The effect of concussion on subsequent musculoskeletal injury risk in high school athletes.

BACKGROUND: Studies have demonstrated an increased risk of musculoskeletal (MSK) injury after concussion in collegiate and professional athletes, but there has been relatively little study of this relationship in younger athletes. OBJECTIVE: To determine the odds of experiencing a subsequent MSK injury after concussion in high school athletes. It was hypothesized that concussion would increase the risk of MSK injury within 365 days of the concussion event. DESIGN: Retrospective observational study. SETTING: Twelve high school sports programs. PARTICIPANTS: Athletes (n = 14,461) from athletic training room records queried between 2010 and 2017. INDEPENDENT VARIABLES: History of concussion and history of concussion and MSK injury in the year preceding MSK injury. MAIN OUTCOME MEASURES: General estimating equation analyses were conducted to examine the odds of MSK injury related to (1) concussion within the preceding 365 days of injury; and (2) concussion and MSK injury within the preceding 365 days of concussion. RESULTS: Respectively, 8% and 8.3% of athletes were identified with a concussion and MSK injury. After controlling for gender and sport, athletes with a concussion and prior MSK injury (odds ratio = 2.19, 95% confidence interval: 1.02-4.67) and athletes with a concussion alone (odds ratio = 1.67, 95% confidence interval: 1.15-2.44) both had higher odds of experiencing a subsequent MSK injury compared to athletes without prior concussion. CONCLUSIONS: High school athletes who sustain a concussion have elevated odds of MSK injury at rates comparable to those for collegiate athletes. These findings support the use of neuromuscular-based rehabilitation and injury prevention protocols in the post-concussion period. These findings may also suggest exploring methods to modify concussion return-to-play criteria with the goal to reduce the risk of future MSK injury.

Factors Affecting Incidence Rate of Exertional Heat Illnesses: Analysis of 6 Years of High School Football Practices in North Central Florida.

BACKGROUND: Although experts have advocated for regionally specific heat safety guidelines for decades, guidelines have not been universally adopted. PURPOSE: To describe the rate and risk factors associated with exertional heat illness (EHI). STUDY DESIGN: Descriptive epidemiology study. METHODS: For a 3-month period (August-October) over 6 years (2013-2018), athletic trainers at 13 high schools in North Central Florida recorded varsity football practice time and length, wet-bulb globe temperature (WBGT), and incidences of EHI, including heat stroke, heat exhaustion, and heat syncope. RESULTS: Athletes sustained 54 total EHIs during 163,254 athlete-exposures (AEs) for the 3-month data collection periods over 6 years (incidence rate [IR], 3.31 /10,000 AEs). Heat exhaustion accounted for 59.3% (32/54), heat syncope 38.9% (21/54), and heat stroke 1.9% (1/54) of all EHIs recorded. Of the EHIs, 94.4% (51/54) were experienced within the first 19 practices. The first 19 practices had an IR of 7.48 of 10,000 AEs, and the remaining 44 practices had an IR of 0.32 of 10,000 AEs, demonstrating that the risk of EHI for practices 1 to 19 was 23.7 times that of the remaining practices. When comparing morning to afternoon practices, 35.2% (19/54) EHI incidents occurred during morning practices. The risk of EHI during practices with WBGT >82°F (27.8°C) was 3.5 times that of practices with WBGT <82°F. CONCLUSION: In the current study, the risk of EHI was greatest in the first 19 practices of the season and during practices with WBGT >82°F. As modifiable risk factors for EHI, increased vigilance and empowerment to adhere to acclimatization guidelines can mitigate EHI risk. Health care providers must continue to advocate for implementation of regulations and the authority to make decisions to ensure patient safety.

Roundtable on Preseason Heat Safety in Secondary School Athletics: Environmental Monitoring During Activities in the Heat.

OBJECTIVE: To develop best-practice recommendations using thermal indices to determine work-to-rest ratios and facilitate further implementation of environmental monitoring for heat safety in secondary school athletics in the United States. DATA SOURCES: A narrative review of the current literature on environmental monitoring for heat safety during athletics was conducted by content experts. A list of action-oriented recommendations was established from the narrative review and further refined using the Delphi method. CONCLUSIONS: Assessment of wet bulb globe temperature at the site of activity and throughout the duration of the event is recommended to assist clinicians and administrators in making appropriate decisions regarding the duration and frequency of activity and rest periods. Activity-modification guidelines should be predetermined and approved by stakeholders and should outline specific actions to be followed, such as the work-to-rest ratio, frequency and timing of hydration breaks, and adjustment of total exercise duration, equipment, and clothing. Furthermore, integration of exertional heat illness injury data with environmental condition characteristics is critical for the development of evidence-based heat safety guidelines for secondary school athletics. Athletic trainers play an essential role in conducting prospective injury data collection, recording onsite wet bulb globe temperature levels, and implementing recommendations to protect the health and safety of athletes.

Volleyball-related injuries in adolescent female players: an initial report.

OBJECTIVE: To determine the prevalence and risk factors associated with musculoskeletal injuries sustained in female adolescent volleyball players. METHODS: Volleyball players (n = 276; 13-18 years), with any level of volleyball experience, were recruited. Participants completed a study-specific survey about their overall sport(s) involvement, training modalities, volleyball experience (beginner, intermediate, advanced), annual volume of volleyball play, injuries accrued during volleyball, and care received for injury. RESULTS: Annual volume of volleyball play was higher in advanced than beginner/intermediate players (490.0 hr/yr versus 302.3 hr/yr; p < 0.0001). Nearly 67% (188/276) of participants incurred one or more volleyball-related injuries over the last year. The ankle (40.6%), fingers (36.6%), knee (21.2%), and shoulder (15.5%) were the most frequently reported injury. Injury prevalence was higher in advanced than beginner/intermediate players (73.5% versus 62.0%; p = 0.04). Beginner/intermediate players have significantly higher odds ratio (OR) of sustaining an elbow injury than advanced players (OR 5.88; p = 0.025). 21.5% of injured players missed more than one month of play. CONCLUSION: More competitive and experienced adolescent female players may incur injuries due to progressively higher volumes of play as experience and competition level increase. Players who have committed to only playing volleyball participated in greater volumes of volleyball play, which increases the odds of sustaining an injury. CLINICAL RELEVANCE: Understanding injury risk factors may improve clinical management and injury prevention.

Comparison of wet bulb globe temperature measured on-site vs estimated and the impact on activity modification in high school football.

Exertional heat stroke is one of the top three causes of death in young athletes, particularly high school football players. Despite evidence that these deaths are completely avoidable with appropriate prevention and treatment, deaths still occur at an alarming rate. Wet bulb globe temperature (WBGT) is the preferred method of both the National Athletic Trainers' Association and American College of Sports Medicine to measure heat intensity. Based on the WBGT, activity modification guidelines (AMG) dictate work-to-rest ratios, activity levels and duration, protective equipment worn, and length and frequency of hydration breaks. Due to the cost of handheld WBGT monitors, smartphone apps that estimate WBGT have been considered an alternative. However, it is unclear how WBGT values estimated by these smartphone apps compare to those measured on-site using handheld WBGT monitors. We compared WBGT values estimated by a commercial smartphone app to those taken on-site at the same time and place. Thirteen athletic trainers measured WBGT in the field during high school football practices over a three-month season in North Central Florida. A paired sample t-test indicated the smartphone app significantly overestimated WBGT (29.0°C ± 4.1°C) compared to on-site measures (26.4°C ± 3.2°C) ( r =0.580; t(943)=-23.38, p <0.0001). The smartphone app-estimated values were consistently greater than on-site measures, resulting in potentially unnecessary activity modifications and cancellations if the app was used in place of on-site handheld WBGT monitors. Despite being significantly cheaper than handheld WBGT monitors, at this time, smartphone apps are not ready for widespread use to guide activity modification decisions.

Sport Specialization and Overuse Injuries in Adolescent Throwing Athletes: A Narrative Review.

A significant number of adolescent athletes throughout the world participate in various throwing-dominant sports, including but not limited to baseball, cricket, handball, softball, track and field throwing events, and water polo. Due to the unique stresses placed on the throwing arm and entire body in these sports, a robust volume of literature has highlighted concerns about sport specialization in these athletes and an associated increased risk of injury, particularly to the dominant shoulder and elbow, with sport specialization. This review will highlight the evidence-based literature for this athletic niche, focusing on risk factors for injury, national and international organizations' recommendations for limiting overuse injuries, principles of conditioning and rehabilitative programs, and potential future areas of research to curb the growing incidence of throwing-related injuries among adolescent throwing athletes.

Unaccounted Workload Factor: Game-Day Pitch Counts in High School Baseball Pitchers-An Observational Study.

BACKGROUND: Throwing injuries are common in high school baseball. Known risk factors include excessive pitch counts, year-round pitching, and pitching with arm pain and fatigue. Despite the evidence, the prevalence of pitching injuries among high school players has not decreased. One possibility to explain this pattern is that players accumulate unaccounted pitch volume during warm-up and bullpen activity, but this has not yet been examined. HYPOTHESES: Our primary hypothesis was that approximately 30% to 40% of pitches thrown off a mound by high school pitchers during a game-day outing are unaccounted for in current data but will be revealed when bullpen sessions and warm-up pitches are included. Our secondary hypothesis was that there is wide variability among players in the number of bullpen pitches thrown per outing. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: Researchers counted all pitches thrown off a mound during varsity high school baseball games played by 34 high schools in North Central Florida during the 2017 season. RESULTS: We recorded 13,769 total pitches during 115 varsity high school baseball starting pitcher outings. The mean ± SD pitch numbers per game were calculated for bullpen activity (27.2 ± 9.4), warm-up (23.6 ±8.0), live games (68.9 ±19.7), and total pitches per game (119.7 ± 27.8). Thus, 42.4% of the pitches performed were not accounted for in the pitch count monitoring of these players. The number of bullpen pitches thrown varied widely among players, with 25% of participants in our data set throwing fewer than 22 pitches and 25% throwing more than 33 pitches per outing. CONCLUSION: In high school baseball players, pitch count monitoring does not account for the substantial volume of pitching that occurs during warm-up and bullpen activity during the playing season. These extra pitches should be closely monitored to help mitigate the risk of overuse injury.

Exercise intervention for unilateral amputees with low back pain: study protocol for a randomised, controlled trial.

BACKGROUND: Atraumatic lower limb amputation is a life-changing event for approximately 185,000 persons in the United States each year. A unilateral amputation is associated with rapid changes to the musculoskeletal system including leg and back muscle atrophy, strength loss, gait asymmetries, differential mechanical joint loading and leg length discrepancies. Even with high-quality medical care and prostheses, amputees still develop secondary musculoskeletal conditions such as chronic low back pain (LBP). Resistance training interventions that focus on core stabilization, lumbar strength and dynamic stability during loading have strong potential to reduce LBP and address amputation-related changes to the musculoskeletal system. Home-based resistance exercise programs may be attractive to patients to minimize travel and financial burdens. METHODS/DESIGN: This study will be a single-assessor-blinded, pre-post-test randomised controlled trial involving 40 men and women aged 18-60 years with traumatic, unilateral transtibial amputation. Participants will be randomised to a home-based, resistance exercise group (HBRX) or a wait-list control group (CON). The HBRX will consist of 12 weeks of elastic resistance band and bodyweight training to improve core and lumbopelvic strength. Participants will be monitored via Skype or Facetime on a weekly basis. The primary outcome will be pain severity (11-point Numerical Pain Rating Scale; NRSpain). Secondary outcomes will include pain impact on quality of life (Medical Outcomes Short Form 36, Oswestry Disability Index and Roland Morris Disability Questionnaire), kinematics and kinetics of walking gait on an instrumented treadmill, muscle morphology (muscle thickness of multifidus, transversus abdominis, internal oblique), maximal muscle strength of key lumbar and core muscles, and daily step count. DISCUSSION: The study findings will determine whether a HBRX program can decrease pain severity and positively impact several physiological and mechanical factors that contribute to back pain in unilateral transtibial amputees with chronic LBP. We will determine the relative contribution of the exercise-induced changes in these factors on pain responsiveness in this population. TRIAL REGISTRATION: ClinicalTrials.gov, ID: NCT03300375 . Registered on 2 October 2017.

Exertional Heat Illnesses and Environmental Conditions During High School Football Practices.

BACKGROUND: Guidelines for preventing exertional heat illnesses (EHIs) during extreme heat stress should be specific to regional environments, age, and sport and should be based on evidence of reducing the risk. Each year in the United States, over 1 million high school football players practice in the August heat; however, no published data describe the incidence of EHIs in these athletes. PURPOSE: To describe the environmental conditions and incidence of EHIs during high school football practices over a 3-month period. STUDY DESIGN: Descriptive epidemiology study. METHODS: For a 3-month period (August-October), athletic trainers at 12 high schools in North Central Florida recorded the practice time and length, environmental conditions (wet-bulb globe temperature), and incidences of EHIs in varsity football athletes. RESULTS: Athletes suffered 57 total EHIs during 29,759 athlete-exposures (AEs) for the 3-month data collection period (rate = 1.92/1000 AEs). August accounted for the majority of all EHIs, with 82.5% (47/57) and the highest rate (4.35/1000 AEs). Of total heat illnesses, heat cramps accounted for 70.2% (40/57), heat exhaustion 22.8% (13/57), and heat syncope 7.0% (4/57). The odds ratio indicated that athletes in August practices that lasted longer than the recommended 3 hours were 9.84 times more likely to suffer a heat illness than those in practices lasting ≤3 hours. CONCLUSION: The highest rate of EHIs was during August. Practices in August that exceeded the recommended 3 hours were associated with a greater risk of heat illnesses. The overall rate of EHIs was lower for the high school football athletes observed in the study compared with that reported for collegiate football athletes in the region. The low rates of EHIs recorded suggest that the prevention guidelines employed by sports medicine teams are appropriate for the region and population. CLINICAL RELEVANCE: Team physicians and athletic trainers should employ evidence-based, region- and population-specific EHI prevention guidelines. Sports medicine teams, coaches, and athletes should be aware of the increased risk of EHIs during August practices and the risk of prolonged practices during August.

Concussion knowledge in high school football players.

CONTEXT: Participating in sports while experiencing symptoms of a concussion can be dangerous. An athlete's lack of knowledge may be one factor influencing his or her decision to report symptoms. In an effort to enhance concussion education among high school athletes, legislation in Florida has attempted to address the issue through parental consent forms. OBJECTIVE: To survey high school varsity football players to determine their level of knowledge about concussions after the initiation of new concussion-education legislation. DESIGN: Cross-sectional study. SETTING: Descriptive survey administered in person during a team meeting. PATIENTS OR OTHER PARTICIPANTS: A total of 334 varsity football players from 11 high schools in Florida. MAIN OUTCOME MEASURE(S): Participants completed a survey and identified the symptoms and consequences of a concussion among distractors. They also indicated whether they had received education about concussions from a parent, formal education, neither, or both. RESULTS: The most correctly identified symptoms were headache (97%), dizziness (93%), and confusion (90%), and the most correctly identified consequence was persistent headache (93%). Participants reported receiving education from their parents (54%) or from a formal source (60%). Twenty-five percent reported never receiving any education regarding concussions. No correlations were found between the method of education and the knowledge of symptoms or consequences of concussion. CONCLUSIONS: The high school football players we surveyed did not have appropriate knowledge of the symptoms and consequences of concussions. Nausea or vomiting, neck pain, grogginess, difficulty concentrating, and personality or behavioral changes were often missed by participants, and only a small proportion correctly identified brain hemorrhage, coma, and death as possible consequences of inappropriate care after a concussion. Even with parents or guardians signing a consent form indicating they discussed concussion awareness with their child, 46% of athletes suggested they had not.

Evaluation of clinical assessment methods for scapular dyskinesis.

PURPOSE: The purposes of this study were to (1) assess the inter-rater reliability and validity of 2 clinical assessment methods of categorizing scapular dyskinesis and (2) quantify the frequency of asymmetry of bilateral scapular motion in injured and uninjured shoulders by use of 3-dimensional (3D) kinematic analysis. METHODS: We evaluated 56 subjects, 35 with shoulder injury and 21 with no symptoms. Two blinded evaluators categorized the scapular motion of all subjects to determine inter-rater reliability using 2 observational methods ("yes/no" and "4 type") to evaluate scapular dyskinesis. Subjects were also instrumented with electromagnetic receivers to assess bilateral 3D scapular kinematics to determine the presence of dyskinesis and establish criterion validity of the 2 methods. RESULTS: The inter-rater percent agreement and the degree of this agreement as measured by kappa statistic showed that the yes/no method produced a higher inter-rater percent agreement (79%, kappa = 0.40) than the 4-type method (61%, kappa = 0.44). The yes/no method had a higher sensitivity (76%) and positive predictive value (74%) when compared with the 3D criterion. A chi(2) analysis found significantly more multiple-plane asymmetries in symptomatic subjects (54%) in flexion compared with asymptomatic subjects (14%) (P = .002). CONCLUSIONS: The yes/no method allows multiple-plane asymmetries to be considered in clinical assessment and therefore renders this a good screening tool for the presence of scapular dyskinesis. Kinematic analysis shows that asymmetries are common in symptomatic and asymptomatic populations. Testing in flexion showed a higher frequency of multiple-plane scapular asymmetries in the symptomatic group. CLINICAL RELEVANCE: Identification of scapular dyskinesis is a key component of the shoulder examination. The clinician's ability to establish the presence or absence of scapular dyskinesis by observation is enhanced using a simple yes/no method especially when testing subjects in shoulder forward flexion. Although scapular asymmetries appear to be a prevalent finding, dyskinesis in the presence of shoulder symptoms should be considered a potential factor contributing to the dysfunction in the presence of shoulder symptoms should be considered a potential factor contributing to the dysfunction.

Glenohumeral rotational range of motion in collegiate overhead-throwing athletes during an athletic season.

CONTEXT: Repetitive throwing at high velocities leads to altered range of motion (ROM) in the dominant shoulder compared with the nondominant shoulder in overhead-throwing athletes. Loss of glenohumeral internal rotation (IR), or glenohumeral internal-rotation deficit (GIRD), is associated with shoulder injuries. Therefore, GIRD should be evaluated during the clinical examination of the thrower's shoulder. OBJECTIVE: To assess glenohumeral ROM in competitive baseball and softball athletes at 3 intervals over the course of an athletic season in order to (1) examine changes in ROM over time and (2) monitor the prevalence of GIRD. DESIGN: Observational, repeated-measures study. SETTING: Collegiate athletic training room. PATIENTS OR OTHER PARTICIPANTS: Forty-eight healthy National Collegiate Athletic Association (NCAA) Division I or Division II athletes (age = 19 + or - 1 years, height = 174 + or - 14 cm, mass = 77.8 + or - 18.1 kg; 19 softball, 29 baseball players). MAIN OUTCOME MEASURE(S): We measured glenohumeral IR, external rotation (ER), total arc (ER + IR), and GIRD at 3 times: prefall, prespring, and postspring. We calculated GIRD in 2 ways: as the difference in IR between dominant and nondominant shoulders and as the percentage of the total arc. RESULTS: In the dominant shoulder, ER increased during the season (F(2,96) = 17.433, P < .001), but IR remained the same (F(2,96) = 1.839, P = .17). The total arc in the dominant shoulder increased between time intervals (F(2,96) = 14.030, P < .001); the mean difference between prefall and postspring measurements was 9.694 degrees (P < .001), and the mean difference between prefall and postspring measurements was 10.990 degrees (P < .001). In the nondominant shoulder, ER increased over the season (F(2,96) = 23.395, P < .001), but IR did not change over the season (F(2,96) = 0.087, P = .90). The total arc in the nondominant shoulder increased between prefall and prespring measurements and between prefall and postspring measurements (F(2,96) = 18.552, P < .001). No changes were noted in GIRD over time. However, more athletes with GIRD were identified with the GIRD (IR difference) calculation in prefall (n = 6) than in prespring (n = 1) and postspring (n = 4) (Cochran Q = 5.2, P = .07). In addition, more athletes with GIRD were identified with the GIRD (% total arc) calculation in postspring (n = 6) than in prefall (n = 5) or prespring (n = 4) (Cochran Q = 2.6, P = .27). CONCLUSIONS: Healthy NCAA Division I and Division II athletes did not display changes in glenohumeral IR over an athletic season. However, they gained in ER and total arc during the season in both shoulders. Future researchers should investigate changes over multiple seasons. The 2 methods of calculating GIRD identified different athletes as having GIRD, indicating that additional investigation is warranted to determine the clinical benefits of each method.

Elbow joint position sense after neuromuscular training with handheld vibration.

CONTEXT: Clinicians use neuromuscular control exercises to enhance joint position sense (JPS); however, because standardizing such exercises is difficult, validations of their use are limited. OBJECTIVE: To evaluate the acute effects of a neuromuscular training exercise with a handheld vibrating dumbbell on elbow JPS acuity. DESIGN: Crossover study. SETTING: University athletic training research laboratory. PATIENTS OR OTHER PARTICIPANTS: Thirty-one healthy, college-aged volunteers (16 men, 15 women, age = 23 + or - 3 years, height = 173 + or - 8 cm, mass = 76 + or - 14 kg). INTERVENTION(S): We measured and trained elbow JPS using an electromagnetic tracking device that provided auditory and visual biofeedback. For JPS testing, participants held a dumbbell and actively identified the target elbow flexion angle (90 degrees ) using the software-generated biofeedback, followed by 3 repositioning trials without feedback. Each neuromuscular training protocol included 3 exercises during which participants held a 2.55-kg dumbbell vibrating at 15, 5, or 0 Hz and used software-generated biofeedback to locate and maintain the target elbow flexion angle for 15 seconds. MAIN OUTCOME MEASURE(S): We calculated absolute (accuracy) and variable (variability) errors using the differences between target and reproduced angles. RESULTS: Training protocols using 15-Hz vibration enhanced accuracy and decreased variability of elbow JPS (P < or = .005), whereas 5-Hz vibration did not affect accuracy (F(1,61) = 2.625, P = .100) but did decrease variability (F(1,61) = 7.250, P = .009). The control condition and 0-Hz training protocol had no effect on accuracy or variability (P > or = .200). CONCLUSIONS: Our results suggest these neuromuscular control exercises, which included low-magnitude, low-frequency handheld vibration, may enhance elbow JPS. Future researchers should examine vibration of various durations and frequencies, should include injured participants and functional multijoint and multiplanar measures, and should examine long-term effects of training protocols on JPS and injury.

Principles of restoring function and sensorimotor control in patients with shoulder dysfunction.

This article reviews the basic principles of restoring sensorimotor (SMS) function and evidence-based outcome assessments and describes their integration into treating patients who have shoulder dysfunction. When integrated clinically, the principles of restoring SMS function act in synergy with those of functional outcome-based practices.

Functional fatigue and upper extremity sensorimotor system acuity in baseball athletes.

CONTEXT: The sensorimotor system controls the balance between upper extremity stability and mobility during athletic performance. Research indicates that fatigue hampers sensorimotor system function; however, few investigators have studied functional fatigue or multijoint, multiplanar measures. OBJECTIVE: To examine the effect of functional fatigue on upper extremity position reproduction in overhead throwing athletes. DESIGN: Single-session, repeated-measures design. SETTING: University musculoskeletal laboratory. PATIENTS OR OTHER PARTICIPANTS: Sixteen healthy collegiate baseball players (age = 21.0 +/- 1.6 years, height = 175.8 +/- 10.2 cm, mass = 82.8 +/- 4.3 kg). INTERVENTION(S): Subjects threw a baseball from a single knee with maximum velocity (every 5 seconds) and rated their level of upper extremity exertion after every 20 throws. Subjects stopped after reporting above level 14 on the Borg scale and began posttests immediately. MAIN OUTCOME MEASURE(S): We measured active multijoint reproduction of 2 positions: arm cock and ball release. Dependent variables were absolute and variable error for 10 joint motions: scapulothoracic internal-external rotation, upward rotation, and posterior tilt; glenohumeral internal-external rotation, horizontal abduction-adduction, and flexion-extension; elbow pronation-supination and flexion-extension; and wrist ulnar-radial deviation and flexion-extension. We calculated acuity for each joint and the entire upper extremity using 3-dimensional variable error. RESULTS: Fatigue occurred after an average of 62 +/- 28 throws and increased 3-dimensional variable error scores (ie, decreased acuity) of the entire upper extremity and all joints in both positions (P < .05) except for the wrist in arm cock. Fatigue increased errors (ranging from 0.6 degrees to 2.3 degrees ) at arm cock for scapulothoracic internal-external rotation, upward rotation, and posterior tilt; glenohumeral internal-external rotation and flexion-extension; elbow flexion-extension; and wrist ulnar-radial deviation and at ball release for scapulothoracic internal-external rotation and upward rotation, glenohumeral horizontal abduction-adduction, elbow pronation-supination, and wrist ulnar-radial deviation and flexion-extension (P < .05). CONCLUSIONS: Functional fatigue affects the acuity of the entire upper extremity, each individual joint, and multiple joint motions in overhead throwers. Clinicians should consider the deleterious effects of upper extremity fatigue when designing injury prevention and rehabilitation programs and should incorporate multijoint and multiplanar endurance exercises. Compromised neuromuscular control of the scapulohumeral relationship may hold pathologic implications for this population as well.

Recovery of upper extremity sensorimotor system acuity in baseball athletes after a throwing-fatigue protocol.

CONTEXT: Research indicates that upper extremity fatigue hampers sensorimotor system acuity. However, no investigators have observed recovery of upper extremity acuity after fatigue. OBJECTIVE: To observe recovery of active position reproduction acuity in overhead throwers after a throwing-fatigue protocol. DESIGN: Single-session, repeated-measures design. SETTING: University musculoskeletal laboratory. PATIENTS OR OTHER PARTICIPANTS: Sixteen healthy collegiate baseball players (age = 21.0 +/- 1.6 years, height = 175.8 +/- 10.2 cm, mass = 82.8 +/- 4.3 kg). INTERVENTION(S): Subjects threw a baseball with maximum velocity (every 5 seconds) from a single knee. Every 20 throws, subjects rated their upper extremity exertion on a Borg scale until reporting a level of more than 14. MAIN OUTCOME MEASURE(S): We used an electromagnetic tracking system to measure active multijoint position reproduction acuity at 5 intervals: prefatigue; immediately postfatigue; and after 4, 7, and 10 minutes of recovery. Blindfolded subjects reproduced their arm-cocked and ball-release positions. Dependent variables were 3-dimensional variable errors of scapulothoracic, glenohumeral, elbow, and wrist joints; endpoint (ie, hand) position error represented overall upper extremity acuity. The independent variable was time (measured prefatigue and at 4 postfatigue intervals). RESULTS: Fatigue significantly affected acuity of scapulothoracic, glenohumeral, and elbow joints and endpoint error for both positions (P < .001). Fatigue significantly affected wrist acuity only for ball release (P < .001). For arm-cocked reproduction, each measure of acuity, except that of the glenohumeral joint, recovered by 7 minutes; for ball release, each measure of acuity recovered within 4 minutes (P > .05). CONCLUSIONS: The sensorimotor system deficits that we observed after fatigue recovered within 7 minutes in most upper extremity joints. Glenohumeral arm-cocked position reproduction acuity failed to recover within 10 minutes. Research indicates that overhead throwers are vulnerable in this position to the capsulolabral injuries commonly observed in throwing athletes. Future researchers should explore this relationship and the effectiveness of exercises aimed at enhancing sensorimotor system acuity and endurance.

Functional multijoint position reproduction acuity in overhead-throwing athletes.

CONTEXT: Baseball players rely on the sensorimotor system to uphold the balance between upper extremity stability and mobility while maintaining athletic performance. However, few researchers have studied functional multijoint measures of sensorimotor acuity in overhead-throwing athletes. OBJECTIVE: To compare sensorimotor acuity between 2 high-demand functional positions and among planes of motion within individual joints and to describe a novel method of measuring sensorimotor function. DESIGN: Single-session, repeated-measures design. SETTING: University musculoskeletal research laboratory. PATIENTS OR OTHER PARTICIPANTS: Twenty-one National Collegiate Athletic Association Division I baseball players (age = 20.8 +/- 1.5 years, height = 181.3 +/- 5.1 cm, mass = 87.8 +/- 9.1 kg) with no history of upper extremity injury or central nervous system disorder. MAIN OUTCOME MEASURE(S): We measured active multijoint position reproduction acuity in multiple planes using an electromagnetic tracking device. Subjects reproduced 2 positions: arm cock and ball release. We calculated absolute and variable error for individual motions at the scapulothoracic, glenohumeral, elbow, and wrist joints and calculated overall joint acuity with 3-dimensional variable error. RESULTS: Acuity was significantly better in the arm-cock position compared with ball release at the scapulothoracic and glenohumeral joints. We observed significant differences among planes of motion within the scapulothoracic and glenohumeral joints at ball release. Scapulothoracic internal rotation and glenohumeral horizontal abduction and rotation displayed less acuity than other motions. CONCLUSIONS: We established the reliability of a functional measure of upper extremity sensorimotor system acuity in baseball players. Using this technique, we observed differences in acuity between 2 test positions and among planes of motion within the glenohumeral and scapulothoracic joints. Clinicians may consider these differences when designing and implementing sensorimotor system training. Our error scores are similar in magnitude to those reported using single-joint and single-plane measures. However, 3-dimensional, multijoint measures allow practical, unconstrained test positions and offer additional insight into the upper extremity as a functional unit.

A comparison of individual joint contributions to multijoint position reproduction acuity in overhead-throwing athletes.

BACKGROUND: Measures of joint position sense often test single-axis motions isolating a single joint. Such methods hamper our ability to apply findings to functional multijoint activities. Using a functional, active, multijoint test, we measured upper-extremity position reproduction in overhead-throwers. We compared acuity among four joints and examined individual joint contributions or patterns of contribution among joints to overall task acuity. METHODS: We used an electromagnetic tracking device to measure reproduction of two functional upper-extremity positions. We calculated absolute, constant and variable error at four upper-extremity joints around multiple axes of rotation: three axes at the scapulothoracic and glenohumeral joints and two axes at the elbow and wrist. To represent individual joint acuity, we calculated 3-dimensional variable error. Additional 3-dimensional variable error scores using deviation in hand position (with reference to the thorax) represented overall task acuity. We used principle component analyses to identify contributions of individual joints or patterns of contribution among joints to overall task acuity for absolute, constant and variable error. FINDINGS: Scapulothoracic and glenohumeral joints displayed better acuity compared with elbow and wrist joints. When examined separately, absolute, constant and variable error scores did not indicate any individual joint contributed more to task acuity. When we examined the principle components of all error score measures together, a distinct proximal-to-distal pattern of joint contribution to overall task acuity emerged. INTERPRETATION: Proximal joints display better reposition acuity compared with distal joints, however proximal joints contribute more to acuity of the overall task. Our results indicate that upper-extremity joints do not function independently in repositioning tasks and measures of absolute, constant and variable errors combined over multiple joints may better represent upper-extremity function.

Functional Fatigue Decreases 3-Dimensional Multijoint Position Reproduction Acuity in the Overhead-Throwing Athlete.

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.