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BACKGROUND: Inactivity while waiting for outpatient physiotherapy worsens the physical deconditioning of older adults after hospital discharge. Exercise programs can minimize the progression of deconditioning. In developing countries, telerehabilitation for older adults on the waiting list is still in the early stages. This study aimed to evaluate the feasibility of the study procedures of a telerehabilitation program for older adults waiting for outpatient physiotherapy after hospital discharge. METHODS: This pragmatic randomized controlled trial recruited older adults (≥ 60 years) with several clinical diagnoses on the waiting list for outpatient physiotherapy in the Brazilian public health system after hospital discharge. The telerehabilitation group (n = 17) received a personalized program of multicomponent remote exercises using a smartphone app. The control group (n = 17) followed the usual waiting list. We assessed recruitment and dropout rates, safety, adherence, and satisfaction. The preliminary effects were verified on clinical outcomes. RESULTS: We recruited 5.6 older adults monthly; dropouts were 12%. No serious adverse events were associated with the telerehabilitation program. The weekly adherence was 2.85 (1.43) days, and in 63.3% of the weeks the participants were enrolled, they performed the exercise program at least twice a week. Participants rated the telerehabilitation program as 9.71 (0.21), and the safety of remote exercises without professional supervision as 8.6 (2.2) on a 0-10 scale. CONCLUSIONS: The telerehabilitation program using a smartphone app was safe and presented high participants' satisfaction and adequate adherence, recruitment, and dropout rates. Therefore, the definitive study can be conducted with few modifications. TRIAL REGISTRATION: Brazilian Registry of Clinical Trials (ReBEC), RBR-9243v7. Registered on 24 August 2020. https://ensaiosclinicos.gov.br/rg/RBR-9243v7 .
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BACKGROUND: Para athletes experience high prevalence and incidence of health problems related to sport. Despite this, there are few longitudinal studies. OBJECTIVE: To describe the characteristics, prevalence, incidence, and severity of health problems in para athletes from one of the Brazilian Paralympic Reference Centers during a sports season and to compare the prevalence of health problems between para athletics, para powerlifting, and para swimming. METHODS: This prospective pilot study was conducted from October 2019 to March 2020. The Oslo Sports Trauma Research Center Questionnaire on Health Problems was used to record injuries and illnesses every week for 24 weeks. The characteristics, prevalence, incidence, and severity of health problems were described for each modality. The prevalence of health problems was compared among the three sport modalities. RESULTS: Thirty-five para athletes participated. Most of the injuries occurred in the shoulder, and most illnesses caused respiratory and gastrointestinal symptoms. The average weekly prevalence and the incidence rate of health problems were 40.6% (95% CI 17.0-64.4) and 12.7 (95% CI 9.6-15.9) per 1000 athlete hours, respectively. Para powerlifting had the highest prevalence of all and substantial health problems; para swimming had the lowest prevalence of injuries; and para athletics had the lowest prevalence of illnesses. CONCLUSIONS: This group of Brazilian para athletes showed a high prevalence and incidence of health problems throughout the season. Para athletics, para powerlifting, and para swimming each had a different prevalence of injuries and illnesses.
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Pessoas com Deficiência , Paratletas , Humanos , Incidência , Projetos Piloto , Estudos Prospectivos , Prevalência , Brasil/epidemiologia , Estações do Ano , Natação , AtletasRESUMO
The upper body and trunk muscles are crucial to perform soccer kicks. Resistance training targeting these muscles may modify the pattern adopted during kicking. This study aimed to investigate the effect of resistance training of the arm and anterior trunk muscles on instep kicking kinematics. Twenty-six male participants were randomly allocated into a training group or control group. The training group underwent resistance training of arm and trunk muscles and practiced the instep kick for 8 weeks. The control group only practiced kicking during the same period. The trunk, hip, and knee kinematics were assessed during the instep kick before and after the intervention. Kinematics were analyzed according to their data distribution with statistical parametric or nonparametric mapping. The effect of the training on the 1-repetition maximum test was analyzed using a repeated-measures multivariate analysis of variance. The training group showed greater hip extension after the training during the backswing phase (Hedge g effect size of 0.316-0.321) and increased 1-repetition maximum for all exercises. There were no other differences. The present study documented the nonlocal effect of strengthening training in which arm and trunk muscle training resulted in changes in hip kinematics during the backswing phase of the instep kick.
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Treinamento Resistido , Futebol , Humanos , Masculino , Futebol/fisiologia , Fenômenos Biomecânicos , Músculo Esquelético/fisiologia , Extremidade SuperiorRESUMO
OBJECTIVE: To identify subgroups of runners' profiles who had or did not have a History of Running-Related Injury in the Shank and Foot (HRRI-SF). DESIGN: Cross-sectional. METHODS: Clinical measures of passive ankle stiffness (measured as ankle position (compliance) to index passive joint stiffness), forefoot-shank alignment, peak torque of ankle plantar flexors, years of running experience, and age were analyzed through Classification and Regression Tree (CART). RESULTS: The CART identified four subgroups of runners with a greater prevalence of HRRI-SF: (1) ankle stiffness ≤0.42°; (2) ankle stiffness >0.42°, age ≤23.5 years, and forefoot varus >19,64°; (3) ankle stiffness >0.42°, age >62.5 years, and forefoot varus ≤19.70°; (4) ankle stiffness >42°, age >62.5 years, forefoot varus >19.70°, and running experience ≤7 years. Three subgroups had a lower prevalence of HRRI-SF: (1) ankle stiffness >0.42° and age between 23.5 and 62.5 years; (2) ankle stiffness >0.42°, age ≤23.5 years, and forefoot varus ≤14.64°; (3) ankle stiffness >0.42°, age >62.5 years, forefoot varus >19.7°, and running experience >7 years. CONCLUSION: One runner profile subgroup showed that higher ankle stiffness could predict HRRI-SF without association with other variables. Distinct interactions among variables characterized the other subgroups' profiles. The identified interactions among the predictors used to characterize the runners' profiles could be used in clinical decision-making.
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Traumatismos do Pé , Corrida , Humanos , Adulto Jovem , Adulto , Pessoa de Meia-Idade , Estudos Transversais , Perna (Membro) , Articulação do Tornozelo , Fatores Etários , Fenômenos BiomecânicosRESUMO
Objectives: Sleep is essential for musculoskeletal and cognitive recovery. Adolescent athletes tend to sleep poorly compared to adults and it may predispose them to sports injuries. Our aims are to estimate whether the quantity/quality of sleep are associated with sports injuries in adolescent athletes and to compare the quantity/quality of sleep between the training and competition seasons, and the school vacation period. Material and Methods: It was a cohort study with 19 track and field athletes of both sexes, aged between 12 and 21 years. We evaluated their sleep-wake habit through actigraphy during three phases: 1 - mid-season, 2 - competition, and 3 - school vacation. The previous six months injury history and the occurrence of injuries in a six-month follow-up were recorded. Logistic regression and variance analysis were performed. The significance level used was 0.05. Results: Wake after sleep onset (WASO) predicted previous injuries (OR=1.144) and time awake (TA) predicted injury occurrence (OR=0.974). TA decreased from phase 2 to phase 3 (p=0.004), total sleep time (TST) increased from phase 2 to phase 3 (p=0.012), and WASO decreased between phases 1 and 2 (p=0.001) and between phases 1 and 3 (p=0.025). Conclusion: Our study demonstrated that the quantity and quality of sleep were associated with musculoskeletal injuries in adolescent track and field athletes. Previous injuries were predicted by WASO and the occurrence of injuries was predicted by TA. Furthermore, during the vacation period they had lower TA and WASO, and higher TST than on school days.
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The purpose of this study was to investigate the angular kinetic energy transfers and expenditure among the trunk (bisegmented), the pelvis and the kick limb during maximal soccer instep kicking, and to characterize kicking kinetics and kinematics. Eighteen adult male amateur soccer players (24.0 ± 4.1 years old) were assessed. Three-dimensional kinematics and ground reaction force were measured. A 6-degrees-of-freedom model was assumed, comprising the upper trunk, lower trunk, pelvis, thigh, shank and foot, and the thoraco-lumbar, lumbo-pelvic, hip, knee, and ankle joints. Angular kinematics and joint moments were computed. Power flow analysis was done by calculating the joint powers (to describe joint-to-segments energy transfers) and the proximal and distal segment powers (to describe segment-to-segment transfers). Power, kinematic and kinetic time series were presented to describe the energy flows' directions. The total mechanical energy expenditure (TMEE) at each joint was also calculated. The TMEEs pointed to substantial energy expenditure at the trunk (27% of the summed work produced by the analyzed joints). In the initial phases of kicking, the trunk generates downward energy flows from the upper to the lower trunk and from the lower trunk to the pelvis, and then to the lower limb, sequentially, which favors angular motions for ball contact. There is a formation and release of a tension arc only at the hip joint, and deceleration of the segments slightly sooner than ball contact, differently from theoretical accounts. There are energy flows, hitherto unknown, among the trunk, pelvis and kick limb, revealing mechanical strategies of kicking.
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Futebol , Adulto , Fenômenos Biomecânicos , Pé , Humanos , Articulação do Joelho , Extremidade Inferior , Masculino , Adulto JovemRESUMO
BACKGROUND: Adherence to the use of recommended measures/criteria for return to sport clearance after anterior cruciate ligament reconstruction is crucial for successful rehabilitation. OBJECTIVES: The purpose of this study was to describe the current clinical practice of Brazilian physical therapists that treat patients after anterior cruciate ligament reconstruction, including the measures/criteria used to support the decision-making process regarding return to sport. The secondary aim was to investigate factors associated with the use of the most recommended measures/criteria for return to sport. METHODS: An electronic survey questionnaire was sent to Brazilian physical therapists. The survey consisted of questions about demographics and professional and clinical practice data related to anterior cruciate ligament reconstruction postoperative rehabilitation and return to sport criteria. Descriptive statistics and chi-square tests were used for analyses. RESULTS: A sample of 439 professionals participated in the survey. Only 6.4% of the physical therapists use the most recommended measures/criteria for return to sport after anterior cruciate ligament reconstruction. Professional certification in Sports Physical Therapy was the only factor associated with the use of these recommended measures/criteria (p=0.02). The measures most used for return to sport clearance were related to physical factors (65.3% to 75.1%), such as range of motion and muscle strength. A small number of professionals use questionnaires to assess functional (16.6%) and psychological (19.1%) aspects of their patients to support the decision-making process. CONCLUSION: In their clinical practice, most Brazilian physical therapists do not use the recommended measures/criteria for return to sport after anterior cruciate ligament reconstruction.
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Lesões do Ligamento Cruzado Anterior/fisiopatologia , Reconstrução do Ligamento Cruzado Anterior , Força Muscular/fisiologia , Brasil , Humanos , Fisioterapeutas , Amplitude de Movimento Articular , Volta ao Esporte , Inquéritos e QuestionáriosRESUMO
OBJECTIVE: To investigate prevalence, incidence and profile of musculoskeletal injuries in para athletes. DESIGN: Systematic review. DATA SOURCES: Searches were conducted in MEDLINE, EMBASE, AMED, SPORTSDiscus, CINAHL and hand searching. ELIGIBILITY CRITERIA: Studies were considered if they reported prevalence or incidence of musculoskeletal injuries in para athletes. Study selection, data extraction and analysis followed the protocol. Meta-analyses were conducted to estimate the prevalence and incidence rate among studies and subgroup analyses investigated whether methodological quality and sample size of the studies influenced on the estimated injury prevalence and incidence. The Grading of Recommendations Assessment, Development and Evaluation system determined the strength of evidence. RESULTS: Forty-two studies were included. The prevalence of musculoskeletal injuries was 40.8% (95% CI 32.5% to 49.8%). Because of imprecision, indirectness and inconsistency, the strength of evidence was very low quality. The incidence of musculoskeletal injuries was 14.3 injuries per 1000 athlete-days (95% CI 11.9 to 16.8). The strength of evidence was low quality because of imprecision and indirectness. The subgroup analyses revealed that the sample size influenced on estimated injury prevalence and methodological quality influenced on estimated incidence. Injuries were more prevalent in the shoulder, for non-ambulant para athletes, and in the lower limbs, for ambulant para athletes. SUMMARY/CONCLUSION: Para athletes show high prevalence and incidence of musculoskeletal injuries. Current very low-quality and low-quality evidence suggests that future high-quality studies with systematic data collection, larger sample size and specificities of para athletes are likely to change estimates of injury prevalence and incidence in para athletes. PROSPERO REGISTRATION NUMBER: CRD42020147982.
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Traumatismos em Atletas , Paratletas , Atletas , Traumatismos em Atletas/epidemiologia , Humanos , Incidência , PrevalênciaRESUMO
BACKGROUND: The use of predictive equation of muscular torque can reduce physical effort and time spent during evaluation. OBJECTIVES: To establish, validate, and test the accuracy of a prediction equation to estimate the hip external rotators (HER) torque in adults and older adults by means of hip extensors (HEX) torque measurement. METHODS: Eighty-three healthy adults (development set) were assessed to test the association of HEX and HER torques and to establish the prediction equation. A separate 36 adults and 15 older adults (validation sets) were assessed to test the ability of the equation to estimate HER torque. Hip isometric strength was assessed by a handheld dynamometer. RESULTS: Simple linear regression analysis revealed that HEX torque was associated with HER torque (r=0.80; p<0.0001), resulting in the following prediction equation: HERtorque=-0.02+(0.58 * HEXtorque). Paired t-test revealed no difference between directly measured and predicted values of HER torque in adults (mean difference=0.02; 95% CI=-0.115, 0.072) and older adults (mean difference=0.05; 95% CI=-0.02, 0.12). CONCLUSION: The HEX and HER torques were strongly correlated. The prediction equation was valid, accurate, and can be used to estimate HER muscle strength in healthy adults and older adults, requiring only the direct measurement of HEX torque.
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Força Muscular/fisiologia , Músculo Esquelético/fisiologia , Quadril/fisiologia , Humanos , Rotação , TorqueRESUMO
BACKGROUND: Modifications of posture in a segment may influence the posture of adjacent and nonadjacent segments and muscular activity. The spine-shoulder and spine-pelvis relationships suggest that the pelvis may influence shoulder posture. OBJECTIVE: To investigate the effect of the active reduction of the anterior pelvic tilt on shoulder and trunk posture during static standing posture and on the electromyographic activity of the scapular upward rotators during elevation and lowering of the arm. METHODS: Thirty-one young adults were assessed in a relaxed standing position and a standing position with 30% active reduction of the anterior pelvic tilt. The pelvic tilt, trunk posture, and forward shoulder posture during the static standing posture and the electromyographic activity during elevation and lowering of the arm were assessed. RESULTS: Paired t-tests indicated that the active reduction of the anterior pelvic tilt reduced the trunk extension (MD=1.09; 95%CI=-2.79 to -1.03). There were no effects on the forward shoulder posture (MD=0.09; 95%CI=-0.92 to 1.09). Repeated measures of analyses of variance indicated an increase in lower trapezius electromyographic activity (MD=3.6; 95%CI=1.28 to 5.92). There was a greater reduction in upper trapezius activity after pelvic tilt reduction during arm elevation (MD=1.52%; 95%CI=-2.79 to -0.25) compared to that during the lowering phase. There were no effects of pelvic tilt reduction on the electromyographic activity of the serratus anterior (MD=3.26; 95%CI=-3.36 to 9.87). CONCLUSION: The influence of pelvic posture on the trunk posture and lower trapezius activation should be considered when assessing or planning exercise for individuals with shoulder or trunk conditions.
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Escápula/fisiologia , Ombro/fisiologia , Músculos Superficiais do Dorso/fisiologia , Eletromiografia , Exercício Físico/fisiologia , Humanos , Postura , Adulto JovemRESUMO
BACKGROUND: A better understanding about the relationship between trunk and hip muscles strength and core stability may improve evaluation and interventions proposed to improve core stability. OBJECTIVES: To investigate if trunk and hip muscles strength predict pelvic posterior rotation during the bridge test with unilateral knee extension. METHODS: This is a cross-sectional study. Sixty-one healthy individuals of both sexes (age, 28±6.4 years, weight, 66.5±10.9kg, height, 167±9.5cm) performed the bridge test with unilateral knee extension. The pelvic posterior rotation during the bridge test was obtained with two-dimensional video analysis. Isometric strength of the trunk extensors and rotators, and hip abductors, external and internal rotators and extensors were measured with a hand-held dynamometer. Multiple linear regression analysis was performed to identify if the strength variables could explain the pelvic posterior rotation during the test. RESULTS: Muscle strength predicted pelvic posterior rotation during the bridge test (r=0.54; p=0.003). Strength of the trunk rotators (p=0.045) and hip internal rotators (p=0.015) predicted reduced magnitude of pelvic posterior rotation during the bridge test, and strength of the hip extensors (p=0.003) predicted increased magnitude of pelvic posterior rotation. CONCLUSIONS: Trunk rotators and hip internal rotators and extensors strength predict 29% of the performance during the bridge test with unilateral knee extension. The strength of these muscles should be evaluated in individuals with increased pelvic posterior rotation during the bridge test with unilateral knee extension.
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Quadril/fisiologia , Força Muscular/fisiologia , Músculo Esquelético/fisiologia , Estudos Transversais , Feminino , Humanos , Masculino , Rotação , Adulto JovemRESUMO
Study Design Controlled laboratory study, cross-sectional. Background Deficits in ankle proprioceptive acuity have been reported in persons with functional instability of the ankle. Passive stiffness has been proposed as a possible mechanism underlying proprioceptive acuity. Objective To compare proprioceptive acuity and passive ankle stiffness in persons with and without functional ankle instability, and to assess the influence of passive joint stiffness on proprioceptive acuity in persons with functional ankle instability. Methods A sample of 18 subjects with and 18 without complaints of functional ankle instability following lateral ankle sprain participated. An isokinetic dynamometer was used to compare motion perception threshold, passive position sense, and passive ankle stiffness between groups. To evaluate the influence of passive stiffness on proprioceptive acuity, individuals in the lateral functional ankle instability group were divided into 2 subgroups: "high" and "low" passive ankle stiffness. Results The functional ankle instability group exhibited increased motion perception threshold when compared with the corresponding limb of the control group. Between-group differences were not found for passive position sense and passive ankle stiffness. Those in the functional ankle instability group with higher passive ankle stiffness had smaller motion perception thresholds than those with lower passive ankle stiffness. Conclusion Unlike motion perception threshold, passive position sense is not affected by the presence of functional ankle instability. Passive ankle stiffness appears to influence proprioceptive acuity in persons with functional ankle instability. J Orthop Sports Phys Ther 2017;47(12):899-905. Epub 7 Oct 2017. doi:10.2519/jospt.2017.7030.
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Articulação do Tornozelo/fisiopatologia , Instabilidade Articular/fisiopatologia , Propriocepção/fisiologia , Adulto , Estudos Transversais , Feminino , Humanos , Masculino , Percepção de Movimento/fisiologia , Amplitude de Movimento Articular , Entorses e Distensões/fisiopatologia , Adulto JovemRESUMO
Study Design Cross-sectional clinical assessment. Background Patellar tendinopathy is not always accompanied by patellar tendon abnormalities (PTAs). Thus, clinical screening tools to help identify patients with patellar tendon pain who have PTAs could enhance clinical decision making and patient prognosis. Objectives To test the diagnostic accuracy of the Victorian Institute of Sport Assessment-Patella (VISA-P) questionnaire, a single-leg decline squat (SLDS), tendon pain history, age, and years of sports participation to identify athletes with symptomatic patellar tendons who have PTAs confirmed on imaging. Methods Data provided by ultrasound examination, the VISA-P questionnaire, the SLDS, tendon pain history, age, and years of sport participation were collected in 43 athletes. A classification and regression tree (CART) model was developed to verify variables associated with PTA occurrence. Likelihood ratios (LRs) were computed for positive and negative tests. Results The SLDS, VISA-P questionnaire, and tendon pain history were associated with PTA occurrence. Athletes with negative results on all 3 tests (CART model) had a lower likelihood of having PTAs (negative LR = 0.3; 95% confidence interval [CI]: 0.2, 0.5). The isolated use of the SLDS or tendon pain history (positive LR = 4.2; 95% CI: 2.3, 7.14 and 4.5; 95% CI: 1.8, 11.1, respectively) had similar influence on probability of PTA presence compared to the CART model (positive LR = 4.1; 95% CI: 2.5, 6.3). Conclusion Although the objective was to investigate a clinical test to identify PTAs, the combined use of the tests had greater accuracy to identify individuals without PTAs. Level of Evidence Diagnosis, level 3b. J Orthop Sports Phys Ther 2016;46(8):673-680. Epub 3 Jul 2016. doi:10.2519/jospt.2016.6192.
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Artralgia/etiologia , Atletas , Ligamento Patelar/anormalidades , Tendinopatia/etiologia , Tendões/anormalidades , Adulto , Fatores Etários , Fenômenos Biomecânicos , Intervalos de Confiança , Estudos Transversais , Teste de Esforço/métodos , Feminino , Humanos , Masculino , Ligamento Patelar/diagnóstico por imagem , Curva ROC , Medição de Risco/métodos , Inquéritos e Questionários , Tendinopatia/diagnóstico , Tendões/fisiopatologia , Fatores de Tempo , UltrassonografiaRESUMO
The purpose of this study was to understand the physical, attitudinal, and assistive characteristics of the home and the therapeutic settings that enable and/or hinder hand use by children with spastic hemiparesis CP. A qualitative study with 7 children with CP, their caregivers, and therapists was conducted. Children were observed at home and in their therapeutic settings to understand the supports and barriers from these environments regarding their use of the affected hand. Semi-structured interviews were conducted with caregivers and therapists. The transcribed interviews and field diaries were used for content analysis. The following thematic categories were drawn from the data analyses: (1) use when needed: from consistent to nonuse of the affected extremity; (2) making decisions: choosing to use or not use the affected extremity; and (3) responsibilities with activities: from complete dependence to independent performance. Discrepancies between caregivers and therapists' attitudes and actions towards children's hands use highlight the specific features from each context that facilitated or hindered children with CP's engagement in functional activities. Recommendations for future studies include investigating the relationship between the identified facilitators and improvements in children's effective hand use in home and clinical settings.
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Paralisia Cerebral/reabilitação , Meio Ambiente , Mãos/fisiopatologia , Terapia Ocupacional , Paresia/reabilitação , Criança , Pré-Escolar , Feminino , Humanos , Masculino , Pesquisa QualitativaRESUMO
OBJECTIVE: The objective of this study was to provide normative data of frontal plane patellar alignment according to McConnell and Arno angles, verify the association between theses angles and identify the presence of patellar rotation in different sports. DESIGN: Cross-sectional. PARTICIPANTS: Nine participants (18 knees) were assessed in a preliminary study to verify the intra and inter-examiner reliabilities of the patellar alignment measures. In the main study, 230 volleyball, basketball, gymnastics and soccer athletes (460 knees) were evaluated in order to obtain normative data of patellar alignment. MAIN OUTCOME MEASURES: Frontal plane patellar alignment (McConnell and Arno angles) measured in standing position by means of photogrammetry. RESULTS: The standardized method demonstrated intra and inter-examiner reliability coefficients varying from .85 to .98. The mean McConnell and Arno angles were 2.05° (±5.9) and 2.89° (±7.57), respectively. A low association was observed (r = .189, p < .0001) between these angles. There was a difference in distribution of medial and lateral rotations, according to the McConnell angle, between different sports (p < .014). CONCLUSIONS: The proposed procedure for measuring patellar alignment according to McConnell and Arno angles proved to be highly reliable. This made possible the establishment of normative data in a large sample of healthy athletes.
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Atletas , Patela/fisiologia , Fenômenos Biomecânicos , Feminino , Voluntários Saudáveis , Humanos , Masculino , Patela/anatomia & histologia , Fotogrametria , Valores de Referência , Reprodutibilidade dos Testes , Rotação , Adulto JovemRESUMO
BACKGROUND: ACL reconstruction is recommended to improve function in subjects with ligament injuries. However, after surgery, some individuals are not able to return to their pre-injury functional level. The mechanisms related to this incapacity are not well understood. STUDY DESIGN: Cross-sectional study. METHODS: Co-contraction levels were assessed in individuals who returned to their pre-injury functional level and in 10 individuals who were not able to return to full activity after unilateral ACL reconstruction. Electromyography of the vastus lateralis and biceps femoris muscles before and after sudden perturbations applied during the stance phase of walking was used to calculate co-contraction. RESULTS: The involved limb had lower co-contraction pre-perturbation than the non-involved limb in both groups (p=0.049). The co-contraction level post-perturbation was significantly higher in the limited return group than in the full return group (p=0.03). CONCLUSION: Decreased co-contraction in the involved limb before perturbation may be caused by sensorial changes resulting from surgery or injury. Increased co-contraction levels observed in the limited return group after perturbation may be a compensatory mechanism to make up for possible decreased intrinsic stability of the knee joint. CLINICAL RELEVANCE: Increased co-contraction after perturbation does not contribute to knee stability.