Impact of Factors that Affect Reading Skill Level on King-Devick Baseline Performance Time.

The King-Devick (K-D) test is often used as part of a multimodal assessment to screen for sport-related concussion. However, the test involves reading numbers, and little is known about variation in baseline performance on the K-D by reading skill level. We conducted a cross-sectional study analyzing data from the Concussion Assessment, Research and Education (CARE) Consortium to assess differences in baseline performance on the K-D associated with factors that impact reading skill level (learning disorder [LD] and primary home language other than English [PHLOTE]), while controlling for covariates (gender, type of sport, attentional issues, history of concussion and modality of administration). We had a sample of 2311 student-athletes (47% female), and multivariate regression indicated an average K-D performance time of 40.4 s. Presence of LD was associated with a 3.3 s slower K-D time (95% CI 1.9-4.7, p < 0.001), and PHLOTE was associated with a 2.6 s slower K-D time (95% CI 1.2-4.0, p < 0.001), after controlling for other covariates. These results suggest caution in the use of normative data with the K-D. Future studies should explore the impact of factors associated with reading skill level on sensitivity of the K-D in detecting concussion.

Health-Related Quality of Life Following Concussion in Collegiate Student-Athletes With and Without Concussion History.

The purpose of this study was to compare global and specific health-related quality of life (HRQOL) throughout concussion recovery between those with and without concussion history. Student-athletes diagnosed with concussion completed global (Short Form-12v2; SF-12) and specific (Hospital Anxiety and Depression Scale: HADS) HRQOL assessments at baseline, 24-48 h, asymptomatic, return-to-play, and 6-months post-injury. Baseline scores were compared to post-injury time points for SF-12 subscores (physical and mental; PCS-12, MCS-12) and HADS subscores (depression and anxiety; HADS-D, HADS-A). We conducted a 2 × 5 mixed model ANOVA for group (with and without concussion history) and time (four post-injury assessments compared to baseline). We did not observe interaction or main effects for group, except those with concussion history had worse HADS-D subscores than those without concussion history. PCS-12 subscores were worse at 24-48 h, asymptomatic, and return-to-play compared to baseline, but returned to baseline 6-months post-injury. MCS-12 subscores did not differ at any time points. HADS-D subscores worsened 24-48 h post-injury, but improved for additional assessments compared to baseline. HADS-A improved post-injury compared to baseline at asymptomatic, return-to-play, and 6-month assessments, but was similar to baseline 24-48 h post-injury. HRQOL physical aspects slightly worsened post-injury and restored to baseline after returning to play.

New insight into organic anion transporters from the perspective of potentially important interactions and drugs toxicity.

The family of organic anion transporters (OATs) includes a group of over 10 transmembrane transporting proteins belonging to the solute carrier 22 subfamilies of the major facilitator superfamily. Their function is related to the transport of a great variety of organic anions against the electrical and chemical gradient. OATs are present in most types of human tissues, including the kidneys, liver, placenta, olfactory epithelium, retina, and choroid plexus tissues. The OATs family plays an important role in the cellular uptake, distribution, excretion, and detoxification of many water-soluble drugs, endogenous compounds, nutrition ingredients, environmental contaminants and toxins, and significantly impacts their efficacy, pharmacokinetics and toxicity, both in a preferable and unfavorable way. OATs demonstrated great potential to participate in many potentially relevant interactions, which may lead to unexpected, but not always detrimental, effects. Wider knowledge about their specific functions in the body, role in disease states, pharmacokinetics interactions, and intraindividual response to therapeutic treatment will allow to predict and prevent OAT-related adverse effects or use favorable interactions in pharmacotherapy, as well as to rationally design therapeutics targeted at individual transporter drugs with improved bioavailability, prolonged half-life or reduced toxicity, and improve safety guidelines concerning drug dosage. This review gathers recent reports regarding OAT-related essential interactions involving components of popular therapeutic herbal products, dietary supplements, and clinically important drugs, their significance and potential suitability in modulating the severity of drug-related side effects and toxicity mechanisms.

An acoustic startle alters knee joint stiffness and neuromuscular control.

Growing evidence suggests that the nervous system contributes to non-contact knee ligament injury, but limited evidence has measured the effect of extrinsic events on joint stability. Following unanticipated events, the startle reflex leads to universal stiffening of the limbs, but no studies have investigated how an acoustic startle influences knee stiffness and muscle activation during a dynamic knee perturbation. Thirty-six individuals were tested for knee stiffness and muscle activation of the quadriceps and hamstrings. Subjects were seated and instructed to resist a 40-degree knee flexion perturbation from a relaxed state. During some trials, an acoustic startle (50 ms, 1000 Hz, 100 dB) was applied 100 ms prior to the perturbation. Knee stiffness, muscle amplitude, and timing were quantified across time, muscle, and startle conditions. The acoustic startle increased short-range (no startle: 0.044 ± 0.011 N·m/deg/kg; average startle: 0.047 ± 0.01 N·m/deg/kg) and total knee stiffness (no startle: 0.036 ± 0.01 N·m/deg/kg; first startle 0.027 ± 0.02 N·m/deg/kg). Additionally, the startle contributed to decreased [vastus medialis (VM): 13.76 ± 33.6%; vastus lateralis (VL): 6.72 ± 37.4%] but earlier (VM: 0.133 ± 0.17 s; VL: 0.124 ± 0.17 s) activation of the quadriceps muscles. The results of this study indicate that the startle response can significantly disrupt knee stiffness regulation required to maintain joint stability. Further studies should explore the role of unanticipated events on unintentional injury.

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.

Effect of strength and proprioception training on eversion to inversion strength ratios in subjects with unilateral functional ankle instability.

OBJECTIVES: To examine the effect of six weeks of strength and proprioception training on eversion to inversion isokinetic strength ratios (E/I ratios) in subjects with unilateral functional ankle instability. METHODS: Thirty eight subjects were randomly assigned to one of four treatment groups: strength training (S); proprioception training (P); strength + proprioception training (B); control (C). Isokinetic strength was tested before and after training using a Kin Com 125 automatic positioning isokinetic dynamometer. Subtalar joint eversion and inversion motions were tested both concentrically and eccentrically through a range of motion involving 40 degrees. All peak torque and average torque values were normalised for body mass. E/I ratios were calculated from average torque and peak torque measures by taking the concentric eversion value and combining it with the eccentric inversion value. Data were analysed using a mixed model analysis of variance with repeated measures on the test factor. Average torque and peak torque E/I ratios at 30 and 120 degrees/s were analysed separately. RESULTS: There were no significant differences in average torque and peak torque E/I ratios of the functionally unstable ankle for any of the groups after training compared with before. CONCLUSIONS: Six weeks of strength and proprioception training (either alone or combined) had no effect on isokinetic measures of strength in subjects with self reported unilateral functional instability. Further studies examining this agonist (concentric) to antagonist (eccentric) muscle group strength ratio are needed.

Impact forces and neck muscle activity in heading by collegiate female soccer players.

Three soccer header types (shooting, clearing and passing) and two heading approaches (standing and jumping) were manipulated to quantify impact forces and neck muscle activity in elite female soccer players. The 15 participants were Division I intercollegiate soccer players. Impact forces were measured by a 15-sensor pressure array secured on the forehead. The electromyographic (EMG) activity of the left and right sternocleidomastoid and trapezius muscles was recorded using surface electrodes. Maximum impact forces and impulses as well as the EMG data were analysed with separate repeated-measures analyses of variance. Impact forces and impulses did not differ among the header types or approaches. Higher values were found for jumping versus standing headers in the mean normalized EMG for the right sternocleidomastoid. In addition, the integrated EMG was greater for the right sternocleidomastoid and right and left trapezius (P < 0.05). The sternocleidomastoid became active earlier than the trapezius and showed greater activity before ball contact. The trapezius became active just before ball contact and showed greater activity after ball contact. The increased muscle activity observed in the neck during the jumping approach appears to stabilize the connection between the head and body, thereby increasing the stability of the head-neck complex.

High-intensity dynamic human muscle performance enhanced by a metabolic intervention.

PURPOSE: The purpose of this study was to quantify the effects of a metabolic treatment on human muscle dynamic performance (strength, work, and fatigue) measured under conditions of acute, exhaustive high-intensity anaerobic isokinetic exercise. METHODS: Unilateral prefatigue and postfatigue peak torque and work values were measured in the quadriceps femoris of 13 subjects using a computer-controlled isokinetic dynamometer, over a 23-d interval. The two experimental treatments were: 1) a glycine and L-arginine salt of alpha-ketoisocaproic acid calcium ("GAKIC"); and 2) isocaloric sucrose (control). Based on a randomized double-blind cross-over repeated measures design, measurements were made before and during an exhaustive anaerobic fatigue protocol to calculate a Fatigue Resistance Index (FRI = [peri-exhaustion torque]\[baseline peak torque]), as well as total work. RESULTS: The FRI and total work for each of the exhaustion sets measured at 0, 5, and 15 min after oral GAKIC treatment were greater than values obtained for isocaloric control treatment (P < 0.02). GAKIC treatment increased the mean resistance to fatigue (FRI) up to 28% over isocaloric control. Overall gain in total muscle work attributable to GAKIC was 10.5 +/- 0.8% greater than control, sustained for at least 15 min. After 24 h, both GAKIC and control concentric forces returned to the same absolute values (P > 0.05): mean FRI = 0.42 +/- 0.05 and mean total work = 4600 +/- 280 J. There were no significant differences attributable to random order of testing. CONCLUSIONS: Compared with isocaloric carbohydrate, oral GAKIC treatment increased muscle torque and work sustained during intense acute anaerobic dynamic exercise; additionally, it increased overall muscle performance by delaying muscle fatigue during the early phases of anaerobic dynamic exercise.

Differential control during maximal concentric and eccentric loading revealed by characteristics of the electromyogram.

Maximal eccentric loading has been associated with higher levels of spindle afferent activity but lower levels of integrated EMG as compared to maximal concentric loading. Elbow flexor EMG was recorded from 17 subjects during concentric (CONC) and eccentric (ECC) elbow flexion at 70 degrees s(-1) using a Kin-Com dynamometer. We hypothesized that peak EMG amplitude would be more sensitive to fluctuations in facilitation by the spindle primary afferents via the segmental stretch reflex pathway, and that the mean EMG would be more reflective of the ongoing level of muscle activation. A ratio of peak to mean EMG (P/M EMG ratio) was predicted to be larger during maximal eccentric loading than maximal concentric loading. The peak EMG (P<0.013) and the P/M EMG ratio (P<0.001) were significantly greater during the ECC condition than the CONC condition. In a subgroup of three subjects who underwent 3 weeks of eccentrically biased weight training, EMG, peak torque and torque variability were assessed before and after training. P/M EMG ratio decreased, while peak torque and torque variability increased following the training. Differences in the P/M EMG ratio appear to reflect differences in the way eccentric and concentric muscle actions are controlled and do not simply represent less control during the eccentric task.

Eversion strength analysis of uninjured and functionally unstable ankles.

OBJECTIVE: Functional ankle instability (FAI) afflicts many athletes. Several causes of FAI have been implicated, including peroneal muscle weakness. Traditional musculoskeletal rehabilitation programs have focused on concentric muscle strength. The purpose of our study was to compare concentric and eccentric isokinetic and isometric eversion ankle strength measurements between subjects identified as having unilateral FAI and subjects having no history of inversion ankle sprain. DESIGN AND SETTING: Employing a matched-pairs technique, subjects with no history of ankle injury were compared with subjects with unilateral FAI using isokinetic and isometric measures of eversion ankle strength. Strength testing was performed in a sports medicine clinic setting. SUBJECTS: Forty-two subjects volunteered for this study: 21 subjects suffered from unilateral FAI (age = 19.3 +/- 1.1 years, wt = 84.0 +/- 9.5 kg, ht = 181.5 +/- 9.2 cm), while 21 subjects served as matched-paired controls (age = 19.5 +/- 1.2 years, wt = 82.5 +/- 10.9 kg, ht = 179.5 +/- 7.9 cm). MEASUREMENTS: Ankle eversion concentric and eccentric strength (peak torque) was assessed at 0 degrees /s, 30 degrees /s, 60 degrees /s, 90 degrees /s, 120 degrees /s, 150 degrees /s, and 180 degrees /s using an isokinetic dynamometer. RESULTS: We found no significant differences in concentric, eccentric, or isometric eversion ankle strength between the 2 groups of subjects. CONCLUSIONS: The exact cause of FAI remains elusive. Based on our results, those who suffer from unilateral FAI do not appear to have eversion strength deficits. Unless clear evidence of weakness exists, clinicians may find that eversion strength training exercises are unnecessary. Future research should examine other causes of FAI, including reciprocal muscle group strength ratios and proprioception deficits.

Concentric versus enhanced eccentric hamstring strength training: clinical implications.

OBJECTIVE: Hamstring injuries can be quite debilitating and often result in chronic problems. Eccentric muscle actions are often the last line of defense against muscle injury and ligament disruption. Traditionally, the focus of hamstring strength rehabilitation has been on concentric muscle actions. The purpose of our study was to compare hamstring muscle strength gains in concentric and eccentric hamstring strength training. DESIGN AND SETTING: A randomized-group design was used to examine differences in 1-repetition maximum (1 RM) and isokinetic strength values among 3 groups of subjects. Subjects were tested in a biomechanics laboratory using an isokinetic dynamometer, while training was carried out in a physical therapy outpatient clinic. SUBJECTS: Twenty-seven healthy male subjects (age = 22.9 +/- 3.1 years, wt = 81.8 +/- 12.9 kg, ht = 178.6 +/- 7.2 cm) participated in this study. Subjects were randomly assigned to 1 of 3 treatment groups: eccentric training, concentric training, or control. MEASUREMENTS: Subjects performed hamstring curls using an isotonic weight training device. Pretest 1 RM weight values were determined for all subjects using a standardized 1 RM protocol. In addition, maximum concentric and eccentric isokinetic strength values for knee-flexion strength were determined. Control group subjects refrained from weight training for 6 weeks. Subjects in the training groups trained 2 days per week for 6 weeks (12 sessions). After 6 weeks of training, all subjects returned for 1RM and isokinetic posttesting. RESULTS: The concentric group improved 19%, while the eccentric group improved 29%. The control group subjects did not show any significant change over the 6 weeks. In addition, there were improvements in eccentric isokinetic peak torque/ body weight ratios at both 60 degrees s and 180 degrees from pretesting to posttesting in the eccentric training group only. CONCLUSIONS: Our results demonstrate the effectiveness of isotonic strength training on the development of hamstring muscle strength. More important is the dramatic effect of eccentric strength training on overall hamstring muscle strength, both isotonic and isokinetic. Clinicians should consider using eccentric hamstring strengthening as part of their rehabilitation protocols for hamstring and knee injuries.

Contrast therapy does not cause fluctuations in human gastrocnemius intramuscular temperature.

OBJECTIVE: Contrast therapy has a long history of use in sports medicine. Edema and ecchymosis reduction, vasodilation and vasoconstriction of blood vessels, blood flow changes, and influences on the inflammatory response are physiologic effects attributed to the ability of this modality to evoke tissue temperature fluctuations. Our purpose was to measure the change in human gastrocnemius intramuscular tissue temperature during a typical contrast therapy treatment. DESIGN AND SETTING: A randomized-group design was used to examine differences between 2 groups of subjects following a 31-minute warm whirlpool (control) and a 31-minute contrast therapy (experimental) treatment. A hydrotherapy room in a small- college sports medicine facility served as the test environment. SUBJECTS: Twenty (7 females and 13 males) healthy college students (age = 20.9 +/- 1.2 years; ht = 178.5 +/- 11.1 cm; wt = 79.2 +/- 21.7 kg) volunteered to participate in this study. Subjects were randomly assigned to either a control or a treatment group. MEASUREMENTS: Intramuscular tissue temperatures in the gastrocnemius were recorded every 30 seconds. RESULTS: There was a significant difference in mean overall temperature change between the experimental group (0.85 degrees C +/- 0.60 degrees C) and the control group (2.10 degrees C +/- 1.50 degrees C). In addition, there were significant differences between the 2 groups at 10, 15, 16, 20, 21, 25, 26, 30, and 31 minutes. At each recording point, the control group temperature change was significantly higher than that of the experimental group. There was no difference in absolute temperatures at the 11-minute recording point between the groups. CONCLUSIONS: Contrast therapy did not lead to significant fluctuations in muscle tissue temperature at 4 cm below the skin's surface. Therefore, it seems unlikely that the physiologic effects attributed to these fluctuations occur. A 1-minute exposure to a cold whirlpool during a typical contrast treatment does not appear to be long enough to significantly decrease tissue temperature after exposure to the warm hydrotherapy environment.

Effect of prophylactic knee bracing on balance and joint position sense.

Prophylactic knee braces are designed to prevent and reduce the severity of ligamentous injuries to the knee. Conflicting evidence is reported concerning their efficacy. The purpose of this study was to determine the effect of prophylactic knee bracing on the proprioceptive parameters of balance and joint position sense. Active and passive joint position sense were assessed using the Cybex II + Isokinetic Dynamometer (Cybex Division of Lumex, Inc, Ronkonkoma, NY). Sway index and center of balance were assessed using the Chattecx Dynamic Balance System (Chattanooga Group, Hixson, TN). Thirty-six male subjects were measured with and without prophylactic knee braces. Joint position sense was measured in degrees of error from four preselected target angles. Sway index and center of balance measures were recorded in centimeters under the following platform conditions: stable, plantar flexion/dorsiflexion, and inversion/eversion. Separate repeated measures ANOVAs were performed to determine if there were differences between the braced and unbraced conditions for center of balance, sway index, and joint position sense. Center of balance with the platform moving in a dorsi/plantar flexion direction was improved while wearing the knee braces. In addition, differences in both center of balance and sway were recorded across the three platform conditions with and without knee bracing. Bracing did not affect joint position sense. The results of this study suggest that prophylactic knee braces have very little impact on proprioceptive feedback mechanisms.