Lateral and functional asymmetries in the lower limbs of college-level female handball players

Abstract Aim: The present study aimed to screen for differences in isokinetic peak torque, hamstrings-to-quadriceps ratio, and proprioception within the lower limbs of female handball athletes. Methods: Twelve college-level female handball athletes with no previous experience with resistance training performed five maximal isokinetic contractions of the knee extensors and knee flexors to determine isokinetic peak torque and hamstring-to-quadriceps ratios. Proprioception was determined by assessing passive position sense on an isokinetic dynamometer. Results: The athletes presented significantly greater (p < 0.01) knee extensors isometric peak torque for the jumping limb (144.9 ± 23.1) when compared to the non-jumping limb (132.9 ± 21.5). The Hamstrings-to-quadriceps ratio was below 0.6 for both limbs, being significantly greater (p < 0.01) for the non-jumping limb (0.56 ± 0.08) when compared to the jumping limb (0.50 ± 0.08). Conclusion: Female handball athletes that do not engage in resistance training can experience functional bilateral asymmetries in the knee extensors and knee-joint instability, as assessed by the hamstrings-to-quadriceps ratio due to the asymmetric characteristics of handball. Regular strength training might correct such asymmetries and instabilities.

The Impact of ACTN3 Gene Polymorphisms on Susceptibility to Exercise-Induced Muscle Damage and Changes in Running Economy Following Downhill Running.

This study aimed to investigate if ACTN3 gene polymorphism impacts the susceptibility to exercise-induced muscle damage (EIMD) and changes in running economy (RE) following downhill running. Thirty-five healthy men were allocated to the two groups based on their ACTN3 gene variants: RR and X allele carriers. Neuromuscular function [knee extensor isometric peak torque (IPT), rate of torque development (RTD), and countermovement, and squat jump height], indirect markers of EIMD [muscle soreness, mid-thigh circumference, knee joint range of motion, and serum creatine kinase (CK) activity], and RE (oxygen uptake, minute ventilation, blood lactate concentration, and perceived exertion) for 5-min of running at a speed equivalent to 80% of individual maximal oxygen uptake speed were assessed before, immediately after, and 1-4 days after a 30-min downhill run (-15%). Neuromuscular function was compromised (P < 0.05) following downhill running with no differences between the groups, except for IPT, which was more affected in the RR individuals compared with the X allele carriers immediately (-24.9 ± 6.9% vs. -16.3 ± 6.5%, respectively) and 4 days (-16.6 ± 14.9% vs. -4.2 ± 9.5%, respectively) post-downhill running. EIMD manifested similarly for both the groups except for serum CK activity, which was greater for RR (398 ± 120 and 452 ± 126 U L-1 at 2 and 4 days following downhill running, respectively) compared with the X allele carriers (273 ± 121 and 352 ± 114 U L-1 at the same time points). RE was compromised following downhill running (16.7 ± 8.3% and 11 ± 7.5% increases in oxygen uptake immediately following downhill running for the RR and X allele carriers, respectively) with no difference between the groups. We conclude that although RR individuals appear to be more susceptible to EIMD following downhill running, this does not extend to the changes in RE.

A single bout of downhill running attenuates subsequent level running-induced fatigue.

Fatigue can be defined as exercise-induced strength loss. During running, fatigue can be partially explained by repetitive low-intensity eccentric contractions-induced muscle damage (EIMD). Previous studies showed that a bout of downhill running (DR) attenuated subsequent EIMD. Thus, we tested if a 30-min DR bout would attenuate fatigue induced by subsequent 60-min level running (LR). Twenty-seven male college students were randomly allocated to an experimental (EXP) or a control (CON) group. All participants performed LR on a treadmill at 70% of the velocity (vVO2peak) corresponding to peak oxygen uptake (VO2peak). Only EXP performed a 30-min DR (- 15%) on a treadmill at 70% vVO2peak fourteen days before LR. Indirect EIMD markers and neuromuscular function were assessed before, immediately and 48 h after DR and LR. Knee extension isometric peak torque (IPT) decreased (- 36.3 ± 26%, p < 0.05) immediately following DR with full recovery reached 48 h post-DR. Muscle soreness developed (p < 0.05) immediately (37 ± 25 mm) and 48 h (45 ± 26 mm) post-DR. IPT and rate of torque development (RTD) at late phases (> 150 ms) from the onset of muscle contraction decreased significantly (- 10.7 ± 6.1% and from - 15.4 to - 18.7%, respectively) immediately after LR for the CON group and remained below baseline values (- 5.6 ± 8.5% and from - 13.8 to - 14.9%, respectively) 48 h post-LR. However, IPT and late RTD were not significantly affected by LR for the EXP group, showing a group x time interaction effect. We concluded that a single DR bout can be used to attenuate fatigue induced by a LR performed fourteen days after.

Co-contraction of the core muscles during Pilates exercise on the Wunda Chair.

BACKGROUND: The co-contraction of the core muscles has been reported as the key mechanism towards spinal stability. Classic Pilates exercises aimed at these muscles are known to improve the stability and strength of the trunk without damaging the deep structures of the spine. OBJECTIVE: To evaluate the co-contraction of the mobilizing (rectus abdominis; longissimus) and stabilizing (multifidus; internal oblique) trunk muscles during Pilates exercises - going up front, mountain climber, and swan. METHODS: Sixteen women, all Pilates practitioners, participated in the study. The stabilizing and mobilizing muscles of the trunk (right side) were submitted to electromyography to calculate the percentage of co-contraction during the exercises. One-way repeated measures analysis of variance (ANOVA) was used to verify the difference in %COCON between stabilizers and mobilizers among the three exercises. The post-hoc Bonferroni test (P< 0.01) was applied when necessary. The paired t-test (P< 0.01) was used to verify the difference in %COCON between stabilizers and mobilizers separately for each exercise. RESULTS: The co-contraction values of the stabilizers were higher than those of the mobilizers for all exercises. The going up front (stabilizers) and the swan (mobilizers) exercises showed the highest %COCON values. CONCLUSIONS: The Pilates method is effective for either rehabilitating pathologies or training the trunk muscles in healthy individuals and athletes.

Avaliação eletromiográfica do exercício swan na Wunda Chair: Co-ativação dos músculos do core / Electromyographic evaluation of the swan exercise in the Wunda Chair: Co-activation of the core muscles

A principal finalidade do método Pilates é desenvolver uma automação dos músculos do core. Sendo assim, o objetivo deste estudo foi analisar a razão eletromiográfica dos músculos Oblíquo Interno (OI) e Reto do Abdômen (RA) localizados na parte anterior do tronco, a razão eletromiográfica dos músculos Multífido (MU) e Longuíssimo do Tórax (LO) localizados na parte posterior do tronco, e também a razão ântero-posterior (A/P=RA+IO/LO+MU) desses músculos durante o exercício swan do método Pilates, realizado sobre a Wunda Chair. Na comparação entre as três razões, foram encontradas diferenças estatísticas (p = 0,0103), apenas entre as razões ântero-posterior (A/P), e entre a razão dos músculos localizados na parte posterior do tronco (MU/LO). Os resultados demonstraram que houve um predomínio na atividade eletromiográfica dos músculos da região posterior em relação aos músculos da região anterior do tronco e que os músculos estabilizadores apresentaram maior atividade eletromiográfica em comparação com os músculos globais ou mobilizadores. O exercício swan pode ser utilizado como forma de treinamento para a musculatura do tronco, e como consequência gerar maior estabilidade a coluna vertebral, pois o exercício prioriza a diminuição da carga sobre a coluna vertebral. (AU)

The main purpose of the Pilates method is to develop an automation of core muscles. Thus, the aim of this study was to analyze the electromyographic ratio of the Internal Oblique (IO) and Rectus Abdominis (RA) muscles located in the anterior part of the trunk, the electromyographic ratio of the Multifidus (MU) and Longissimus Thoracis (LO) muscles, located in the posterior part of the trunk, and also the ratio antero- posterior (A/P=RA+IO/LO+MU) of these muscles during the swan exercise of the Pilates, performed on the Wunda Chair. In the comparison between the three ratios, statistical differences (p = 0.0013) were found only between the antero-posterior (A/P) ratios and the ratio of the muscles located in the posterior part of the trunk (MU/LO). The results showed a predominance of the electromyographic activity in the muscles of the posterior region in relation to the muscles of the anterior region of the trunk. The stabilizing muscles presented greater electromyographic activity in comparison to the global or mobilizing muscles. The swan can be used as training for the trunk muscles, and therefore generates greater stability of the spine, since exercise prioritizes the decrease of the load on the spine. (AU)

Comparison of the effects of different physical activities on laterality and asymmetry values through side bridge test

Aim: To compare the effects of different physical activities on laterality and asymmetry values through the side bridge test. Methods: the assessments were carried out in 45 subjects between 18 and 30 years old, 15 Crossfit-trained individuals, 15 weight trained and 15 sedentary. The subjects performed the side bridge test on both sides. After checking the normality and homogeneity of the data, we selected the appropriate statistical analysis for the comparison of the variables, adopting a significance level of α <0.05. Results: there was no statistical difference in the balance ratio; however, significant difference was found in the side bridge test endurance time, in which the Crossfit group obtained longer times on both sides than the other two groups. The side bridge test is a test of simple execution and that in this study the Crossfit group presented better results in the endurance time in the side bridge test. Conclusion: the results of the ratio asymmetry and endurance time are not sufficient to evaluate the resistance of the core muscles but could be an evaluation tool, the side bridge test can be introduced in postural training programs.(AU)

Rate of force development and muscle activation of trunk muscles in women with and without low back pain: A case-control study.

OBJECTIVE: To evaluate the rate of force development (RFD) and the rate of electromyography rise (RER) of global and local trunk muscles in women with and without low back pain. DESIGN: Cross-sectional study. SETTING: Laboratory setting. PARTICIPANTS: Twenty-eight women divided into low back pain (LBP, n = 14) and control groups (CG, n = 14) participated in this study. MAIN OUTCOME MEASURES: Subjects performed isometric contractions of trunk using an isokinetic dynamometer, and simultaneously the electromyography (EMG) signals were collected for global (rectus abdominis and longissimus thoracic) and local (internal oblique and multifidus) muscles. All variables were calculated using Matlab software. RESULTS: Symptomatic subjects showed lower RFD during trunk extension and it was correlated to a reduced RER mainly in the trunk extensor musculature (p < 0.05). During trunk flexion, LBP exhibited a delayed time to reach peak RFD (p < 0.05) compared to CG. RER for global anterior muscle was higher than for local muscle (p < 0.05) and it was more persistent in asymptomatic women. CG also presented greater activation amplitude for both agonist and antagonist trunk muscles, mainly the global ones. CONCLUSION: Symptomatic women showed lower RFD and it was correlated to a reduced capacity of rapid muscle activation mainly in the trunk extensor musculature.

Análise do COP e sentido de posição em jogadores universitários de futebol com e sem instabilidade de tornozelo / The analysis of COP and joint position sense in university soccer players with and without ankle instability

Resumo O objetivo do estudo foi comparar o comportamento do COP e do sentido de posição articular passivo em indivíduos com e sem instabilidade de tornozelo, e correlacionar as variáveis de COP e sentido de posição articular passivo. Participaram 20 indivíduos, divididos em dois grupos: grupo estável (GE) e grupo instável (GI). A avaliação do COP foi feita com o teste de apoio unipodal, com olhos abertos e fechados sobre uma plataforma de força. O teste de reposicionamento articular passivo foi realizado com os olhos vendados. O tornozelo foi posicionado em um ângulo alvo (10° e 20°) e o dinamômetro movia passivamente o tornozelo, então os participantes eram instruídos a apertar o botão para parar o movimento quando sentissem que o tornozelo estava no ângulo alvo, obtendo assim o erro angular absoluto (EAA). Foram obtidas as variáveis: deslocamento total (DT); desvio padrão ântero-posterior (DPap) e médio-lateral (DPml); velocidade média total (VMT); velocidade média ântero-posterior (VMap) e médio-lateral (VMml). A comparação entre dados que apresentaram distribuição normal foi feita com o teste t de Student, enquanto que para DT e DPml foi utilizado o teste de Mann-Whitney. Da mesma forma, foram usados os testes de Pearson e Spearman para correlacionar as variáveis. Foi adotado α < 0,05. Houve diferença entre EAA-10° (p < 0,05). Foram encontradas fortes correlações entre: EAA-10° e VMT (p < 0,01 r = −0,867); EAA-10° e VMap (p < 0,01 r = −0,854); EAA-10° e VMml (p < 0,01 r = −0,771), na condição olhos abertos, e EAA-10° e DT (p < 0,05 r = −0,666); EAA-10° e DPap (p < 0,05 r = −0,685) e EAA-10° e VMml (p < 0,05 r = −0,766) na condição olhos fechados. Entorses de tornozelo prejudicam o sentido de posição, sem afetar o equilíbrio.(AU)

Abstract The aim of the study was to compare the behavior of COP and passive ankle position sense in subjects with and without functional ankle instability. Took part in this study 20 subjects, divided into two groups: stable group (SG) and unstable group (UG). The COP evaluation was made with the single-leg balance test, with eyes opened and closed, on a force plate. The passive ankle position sense test was performed with subjects blindfolded. The ankle was positioned in a target angle (10° and 20°) and the dynamometer moved passively the ankle, then the subjects were instructed to push the stop button when they feel that the ankle was on the target angle, obtaining the absolute angular error (AAE). The following variables were obtained: total displacement (TD); antero-posterior (SDap) and medio-lateral standard deviation (SDml); total mean velocity (TMV); antero-posterior (MVap) and medio-lateral mean velocity (MVml). The comparison between the data with normal distribution was made with the Student's t test, while to the TD and SDml was used the Mann-Whitney test. The correlations were performed with the Pearson and Spearman tests. We adopted α < 0.05. We observed difference between AAE-10° (p < 0.05). Strong correlations were found between: AAE-10° and TMV (p < 0.01 r = −0.867); AAE-10° and MVap (p < 0.01 r = −0.854); AAE-10° and MVml (p < 0.01 r = −0.771), with eyes opened, and AAE-10° and TD (p < 0.05 r = −0.666); AAE-10° and SDap (p < 0.05 r = −0,685) and AAE-10° and MVml (p < 0.05 r= −0.766) with eyes closed. Ankle sprains harm the joint position sense without affecting the balance.(AU)

Comparação dos parâmetros de força e propriocepção entre indivíduos com e sem instabilidade funcional de tornozelo / Comparación entre los parámetros de fuerza y propiopercepción entre sujetos con y sin inestabilidad funcional del tobillo / Comparison of strength and proprioception parameters between subjects with and without functional ankle instability

Após a entorse de tornozelo, 40% dos indivíduos continuam a relatar uma sensação de instabilidade articular que está relacionada à disfunção músculo-esquelética denominada instabilidade funcional do tornozelo (IFT). Contudo, o mecanismo como ocorre esta disfunção músculo-esquelética ainda permanece desconhecido. Nesse sentido, o conhecimento das alterações músculo-esqueléticas que ocorrem em indivíduos com IFT pode ser um fator importante para traçar intervenções preventivas mais efetivas. Dessa forma, o objetivo deste estudo foi comparar o pico de torque (PT) concêntrico de inversão (INV) e eversão (EVE), a razão convencional (EVE/INV) e o reposicionamento articular passivo em indivíduos com e sem IFT em atletas recreacionais do gênero feminino. A amostra foi composta por 22 voluntárias na faixa etária entre 18 e 25 anos que foram divididas em grupo controle e grupo com IFT. A avaliação do torque foi realizada em um dinamômetro isocinético com cinco contrações máximas concêntricas a velocidades de 60 e 120 graus.s-1 no movimento de INV e EVE e reposicionamento articular passivo com ângulo-alvo de 10° e 20° de inversão. Foram analisados os dados de PT, razão convencional e média do erro absoluto do ângulo-alvo. A análise estatística foi feita com o teste t-Student para amostras independentes. Foi encontrado que indivíduos com IFT apresentaram diminuição da força eversora comparados aos indivíduos controle, bem como desequilíbrio da razão muscular, que podem aumentar a predisposição deste grupo a entorses de tornozelos.

Después del esguince de tobillo, el 40% de los sujetos siguen informando que hay una sensación de inestabilidad articular que se relaciona con la disfunción del musculo-esquelética llamada inestabilidad funcional del tobillo (IFT). Sin embargo, todavía no se conoce el mecanismo que es responsable por esta disfunción musculo-esquelética. En este sentido, el conocimiento de las alteraciones musculo-esqueléticas que ocurren en personas con IFT puede ser un factor importante para planear intervenciones preventivas más eficaces. De esta manera, esta investigación tiene como objetivo comparar el momento de torque (PT) de inversión concéntrica (INV) y eversión (EVE), la razón convencional (EVE/INV) y el reposicionamiento pasivo de las articulaciones en personas con y sin IFT en atletas recreacionales del género femenino. La muestra está compuesta por 22 voluntarios en la franja etaria entre 18 y 25 años, los cuales se dividieron en un grupo control y un grupo con IFT. La evaluación del torque se realizó en un dinamómetro isocinético con cinco contracciones máximas concéntricas con velocidades de 60 y 120 grados.s-1 en un movimiento de INV y EVE y reposicionamiento pasivo de la articulación con ángulo objetivo de 10° y 20° de inversión. Se analizó los datos del PT, de la razón convencional y la media del error absoluta del ángulo objetivo. Para el análisis, se utilizó la prueba t-Student para muestras independientes. Si comparados con las personas control se observó que las personas con IFT presentaron una disminución de la fuerza eversora y también un desequilibrio de la razón muscular, lo que puede aumentar la susceptibilidad de éstos a los esguinces de tobillos.

After an ankle sprain 40% of individuals continue to report a sensation of joint instability that is related to musculoskeletal dysfunction called functional ankle instability (FAI). However, a mechanism like this musculoskeletal dysfunction occurs remains unknown. In this sense, the knowledge of musculoskeletal changes that occur in individuals with FAI may be an important factor to plot more effective preventive interventions. Thus, the aim of this study was to compare peak torque (PT) concentric inversion (INV) and eversion (EVE), conventional ratio (EVE/ INV) and passive joint repositioning in individuals with and without FAI in recreational athletes females. The sample consisted of 22 volunteers aged 18-25 years who were divided into control group and the group with FAI. The torque rating was performed on an isokinetic dynamometer with five maximal concentric contractions at speeds of 60 and 120 graus.s-1 in INV and EVE movement and passive joint repositioning to target angle of 10° and 20° of inversion. PT data, conventional ratio and average absolute error of the target angle were analyzed. Statistical analysis was performed using the Student t-test for independent samples. Found that individuals with LFS showed decreased evertor strength compared to control subjects, as well as unbalanced muscle ratio, which may increase the susceptibility of this group to ankle sprains.

Discriminant analysis of neuromuscular variables in chronic low back pain.

BACKGROUND: Investigation and discrimination of neuromuscular variables related to the complex aetiology of low back pain could contribute to clarifying the factors associated with symptoms. OBJECTIVE: Analysing the discriminative power of neuromuscular variables in low back pain. METHODS: This study compared muscle endurance, proprioception and isometric trunk assessments between women with low back pain (LBP, n=14) and a control group (CG, n=14). Multivariate analysis of variance and discriminant analysis of the data were performed. RESULTS: The muscle endurance time (s) was shorter in the LBP group than in the CG (p=0.004) with values of 85.81 (37.79) and 134.25 (43.88), respectively. The peak torque (Nm/kg) for trunk extension was 2.48 (0.69) in the LBP group and 3.56 (0.88) in the GG (p=0.001); for trunk flexion, the mean torque was 1.49 (0.40) in the LBP group and 1.85 (0.39) in the CG (p=0.023). The repositioning error (degrees) before the endurance test was 2.66 (1.36) in the LBP group and 2.41 (1.46) in the CG (p=0.664), and after the endurance test, it was 2.95 (1.94) in the LBP group and 2.00 (1.16) in the CG (p=0.06). Furthermore, the variables showed discrimination between the groups (p=0.007), with 78.6% of the individuals with low back pain correctly classified in the LBP group. In turn, variables related to muscle activation showed no difference in discrimination between the groups (p=0.369). CONCLUSION: Based on these findings, the clinical management of low back pain should consist of both resistance and strength training, particularly in the extensor muscles.

Coactivación muscular del miembro inferior de jóvenes y ancianos saludables durante la marcha con doble tarea funcional / Coativação muscular dos membros inferiores de jovens e idosas saudáveis durante marcha com dupla tarefa funcional / Lower limb muscle coactivation levels in healthy younger and older adults during functional dual-task gait

The purpose of this study was to investigate the influence of daily cognitive task on stiffness of old and young female adults during the gait. The study included 17 physically active younger and 18 older women, with low risk of falls. The volunteers were asked to walk on the treadmill at two different gait conditions: normal gait and functional dual-task gait. The electromyographic signals were collected of the lower limb muscles. The percentage of coactivation for the tibialis anterior/gastrocnemius lateralis and tibialis anterior/soleus were significantly higher in elderly than in younger in the normal gait and dual-task gait. Our results suggest that the elderly have a greater stiffness in the ankle joint during gait normal and daily dual task gait. Thus, we conclude that challenging cognitively situations during the gait may increase the risk of falls in this population.

O objetivo deste estudo foi investigar a influência de uma tarefa cognitiva cotidiana sobre a coativação muscular de mulheres idosas e jovens durante a marcha. Participaram do estudo 17 mulheres jovens fisicamente ativas e 18 mulheres idosas com baixo risco de quedas. Os voluntários foram orientados a caminhar sobre uma esteira em duas diferentes condições de marcha: marcha normal e marcha com dupla-tarefa cotidiana. Os sinais eletromiográficos foram coletados dos músculos dos membros inferiores. A porcentagem de coativação para tibial anterior/gastrocnêmio lateral e tibial anterior/sóleo foram significativamente maiores em idosos do que em jovens na marcha normal e marcha com dupla-tarefa. Nossos resultados sugerem que os idosos tem maior coativação muscular no tornozelo durante a marcha normal e marcha com dupla tarefa cotidiana. Assim, nós concluimos que situações cognitivamente desafiadoras durante a marcha podem aumentar o risco de quedas em idosos.

El objetivo de este estudio fue investigar la influencia de una tarea cognitiva diaria en la co-activación muscular en ancianos y jóvenes durante la marcha. Los participantes del estudio fueron 17 ancianos y 18 jóvenes físicamente activos con bajo riesgo de caídas. Los voluntarios caminaron sobre una cinta de correr en dos condiciones diferentes: la marcha normal y la marcha con doble tarea cotidiana. Las electromiografía se obtuvo de los músculos de las extremidades inferiores. El porcentaje de co-activación de los tibialis anterior/gastrocnemius lateralis and tibialis anterior /soleus fueron significativamente mayores en los ancianos que en los sujetos jóvenes durante la marcha normal y marcha con doble tarea. Nuestros resultados sugieren que los ancianos tienen un mayor coactivación muscular en el tobillo durante la marcha normal y marcha con doble tarea cotidiana. Por lo tanto, se concluye que las situaciones cognitivamente desafiantes durante la marcha puede aumentar el riesgo de caídas en los ancianos.

Motor readiness and joint torque production in lower limbs of older women fallers and non-fallers.

This study aimed to evaluate the motor response time and ability to develop joint torque at the knee and ankle in older women with and without a history of falls, in addition to investigating the effect of aging on these capacities. We assessed 18 young females, 21 older female fallers and 22 older female non-fallers. The peak torque, rate of torque development, rate of electromyography (EMG) rise, reaction time, premotor time and motor time were obtained through a dynamometric assessment and simultaneous electromyography. Surface EMGs of the rectus femoris (RF), vastus lateralis (VL), biceps femoris (BF), gastrocnemius lateralis (GL) and tibialis anterior (TA) muscles were recorded. Knee extension and flexion peak torques were lower in older fallers than in non-fallers. Knee extension and flexion and ankle plantarflexion and dorsiflexion peak torques were lower in both older groups than in the younger group. The rate of EMG rise of the BF and the motor time of the TA were lower and higher, respectively, in older fallers than in the younger adults. The time to reach peak torque in knee extension/flexion and ankle plantarflexion/dorsiflexion and the motor times of the RF, VL, BF and GL were higher in both older groups than in the younger groups. The motor time of the TA during ankle dorsiflexion and the knee extension peak torque were the major predictors of falls in older women, accounting for approximately 28% of the number of falls. Thus, these results further reveal the biomechanical parameters that affect the risk of falls and provide initial findings to support the prescription of exercises in fall prevention programs.

Back extensor muscle fatigue at submaximal workloads assessed using frequency banding of the electromyographic signal.

BACKGROUND: Changes in the mean or median frequency of the electromyographic (EMG) power spectrum are often used to assess skeletal muscle fatigue. A more global analysis of the spectral changes using frequency banding may provide a more sensitive measure of fatigue than changes in mean or median frequency. So, the aim of the present study was to characterize changes in different power spectrum frequency bands and compare these with changes in median frequency. METHODS: Twenty male subjects performed isometric contractions of the back muscles in an isometric dynamometer at 30%, 40%, 50% and 60% of maximum voluntary contraction. During each contraction, surface EMG signals were recorded from the right and left longissimus thoracis muscles, and endurance time was measured. The EMG power spectra were divided into four frequency bands (20-50 Hz; 50-80 Hz; 80-110 Hz; 110-140 Hz) and changes in power in each band with fatigue were compared with changes in median frequency. FINDINGS: The percentage changes in 20-50 Hz band were greater than in all other and the rate of change in power, indicated by the slope, was also greatest in 20-50 Hz band. Also, 20-50 Hz band had a greater change in power than the median frequency. INTERPRETATION: Power in the low frequency part of the EMG power spectrum increases with fatigue in a load-dependent manner. The rate of change in low frequency power may be a useful indicator of fatigue rate or "fatigability" in the back muscles. Also, changes in low frequency power are more evident than changes in the median frequency.

Effect of load level on the emg spectra of longissimus thoracis muscle during isometric fatiguing contractions.

The present study analyzed the effect of different magnitudes of isometric contraction of longissimus thoracis muscle until fatigue by means power spectra analysis. Eight healthy male subjects volunteered for this study The electromyography signals were sampled at 1 kHz using surface electrodes placed bilaterally over the longissimus thoracis muscle at the level L1. The isometric contraction was made at 30% and 60% of isometric maximal voluntary contraction (MVC) randomly in the MA ISOSTATION 2001 with the trunk at 45 degrees of flexion. A gain of 1000, a high pass filter at 20 Hz and low pass filter at 500 Hz was used. The endurance time with the load of 30% was longer than the load of 60%. It was found a significant drop in the median frequency and in the mean power frequency for both loads in both sides with progression of time. Also, analyzing the load effect, it was found significant differences in the total power and peak power for the longissimus thoracis in the interval of 0-100%, with lower values to 30%. The present study allows verifying the longissimus thoracis muscular fatigue by means the electromiographics parameters. It was showed that the total power and the peak power variables are sensible due changes in the load, once there are low values for the low loads.

Determinação do limiar de fadiga eletromiográfico obtido por protocolo fatigante e protocolo fixo de 30 segundos para o músculo longuíssimo do tórax / Electromyographic fatigue threshold identification obtained by means of a fatiguing protocol and a 30 seconds protocol to the longissimus thoracis muscle

O presente estudo tem por objetivo comparar o limiar de fadiga eletromiográfico (EMGLF) do músculo longuíssimo do tórax obtido durante exercício isométrico fatigante com o limiar obtido durante os primeiros 30 segundos do teste. Participaram deste estudo 20 voluntários do gênero masculino. Para a captação dos sinais eletromiográficos foram utilizados eletrodos de superfície bipolares passivos de Ag/AgCl dispostos sobre os músculos longuíssimo do tórax direito e esquerdo, no nível da vértebra L1 a 3 cm lateralmente, com distância inter-eletrodos de 3 cm. Os resultados demonstraram não haver diferenças significativas entre os limiares, indicando que é possível a identificação do EMGLF pelo protocolo de 30 segundos para o músculo longuíssimo do tórax. Desta forma, futuros estudos devem ser realizados sobre este protocolo para avaliar indivíduos portadores de dor lombar para verificar se esta otimização minimizaria as interferências de fatores subjetivos.

The objective of the present study was to compare the electromyographic fatigue threshold (EMGFT) of the longissimus thoracis muscle obtained by means of a fatiguing test with the threshold obtained during the first 30 seconds of test. Twenty (20) male subjects participated to this study. To capture the electromyographic signs it was used bipolar passive surface electrodes (Ag/AgCl) placed over the longissimus muscle of thoracis left and right side, 3 cm lateral at L1, with an inter-electrode distance of 3 cm. The results showed that there is no difference between the thresholds, indicating that it is possible the identification of the EMGFT by means of 30 seconds protocol to the longissimus thoracis muscle. Further studies should be conducted about this protocol to evaluate low back pain patients to verify if this protocol could minimize subjective factors.

Estudo sobre o efeito da combinação de cargas na determinação do limiar de fadiga eletromiográfi co dos músculos eretores da espinha / Study about the effect of the load combination on the electromyographic fatigue threshold determination of the erector spinae muscle

O objetivo deste estudo foi analisar o efeito da combinação de diferentes percentuais de cargas na determinação do limiar de fadiga eletromiográfi co (EMGLF) dos músculos eretores da espinha (ER). Participaram deste estudo oito voluntários do sexo masculino. Os eletrodos foram posicionados sobre o músculo ER bilateralmente (L1). O voluntário executou contrações isométricas até a exaustão com 30%, 40%, 50% e 60% da contração isométrica voluntária máxima. O EMGLF-C4 é aquele obtido com a utilização das quatro cargas; o EMGLF-C3/4/5, combinando cargas de 30, 40 e 50%; o EMGLF-C3/4/6, combinando cargas de 30, 40 e 60%; o EMGLF-C3/5/6, combinando cargas de 30, 50 e 60%, e o EMGLF-C4/5/6 combinando cargas de 40, 50 e 60%. Para a comparação entre as combinações de carga utilizou-se o teste de Friedman (p<0,05), e para a comparação entre os lados utilizou-se o teste de Wilcoxon (p<0,05). Observou-se que ao comparar o EMGLF-C4 com as outras combinações de cargas, não há diferenças signifi cativas no ER do lado direito, já no ER do lado esquerdo esta semelhança não ocorre somente com o EMGLF-C4/5/6. Concluiu-se que as combinações propostas para determinação do EMGLF apresentam índices semelhantes bilateralmente e que unilateralmente apenas para o lado esquerdo a combinação de cargas entre 40%, 50% e 60% não apresenta semelhança, permitindo com isso otimizar o presente protocolo quanto ao percentual de carga utilizado e o número de percentuais.

The objective of this study was to analyze the effect of load combination on the electromyographic fatigue threshold (EMGFT) of the erector spinae muscle (ES). Eight male subjects have participated of this study. Surface electrodes were attached bilaterally on the ES (L1). The subjects executed isometric contractions with loads of 30%, 40%, 50% and 60% of the maximum voluntary isometric contraction until the exhaustion. The EMGLF-C4 was obtained throughout four loads and then was obtained the EMGLF-C3/4/5, throughout loads of 30, 40 e 50%, the EMGLF-C3/4/6, throughout loads of 30, 40 e 60%, the EMGLF-C3/5/6, throughout loads of 30, 50 e 60%, and the EMGLF-C4/5/6 throughout loads of 40, 50 e 60%. To the comparison among the combinations it was used a Friedman test (p<0,05), and to the comparison between sides it was used a Wilcoxon test (p<0,05). When comparing the EMGLF-C4 with the combinations of loads, there are no signifi cant differences in the ES of the right side, but in the ES of the left side similar results didn’t happened with the EMGLF-C4/5/6. The present study concluded that the ES presented similar indexes bilaterally and that unilaterally just to the left side the combination of loads among 40%, 50% and 60% didn’t present similar results, allowing us to optimize the percent of load and the number of loads of the present protocol.

Electromyographic analisys of biceps brachii and erector spinae muscles before and after a fatiguing dynamic test / Análise eletromiográfica dos músculos bíceps do braço e eretores da espinha antes e após um teste isotônico fadigante

The increased number of musculoskeletal injuries can be caused by the lack attention to load level, as well as the posture and time of execution of an overloaded exercise. This way, the objective of this study was to analyze the effect of repetitive barbell biceps curl exercise over biceps brachii and erector spinae muscle electromyographic parameters. Ten healthy male subjects (20,91±1,37 years), without musculoskeletal diseases, performed the biceps curl exercise until fatigue, with 25%, 35% and 45% of 1 repetition maximum. The electromyographic activity of biceps brachii and erector spinae muscles was analyzed during isometric contraction performed before and immediately after fatiguing tests. The muscular fatigue was identified through the increase of root mean square and decrease of median frequency during isometric contractions. The results demonstrated these characteristics of fatigue after fatiguing test (p<0,05) for both muscles, showing a relationship time-load dependent for these electromyographic parameters. No significant differences were found between left and right muscles in the parameters analyzed. The experimental procedures allowed identify the muscular fatigue on biceps brachii muscles and erector spinae activity during barbell biceps curl and the dependence with load and number of repetition...