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1.  The Independent and Interactive Effects of Navicular Drop and Quadriceps Angle on Neuromuscular Responses to a Weight-Bearing Perturbation 
Journal of Athletic Training  2006;41(3):251-259.
Context: Little is known about the effects of static alignment on neuromuscular control of the knee during dynamic motion.
Objective: To evaluate the isolated and combined effects of quadriceps angle (QA) and navicular drop (ND) on neuromuscular responses to a weight-bearing perturbation.
Design: Mixed-model, repeated-measures design.
Setting: Sports medicine and athletic training research laboratory.
Patients or Other Participants: Seventy-nine National Collegiate Athletic Association Division I collegiate female athletes, classified with below-average ND and QA (LND-LQA); below-average ND and above-average QA (LND-HQA); above-average ND and below-average QA (HND-LQA); or above-average ND and QA (HND-HQA).
Intervention(s): A lower extremity perturbation device produced a forward and either internal or external rotation of the trunk and femur on the weight-bearing tibia to evoke a reflex response.
Main Outcome Measure(s): Neuromuscular responses were examined in the quadriceps, hamstrings, and gastrocnemius muscles: preperturbation amplitude 50 milliseconds before the perturbation, reflex time, and postperturbation amplitude 150 milliseconds immediately postperturbation.
Results: Navicular drop had the greatest effect on preperturbation amplitude of the lateral hamstrings and postperturbation amplitude of all muscles, with greater activation amplitude noted in subjects in the HND classifications. Quadriceps angle primarily affected reflex time of the quadriceps; in subjects with LQA, reflex time was faster for internal rotation than external rotation perturbations. The interaction between ND and QA had the greatest effect on reflex time of the lateral hamstrings. For internal rotation perturbations, subjects in the LND classifications had faster reflex times in the lateral hamstrings if they had HQA values rather than LQA values. With external rotation perturbations, HND-LQA subjects had slower reflex times than those in all other alignment classifications.
Conclusions: Navicular drop and QA have both independent and interactive effects on neuromuscular responses to a weight-bearing, rotational perturbation. These interactive effects highlight the importance of considering the entire lower extremity posture rather than a single alignment characteristic, given the potential for one alignment factor to compensate for or interact with another.
PMCID: PMC1569553  PMID: 17043692
long latency reflex time; lower extremity alignment; anatomical risk factors
2.  Development and Reliability of the Ankle Instability Instrument 
Journal of Athletic Training  2006;41(2):154-158.
Context: Functional ankle instability has been defined in a variety of ways. Factors that are frequently used in this definition include a history of a severe ankle sprain, a history of multiple ankle sprains, and a recurrent feeling of instability or “giving way.” With all the variations in defining functional ankle instability, it becomes increasingly important to develop a more consistent framework for assessing this instability.
Objective: To develop a new ankle instability assessment tool, the Ankle Instability Instrument, and evaluate the reliability of this instrument.
Design: Test-retest reliability was evaluated using intraclass correlation coefficients (2,1) for each item, each factor, and the total score between test days 1 and 2. Cronbach alpha was calculated to estimate internal consistency of the 12 items.
Setting: Classrooms, offices, athletic fields, and private residences.
Patients or Other Participants: College students (29 males, 72 females, age = 20.7 ± 2.7 years), including 73 (72%) with and 28 (28%) without a history of ankle injury.
Main Outcome Measure(s): Subjects were asked to complete the Ankle Instability Instrument on 2 occasions approximately 1 week apart.
Results: An exploratory factor analysis of the Instrument produced 3 factors and reduced it from 21 to 12 items. The factors accounted for 32.3%, 10.7%, and 7.0% of the variance, respectively. Together, these factors accounted for 50.0% of the variance in the responses to the Instrument. Test-retest reliability ranged from .70 (SEM = 0.28) to .98 (SEM = 0.06) for the individual items and .95 (SEM = 1.85) for the Instrument overall. The Cronbach alpha coefficient was .92 for factor 1 (severity of initial ankle sprain), .87 for factor 2 (history of ankle instability), .81 for factor 3 (instability during activities of daily life), and .89 for the Instrument overall.
Conclusions: The creation of the Ankle Instability Instrument is a first step in recognizing a more objective way of identifying patients suffering from functional ankle instability. The high reliability we found shows that self-reporting of ankle symptoms is a feasible, appropriate way to obtain information on the presence of instability symptoms. Additionally, through this preliminary study, we found 3 factors that represent unique and important components of functional ankle instability. Clinicians and researchers can, therefore, use these 12 items, either alone or in combination with other information, to determine if functional ankle instability is present.
PMCID: PMC1472648  PMID: 16791299
ankle assessment; ankle sprain; functional ankle instability
3.  Reduced Quadriceps Activation After Lumbar Paraspinal Fatiguing Exercise 
Journal of Athletic Training  2006;41(1):79-86.
Context: Although poor paraspinal muscle endurance has been associated with less quadriceps activation (QA) in persons with a history of low back pain, no authors have addressed the acute neuromuscular response after lumbar paraspinal fatiguing exercise.
Objective: To compare QA after lumbar paraspinal fatiguing exercise in healthy individuals and those with a history of low back pain.
Design: A 2 × 4 repeated-measures, time-series design.
Setting: Exercise and Sport Injury Laboratory.
Patients or Other Participants: Sixteen volunteers participated (9 males, 7 females; 8 controls and 8 with a history of low back pain; age = 24.1 ± 3.1 years, height = 173.4 ± 7.1 cm, mass = 72.4 ± 12.1 kg).
Intervention(s): Subjects performed 3 sets of isometric lumbar paraspinal fatiguing muscle contractions. Exercise sets continued until the desired shift in lumbar paraspinal electromyographic median power frequency was observed. Baseline QA was compared with QA after each exercise set.
Main Outcome Measure(s): An electric burst was superimposed while subjects performed a maximal quadriceps contraction. We used the central activation ratio to calculate QA = (FMVIC/[FMVIC + FBurst])* 100, where F = force and MVIC = maximal voluntary isometric contractions. Quadriceps electromyographic activity was collected at the same time as QA measurements to permit calculation of median frequency during MVIC.
Results: Average QA decreased from baseline (87.4% ± 8.2%) after the first (84.5% ± 10.5%), second (81.4% ± 11.0%), and third (78.2% ± 12.7%) fatiguing exercise sets. On average, the group with a history of low back pain showed significantly more QA than controls. No significant change in quadriceps median frequency was noted during the quadriceps MVICs.
Conclusions: The quadriceps muscle group was inhibited after lumbar paraspinal fatiguing exercise in the absence of quadriceps fatigue. This effect may be different for people with a history of low back pain compared with healthy controls.
PMCID: PMC1421484  PMID: 16619099
superimposed burst technique; quadriceps muscle inhibition; low back pain
4.  Quadriceps Inhibition After Repetitive Lumbar Extension Exercise in Persons With a History of Low Back Pain 
Journal of Athletic Training  2006;41(3):264-269.
Context: A neuromuscular relationship exists between the lumbar extensor and quadriceps muscles during fatiguing exercise. However, this relationship may be different for persons with low back pain (LBP).
Objective: To compare quadriceps inhibition after isometric, fatiguing lumbar extension exercise between persons with a history of LBP and control subjects.
Design: A 2 × 3 factorial, repeated-measures, time-series design with independent variables of group (persons with a history of LBP, controls) and time (baseline, postexercise set 1, postexercise set 2).
Setting: University research laboratory.
Patients or Other Participants: Twenty-five subjects with a history of LBP were matched by sex, height, and mass to 25 healthy control subjects.
Intervention(s): Electromyography median frequency indexed lumbar paraspinal muscular fatigue while subjects performed 2 sets of isometric lumbar extension exercise. Subjects exercised until a 15% downward shift in median frequency for the first set and a 25% shift for the second set were demonstrated.
Main Outcome Measure(s): Knee extension force was measured while subjects performed an isometric maximal quadriceps contraction. During this maximal effort, a percutaneous electric stimulus was applied to the quadriceps, causing a transient, supramaximal increase in force output. We used the ratio between the 2 forces to estimate quadriceps inhibition. Quadriceps electromyographic activity was recorded during the maximal contractions to compare median frequencies over time.
Results: Both groups exhibited significantly increased quadriceps inhibition after the first (12.6% ± 10.0%, P < .001) and second (15.2% ± 9.7%, P < .001) exercise sets compared with baseline (9.6% ± 9.3%). However, quadriceps inhibition was not different between groups.
Conclusions: Persons with a history of LBP do not appear to be any more or less vulnerable to quadriceps inhibition after fatiguing lumbar extension exercise.
PMCID: PMC1569566  PMID: 17043693
superimposed burst technique; neuromuscular activity; knee
5.  Fatigue, Vertical Leg Stiffness, and Stiffness Control Strategies in Males and Females 
Journal of Athletic Training  2006;41(3):294-304.
Context: Fatigue appears to influence musculoskeletal injury rates during athletic activities, but whether males and females respond differently to fatigue is unknown.
Objective: To determine the influence of fatigue on vertical leg stiffness (K VERT) and muscle activation and joint movement strategies and whether healthy males and females respond similarly to fatigue.
Design: Repeated-measures design with all data collected during a single laboratory session.
Setting: Laboratory.
Patients or Other Participants: Physically active males (n = 11) and females (n = 10).
Intervention(s): Subjects performed hopping protocols at 2 frequencies before and after fatigue, which was induced by repeated squatting at submaximal loads.
Main Outcome Measure(s): We measured K VERT with a forceplate and peak muscle activity of the quadriceps, hamstrings, gastrocnemius, soleus, and anterior tibialis muscles with surface electromyography. Sagittal-plane kinematics at the knee and ankle were recorded with an electrogoniometer.
Results: After fatigue, K VERT was unchanged for all subjects. However, both males and females demonstrated reduced peak hamstrings ( P = .002) and anterior tibialis ( P = .001) activation, coupled with increased gastrocnemius ( P = .005) and soleus ( P = .001) peak activity, as well as increased quadriceps-hamstrings ( P = .005) and gastrocnemius/soleus-anterior tibialis coactivation ratios ( P = .03) after fatigue. Overall, females demonstrated greater quadriceps-hamstrings coactivation ratios than males, regardless of the fatigue condition ( P = .026). Only females showed increased knee flexion at initial contact after fatigue during hopping ( P = .03).
Conclusions: Although K VERT was unaffected, the peak muscle activation and joint movement strategies used to modulate K VERT were affected after fatigue. Once fatigued, both males and females used an ankle-dominant strategy, with greater reliance on the ankle musculature and less on the knee musculature. Also, once fatigued, all subjects used an antagonist inhibition strategy by minimizing antagonist coactivation. Overall, females used a more quadriceps-dominant strategy than males, showing greater quadriceps activity and a larger quadriceps-hamstrings coactivation ratio. Changes in muscle activation and coactivation ratios because of fatigue and sex are suggested to alter knee joint stability and increase anterior cruciate ligament injury risk.
PMCID: PMC1569557  PMID: 17043698
electromyography; anterior cruciate ligament; coactivation; injury prevention
6.  Effects of Pronated and Supinated Foot Postures on Static and Dynamic Postural Stability 
Journal of Athletic Training  2005;40(1):41-46.
Context: The foot is the most distal segment in the lower extremity chain and represents a relatively small base of support on which the body maintains balance (particularly in single-leg stance). Although it seems reasonable that even minor biomechanical alterations in the support surface may influence postural-control strategies, the implications of a hypermobile or hypomobile foot on balance have received little attention to date.
Objective: To determine if supinated and pronated foot types influence measures of static and dynamic balance.
Design: Participants were assigned to 1 of 3 groups depending on foot type, as defined by navicular-drop measures: pronated (≥10 mm), neutral (5–9 mm), or supinated (≤4 mm). Measures of static and dynamic balance were obtained for each participant and compared across groups.
Setting: Sports medicine and athletic training research laboratory.
Patients or Other Participants: Sixteen individuals with pronated (navicular drop = 13.0 ± 3.7 mm), neutral (navicular drop = 6.2 ± 1.1 mm), or supinated (navicular drop = 2.2 ± 1.7 mm) foot postures volunteered to participate in the study.
Main Outcome Measure(s): We used the Chattecx Balance System to measure center of balance, stability index, and postural sway during static single-limb stance under eyes-open and eyes-closed conditions. Center of balance was defined as the point on the foot at which the body weight was equally distributed between the medial-lateral and anterior-posterior quadrants and was recorded in centimeters. Stability index was defined as the mean deviation in sway around the center of balance. Postural sway was expressed as the maximum sway distance recorded (cm) in the medial-lateral and anterior-posterior directions. The Star Excursion Balance Test was used to measure dynamic balance, which was reported as the reach distance (cm) in each of the 8 directions tested. The average of 3 trials of each measure was calculated and normalized to the subject's height.
Results: We found no difference in center of balance or postural sway as a function of foot type. The stability index was greater in pronators than in supinators, but neither group was different from those with neutral foot types. Dynamic reach differed among groups but only in some directions. Generally, pronators reached farther in the anterior and anterior medial directions and supinators reached farther in the posterior and posterio-lateral directions. In the lateral direction, supinators reached farther than pronators but not farther than neutrals.
Conclusions: Our results suggest that postural stability is affected by foot type under both static and dynamic conditions. These differences appear to be related to structural differences as opposed to differences in peripheral input. These effects should be considered when clinicians use such balance measures to assess injury deficits and recovery.
PMCID: PMC1088344  PMID: 15902323
postural sway; proprioception; foot mechanics; foot injury; limits of stability; arch height
7.  Functional-Performance Deficits in Volunteers With Functional Ankle Instability 
Journal of Athletic Training  2005;40(1):30-34.
Context: Although functional-performance tests are dynamic measures used to assess general lower body function, studies investigating these tests for ankle instability have yielded conflicting results.
Objective: To determine if a relationship exists between a measure of functional ankle instability and deficits in functional performance.
Design: A case-control study correlating subject performance on a set of lower extremity functional-performance tests with a measure of ankle instability.
Setting: University athletic training research laboratory.
Patients or Other Participants: We recruited 60 participants (43 females, 17 males, age = 22.4 ± 4.9 years, height = 169.9 ± 9.7 cm, mass = 72.6 ± 16.3 kg; 42 injured, 18 uninjured) to participate in the study. Six questions were used to determine if functional ankle instability was present in each participant. A point was added for each yes response to produce an index that represents a continuous variable of functional ankle instability.
Main Outcome Measure(s): Four unilateral hopping tests were used in this study: figure-of-8 hop, side hop, up-down hop, and single hop. For the first 3 tests, the total time was recorded with a handheld stopwatch to the nearest 0.01 second; for the single hop-for-distance test, the distance was recorded to the nearest 0.01 m. Correlations were computed with the functional ankle instability index and each of the 4 functional-performance tests.
Results: No relationship was revealed between the functional ankle instability index and single hop for distance or up-down hop, with r values of −.008 and .245, respectively. A significant relationship was found between the functional ankle instability index and the side hop (r = .35, P ≤ .01) and the figure-of-8 hop (r = .31, P ≤ .02).
Conclusions: A positive relationship existed between functional ankle instability and performance deficits on the side hop and figure-of-8 hop. Conversely, a relationship did not exist between functional ankle instability and frontal-plane functional-performance activities.
PMCID: PMC1088342  PMID: 15902321
side hop; figure-of-8 hop
8.  Functional Fatigue Decreases 3-Dimensional Multijoint Position Reproduction Acuity in the Overhead-Throwing Athlete 
Journal of Athletic Training  2004;39(4):316-320.
Objective: To determine the effects of functional fatigue on active multijoint position reproduction in overhead-throwing athletes.
Design and Setting: A standard, repeated-measures, randomized-ordered, counterbalanced, 2-period (crossover) design was used. During the first test session, we randomly assigned subjects to either the nonfatigue or fatigue condition. Subjects underwent pretest measurements and then either a functional fatigue protocol or rest period, followed by posttest measurements. After a recovery period, subjects crossed over to the opposing condition for the second testing session.
Subjects: Thirteen overhead-throwing athletes competing in National Collegiate Athletic Association Division I or club baseball, with no history of upper extremity or central nervous system disorders, volunteered for this study.
Measurements: We measured active multijoint position reproduction accuracy in 3 dimensions using an electromagnetic tracking device. We noted each subject's ability to reproduce 3 positions corresponding with distinct moments of his throwing motion. A variable error score was calculated to compare the locations of the reproduced points with reference to the target point.
Results: A significant difference occurred between the pretest and posttest error scores in the fatigue condition. Comparisons between positions indicated that more errors were seen in the arm-cocked position than in the follow-through position under both fatigue and nonfatigue conditions.
Conclusions: Functional fatigue decreased joint position sense acuity in overhead-throwing athletes. Our findings using this novel testing measurement method are in agreement with past research, with one exception. The trend toward higher error scores in the arm-cocked position would appear to contradict findings that sensorimotor system acuity increases toward end ranges of motion.
PMCID: PMC535523  PMID: 15592603
joint position sense; 3-dimensional motion analysis
9.  Balance Recovers Within 20 Minutes After Exertion as Measured by the Balance Error Scoring System 
Journal of Athletic Training  2004;39(3):241-246.
Objective:
To determine a balance recovery timeline after a functional exertion protocol using the Balance Error Scoring System (BESS).
Design and Setting:
Five subject groups (4 test, 1 control) were tested 3 times during 1 session: once before the exertion protocol (pretest) and twice after the exertion protocol (posttest I and posttest II). Posttest I occurred at staggered intervals of 0, 5, 10, and 15 minutes, depending on experimental group assignment, and posttest II occurred at 20 minutes.
Subjects:
One hundred subjects (80 test, 20 control) volunteered to participate in this study. None of the subjects had a balance disorder, mild head injury, or lower extremity injury in the 6 months before testing.
Measurements:
We assessed balance using the BESS, assigning a score for each stance-surface condition.
Results:
We found a significant decrease in BESS performance after the exertion protocol in all test groups, with exertion having the greatest effect on the tandem and single-leg stance conditions. All subjects recovered by posttest II, which was administered 20 minutes after cessation of the exertion protocol.
Conclusions:
Athletic trainers need to be aware of the effect of exertion when administering the BESS after physical activity. Athletic trainers can expect the BESS performance of healthy athletes to return to baseline levels within 20 minutes of rest.
PMCID: PMC522146  PMID: 15496993
postural stability; fatigue; recuperation; concussion
10.  Performance on the Balance Error Scoring System Decreases After Fatigue 
Journal of Athletic Training  2004;39(2):156-161.
Objective:
To determine the immediate effects of a whole-body fatigue protocol on performance of the Balance Error Scoring System (BESS), a postural-stability test commonly used as part of a concussion-assessment battery.
Design and Setting:
Subjects were assigned to a fatigue or control group and were assessed before and immediately after a 20-minute fatigue protocol or rest period.
Subjects:
Fourteen fatigue subjects and 13 control subjects participated in this study. All subjects were male and free of vestibular disorders, and none had suffered a mild head injury or lower extremity injury in the preceding 6 months, as described through self-report.
Measurements:
We measured performance on the BESS for 9 stance-surface conditions and summed each condition to obtain a total score. Using the Borg scale, we also measured ratings of perceived exertion before, during, and after the fatigue protocol or rest period.
Results:
We found a significant increase in total errors from pretest to posttest in the fatigue group (14.36 ± 4.73 versus 16.93 ± 4.32), a significant decrease in errors in the control group (13.32 ± 3.77 versus 11.08 ± 3.88), and a significant difference between groups on the posttest. The rating of perceived exertion scores were significantly different between the fatigue and control groups at the middle (13.29 ± 1.59 versus 6.23 ± 0.83) and end (15.86 ± 2.38 versus 6.15 ± 0.55) of the fatigue or rest period.
Conclusions:
The BESS error scores increased immediately after the fatigue protocol, demonstrating that balance ability diminished. Clinicians who use the BESS as part of their sideline assessment for concussion should not administer the test immediately after a concussion due to the effects of fatigue.
PMCID: PMC419510  PMID: 15173867
balance; exertion; concussion; injury assessment
11.  Repeat Administration Elicits a Practice Effect With the Balance Error Scoring System but Not With the Standardized Assessment of Concussion in High School Athletes 
Journal of Athletic Training  2003;38(1):51-56.
Objective:
To assess whether repeated administration of the Standardized Assessment of Concussion (SAC) and Balance Error Scoring System (BESS) demonstrates a practice effect in high school athletes.
Design and Setting:
Subjects were assigned to either a control or practice group. Subjects in the control group were assessed twice, 30 days apart. Subjects in the practice group were assessed on 5 occasions. Four assessments were performed within a 7-day period and 1 more assessment 30 days after the initial test.
Subjects:
Thirty-two uninjured high school athletes participated in this investigation. Sixteen were randomly assigned to a control group and 16 to a practice group.
Measurements:
We measured performance on the SAC and on 6 test conditions of the BESS.
Results:
We found a significant time-by-group interaction on BESS performance on the day-30 test session. A significant practice effect of the BESS was found during the course of repeated administrations in the practice group. After repeated testing, the number of BESS errors decreased with each test session, and error scores on day 5 (10.94 ± 2.17) and day 7 (9.44 ± 3.32) were significantly lower than the baseline score (12.88 ± 3.34). We did not find group differences or a practice effect on the SAC (baseline score = 26.16).
Conclusions:
Our results revealed no practice effect with the SAC and a slight practice effect with repeated administrations of the BESS, especially with the single-leg stance on foam. Clinicians must acknowledge the potential for practice effects when readministering these concussion assessments to track recovery of an athlete or as a guide in return-to-play decision making.
PMCID: PMC155511  PMID: 12937472
postural stability; serial assessments; cognitive assessment
12.  Subtalar Pronation Does Not Influence Impact Forces or Rate of Loading During a Single-Leg Landing 
Journal of Athletic Training  2003;38(1):18-23.
Objective:
To identify the influence of static subtalar pronation (as measured by weight-bearing navicular drop [ND]) on ground impact forces and rate of loading during a single-leg landing.
Design and Setting:
Subjects were grouped (n = 16 per group) on the basis of weight-bearing ND scores (supinators, <5 mm; neutral, 5–10 mm; pronators, >10 mm). Subjects performed 5 single-leg landings, dropping from a 0.3-m height onto a force platform. An electrogoniometer simultaneously recorded sagittal knee range of motion during the landing task.
Subjects:
Forty-eight healthy volunteers participated.
Measurements:
Peak vertical force was defined as the highest force recorded in the Fz direction during landing. Rate of loading was defined as the peak vertical force divided by the time to reach the peak vertical force. Knee-flexion excursion was defined as the change in knee-flexion range from initial contact to peak vertical force.
Results:
Peak vertical force (P = .769) and rate of loading (P = .703) did not differ among groups. Although secondary analyses identified significant negative correlations between peak force and rate of loading with knee excursion, the amount of knee excursion was similar among groups (P = .744).
Conclusions:
Our results de-emphasize the influence of static anatomical foot alignment on impact forces and absorption during a single-leg drop landing and provide further support for the role of knee flexion in dissipation of landing forces. Further investigations are needed to fully elucidate the role of subtalar pronation and other lower extremity alignment factors in force dissipation during dynamic functional activities.
PMCID: PMC155506  PMID: 12937467
drop jump; subtalar motion; landing style; force absorption
13.  Strength, Functional Outcome, and Postural Stability After Anterior Cruciate Ligament Reconstruction 
Journal of Athletic Training  2002;37(3):262-268.
Objective: To compare postural stability, single-leg hop, and isokinetic strength measurements in subjects after anterior cruciate ligament (ACL) reconstruction with an age- and activity-matched control group.
Design and Setting: Subjects reported to a sports medicine/athletic training research laboratory for testing. Subjects reported for one testing session for a total test time of 1 hour.
Subjects: Twenty subjects with ACL reconstructions (ACLRs) and 20 age- and activity-matched controls were selected to participate in this study. An arthroscopically assisted central one-third bone-patellar tendon procedure was used to repair the ACLs.
Measurements: We measured concentric and eccentric peak torque (Nm) measurements of the knee extensors and flexors at 120° and 240°/second on an isokinetic dynamometer. Unilateral and bilateral dynamic postural stability was measured as a stability index in the anterior-posterior and medial-lateral planes with the Biodex Stability System. We tested single-leg hop for distance to measure objective function.
Results: We found no significant difference between the ACLR and control subjects for stability index or knee-flexion peak torque scores. On the single-leg hop for distance, the ACLR subjects hopped significantly shorter distances with the involved limb than the uninvolved limb. Furthermore, the ACLR subjects' single-leg hop distance was significantly less when the involved limb was compared with the control-group matched involved limb, and the ACLR subjects performed significantly better when the uninvolved limb was compared with the control-group matched uninvolved limb. The ACLR subjects produced significantly greater torque in the uninvolved leg than in the involved leg. In addition, the peak torque was significantly less for the involved limb in the ACLR group when compared with the matched involved limb of the control group.
Conclusions: After ACLR (mean = 18 ± 10 months), single-leg hop-for-distance scores and quadriceps strength were not within normal limits when compared with the contralateral limb. Our results suggest that bilateral and single-limb postural stability in the ACLR group was not significantly different than the control group at an average follow-up of 18 months after surgery.
PMCID: PMC164354  PMID: 12937583
ACL reconstruction; balance; single-leg hop; isokinetic strength; Biodex stability system
14.  Removal Tools are Faster and Produce Less Force and Torque on the Helmet Than Cutting Tools During Face-Mask Retraction 
Journal of Athletic Training  2002;37(3):246-251.
Objective: To investigate the retraction time, forces, and torques applied to the football helmet during removal of the face mask with different face-mask removal tools.
Design and Setting: Subjects retracted the face mask of a football helmet mounted to a force platform in a laboratory setting. They removed a standard face mask by cutting or removing (or both) the lateral plastic loop straps using 4 different tools: the Trainer's Angel (TA), FM Extractor (FM), power screwdriver (SD), and Quick Release System (QR) in a counterbalanced fashion.
Subjects: Eighteen certified athletic trainers participated in this study.
Measurements: We started measuring time when the subject picked up the tool and ended when the face mask was in a fully retracted position. Maximum forces and torques were measured from the force platform during the retraction process.
Results: The SD and QR retracted the face mask significantly faster than the TA and FM. Forces producing superior-inferior translation were least with the SD. The SD and QR produced less lateral translation and rotation and lateral flexion moment than the TA and FM. The FM produced less torque in the lateral flexion moment than the TA.
Conclusions: Tools that removed the loop straps (SD, QR) were faster and produced less force and torque on the helmet than the tools that cut through the loop straps (TA, FM).
PMCID: PMC164351  PMID: 12937580
cervical spine injury; loop straps; equipment removal
15.  Chronic Ankle Instability Does Not Affect Lower Extremity Functional Performance 
Journal of Athletic Training  2002;37(4):507-511.
Objective: To determine if functional performance is impaired in individuals with self-reported chronic ankle instability.
Design and Setting: We used a between-groups design to assess 3 functional variables. All data were collected at a Division III college and a military academy. Before testing, all subjects performed a 5-minute warm-up, followed by a series of stretches for the lower extremity muscles. Subjects then performed cocontraction, shuttle run, and agility hop tests in a counterbalanced fashion. Three trials for each functional test were completed and averaged for analysis.
Subjects: Twenty men with a history of at least 1 significant ankle sprain and episodes of at least 1 repeated ankle injury or feelings of instability or “giving way” were compared with 20 men with no prior history of ankle injury. Subjects were matched by age, height, weight, and activity level.
Measurements: Time to completion was measured in seconds for the cocontraction and the shuttle run tests. The agility hop test was measured on an error point scale.
Results: Using 3 separate, independent, 2-tailed t tests, we found no significant difference between groups for the cocontraction (P = .452), shuttle run (P = .680), or agility hop (P = .902) tests.
Conclusions: Chronic ankle instability is a subjectively reported phenomenon defined as the tendency to “give way” during normal activity. Although athletes commonly complain of subjective symptoms associated with chronic ankle instability, our findings suggest that these symptoms do not negatively influence actual functional performance. Future researchers should evaluate other, more demanding functional-performance tests to further substantiate these findings.
PMCID: PMC164385  PMID: 12937575
functional ankle instability; proprioception; mechanoreceptors; agility test
16.  The Effect of a Neoprene Shoulder Stabilizer on Active Joint-Reposition Sense in Subjects With Stable and Unstable Shoulders 
Journal of Athletic Training  2002;37(2):141-145.
Objective: To compare the effects of shoulder bracing on active joint-reposition sense in subjects with stable and unstable shoulders.
Design and Setting: Two subject groups, with stable and unstable shoulders, participated in an active joint-reposition test of the shoulder under braced and unbraced conditions.
Subjects: Forty subjects (22 men, 18 women; age = 21.85 ± 3.12 years; height = 173.97 ± 10.08 cm; weight = 71.27 ± 11.68 kg) were recruited to participate in this study. Twenty Division I athletes were referred to us for shoulder instability, which was subsequently confirmed with clinical assessment. The remaining 20 subjects were recruited from a similar student population and assessed as having stable shoulders.
Measurements: Each subject's ability to perceive joint position sense in space was tested by actively reproducing 3 preset angles (10° from full external rotation, 30° of external rotation, and 30° of internal rotation) with and without a shoulder brace. Full, active external-rotation range of motion was assessed before active joint-reposition sense testing.
Results: While wearing the shoulder brace, the group with unstable shoulders demonstrated significant improvement in the accuracy of active joint repositioning at 10° from full external rotation in comparison with the stable group. Furthermore, those with unstable shoulders demonstrated significantly less full external rotation than did those with stable shoulders, and the brace reduced full external rotation only for those with stable shoulders.
Conclusions: Our findings suggest that shoulder active joint-reposition sense in subjects with unstable shoulders can be improved at close to maximal external rotation by wearing a shoulder brace. This effect does not appear to be related to restriction of shoulder external rotation.
PMCID: PMC164336  PMID: 12937426
proprioception; glenohumeral joint; bracing
17.  Acute Orthotic Intervention Does Not Affect Muscular Response Times and Activation Patterns at the Knee 
Journal of Athletic Training  2002;37(2):133-140.
Objective: To evaluate the short-term effect of a semirigid foot orthotic device on response times and activation patterns of knee musculature in individuals with hyperpronation after a lower extremity perturbation in a single-leg, weight-bearing stance.
Design and Setting: We used a lower extremity perturbation device designed to produce a forward and either internal or external rotation of the trunk and femur on the weight-bearing tibia to evoke a reflex response. Subjects were tested both with and without orthotic devices.
Subjects: Seventeen (13 male, 4 female) volunteers (age, 20.6 ± 1.8 years; height, 181.0 ± 8.1 cm; weight, 87.4 ± 19.5 kg; navicular drop, 12.1 ± 1.8 mm) with a navicular drop greater than 10 mm volunteered for this study.
Measurements: Long latency reflex times were recorded via surface electromyography for the medial and lateral hamstrings, gastrocnemius, and quadriceps muscles.
Results: A dependent-sample t test revealed a significant decrease in navicular drop with orthotic intervention (P < .0001). With that confirmed, separate repeated-measures analyses of variance with 2 within factors (orthotic condition and muscle) revealed no significant difference in muscle response time between orthotic and nonorthotic conditions for either internal or external rotation perturbation. Although we found a main effect for muscle for both internal (P < .0001) and external (P < .0001) rotation, indicating a preferred muscle activation order, this activation order did not differ between orthotic and nonorthotic conditions (internal rotation P = .674, external rotation P = .829).
Conclusions: Our findings suggest that a short-term application of a semirigid orthotic device does not alter muscle response times or activation patterns of the muscles that stabilize the knee. Further research is needed to determine whether changes in activation patterns may occur over time since mechanical adaptations occur with long-term wear.
PMCID: PMC164335  PMID: 12937425
hyperpronation; subtalar pronation; electromyography; long latency reflex
18.  Duration of Maintained Hamstring Flexibility After a One-Time, Modified Hold-Relax Stretching Protocol 
Journal of Athletic Training  2001;36(1):44-48.
Objective:
Previous research suggests proprioceptive neuromuscular facilitation (PNF) stretching techniques produce greater increases in range of motion than passive, ballistic, or static stretching methods. The purpose of our study was to measure the duration of maintained hamstring flexibility after a 1-time, modified hold-relax stretching protocol.
Design and Setting:
The study had a 1 × 1 mixed-model, repeated-measures design. The independent variables were group (control and experimental) and time (0, 2, 4, 6, 8, 16, and 32 minutes). The dependent variable was hamstring flexibility as measured in degrees of active knee extension with the hip flexed to 90°. Measurements were taken in a preparatory military academy athletic training room.
Subjects:
Thirty male subjects (age, 18.8 ± 0.63 years; height, 185.2 ± 14.2 cm; weight, 106.8 ± 15.7 kg) with limited hamstring flexibility in the right lower extremity were randomly assigned to a control (no-stretch) group or an experimental (stretch) group.
Measurements:
All subjects performed 6 warm-up active knee extensions, with the last repetition serving as the prestretch measurement. The experimental group received 5 modified (no-rotation) hold-relax stretches, whereas the control group rested quietly supine on a table for 5 minutes. Posttest measurements were recorded for both groups at 0, 2, 4, 6, 8, 16, and 32 minutes.
Results:
The repeated-measures analysis of variance revealed a significant group-by-time interaction, a significant main effect for group, and a significant main effect for time. Dunnett post hoc analysis revealed a significant improvement in knee-extension range of motion in the experimental group that lasted 6 minutes after the stretching protocol ended.
Conclusions:
Our findings suggest that a sequence of 5 modified hold-relax stretches produced significantly increased hamstring flexibility that lasted 6 minutes after the stretching protocol ended.
PMCID: PMC155401  PMID: 12937514
active knee-extension test; knee joint range of motion
19.  Neuromuscular Response Characteristics in Men and Women After Knee Perturbation in a Single-Leg, Weight-Bearing Stance 
Journal of Athletic Training  2001;36(1):37-43.
Objective:
We examined whether muscle response times and activation patterns in the lower extremity differed between men and women in response to a rotational knee perturbation while standing in a single-leg, weight-bearing stance.
Design and Setting:
We used a lower extremity perturbation device to produce a sudden, forward, and either internal or external rotation moment of the trunk and femur relative to the weight-bearing tibia. Subjects completed 10 trials of both internal and external rotation perturbation; the first 5 acceptable trials were averaged and used for data analysis. Two separate, repeated-measures analyses of variance were used to compare myoelectric response times and activation patterns between men and women for both internal and external rotation perturbation.
Subjects:
Thirty-two female (19 lacrosse, 13 soccer) and 32 male (lacrosse) healthy intercollegiate athletes participated in the study.
Measurements:
We used surface electromyography to record long latency reflex times of the medial and lateral quadriceps, hamstring, and gastrocnemius muscles.
Results:
Women responded faster than men, primarily due to a shorter latency in quadriceps activation. However, men and women exhibited no difference in muscle-recruitment order.
Conclusions:
Although men and women demonstrated similar muscle-recruitment patterns to an imposed lower extremity perturbation, women tended to activate their quadriceps earlier than men. Whether this earlier quadriceps activation diminishes the ability of the hamstrings to adequately stabilize the knee joint or subjects the anterior cruciate ligament to greater risk of injury is still unknown and requires further study. Furthermore, although surface electromyography and measurement of myoelectric response times are useful in evaluating the timing, activation order, and coactivity patterns of the knee musculature, future studies should evaluate sex differences across the complete response continuum, including measures of intrinsic muscle stiffness, electromechanical delay, and time to force production.
PMCID: PMC155400  PMID: 12937513
electromyography; long latency reflex; anterior cruciate ligament
20.  Effect of Mild Head Injury on Postural Stability in Athletes 
Journal of Athletic Training  1996;31(4):300-306.
Objective:
Athletic trainers and team physicians are often faced with the dilemma of when to return athletes to participation following mild head injury. Unfortunately, clinicians rarely have quantitative information on which to base their decisions. The purpose of this investigation was to identify postural stability changes in athletes with acute mild head injury.
Design and Setting:
High school and college male athletes were prescreened for postural stability before the start of their season. Subjects suffering injury during the season returned for testing on days 1, 3, 5, and 10 following injury, and 1 month postseason. Control subjects were selected for comparisons.
Subjects:
Ten prescreened subjects (age = 17.4 ± 2.2 yr; ht = 183.8 + 8.1 cm; wt = 87.7 + 17.3 kg) returned for testing following an injury. Ten matched control subjects (age = 18.6 ± 2.6 yr; ht = 185.7 ± 6.7 cm; wt = 84.5 ± 19.5 kg) were selected for comparisons. Additionally, nine subjects (eight male and one female) (age = 19.9 ± 4.2 yr; ht = 182.3 + 10.9 cm; wt = 89.6 ± 25.2 kg) who had sustained a mild head injury from other varsity sports teams were recruited. Nine matched controls (age = 22.1 ± 3.3 yr; ht = 181.0 ± 9.9 cm; wt = 84.9 ± 25.6 kg) were again utilized.
Measurements:
Sway index and center of balance were measured using the Chattecx Balance System during three eye conditions and three surface conditions for all subjects.
Results:
Repeated measures analyses of variance (ANOVA) for each prescreened subject's sway index revealed significant differences between injured subjects and control subjects on day 1 postinjury as compared with the prescreening and/or subsequent tests. The analysis for sway index and center of balance inclusive of all 19 subjects with mild head injury and all 19 control subjects demonstrated increased postural sway compared with control subjects on day 1 postinjury during all plafform conditions, and on day 3 during the foam platform condition. The analysis for center of balance using the same subjects revealed that injured subjects maintained their center of balance farther away on day 1 postinjury compared with subsequent tests (p < .05).
Conclusions:
These findings suggest that computerized dynamic posturography is a useful tool in objectively assessing postural stability in subjects with mild head injuries. Subjects with mild head injury appear to demonstrate impaired postural stability 1 to 3 days following injury. This information should aid clinicians in determining when an athlete can safely return to participation.
Images
PMCID: PMC1318912  PMID: 16558414
concussion; balance; postural sway
21.  1994 Athletic Trainer Employment and Salary Characteristics 
Journal of Athletic Training  1996;31(3):215-218.
Objective:
The purpose of this study was to determine: 1) demographics and professional credentials of recently hired athletic trainers, 2) the association between these characteristics and the high school, clinical, and collegiate setting, and 3) which of these factors best predicted salary.
Design and Setting:
A survey was sent to all prospective employers. Of the 472 surveys sent, 282 (60%) were returned.
Subjects:
Prospective employers who were listed on the NATA job vacancy notices from January 1, 1994 to October 1, 1994.
Measurements:
Employers selected a job description for their position opening and indicated the characteristics of the people they hired. The job descriptions were placed into three categories. A chi-square analysis was used to determine the degree of association between applicant characteristics and job descriptions. Employee characteristics were coded and a stepwise multiple regression analysis was performed to determined which of the characteristics best predicted salary. Analyses of variance were performed to determine differences among the three practice settings and as follow-up analyses to the multiple regression. An analysis of variance was also performed to compare salaries based on job description and teaching responsibilities.
Results:
No association was found between the employment setting and gender, ethnicity, marital status, educational route, physical therapy, credential, or EMT certification. There was an association between the CPR instructor's credential and employment setting and between highest degree attained and employment setting.
Conclusions:
The results suggest that these factors were most closely associated with employment in the collegiate setting. With regard to salary, it was determined that a doctoral degree, a master's degree, and marital status were the best predictors of salary.
PMCID: PMC1318506  PMID: 16558401
Survey; employment setting; credentials
22.  Effect of ACL Reconstruction and Tibial Rotation on Anterior Knee Laxity 
Journal of Athletic Training  1995;30(3):243-246.
The anterior cruciate ligament (ACL) is the primary restraint to anterior translation of the tibia on the femur. Research suggests that resistance to anterior translation changes as the tibia is rotated internally and externally. This study assessed the degree to which ACL reconstruction and tibial rotation affects anterior knee laxity. Nine subjects with ACL lesions and functional instabilities participated in the study. Subjects were measured 1 to 10 days before surgery and 6 to 8 months after ACL reconstruction using the KT-1000 knee arthrometer. A mechanical leg stabilizer was used to assess anterior translation at 20° of knee flexion in three positions: internal rotation of 15°, neutral, and external rotation of 15°. Subjects were measured at 89 and 67 N of anterior force. Data were analyzed with a three-factor (test × position × force) repeated measures ANOVA. Following surgery, reduction in laxity (mm) for the three positions (internal rotation, neutral, and external rotation) was 1.9, 2.8, and 3.4, respectively, at 89 N and 1.5, 2.0, and 2.6, respectively, at 67 N. The degree of reduction in laxity (presurgery to postsurgery) was dependent upon rotation and force, and was greatest in external rotation and least in internal rotation pre- to postsurgery. We concluded that ACL reconstruction using a patellar tendon graft significantly decreased anterior tibial translation at all three positions, but a greater amount of reduction was observed postsurgically at the externally rotated position. This supports the theory that mechanical blocks and secondary restraints such as a taut mid-third of the iliotibial tract may interfere with clinical laxity tests in some positions of tibial rotation. Fixing the tibia in an externally rotated position may decrease the effect of secondary restraints and improve sensitivity in testing for ACL laxity.
Images
PMCID: PMC1317869  PMID: 16558343
23.  Ankle Bracing and the Neuromuscular Factors Influencing Joint Stiffness 
Journal of Athletic Training  2009;44(4):363-369.
Context:
Health care professionals commonly prescribe external stabilization to decrease the incidence and severity of ankle sprains. The mechanism for this decrease is not clearly understood. Examining the effects of ankle bracing on biomechanical stability and influencing factors may provide important information regarding the neuromuscular effects of bracing.
Objective:
To study the effects of 2 different ankle braces on the neuromuscular factors influencing ankle stiffness.
Design:
Mixed-model repeated-measures design.
Setting:
Research laboratory.
Patients or Other Participants:
Twenty-eight physically active participants composing 2 groups: 14 with unilateral functional ankle instability (age  =  26.19 ± 6.46 years, height  =  166.07 ± 12.90 cm, mass  =  69.90 ± 13.46 kg) and 14 with bilaterally stable ankles (age  =  23.76 ± 5.82 years, height  =  174.00 ± 11.67 cm, mass  =  68.60 ± 13.12 kg).
Intervention(s):
Participants were fitted with surface electromyography electrodes over the peroneus longus, peroneus brevis, tibialis anterior, and soleus muscles. Each participant received transient motion oscillations to his or her ankle on a custom-built medial-lateral swaying cradle in each of 3 conditions: no ankle brace (NB), lace-up brace (LU), and semirigid brace (SR).
Main Outcome Measure(s):
Ankle stiffness as measured by the cradle and preactivation levels (percentage of maximal voluntary isometric contraction) of the 4 test muscles.
Results:
Stiffness levels increased across brace conditions (NB  =  24.79 ± 6.59 Nm/rad, LU  =  28.29 ± 7.05 Nm/rad, SR  =  33.22 ± 8.78 Nm/rad; F2,52  =  66.185, P < .001). No differences were found between groups for rotational stiffness (stable  =  27.36 ± 6.17 Nm/rad, unstable  =  30.18 ± 8.21 Nm/rad; F1,26  =  1.084, P  =  .307). Preactivation levels did not change for any of the tested muscles with the application of an ankle brace (F2,52  =  1.326, P  =  .275).
Conclusions:
The increase in ankle rotational stiffness with the addition of an ankle brace and the lack of any demonstrable neuromuscular changes suggested ankle braces passively contributed to the stability of the system.
PMCID: PMC2707072  PMID: 19593418
stability; preactivation; reflexes; orthoses
24.  Absolute Serum Hormone Levels Predict the Magnitude of Change in Anterior Knee Laxity across the Menstrual Cycle 
This study aimed to determine whether absolute sex hormone concentrations predict the magnitude of knee joint laxity changes across the menstrual cycle. Twenty-two females (18–30 years, body mass index ≤30), who reported normal menstrual cycles for the previous 6 months were tested daily across one complete menstrual cycle for serum levels of estradiol (E = pg/mL), progesterone (P = ng/mL), and testosterone (T = ng/dL), and knee joint laxity (KLax = mm displacement at 134N) measured with a standard knee arthrometer. The change in KLax across the cycle (maximum–minimum), and minimum (early follicular) and peak (postovulatory) hormone concentrations were recorded for each subject. A stepwise linear regression determined if the minimum, peak, or absolute change in hormone concentrations would predict the magnitude of change in KLax across the cycle. KLax changed on average 3.2 ± 1.1 mm across the menstrual cycle (range, 1.5–5.3 mm). Minimum levels of E (39.9 ±11.8 pg/mL) and P (0.61 ± 0.27 ng/mL), coupled with peak concentrations of E (199.6 ± 54.9 pg/mL) and T (22.5 ± 10.5 ng/dL) explained 57.6% of the change in KLax across the cycle. Greater absolutechanges in KLax were observed in response to peak E and T levels when minimum E concentrations were lower and minimum P concentrations were higher in the early follicular phase. The absolute minimum concentrations of E and P in the early follicular phase appear to be important factors in determining the sensitivity of the knee joint’s response to changing hormone levels.
doi:10.1002/jor.20021
PMCID: PMC1993900  PMID: 16435345
hormone pulsatility; estradiol; progesterone; testosterone; joint behavior
25.  Effect of Coupling Medium Temperature on Rate of Intramuscular Temperature Rise Using Continuous Ultrasound 
Journal of Athletic Training  2000;35(4):417-421.
Objective:
We determined the effects of coupling medium temperature on the rate of intramuscular temperature rise (RTR) during continuous ultrasound.
Design and Setting:
Ultrasound was applied in a continuous mode at a frequency of 1 MHz and intensity of 1.5 W/cm². Each subject received 3 treatments, using water-based coupling gel at temperatures of 18°C, 25°C, and 39°C. All treatments were performed in an athletic training room under controlled environmental conditions.
Subjects:
Eighteen healthy male subjects (mean age = 23.6 ± 3.5 years; height = 177.8 ± 6.9 cm; weight = 76.6 ± 8.2 kg; calf size = 37.6 ± 2.4 cm) participated in this study.
Measurements:
A thermistor was inserted into the left medial triceps surae at a depth of 5 cm, and baseline tissue temperatures were recorded before treatment. Intramuscular temperature was recorded every 30 seconds until the temperature rose 4°C above baseline or until discomfort was felt. RTR was calculated by dividing the absolute temperature change by treatment time.
Results:
A 1-way, repeated-measures analysis of variance revealed a significant difference in RTR among gel temperatures, RTR was significantly faster using the 25°C gel compared with the 18°C and 39°C gels. There was no difference between the 18°C and 39°C gel treatments.
Conclusions:
These results suggest that the use of a cooled or heated gel may be counterproductive when maximal thermal effects are desired within a given time frame.
PMCID: PMC1323367  PMID: 16558655
modalities; thermal; water-based gel

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