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PURPOSE: Recent advancements in elastography techniques, specifically supersonic shearwave elastography (SWE), have enabled non-invasive assessment of muscle stiffness. However, there is limited research on the immediate and short-term effects of eccentric exercise-induced muscle damage (EIMD) in well-trained individuals. This study aimed to follow up on the effects of eccentric training on the biceps brachialis stiffness by supersonic shearwave imaging (SSI) as well as the soreness and elbow flexion maximal voluntary isometric contraction (MVIC), immediately post-intervention, at 10 min, 48 h, and 96 h in well-trained men. METHODS: Thirteen well-trained males participated in the study. Baseline measurements of elastography images, MVIC of the elbow flexors, and muscle soreness were obtained. The participants performed an eccentric exercise protocol (4 sets X 10 repetitions) on the dynamometer isokinetic and elastography measurements were repeated immediately post-exercise, at 10 min, 48 h, and 96 h. RESULTS: Significant reductions in stiffness (measured by shear modulus (µ)) were observed immediately and at 10 min post-exercise. MVIC exhibited significant reductions immediately after, 10 min, and 48 h compared to baseline measurements. Muscle soreness peaked at 48 h, persisting until 96 h. CONCLUSIONS: The BB stiffness and MVIC reduction immediately post-eccentric exercise in well-trained men, suggest the potential involvement of mechanical stress and sarcomere rupture. Trained individuals may exhibit a distinct response to EIMD compared to untrained individuals, highlighting the applicability of elastography in monitoring acute biomechanical changes following high-intensity exercise.

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This study combined surface electromyography with panoramic ultrasound imaging to investigate whether non-uniform excitation could lead to acute localized variations in cross-sectional area and muscle thickness of the clavicular and sternocostal heads of pectoralis major (PM). Bipolar surface electromyograms (EMGs) were acquired from both PM heads, while 13 men performed four sets of the flat and 45° inclined bench press exercises. Before and immediately after exercise, panoramic ultrasound images were collected transversely to the fibers. Normalized root mean square (RMS) amplitude and variations in the cross-sectional area and muscle thickness were calculated separately for each PM head. For all sets of the inclined bench press, the normalized RMS amplitude was greater for the clavicular head than the sternocostal head (P < 0.001), and the opposite was observed during the flat bench press (P < 0.001). Similarly, while greater increases in cross-sectional area were observed in the clavicular than in the sternocostal head after the inclined bench press (P < 0.001), greater increases were quantified in the sternocostal than in the clavicular head after the flat bench press exercise (P = 0.046). Therefore, our results suggest that the PM regional excitation induced by changes in bench press inclination leads to acute, uneven responses of muscle architecture following the exercise.

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Previous evidence suggests the intense resistance training session can increase the muscle hardness, while stretching protocols with high intensity and volume can decrease it. However, it remains unknown the effects of an exercise and a less intensive stretching maneuver on muscle stiffness of well-trained men. Herein we (i) analyze the acute effects of heavy bench press exercise on the pectoralis major muscle shear modulus of well-trained men and (ii) assess the effectiveness of a 1-min stretching maneuver applied on this muscle after the exercise using shear wave elastography. Fourteen participants performed three sets of bench press from 8 to 13 repetitions maximum. Immediately after the exercise, their right shoulder was passively stretched for 1 min (stretched side) while their left arm stayed relaxed along the side of the body (control side). Elastographic images were acquired for the pectoralis major mid-region of both sides before the exercise, immediately after the intervention and after 5 min of rest. Our results revealed that both the bench press exercise and the static stretching does not affect the pectoralis major shear modulus of well-trained men. Conversely, the shear modulus significantly decreased at 5 min after intervention with respect to immediately after, for both the stretched (from 5.52 to 4.29 kPa) and the control sides (from 5.87 to 4.56 kPa). Therefore, both resistance training session and 1-min static stretching were not sufficient to significantly change the pectoralis major muscle stiffness of well-trained men.

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O objetivo do estudo foi comparar a variação da espessura muscular (EM) ao longo do peitoral maior (PM) após três séries de 8 a 12 repetições máximas de supino reto. A amostra foi composta por 12 homens treinados. O comportamento da EM foi avaliado pré e imediatamente após a realização do exercício através de ultrassonografias, em três sítios do feixe esternal do PM: medial (próximo ao esterno), central e lateral (próximo ao úmero). Como resultado, o sítio medial apresentou variação relativa da EM de 14,78%, o central de 11,83% e o lateral de 10,04%, com diferença significativa apenas entre o sítio medial quando comparado ao lateral (p=0,036). Tal efeito pode estar relacionado a maior ativação do trecho medial do PM durante o supino reto ou pela específica morfologia do PM.

The aim of this study was to compare the variation of muscle thickness (MT) over the pectoralis major muscle (PM) after 3 sets of 8 to 12 repetitions of bench press. The sample was consisted of 12 trained men. Ultrasound images were acquired, to analyze the MT behavior, at three sites of the PM's sternal head: medial, central and lateral. The medial site had a MT relative variation of 14.78%, the central one of 11.83% and the lateral one of 10.04%, with a statistical difference observed only between the medial site when compared to the lateral site (p = 0.036); The possible cause of these effects might be related to a possible greater activation of the medial site during the bench press or due to PM's morphology. We conclude that the PM shows heterogeneous MT acute variation.

El objetivo del estudio fue comparar la variación de la espesura muscular (EM) a lo largo del pectoral mayor (PM) después de tres series de 8 a 12 repeticiones de press de banca. El comportamiento de la EM fue evaluado pre e inmediatamente después de la realización del ejercicio con ultrasonografías, en tres sitios de la cabeza esternal del PM: medial (cerca del esternón), central y lateral (cerca del húmero). Como resultado, el sitio medial presentó 14,78% de variación relativa de la EM, el central 11,83% y el lateral 10,04%, con diferencia significativa apenas entre el sitio medial cuando comparado al lateral (p = 0,036) . Este efecto puede estar relacionado con la mayor activación del sitio medial del PM durante el press de banca o por la morfología del PM.

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Habitual loading and resistance training (RT) can lead to changes in muscle and tendon morphology as well as in its mechanical properties which can be measured by Shear Wave Elastography (SWE) technique. The objective of this study was to analyze the Vastus Lateralis (VL) and patellar tendon (PT) mechanical properties adaptations to an 8-week RT protocol using SWE. We submitted 15 untrained health young men to an 8-week RT directed for knee extensor mechanism. VL and PT shear modulus (µ) were assessed pre and post intervention with SWE. PT thickness (PTT), VL muscle thickness (VL MT) and knee extension torque (KT) were also measure pre and post intervention to ensure the RT efficiency. Significant increases were observed in VL MT and KT (pre = 2.40 ± 0.40 cm and post = 2.63 ± 0.35 cm, p = 0.0111, and pre = 294.66 ± 73.98 Nm and post = 338.93 ± 76.39 Nm, p = 0.005, respectively). The 8-week RT was also effective in promoting VL µ adaptations (pre = 4.87 ± 1.38 kPa and post = 9.08.12 ± 1.86 kPa, p = 0.0105), but not in significantly affecting PT µ (pre = 78.85 ± 7.37 kPa and post = 66.41 ± 7.25 kPa, p = 0.1287) nor PTT (baseline = 0.364 ± 0.053 cm and post = 0.368 ± 0.046 cm, p = 0.71). The present study showed that an 8-week resistance training protocol was effective in adapting VL µ but not PT µ. Further investigation should be conducted with special attention to longer interventions, to possible PT differential individual responsiveness and to the muscle-tendon resting state tension environment.

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The grey level of co-occurrence matrix (GLCM) is a texture analysis approach accounting for spatial distribution of the pixels from an image and can be a promising method for exercise-induced muscle damage (EIMD) studies. We followed up the time changes of two GLCM texture parameters and echo intensity (EI) on ultrasound images after eccentric contractions. Thirteen untrained women performed two sets of ten elbow flexions eccentric contractions. Ultrasound images were acquired at baseline and 24 h, 48 h, 72 h and 96 h after exercise. Two GLCM texture parameters were calculated for the brachialis muscle: contrast (CON) and correlation (COR). Peak torque, EI, muscle thickness (MT) and soreness were measured. The peak torque and soreness decreased immediately after the intervention in comparison with all the measures. MT increased immediately after the intervention remaining for 72 h (P<0·05). Significant increases (P<0·05) were observed for COR (48, 72 and 96 h) and EI only at 72 and 96 h. The increasing COR represents high similarity between grey levels, which could be observed on US images after few days on eccentric training for elbow flexors.

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One of the fundamental adaptations observed with resistance training (RT) is muscle hypertrophy. Conventional and isokinetic machines provide different forms of mechanical stress, and it is possible that these two training modes could promote differing degrees of hypertrophic adaptations. There is a lack of data comparing the selective hypertrophy of the quadriceps musculature after training with a conventional knee extension machine versus an isokinetic machine. The purpose of this study was to evaluate the selective hypertrophy of the quadriceps musculature and knee extension maximal isometric torque after 14 weeks of conventional versus isokinetic RT. Thirty-five men were assigned to three groups: control group and training groups (conventional and isokinetic) performed three sets of unilateral knee extensions per session with a progressive loading scheme twice a week. Prior to and following the intervention, maximal isometric knee extensor torque was measured using an isokinetic dynamometer, and muscle thickness (MT) of quadriceps femoris muscles was assessed via ultrasound. The results indicated non-uniform changes in MT between the muscles that comprise the quadriceps femoris group. For the conventional group, significantly greater increases in rectus femoris thickness were evident versus all other quadriceps muscles (14%). For the isokinetic group, increases in RF thickness (11%) were significantly greater in comparison with the vastus intermedius only. Although the muscle thickness did not increase for all the quadriceps femoris muscles, the relative rectus femoris adaptation suggested a selective hypertrophy favouring this portion.

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Ultrasound (US) is an important tool for diagnosing of many musculoskeletal tissue conditions. Image texture analysis can be used to characterize this tissue. The complexity curve (CC) is a technique commonly used to characterize the number of grey-level transitions in an image. Variability and reliability of US texture measures in the muscle tissue are unavailable in the literature. The aim of this study was to determine the variability and reliability of five CC texture parameters from US images of healthy Biceps Brachialis and Gastrocnemius Lateralis (GL) muscles, with longitudinal and transversal orientations of the probe. Eight images per subject were obtained for 30 men in 2 days. Mean, standard deviation, coefficient of variation and intraclass correlation coefficient for the five parameters were calculated for regions of interest. Results showed that the variability was similar for both muscles and most of the parameters showed satisfactory reliability (r > 0·7) for the Biceps Brachialis with the transverse scan and for the GL with the longitudinal scan.

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In its last position stand about strength training, the American College of Sports Medicine recommends a rest interval (RI) between sets ranging between 1 and 3 min, varying in accordance with the objective. However, there is no consensus regarding the optimal recovery between sets, and most studies have investigated fixed intervals. Therefore, the aim of this study was to analyse the effects of fixed versus self-suggested RI between sets in lower and upper body exercises performance. Twenty-seven healthy subjects (26 ± 1.5; 75 ± 15 kg; 175 ± 12 cm) were randomly assigned into two groups: G1: lower body exercises and G2: upper body exercises. Squat and leg press 1 repetition maximum (1RM) were tested for the G1 and bench press and biceps curl 1RM for G2. After the 1RM tests, both groups performed three sets to concentric failure with 75% of 1RM in combination with different RIs (2 min or self-suggested) on separate days and the exercises performance was evaluated by the number of repetitions. The results demonstrated no significant differences in the number of repetitions between 2 min and self-suggested RIs that presented similar reductions with the sets progression. It was also shown that the self-suggested RI spent less time recovering than the 2 min RI group on average. This suggests that for individuals with previous experience, the self-suggested RI can be an effective option when using workloads commonly prescribed aiming hypertrophy. Also, the self-suggested RI can reduce the total training session duration, which can be a more time-effective strategy.

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BACKGROUND: Muscle activity is studied during trunk stabilization exercises using electromyograms (EMG) in time domain. However, the frequency domain analysis provides information that would be important to understand fatigue process. OBJECTIVE: To assess EMG of lumbar multifidus (LM) and erector spinae (ES) muscles, in time and frequency domains, during back bridge exercise. METHODS: Nineteen healthy young men performed the exercise for one minute and EMG was monitored by surface electromyography. Normalized root mean square (RMS) value and spectral median frequency (MF) were compared between beginning and final epochs of test. The dynamics of the MF during whole test was also obtained by short-time Fourier transform. RESULTS: RMS values were about 30% of maximum voluntary contraction, and LM muscle showed greater MF than ES, which did not decrease at the final of exercise. However, the slope of MF was significant mainly for LM. CONCLUSIONS: Muscle activation of 30% is sufficient to keep lumbar stability and is suitable to improve muscular endurance. The significance of MF slope without decreasing at the final of exercise indicates challenging muscular endurance without imply on high fatigability. Due to lower muscular demand, this exercise might be recommended for trunk stabilizing for low back pain patients.

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Os objetivos do estudo foram comparar o torque isométrico máximo de flexão plantar, em duas posições de joelho e analisar a variação da atividade miolétrica dos músculos do tríceps sural nas duas condições. A amostra composta de 14 homens saudáveis. O pé direito dos participantes foi fixado ao adaptador do aparelho isocinético com o tornozelo em 90 graus. Duas contrações isométricas voluntárias máximas de cinco segundos foram obtidas para cada posição do joelho: estendido e com 90 graus de flexão. Foram analisados o pico de torque flexor plantar médio e o valor RMS do sinal eletromiográfico (EMG) dos três segundos intermediários do gastrocnêmio lateral (GNL), gastrocnêmio medial (GNM) e sóleo para cada posição. Os torques médios nas posições de joelho em extensão e flexão foram 100,4 ± 17,4 Nm e 72,6 ± 18,4 Nm, respectivamente. Os gastrocnêmios apresentaram uma redução do valor RMS relativo com o joelho em flexão (40,5 ± 10,5 e 31,7 ± 25,6% para o GL e GM, respectivamente) enquanto o sóleo aumentou nessa condição (35,6 ± 28,9%). A redução do torque de flexão plantar parece estar associada ao resultado de um compromisso entre a inibição da atividade mioelétrica dos GNM e GNL, e otimização da ativação do sóleo. Os resultados podem contribuir no auxílio da prescrição de exercícios direcionados para o tríceps sural, enfatizando a ativação de diferentes músculos com variações no ângulo articular do joelho.

The aim of this study was to compare the maximum torque of plantar flexors using two knee positions and analyze the mioelectric activity variation of the muscles in both conditions. The sample was composed of 14 healthy men. The participants were positioned on the dynamometer with the right foot attached to the adapter in neutral position (ankle at 90º). Two five seconds of two consecutives maximum isometric voluntary contractions were obtained for each knee position: full extended and 90o. The gastrocnemius lateralis (GNL), medialis (GNM) and soleus RMS value of eletomyography signal and the plantar flexor peak torque average were acquired during three intermediate seconds. The average torques in the knee positions of extension and flexion were 100.4 ± 17.4 Nm and 72.6 ± 18.4 Nm respectively. With the knee flexed, the gastrocnemius presented a decreased activation (40.5 ± 10.5 e 31.7 ± 25.6% for lateral and medial, respectively) while the soleus showed an increased (35.6 ± 28.9%). The reduction of torque appears to result from a compromise between the inhibition of myoelectric activity of the gastrocnemius medialis and lateralis, while the soleus activation is optimized. The results may contribute to exercise prescription plantar flexors muscles emphasizing the different muscles activation varying the knee position.

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Several indicators have been used to analyze scientific journals, with the impact factor and the number of citations in a 2-yr calendar time frame (2-YRC) being the most common factors. However, considering that the Journal of Applied Physiology (JAPPL) appears monthly and that calculations of these indicators are based on citations of papers published in previous years, we hypothesized that articles published at the beginning of the year would be cited more in the 2-YRC compared with those appearing in the last issues of the year, a phenomena known as a relative age effect. Our objective was to confirm the existence of a relative age effect in the 2-YRC for original articles published in JAPPL. From 2005 to 2008, a total of 1,726 original articles were published, according to the Web of Science, and 9,973 citations in 2-YRC, varying from 0 to 45, with a mean of 5.78 for individual papers. Although there were no differences in the number of original articles published in a given month (P = 0.99), the 2-YRC varied considerably throughout the year, being higher for those earlier issues of the year, as shown by the linear regression analysis (r(2) = 0.76; P < 0.001). The 2-YRC began at 6.62 during the first 3 mo of the year, dropping by 10% at each 3-mo period. In summary, the longer an article has been out there, the more citations it collects. The relative age effect is a potential confounding variable for the assessment and interpretation of 2-YRC (using calendar years) from JAPPL original articles.

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The specific tension index (STI) estimates the ratio of maximum torque (TQ) to muscle volume (MV) for a specific task and includes muscle thickness as a parameter, which can be directly evaluated by ultrasound. The objective of the present study was to compare TQ, MV and STI of the elbow flexors between strength-trained and untrained subjects. Forty men, including 11 subjects strength trained for at least two years [trained group (TG): 23.5 ± 3.1 years; 182.1 ± 4.9 cm; 88.1 ± 8.4 kg] and 29 untrained subjects [untrained group (UG): 29.8 ± 1.6 years; 172.4 ± 6.6 cm; 76.4 ± 8.1 kg], participated in the study. The STI of the elbow flexors, expressed as the TQ/MV ratio, was calculated for both groups. Muscle thickness measured by ultrasound was used to estimate MV. TQ of the elbow flexors was estimated using maximum isometric voluntary contractions. The Mann-Whitney test was used to determine possible differences in TQ, STI and MV between groups. MV and TQ were significantly higher in TG (526.07 ± 86.13 cm3; 112.04 ± 24.18 Nm) than UG (385.40 ± 80.89 cm3; 88.46 ± 13.77 Nm). There was no significant difference in the STI between TG (0.213 ± 0.03 Nm.cm3-) and UG (0.233 ± 0.02 Nm.cm3-). Although stronger, trained subjects presented elbow flexor STI values similar to those of the untrained group, a finding suggesting the maintenance of the linearity of the force-volume ratio. TQ and MV estimates were found to be reliable parameters for the distinction between groups. The STI may contribute to a more applied analysis in clinical practice and in the prescription of physical activity as an indicator of inadequate levels of overload and of the risk of injury.

The specific tension index (STI) estimates the ratio of maximum torque (TQ) to muscle volume (MV) for a specific task and includes muscle thickness as a parameter, which can be directly evaluated by ultrasound. The objective of the present study was to compare TQ, MV and STI of the elbow flexors between strength-trained and untrained subjects. Forty men, including 11 subjects strength trained for at least two years [trained group (TG): 23.5 ± 3.1 years; 182.1 ± 4.9 cm; 88.1 ± 8.4 kg] and 29 untrained subjects [untrained group (UG): 29.8 ± 1.6 years; 172.4 ± 6.6 cm; 76.4 ± 8.1 kg], participated in the study. The STI of the elbow flexors, expressed as the TQ/MV ratio, was calculated for both groups. Muscle thickness measured by ultrasound was used to estimate MV. TQ of the elbow flexors was estimated using maximum isometric voluntary contractions. The Mann-Whitney test was used to determine possible differences in TQ, STI and MV between groups. MV and TQ were significantly higher in TG (526.07 ± 86.13 cm3; 112.04 ± 24.18 Nm) than UG (385.40 ± 80.89 cm3; 88.46 ± 13.77 Nm). There was no significant difference in the STI between TG (0.213 ± 0.03 Nm.cm3-) and UG (0.233 ± 0.02 Nm.cm3-). Although stronger, trained subjects presented elbow flexor STI values similar to those of the untrained group, a finding suggesting the maintenance of the linearity of the force-volume ratio. TQ and MV estimates were found to be reliable parameters for the distinction between groups. The STI may contribute to a more applied analysis in clinical practice and in the prescription of physical activity as an indicator of inadequate levels of overload and of the risk of injury.

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O objetivo deste estudo foi caracterizar as componentes temporais e espectrais dos abalos musculares em diferentes níveis de contração muscular através da acelerometria. Participaram do estudo 15 indivíduos do sexo masculino e 12 do feminino, todos destros. O experimento constou de um teste de carga máxima (CM) que permitiu determinar cinco cargas percentuais administradas durante os testes de força (20 por cento, 40 por cento, 60 por cento, 80 por cento e 100 por cento da CM), em isometria e por oito segundos cada. Um acelerômetro biaxial foi colocado sobre o ventre muscular do bíceps braquial direito. A raiz média quadrática (valor RMS), um parâmetro temporal, e a freqüência média (FME), um parâmetro espectral, foram extraídas dos sinais de acelerometria (sinal de MMG). Estes parâmetros foram analisados nas direções X (perpendicular às fibras) e Y (paralela às fibras). Ambos os grupos apresentaram comportamento decrescente da FME (Y) com a carga, sendo mais pronunciado para o grupo feminino. A variável FME (X), no grupo feminino, apresentou comportamento semelhante à FME (Y), sendo apenas observada diferença estatística significativa entre 20 por cento da CM e todas as demais cargas (p = 0,0022 para 40 por cento e p < 0,0001 para as demais). O grupo masculino não apresentou diferença estatística significativa entre as cargas. O valor RMS (Y) apresentou comportamento crescente com a carga para ambos os grupos, havendo diferenças entre as cargas de 20 por cento e 40 por cento da CM (p = 0,000) e 80 por cento, e 100 por cento da CM (p = 0,01) para o grupo masculino. No entanto, não foi observada diferença estatística significativa entre as cargas para o grupo feminino. Discute-se que durante a contração muscular ocorrem variações não uniformes do diâmetro da fibra, além de oscilações laterais de baixa freqüência. Estas informações parecem ter forte correlação com a tipagem de fibras, o que poderia contribuir para melhor esclarecer os possíveis mecanismos envolvidos durante o processo de gradação da força muscular.

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