Debilitating shoulder pain is prevalent among wheelchair users, however the causes remain unknown. Shoulder pain is reported to be greater among those who began wheeling after skeletal maturity (adulthood-onset, AO) than among those who began wheeling prior to skeletal maturity (childhood-onset, CO). It is unclear whether functional load-bearing from manual wheelchair use affects glenohumeral bone and cartilage morphology. Bone is known to adapt to loading, however the literature is conflicting regarding cartilages capacity to adapt to loading. We performed a pilot study to quantify bone and cartilage morphology at the glenohumeral joint of manual wheelchair users (nCO=3, nAO=5) and age- and gender-matched able-bodied controls (nC=8). Bone morphology (volumetric bone mineral density (vBMD) and normalized cross-sectional area (nCSA)) was evaluated using quantitative computed tomography. Bone density distribution was assessed across the glenoid and, for the first time, across the humeral head using a novel quantitative CT-Osteoabsorptiometry method. Cartilage morphology (thickness, volume, and surface area) was evaluated using quantitative magnetic resonance imaging, in the first assessment at 3T MRI. This novel combination of methods provides complementary quantitative data of glenohumeral bone and cartilage morphology. Compared to the AO, the CO in our study had significantly higher (p<0.05) glenoid subchondral nCSA, non-significantly lower glenoid subchondral vBMD, and non-significantly higher humeral head and glenoid trabecular vBMD. A reasonable cross-sectional study (n=22) would likely show higher humeral head and glenoid trabecular vBMD and glenoid subchondral nCSA in CO subjects but would not find differences in nCSA of humeral head total, trabecular, and cortical bone, or glenoid trabecular bone. Surprisingly, vBMD was (non-significantly) lower in the wheelchair users than in the able-bodied controls, however activity levels varied considerably. Significant correlations were found between humeral head and glenoid trabecular vBMD (r=0.94), and between humeral head trabecular vBMD and physical activity scores (r=0.84). Given the small effect sizes and the large variance in humeral head and glenoid cartilage thickness, volume, and surface area, it is not likely that further study of these parameters would provide insight into wheelchair users shoulder pain. Gaining a better understanding of how glenohumeral bone and cartilage respond to wheelchair use would allow for rehabilitation programs and wheelchair-design to be tailored to childhood-onset and adulthood-onset wheelchair users.

Throwing with power and accuracy is a uniquely human behavior and a potentially important mode of early hunting. Chimpanzees, our closest living relatives, do occasionally throw, although with much less velocity. At some point in our evolutionary history, hominins developed the ability to produce high performance throws. The anatomical changes that enable increased throwing ability are poorly understood and the antiquity of this behavior is unknown. In this thesis, I examine how anatomical shifts in the upper body known to occur during human evolution affect throwing performance. I propose a new biomechanical model for how humans amplify power during high-speed throwing using elastic energy stored and released in the throwing shoulder. I also propose and experimentally test a series of functional hypotheses regarding how four key shifts in upper body anatomy affect throwing performance: increased torso rotational mobility, laterally oriented shoulders, lower humeral torsion, and increased wrist hyperextensability. These hypotheses are tested by collecting 3D body motion data during throws performed by human subjects in whom I varied anatomical parameters using restrictive braces to examine their effects on throwing kinematics. These data are broken down using inverse dynamics analysis into the individual motions, velocities, and forces acting around each joint axis. I compare performance at each joint across experimental conditions to test hypotheses regarding the relationship between skeletal features and throwing performance. I also developed and tested a method for predicting humeral torsion using range of motion data, allowing me to calculate torsion in my subjects and determine its effect on throwing performance. My results strongly support an important role for elastic energy storage in powering humans’ uniquely rapid throwing motion. I also found strong performance effects related to anatomical shifts in the torso, shoulder, and arm. When used to interpret the hominin fossil record, my data suggest high-speed throwing ability arose in a mosaic-like fashion, with all relevant features first present in Homo erectus. What drove the evolution of these anatomical shifts is unknown, but as a result the ability to produce high-speed throws was available for early hunting and likely provided an adaptive advantage in this context. / Anthropology

Bakgrund: Axelskador är vanligt förekommande inom idrott. Det finns ett tydligt samband mellan axelskador och idrotter som innefattar hand- och armrörelser ovanför huvudhöjd, som till exempel handboll. Axellederna utsätts för såväl hård fysisk kontakt som hög belastning vid repetitiva kaströrelser vilket ställer stora krav på axelledens strukturer. Prevalensen av aktuell eller tidigare axelskada rapporteras vara mellan 58 till 75 % hos spelarna. Syfte: Syftet med studien var att undersöka hur ett preventivt träningsprogram riktat mot riskfaktorer för skada i axelleden, utfört under åtta veckor i slutskedet av tävlingssäsong, påverkade prevalensen av överbelastningsskador i axelleden hos elithandbollsspelare i Sverige. Hur påverkas prevalensen av överbelastningskador och av allvarliga överbelastningsskador i axelleden under åtta veckor med samtidigt genomförande av ett preventivt träningsprogram för axelleden på elithandbollsspelare i Sverige? Metod: Studien var av kvasi-experimentell design vilken bestod av sex mättillfällen under åtta veckor. Nio elithandbollslag aktiva i Mellansverige rekryterades, varav 110 av 162 tillgängliga spelare inkluderades vid studiestart. Exkludering under och efter studieperioden gjorde att analysen utfördes på ett färre antal spelare. Lagen delades in i interventions- (n = 48) eller kontrollgrupp (n = 32) genom stratifierat urval, medelålder (± SD) 22.0 (3.3) respektive 21.9 (4.0). Interventionsgruppen tilldelades ett preventivt träningsprogram bestående av tre övningar i syfte att förbättra riskfaktorer för axelskador hos ”overhead athletes”. Kontrollgruppen tilldelades ingen intervention. Träningsprogrammet utvärderades genom att analysera prevalensen av överbelastningsskada och allvarlig överbelastningsskada i axelleden mätt med en modifierad version av The Oslo Sports Trauma Research Centre Overuse Injury Questionnaire. Resultat: Totalt 455 överbelastningssymtom rapporterades hos 42 spelare (53 %) varav 95 symtom var allvarliga hos 18 spelare (23 %). Prevalensen av överbelastningsskada minskade för både interventions- och kontrollgruppen från 42 % (95 % CI 28-56 %) till 25 % (95 % CI 13-37 %) respektive 53 % (95 % CI 36-70 %) till 31 % (95 % CI 15-47 %). Prevalensen av allvarliga överbelastningsskador minskade för både interventions- och kontrollgruppen från 15 % (95 % CI 5-25 %) till 6 % (95 % CI -1-13 %) respektive 19 % (95 % CI 5-32 %) till 13 % (95 % CI 1-24 %). Det fanns ingen signifikant skillnad mellan grupperna gällande prevalensen efter åtta veckors intervention. Allvarlighetspoängen minskade genomgående med en signifikant skillnad (p = 0.001) över tid för båda grupperna där kontrollgruppen förbättrades något mer. Det fanns en tendens till skillnad mellan grupperna (p = 0.064) gällande allvarlighetspoäng. Slutsats: Resultaten av denna studie visar på att prevalensen av allvarlig överbelastningsskada i axelleden hos elithandbollsspelare i Sverige möjligtvis kan reduceras till viss del genom utförande av ett preventivt träningsprogram två eller fler gånger per vecka under åtta veckor. Prevalensen av allvarliga symtom för överbelastningsskada minskade till ett något lägre värde för interventionsgruppen. Skillnaden för prevalens av överbelastningsskada inom interventionsgruppen, undergrupperade på antal utförda förebyggande träningspass, var signifikant (p = 0.044). Allvarlighetspoängen minskade i båda grupperna under studien. Det fanns en tendens till signifikant skillnad mellan grupperna (p = 0,.064), där kontrollgruppen förbättrades något mer trots ett högre värde vid mätning vecka 8. Axelskada och dysfunktioner hos ”overhead athletes” kan orsakas av olika faktorer vilket innebär att även riskfaktorerna bakom var och en av dessa tillstånd kan variera. Det är därför viktigt att upplysa om att träningsprogrammets påverkan på individnivå kan se annorlunda ut jämfört med resultatet på gruppnivå i den större populationen. / Background: Shoulder injuries are common in sport. In particular there is a clear relationship between shoulder injuries and sports that includes hand- and arm movements over the head, for example handball. In handball, the shoulder joints are exposed to hard physical contact as well as high loads during repetitive throwing which puts high demands on the structures inside and surrounding the shoulder joint. The prevalence of current or previous shoulder injuries is reported to be between 58 to 75 % in studies of handball players. Aim: The purpose of this study was to investigate how a preventive training program aimed at risk factors for shoulder injuries in the shoulder joint, performed during eight weeks in the final stage of competitive season, affected the prevalence of overuse injuries in the shoulder joint for elite handball players in Sweden.  How is the prevalence of overuse injuries and severe overuse injuries in the shoulder joints of elite Swedish handball players affected by the implementation of an eight-week preventive training program? Method: The study was of a quasi-experimental design which consisted of six measurements taken during eight weeks. Nine elite handball teams active in the middle regions of Sweden were recruited, from which 110 of the 162 available players were included. Exclusions during and after the study period reduced the number of players. The teams were divided into an intervention (n = 48) or control group (n = 32) through stratified sampling, with mean age (± SD) 22.0 (3.3) and 21.9 (4.0), respectively. The intervention group was assigned a preventive exercise program consisting of three exercises with the purpose of improving riskfactors for shoulder injuries for overhead athletes. The control group was not assigned any intervention. The training program was evaluated by analyzing the prevalence of overuse and severe overuse symptoms in the shoulder measured with a modified version of The Oslo Sports Trauma Research Centre Overuse Injury Questionnaire. Results: A total of 455 overuse symptoms were reported by 42 players (53 %) of which 95 symptoms in 18 players (23 %) were severe. The prevalence of overuse injuries decreased in both the intervention and the control group from 42 % (95 % CI 28-56 %) to 25 % (95 % CI 13-37 %) and 53 % (95 % CI 36-70 %) to 31 % (95 % CI 15-47 %), respectively. The prevalence of severe overuse injuries decreased in both the intervention and the control group from 15 % (95 % CI 5-25 %) to 6 % (95 % CI -1-13 %) and 19 % (95 % CI 5-32 %) to 13 % (95 % CI 1-24 %), respectively. There was no significant difference between the groups regarding prevalence after the intervention of eight weeks. Severity score consistently decreased with a significant difference over time (p = 0.001) for both groups, with a slightly greater improvement in the control group. There was a tendency towarda difference between the groups (p = 0.064) regarding the severity score. Conclusions: The results of this study show that the prevalence of severe overuse injuries in the shoulder joint of elite handball players in Sweden might be reduced to some extent by performing a preventive exercise program two or more times per week for eight weeks. The prevalence of severe symptoms of overload injury decreased to a slightly lower value for the intervention group. The difference of prevalence of overuse injuries within the intervention group, stratified by the number of executed preventive exercise programs (&lt;2 and ≥2), was significant (p = 0.044). Severity score decreased in both groups during the study. However, there was a tendency to a significant difference between the groups (p = 0.064), where the control group improved slightly more in spite of a higher value when measured at week 8. Shoulder injury and dysfunctions of overhead athletes can be caused by various factors, which means that the riskfactors for each of these conditions may vary. It is therefore important to highlight that the effects of a training program may be different at the individual level compared with the results at group level.

Bakgrund: Cerebral syrebrist är ett problem som kan ge katastrofala konsekvenser även hos friska individer. Patienter som skall genomgå axeloperation i beach-chair position är en patientgrupp som har högre risk att drabbas av cerebral syrebrist (CDE). CDE är dock svårt att detektera med konventionell intraoperativ övervakning.Syfte: Att undersöka förekomst av CDE hos sövda patienter som genomgår axelkirurgi i beach-chair position samt att identifiera de specifika riskfaktorer för CDE och åtgärder som anestesisjuksköterskan kan utföra för att reducera dessa.Metod: Deskriptiv litteraturstudie med systematisk ansats.Resultat: Incidensen av uppmätta CDE varierade i de olika studierna mellan 3 % och 80 %. Anestesisjuksköterskan kan minska risk för CDE genom att preoperativt bedöma riskfaktorer i patientens anamnes samt intraoperativt genom blodtrycksreglering, ventilationsförändring, kontroll av beach-chair position samt kontroll av huvudets position.Slutsats: Genom att anestesisjuksköterskan uppmärksammar specifika riskfaktorer i patientens anamnes samt utför intraoperativa åtgärder som syftar till att säkerställa adekvat blodtryck och optimal syresättning kan risken för CDE minska. Mätning av cerebral syresättning med NIRS rekommenderas som ett komplement för att detektera förekomst av CDE. / Background: Cerebral desaturation is a problem, which may result in catastrophic consequences even with healthy individuals. Patients who will undergo shoulder surgery in beach-chair position are at higher risk to be affected by cerebral desaturation events (CDE). However, CDE is hard to detect with conventional intraoperative surveillance.Purpose: To investigate incidence of CDE with anesthetized patients undergoing shoulder surgery in beach-chair position, and to identify the specific risk factors and measures the nurse anesthetist may perform to reduce those.Method: Descriptive literature review with systematic approach.Result: The incidence of measured CDE varied between 3% and 80% in the different studies. The nurse anesthetist may reduce the risk for CDE by preoperatively assess the risk factors in the medical history of the patient and intraoperatively by regulation of the blood pressure, changes in ventilation, control of beach-chair position and control of the patients head position.Conclusion: By paying attention to specific risk factors in the patients medical history and performing intraoperative measures to ensure adequate blood pressure and optimal saturation the risk for CDE may be lowered. Measuring cerebral saturation with NIRS technology is recommended as a complement to be able to detect incidence of CDE.

Computer generated three-dimensional (3-D) models are being used at increasing rates in the fields of entertainment, education, research, and engineering. One of the aspects of interest includes the behavior and function of the musculoskeletal system. One such tool used by engineers is the finite element method (FEM) to simulate the physics behind muscle mechanics. There are several ways to represent 3-D muscle geometry, namely a bulk, a central line of action and a spline model. The purpose of this study is to exmine how these three representations affect the overall outcome of muscle movement. This is examined in a series of phases with Phase I using primitive geometry as a simplistic representation of muscle. Phases II and III add anatomical representations of the shoulder joint with increasing complexity. Two methods of contraction focused on an applied maximal force (Fmax) and prescribed displacement. Further analyses tested the variability of material properties as well as simulated injury scenarios. The results were compared based on displacement, von Mises stress and solve time. As expected, more complex models took longer to solve. It was also supported that applied force is a preferred method of contraction as it allows for antagonistic and synergistic interaction between muscles. The most important result found in these studies was the consistency in the levels of displacement and stress distribution across the three different 3-D representations of muscle. This stability allows for the interchangeability between the three different representations of muscles and will permit researchers to choose to use either a bulk, central line of action or a spline model. The determination of which 3-D representation to use lies in what physical phenomenon (motion, injury etc.) is being simulated.

Unbalanced muscle forces in the shoulder joint may lead to functional impairment in the setting of rotator cuff tear and progressive arthritis in cuff tear arthropathy. A model, which predicts muscle forces for common shoulder movements, could be used to help in treatment decision-making and in improving the design of total shoulder prosthesis. Unfortunately, the shoulder has many muscles that overlap in function leading to an indeterminate system. A finite element model employing an optimization algorithm could be used to reduce the number of degrees of freedom and predict loading of the glenohumeral joint. The goal of this study was to develop an anatomically and physiologically correct computational model of the glenohumeral joint. This model was applied to: 1) estimate the force in each muscle during the standard glenohumeral motions (flexion/extension, abduction/adduction and internal/ external rotation), and 2) determine stress concentrations within the scapula during these motions. These goals were realized through the following steps: First, a three dimensional bone reconstruction was performed using computed tomography (CT) scan data. This allowed for a precise anatomical representation of the bony components. Then muscle lever arms were estimated based on the reconstructed bones using computer-aided design software. The origins, insertions, and muscle paths were obtained from the literature. This model was then applied to estimate the forces within each of the muscles that are necessary to stabilize the joint at a fixed position. Last, finite element analysis of the scapula was performed to study the stress concentrations. These were identified and related to the morphology of the bone. A force estimation algorithm was then developed to determine the necessary muscle force distribution. This algorithm was based on an applied external moment at the joint, and the appropriate selection of muscles that could withstand it, ensuring stability, while keeping the reaction force at a minimum. This method offered an acceptable solution to the indeterminate problem, a unique solution was found for each shoulder motion. The model was then applied to determine the stress concentration within various regions of the scapula for each of the shoulder motions. The rotator cuff was found to act as the main stabilizer under rotation, and had a significant stabilizing role under flexion and abduction. The finite element model of the shoulder that was developed can be used to gain a better understanding of the load transfer mechanisms within the glenohumeral joint and the impact of muscle forces on scapular morphology. This information can then be used to assist with treatment decision-making for rotator cuff tears and with the design of new implants for total shoulder arthroplasty.

Rotatorenmanschettenrupturen (RM-Rupturen) haben eine hohe Prävalenz in der Bevölkerung und kommen mit zunehmendem Alter gehäuft vor (Ozaki et al. 1988, Milgrom et al.1995). Die operative Rekonstruktion der RM gilt als Goldstandard der Behandlung. Unbehandelt neigen RM-Rupturen zu Progression und zu fettiger Infiltration des Muskelbauchs und zu Abnahme der Sehnenqualität (Goutallier et al. 1994). Im weiteren Verlauf droht eine Defektarthropathie mit schmerzhafter Bewegungsseinschränkung und hochgradigem Funktionsverlust der Extremität. Eine zeitgerechte Rekonstruktion der RM kann diesen Verlauf günstig beeinflussen und die Funktion des Schultergelenkes signifikant verbessern (Deutsch et al. 1997, Gladstone et al. 2007). Mit zunehmendem Funktionsanspruch, auch noch im fortgeschrittenen Alter, gewinnt die Rekonstruktion der RM zunehmend an Bedeutung (Worland et al. 1999). Die Rerupturrate der operativen Rekonstruktion ist hoch und wird je nach Autor mit bis zu 94% angegeben (Boileau et al. 2005, Galatz et al. 2004). Uneinigkeit herrscht in der Literatur über die Art der Primärrefixation der Sehne im Knochen (Bishop et al. 2006, Boileau et al. 2005, Galatz et al. 2004). Mehrere Autoren berichten, dass die Nahtankerreparatur der transossären Refixation gleichwertig bzw. überlegen ist (Reed et al., 1996, Klinger et al. 2007). Des Weiteren wird die Anzahl und das Platzierungsmuster der Nahtanker, im Hinblick auf die Primärstabilität, kontrovers diskutiert (Apreleva et al. 2002, Craft et al. 1996, Rossouw et al. 1997). 52 Ziel des Schulterchirurgen sollte es sein, eine möglichst hohe Primärfestigkeit der Rekonstruktion zu erreichen, des Weiteren sollte die Refixationsmethode die spannungsfreie Einheilung der Sehne ermöglichen, den Patienten möglichst schnell einer aktiven Rehabilitation zuführen und die Rerupturrate möglichst gering halten (Kim et al. 2005). Ziel der Arbeit war es zu zeigen, ob eine weitere Reihe Nahtanker eine höhere Primärstabilität in Abhängigkeit des verwendeten Nahtmaterials bietet. Hierzu wurden 32 frische Schafsschultern in 4 Gruppen zu je 8 Präparaten aufgeteilt. Eine vollständige RM-Ruptur wurde simuliert und anschließend wurden die Rupturen entweder mit einer Einreihen-Nahtankerversorgung (single-row-Technik) oder mit einer Zweireihen-Nahtankerversorgung (double-row-Technik) refixiert. Dabei kamen 2 verschiedene Nahtmaterialien zum Einsatz (nicht resorbierbares Polyesterfadenmaterial (Ethibond®) und nicht resorbierbares Polyethylenfadenmaterial (HiFi®) der Stärke 2.0). Die Präparate wurden in einer Zugmaschine auf ihre Zugfestigkeit getestet. Die double-row-Technik in Kombination mit nicht-resorbierbarem Polyethylenfadenmaterial (HiFi®, Gruppe IV) erzielte hierbei eine signifikant höhere Ausreißfestigkeit als die anderen Versorgungen. Mehrere Fixationspunkte der Verbindung Knochen-Faden/Naht-Sehne bei der double- row-Technik erreichen so durch eine gleichmäßige Lastverteilung eine höhere Zugfestigkeit Inwieweit diese erhöhte Primärfestigkeit eine Verbesserung des klinischen Ergebnisses und eine Reduktion der Rerupturrate erbringen kann, muss durch zukünftige klinisch-prospektive Studien validiert werden. Der Einsatz dieser kostenintensiven und operativ anspruchsvollen Methode ist unseres Erachtens nur dann gerechtfertigt, wenn die Anzahl an Revisionseingriffen hierdurch signifikant gesenkt werden kann.

Apie sergančiųjų onkologinėmis ligomis reabilitaciją Lietuvoje pradėta kalbėti tik prieš dešimtmetį. Onkologinių pacienčių gyvenimo kokybę galima pagerinti laiku taikant reabilitacinį gydymą tiek tada, kai ligą galima išgydyti, tiek tada, kai numatoma bloga ligos prognozė. Standartiniai vėžio gydymo būdai yra operacija, spindulinė terapija, chemoterapija bei reabilitacija. Po chirurginio ir kombinuoto kompleksinio gydymo 25 proc. onkologinių ligonių vargina funkciniai sutrikimai, komplikacijos. Reabilitacijos metu siekiama optimaliai atkurti paciento fiziologinį, psichologinį, socialinį bei profesinį statusą. Tyrimo tikslas - įvertinti pacienčių po krūties vėžio chirurginio gydymo funkcinės būklės ir gyvenimo kokybės pokyčius antrame reabilitacijos etape. Tyrimo uždaviniai: 1. Įvertinti ir palyginti pacienčių, kurioms taikytas skirtingas krūties vėžio chirurginis gydymas (limfmazgiai buvo šalinti arba nešalinti) peties sąnario judesių amplitudės dinamiką prieš ir po reabilitacijos; 2. Išsiaiškinti, abiejose tiriamųjų grupėse, (pacientėms buvo šalinti arba nešalinti limfmazgiai), ar rankos, plaštakos patinimas įtakoja peties sąnario judesių amplitudės pokyčius; 3. Įvertinti abiejose tiriamųjų grupėse (pacientėms buvo šalinti arba nešalinti limfmazgiai), kaip skausmas nesveikos krūties srityje įtakoja peties sąnario judesių amplitudės pokyčius; 4. Įvertinti ir palyginti pacienčių, kurioms taikytas skirtingas krūties vėžio chirurginis gydymas (limfmazgiai buvo šalinti arba... [toliau žr. visą tekstą] / In Lithuania the discussion on rehabilitation of oncological illnesses started only a decade ago. The quality of life of those suffering from oncological illness can be improved by timely rehabilitation when the disease can be cured, as well as when the foreseeable forecast is negative. Surgery, radiation therapy, chemotherapy and rehabilitation are conventional treatments of cancer. Surgical and combined integrated treatment leaves 25% of oncological patients suffering from functional disorders and negative side-effects. Rehabilitation aims to optimally restore physiological, psychological, social as well as professional status of the patient. Aim of Research: to investigate the changes in second rehabilitation stage on patients exposed to surgical treatment of breast cancer functional condition and quality of life. Primary goals: 1. Evaluate and compare dynamic amplitude movement of shoulder joint before and after rehabilitation of patients, which had different surgical treatment of breast cancer (with removed or not removed lymphatic nodes). 2. Ascertain does hand’s tumescence has an impact on shoulder’s joint amplitude movement changes in both exploratory groups (with removed or not removed lymphatic nodes). 3. Evaluate how the pain in unhealthy breast area impacts shoulder’s joint amplitude movement changes in both exploratory groups (with removed or not removed lymphatic nodes). 4. Evaluate and compare general health condition and quality of life before and after... [to full text]

Thesis (M.Tech.: Chiropractic)-Dept. of Chiropractic,Durban Institute of Technology, 2005 xxi, 132, 34 leaves ; ill. ; 30 cm / To assess and quantify the number, severity and specific location of myofascial trigger points within the shoulder rotator muscle group. To assess the internal/external ratio of the dominant shoulder in throwing athletes using a Cybex 700 dynamometer, after intervention and to establish a comparable clinical profile of the participants.

Water polo is a highly dynamic and physically demanding sport that has heretofore not inspired nearly as much research as other overhead sports such as baseball or swimming. As in almost all overhead sports, water polo puts its players at high risks for shoulder injuries since the motions required to perform the sport at an optimum level push the limits of normal shoulder function. Human shoulders are inherently unstable as a tradeoff to their flexibility. Because of this instability, many structures are required to work concurrently to keep the shoulder in place. These structures include muscles, ligaments and cartilages. It is important to recognize that the shoulder is not a singular joint in itself but rather a highly mobile complex that can perform many nuanced motions. Shoulder instability can cause a variety of injuries such as impingement, which occurs often among overhead athletes. This malady refers to a pathologic limitation of normal subacromial space that causes structures to be in abnormal contact with each other, which causes abrasive and pinching forces. These forces can result in a range of shoulder maladies including bursitis, tendinitis, and tearing of muscles and ligaments. Impingement is very apparent in both swimmers and water polo players due to the repetitive stresses present in each sport. In swimmers, impingement has been relatively well researched; the freestyle stroke utilized in water polo, however, is fundamentally different in that water polo players keep their heads and chests erect out of the water with a stroke known as head-up freestyle. Hitherto unknown are the biomechanics of this stroke and the extent to which impingement in water polo players is caused and/or worsened by this form of freestyle. The proposed research is a two-part study to investigate the biomechanics of water polo head-up freestyle as a first step to understanding its role in impingement in water polo players. First, experienced water polo players with healthy shoulders approved by the IRB committee of Scripps College will be recruited in this study, and their head-up freestyle kinematic sequences and muscle activities will be recorded by synchronized high-speed cinematography and fine-wire electromyography. These data will be compared to those of head-down freestyle in the literature to understand the biomechanical differences between head-up in and head-down. Part II of the study will recruit experienced water polo players with existing shoulder impingement in addition to those with healthy shoulders in Part I, and their head-up freestyle will be recorded in the same manner. These data will be compared to those in Part I to understand how the head-up stroke differs between impinged and healthy shoulders. This research will provide a basis for the understanding of impingement in head-up freestyle to ultimately increase the safety of the players. Further studies should be conducted to compare the patterns of biomechanical differences between healthy and impinged shoulders in head-up vs. head-down, analyze impingement in each phase of the head-up swim stroke, and investigate how the rate of impingement is altered by fatigue and poor technique.