ankle instability.

Neuromechanical coupling in the regulation of muscle tone and joint stiffness

The ability of the nervous system to accommodate changes to joint mechanics is crucial in the maintenance of joint stability and the prevention of injury. This neuromechanical coupling is achieved through several mechanisms such as the central and peripheral regulation of muscle tone and subsequent alterations to joint stiffness. Following joint injury, such as a ligamentous sprains, some patients develop functional instability or require surgery to stabilize the joint, while others are able to cope and display limited impairments. Several researchers have attempted to explain these divergent outcomes, although research using proprioceptive tasks and quantifying reaction times has led to equivocal results. Recent innovations have allowed for the simultaneous measurement of mechanical and nervous system function among these subsets. The intent of this review was to explore the relationships between joint stiffness and nervous system function, and how it changes following injury. By better understanding these mechanisms, researchers and clinicians may better develop and implement rehabilitation protocols to target individual deficits among injured populations.