INTRODUCTION: Reaction time may be broadly defined as the time between stimulus presentation and a response. Analysis of reaction time in terms of rate of force development (RFD), peak force, and surface electromyography (EMG) may help bridge the gaps in knowledge pertaining to the neuromuscular system's role in reaction time. The purpose of the present study was to identify predictors of reaction time using digital hand grip dynamometry and EMG. It was hypothesized that RFD and rate of EMG rise (RER) at the onset of a contraction would correlate with reaction time. METHODS: For grip testing, participants were instructed to squeeze a handheld dynamometer with the right hand "…as hard and fast as possible" for 5 seconds upon hearing a "beep" from the computer. A total of 5 attempts were performed, with 1-minute rest periods. Bipolar surface EMG signals were detected from the right first dorsal interosseous (FDI) and flexor carpi radialis (FCR) muscles throughout grip testing. Bivariate correlations (Pearson r) were used to examine the statistical associations. The 95% confidence interval (CI) for each Pearson r was also computed. An alpha level of p ≤ 0.05 was used to reject the null hypothesis. RESULTS: Significant correlations were observed between reaction time and all other measures of grip force (r = -0.507 to -0.557, p= 0.016 to 0.042), except for time until peak force (r = 0.029, p = 0.915). As FDI EMG amplitude increased reaction time decreased (r = -0.664, p = .005). CONCLUSION: Many of the grip force variables were significantly associated with reaction time. Peak force and rapid force variables showed significant correlations with reaction time. While no significant correlations for any of the FDI RER or FCR variables were found, EMG amplitude from the FDI presented the strongest bivariate correlation. As FDI EMG amplitude, peak force, and rapid force variables increased reaction time decreased. These findings give some insight into the neuromuscular system's role in hand grip tasks and help broaden the current understanding of variables that may be used to assess or improve reaction time in the clinical setting.

INTRODUÇÃO: As distrofias musculares de cinturas (DMC) representam um grupo heterogêneo de desordens hereditárias e degenerativas da musculatura esquelética, com evolução progressiva, caracterizadas pelo acometimento predominante das cinturas escapular e/ou pélvica. São classificadas de acordo com o padrão de herança e o gene envolvido, podendo ser autossômicas dominantes ou autossômicas recessivas. No presente estudo, foi feita a análise de pacientes com diagnóstico de distrofia muscular de cinturas 2B (DMC2B). Trata-se de condição autossômica recessiva, cujo gene envolvido na sua fisiopatologia é o DYSF; sua mutação pode associar-se a alterações na proteína disferlina. OBJETIVOS: Avaliar a distribuição da fraqueza muscular na distrofia muscular de cinturas 2B com ênfase no acometimento dos membros superiores; realizar avaliação objetiva da força muscular para preensão palmar e pinças; correlacionar a força muscular dos diferentes movimentos com a idade de início dos sintomas, idade na ocasião da avaliação, tempo de evolução da doença e capacidade funcional. METODOLOGIA: Estudo prospectivo, observacional, corte transversal, caso-controle. Foi feita avaliação clínica da força muscular de membros superiores e superiores dos pacientes, através de instrumentos clínicos específicos e dinamômetro de pinça e de preensão palmar; adicionalmente, foram aplicadas escalas de capacidade funcional (Escala de Vignos e Escala de Brooke). RESULTADOS: Foram avaliados 12 pacientes com diagnóstico molecular confirmado de DMC2B e recrutados 41 pacientes para o grupo controle. Os grupos não diferiram por gênero nem nas médias etárias. A média da idade de início dos sintomas dos pacientes foi de 26,9 anos (DP 10,05); a idade média na ocasião da avaliação foi de 43,6 anos (DP 9,34). A avaliação clínica da força muscular evidenciou maior acometimento de membros inferiores em relação aos membros superiores. A dinamometria de pinça (bidigital e trigidital) e de preensão palmar evidenciou diferença significativa entre os pacientes e o grupo controle para todos os movimentos citados. Os valores de CK apresentaram média de 2769 U/L (cerca de quinze vezes o limite superior de normalidade). As escalas de avaliação de capacidade funcional evidenciaram uma correlação significativa entre a idade do paciente na ocasião da avaliação e o escore na escala de Brooke. CONCLUSÃO: A análise do padrão de fraqueza dos pacientes com DMC2B evidenciou acometimento de membros inferiores e também de membros superiores. A análise objetiva com dinamometria demonstrou acometimento em todos os movimentos avaliados, evidenciando o envolvimento distal de membros superiores. A análise da capacidade funcional de membros superiores apresentou correlação com idade na avaliação (quanto maior a idade do paciente, maior o grau de incapacidade para membros superiores). Os valores de CK e de força muscular correlacionaram-se com a idade do início dos sintomas e idade na avaliação, ou seja, o início mais precoce da doença correlacionou-se com quadros mais graves (maiores valores de CK e maior envolvimento de força muscular - principalmente distal de membros superiores) / INTRODUCTION: Limb-girdle muscular dystrophies (LGMD) are a heterogeneous group of hereditary and degenerative disorders of the skeletal muscle, with progressive evolution, characterized by the predominant involvement of the scapular and / or pelvic girdles. They are classified according to the inheritance pattern and the involved gene, being autosomal dominant or autosomal recessive. In the present study, we evaluated patients with a diagnosis of 2D (LGMD2B). The LGMD2B is an autosomal recessive condition whose gene involved in its pathophysiology is DYSF; its mutation may be associated with changes in protein dysferlin. OBJECTIVES: To assess the distribution of muscle weakness in 2D womb muscular dystrophy with emphasis on upper limb involvement; perform objective evaluation of muscle strength for palmar grip and forceps; to correlate the muscular strength of the different movements with the age of onset of symptoms, age at the time of evaluation, duration of disease and functional capacity. METHODS: Prospective, observational, cross-sectional, case-control study. Clinical evaluation of the muscular strength of the upper and upper limbs of the patients was made through specific clinical instruments and pinch dynamometer and palmar grip; In addition, functional capacity scales were applied (Vignos Scale and Brooke Scale). RESULTS: Twelve patients with confirmed molecular diagnosis of DMC2B were evaluated and 41 patients were recruited for the control group. The groups did not differ by gender nor in the age groups. The mean age of onset of the patients\' symptoms was 26.9 years (SD 10.05); the mean age at the time of the evaluation was 43.6 years (SD 9.34). The clinical evaluation of muscle strength showed a greater involvement of the lower limbs in relation to the upper limbs. Pinch dynamometry (bidigital and trigidital) and handgrip dynamometry showed a significant difference between the patients and the control group for all the mentioned movements. CK values presented a mean of 2769 U / L (about eight times the upper limit of normality); there was a significant negative correlation (p <0.01) between the age of the patient at the time of the evaluation and the maximum value of CK. The functional capacity evaluation scales showed a significant correlation between the age of the patient at the time of the evaluation and the score on the Brooke scale. The correlation values between the muscular strength between the different movements evaluated and the age of onset of symptoms, age at the time of evaluation and time of evaluation of the disease presented values of significance close to 0.05 for the upper limb distal muscles and age of onset and age at the time of evaluation. CONCLUSION: The analysis of the weakness pattern of patients with LGMD2B showed involvement of lower limbs as well as upper limbs. Objective analysis with dynamometry showed involvement in all the movements evaluated, showing the distal involvement in the upper limbs. The analysis of functional capacity of upper limbs showed correlation with age in the evaluation (the higher the patient\'s age, the greater the degree of incapacity for upper limbs). The values of CK and muscle strength correlated with the age of onset of symptoms and age at the assessment, ie the earlier onset of the disease was correlated with more severe conditions (higher CK values and greater involvement of muscle strength - mainly distal upper limbs)