Force produced after stretch in sarcomeres and half-sarcomeres isolated from skeletal muscles

The goal of this study was to evaluate if isolated sarcomeres and half-sarcomeres produce a long-lasting increase in force after a stretch is imposed during activation. Single and half-sarcomeres were isolated from myofibrils using micro-needles, which were also used for force measurements. After full force development, both preparations were stretched by different magnitudes. The sarcomere length (SL) or half-sarcomere length variations (HSL) were extracted by measuring the initial and final distances from the Z-line to the adjacent Z-line or to a region externally adjacent to the M-line of the sarcomere, respectively. Half-sarcomeres generated approximately the same amount of isometric force (29.0 ± SD 15.5 nN·μm(−2)) as single sarcomeres (32.1 ± SD 15.3 nN·μm(−2)) when activated. In both cases, the steady-state forces after stretch were higher than the forces during isometric contractions at similar conditions. The results suggest that stretch-induced force enhancement is partly caused by proteins within the half-sarcomere

Influence of competitive level and tactical position on parameters of aerobic performance in professional soccer athletes from Brazil

Este estudo objetivou verificar a influência do nível competitivo e da posição tática sobre parâmetros relacionados ao desempenho aeróbio de atletas profissionais de futebol. Foram analisadas 453 avaliações ergoespirométricas de atletas profissionais de futebol (42 goleiros, 92 zagueiros, 61 laterais, 174 meio-campistas e 84 atacantes) que atuavam em quatro níveis competitivos: Campeonato Nacional Série A; Série B; Série C; e Campeonato Estadual. Não foram encontradas diferenças nos valores médios de consumo máximo de oxigênio (VO2max) e segundo limiar ventilatório (LV2) entre os níveis competitivos (p > 0,05). Os goleiros apresentaram VO2max e LV2 (56 e 50 mL/kg/min, respectivamente) significativamente inferiores aos zagueiros (59 e 52 mL/kg.min; p = 0,002 e p = 0,028), laterais (60 e 53 mL/kg.min; p ; 0.05). The goalkeepers showed VO2max and LV2 (56 and 50 mL/kg.min, respectively) significant lower than full backs (59 and 52 mL/kg.min; p = 0.002 e p = 0.028), sideways (60 and 53 mL/kg.min; p = 0.000 e p = 0.004), midfields (59 and 52 mL/kg.min; p = 0.002 e p = 0.031) and forwards (59 and 52 mL/kg.min; p = 0.047 e p = 0.036). Therefore, the findings suggest that: 1) the aerobic performance does not differ according the competitive level; and 2) the goalkeepers have aerobic performance inferior to out-field players, which do not show differences between them

Triceps surae muscle architecture adaptations to eccentric training

Eccentric exercises have been used in physical training, injury prevention, and rehabilitation programs. The systematic use of eccentric training promotes specific morphological adaptations on skeletal muscles. However, synergistic muscles, such as the triceps surae components, might display different structural adaptations due to differences in architecture, function, and load sharing. Therefore, the purpose of this study was to determine the effects of an eccentric training program on the triceps surae (GM, gastrocnemius medialis; GL, gastrocnemius lateralis; and SO, soleus) muscle architecture. Methods: Twenty healthy male subjects (26 ± 4 years) underwent a 4-week control period followed by a 12-week eccentric training program. Muscle architecture [fascicle length (FL), pennation angle (PA), and muscle thickness (MT)] of GM, GL, and SO was evaluated every 4 weeks by ultrasonography. Results: Fascicle lengths (GM: 13.2%; GL: 8.8%; SO: 21%) and MT (GM: 14.9%; GL: 15.3%; SO: 19.1%) increased from pre- to post-training, whereas PAs remained similar. GM and SO FL and MT increased up to the 8th training week, whereas GL FL increased up to the 4th week. SO displayed the highest, and GL the smallest gains in FL post-training. Conclusion: All three synergistic plantar flexor muscles increased FL and MT with eccentric training. MT increased similarly among the synergistic muscles, while the muscle with the shortest FL at baseline (SO) showed the greatest increase in FL

A Preseason Training Program With the Nordic Hamstring Exercise Increases Eccentric Knee Flexor Strength and Fascicle Length in Professional Female Soccer Players

# Background Training programs that include the Nordic hamstring exercise (NHE) have been shown to increase eccentric knee flexor strength and biceps femoris fascicle length in male athletes. However, the effect of NHE on female athletes remains unknown. # Purpose To investigate the collective and individual responses of professional female soccer players engaged in a preseason training program with the NHE regarding eccentric knee flexor strength and biceps femoris long head fascicle length. # Study Design Quasi-experimental study. # Methods Sixteen amateur female soccer players (without a NHE training routine) were evaluated 8-weeks apart to: (1) assess reliability of eccentric knee flexor strength and biceps femoris fascicle length measures; and (2) determine the typical error of measures that would be used to discriminate training responders and non-responders. The NHE training group had 17 professional female soccer players who performed an 8-week training program with the NHE during preseason. Within-group analysis was performed with paired sample t-tests (pre- vs. post-training), and individual responses were determined using the typical error criteria. # Results The non-trained group’s data demonstrated that measures of strength (ICC=0.82-0.87, typical error = 12-13 N) and fascicle length (ICC=0.92-0.97; typical error = 0.19-0.38 cm) were reliable. In the NHE training group, both limbs increased the eccentric knee flexor strength (\~13%; ES=0.74-0.82) and the biceps femoris fascicle length (\~6%; ES=0.44-0.65). Twelve players (\~71%) were considered responders to the NHE training program for the eccentric knee flexor strength, while eight athletes (\~47%) were responders for the biceps femoris fascicle length. # Conclusion The 8-week preseason training program with the NHE increased both eccentric knee flexor strength and biceps femoris fascicle length in professional female soccer players. More than two-thirds of players demonstrated a meaningful increase in eccentric strength, while nearly half achieved consistent fascicle length increases with the NHE training

The effect of quadriceps muscle length on maximum neuromuscular electrical stimulation evoked contraction, muscle rchitecture, and tendon-aponeurosis stiffness

Muscle-tendon unit length plays a crucial role in quadriceps femoris muscle (QF) physiological adaptation, but the influence of hip and knee angles during QF neuromuscular electrical stimulation (NMES) is poorly investigated. We investigated the effect of muscle length on maximum electrically induced contraction (MEIC) and current efficiency. We secondarily assessed the architecture of all QF constituents and their tendon-aponeurosis complex (TAC) displacement to calculate a stiffness index. This study was a randomized, repeated measure, blinded design with a sample of twenty healthy men aged 24.0 ± 4.6. The MEIC was assessed in four different positions: supine with knee flexion of 60◦ (SUP60); seated with knee flexion of 60◦ (SIT60); supine with knee flexion of 20◦ (SUP20), and seated with knee flexion of 20◦ (SIT20). The current efficiency (MEIC/maximum tolerated current amplitude) was calculated. Ultrasonography of the QF was performed at rest and during NMES to measure pennation angle (θp) and fascicle length (Lf ), and the TAC stiffness index. MEIC and current efficiency were greater for SUP60 and SIT60 compared to SUP20 and SIT20. The vastus lateralis and medialis showed lower θp and higher Lf at SUP60 and SIT60, while for the rectus femoris, in SUP60 there were lower θp and higher Lf than in all positions. The vastus intermedius had a similar pattern to the other vastii, except for lack of difference in θp between SIT60 compared to SUP20 and SIT20. The TAC stiffness index was greater for SUP60. We concluded that NMES generate greater torque and current efficiency at 60◦ of knee flexion, compared to 20◦ . For these knee angles, lengthening the QF at the hip did not promote significant change. Each QF constituent demonstrated muscle physiology patterns according to hip and/or knee angles, even though a greater Lf and lower θp were predominant in SUP60 and SIT60. QF TAC index stiffened in more elongated positions, which probably contributed to enhanced force transmission and slightly higher torque in SUP60. Our findings may help exercise physiologist better understand the impact of hip and knee angles on designing more rational NMES stimulation strategies

Effect of 830 nm low-level laser therapy in exercise-induced skeletal muscle fatigue in humans

Abstract This study aimed to investigate the effect of 830 nm low-level laser therapy (LLLT) on skeletal muscle fatigue. Ten healthy male professional volleyball players entered a crossover randomized double-blinded placebocontrolled trial. Active LLLT (830 nm wavelength, 100 mW output, spot size 0.0028 cm 2 , 200 s total irradiation time) or an identical placebo LLLT was delivered to four points on the biceps humeri muscle immediately before exercises. All subjects performed voluntary biceps humeri contractions with a load of 75% of the maximum voluntary contraction (MVC) force until exhaustion. After active LLLT the mean number of repetitions was significantly higher than after placebo irradiation [mean difference 4.5, standard deviation (SD) ±6.0, P=0.042], the blood lactate levels increased after exercises, but there was no significant difference between the treatments. We concluded that 830 nm LLLT can delay the onset of skeletal muscle fatigue in highintensity exercises, in spite of increased blood lactate levels

The effect of quadriceps muscle length on maximum neuromuscular electrical stimulation evoked contraction, muscle architecture, and tendon-aponeurosis stiffness

Muscle-tendon unit length plays a crucial role in quadriceps femoris muscle (QF) physiological adaptation, but the influence of hip and knee angles during QF neuromuscular electrical stimulation (NMES) is poorly investigated. We investigated the effect of muscle length on maximum electrically induced contraction (MEIC) and current efficiency. We secondarily assessed the architecture of all QF constituents and their tendon-aponeurosis complex (TAC) displacement to calculate a stiffness index. This study was a randomized, repeated measure, blinded design with a sample of twenty healthy men aged 24.0 ± 4.6. The MEIC was assessed in four different positions: supine with knee flexion of 60° (SUP60); seated with knee flexion of 60° (SIT60); supine with knee flexion of 20° (SUP20), and seated with knee flexion of 20° (SIT20). The current efficiency (MEIC/maximum tolerated current amplitude) was calculated. Ultrasonography of the QF was performed at rest and during NMES to measure pennation angle (θp) and fascicle length (Lf), and the TAC stiffness index. MEIC and current efficiency were greater for SUP60 and SIT60 compared to SUP20 and SIT20. The vastus lateralis and medialis showed lower θp and higher Lf at SUP60 and SIT60, while for the rectus femoris, in SUP60 there were lower θp and higher Lf than in all positions. The vastus intermedius had a similar pattern to the other vastii, except for lack of difference in θp between SIT60 compared to SUP20 and SIT20. The TAC stiffness index was greater for SUP60. We concluded that NMES generate greater torque and current efficiency at 60° of knee flexion, compared to 20°. For these knee angles, lengthening the QF at the hip did not promote significant change. Each QF constituent demonstrated muscle physiology patterns according to hip and/or knee angles, even though a greater Lf and lower θp were predominant in SUP60 and SIT60. QF TAC index stiffened in more elongated positions, which probably contributed to enhanced force transmission and slightly higher torque in SUP60. Our findings may help exercise physiologist better understand the impact of hip and knee angles on designing more rational NMES stimulation strategies

Adherence to antibiotic treatment guidelines and outcomes in the hospitalized elderly with different types of pneumonia

Background: Few studies evaluated the clinical outcomes of Community Acquired Pneumonia (CAP), Hospital-Acquired Pneumonia (HAP) and Health Care-Associated Pneumonia (HCAP) in relation to the adherence of antibiotic treatment to the guidelines of the Infectious Diseases Society of America (IDSA) and the American Thoracic Society (ATS) in hospitalized elderly people (65 years or older). Methods: Data were obtained from REPOSI, a prospective registry held in 87 Italian internal medicine and geriatric wards. Patients with a diagnosis of pneumonia (ICD-9 480-487) or prescribed with an antibiotic for pneumonia as indication were selected. The empirical antibiotic regimen was defined to be adherent to guidelines if concordant with the treatment regimens recommended by IDSA/ATS for CAP, HAP, and HCAP. Outcomes were assessed by logistic regression models. Results: A diagnosis of pneumonia was made in 317 patients. Only 38.8% of them received an empirical antibiotic regimen that was adherent to guidelines. However, no significant association was found between adherence to guidelines and outcomes. Having HAP, older age, and higher CIRS severity index were the main factors associated with in-hospital mortality. Conclusions: The adherence to antibiotic treatment guidelines was poor, particularly for HAP and HCAP, suggesting the need for more adherence to the optimal management of antibiotics in the elderly with pneumonia

Adaptações neuromusculares de extensores de joelho ao treinamento excêntrico em dinamômetro isocinético

O exercício excêntrico é utilizado como uma estratégia de treinamento de força em atletas e sujeitos saudáveis de diferentes faixas etárias. Esse tipo de exercício também é largamente difundido na área da reabilitação musculoesquelética, sendo o quadríceps femoral o músculo mais frequentemente investigado devido à sua relevância clínica. O tema dessa tese de Doutorado é a adaptação do sistema neuromuscular ao treinamento excêntrico de extensores de joelho. No Capítulo I, um estudo de revisão procurou descrever os diferentes métodos empregados pelos cientistas para o treinamento excêntrico de extensores de joelho, assim como avaliar as adaptações neurais, morfológicas e na produção de força muscular de sujeitos saudáveis. Após busca sistematizada nas bases de dados, 26 estudos foram incorporados ao nosso estudo de revisão. Os programas de treinamento excêntrico realizados em dinamômetro isocinético e em equipamentos isotônicos (leg-press e cadeira extensora de joelho) foram descritos e discutidos. Os resultados desses estudos indicam um efeito positivo do treinamento excêntrico sobre a força e a ativação muscular, especialmente em testes excêntricos, assim como uma significativa resposta hipertrófica. Porém, resultados conflitantes e lacunas identificadas na literatura incentivaram a realização de dois estudos originais para verificar: (1) o comportamento temporal das adaptações neurais e morfológicas ao treinamento excêntrico de extensores de joelho e suas contribuições para os ganhos de força (Capítulo II); e (2) as adaptações específicas de músculos sinergistas da extensão de joelho: reto femoral (RF) e vasto lateral (VL) (Capítulo III). Vinte homens saudáveis realizaram um período controle de quatro semanas sem treinamento, seguido por um programa de 12 semanas de treinamento excêntrico em dinamômetro isocinético. Avaliações de torque, eletromiografia e ultrassonografia de extensores de joelho foram realizadas a cada quatro semanas. Um maior ganho de força foi verificado nos testes excêntricos, seguido pelos testes isométricos e concêntricos. A ativação muscular nos testes excêntricos e isométricos aumentou após quatro e oito semanas de treinamento, respectivamente, ao passo que os testes concêntricos não apresentaram alteração da atividade eletromiográfica. Os valores de espessura muscular, área de secção transversa anatômica e comprimento de fascículo aumentaram após quatro e oito semanas de treinamento, mas não modificaram entre a oitava e a 12ª semana de intervenção. As adaptações na geometria fascicular dos músculos RF e VL foram semelhantes ao longo do programa de treinamento. Nossos achados sugerem que: (1) existe um forte efeito da especificidade do exercício excêntrico sobre os aumentos de força e ativação muscular; (2) os ganhos de força excêntrica e isométrica até a oitava semana de treinamento estão relacionados a adaptações neurais e morfológicas mensuráveis, enquanto outros mecanismos podem estar relacionados aos ganhos nas quatro últimas semanas de intervenção; (3) o ganho de força concêntrica não é afetado por adaptações neurais; (4) o treinamento excêntrico aumenta o comprimento, mas não o ângulo de penação fascicular; (5) as adaptações na arquitetura muscular podem ocorrer nas primeiras semanas de treinamento; e (6) apesar das diferenças estruturais e funcionais, RF e VL apresentam índices semelhantes de adaptação.Eccentric exercise is used as a strategy for strength training in athletes and healthy subjects with different ages. This type of exercise is also frequently used in musculoskeletal rehabilitation, and the quadriceps femoris is the most frequently investigated muscle due its clinical relevance. The theme of this PhD thesis is the adaptation of the neuromuscular system to knee extensor eccentric training. In Chapter I, a review study aimed at describing the different methods employed by scientists for knee extensor eccentric training, as well as for evaluating the neural, morphological and muscular strength adaptations in healthy subjects. After a systematized search in related data bases, 26 studies were incorporated to our review study. Eccentric training programs performed in isokinetic dynamometers and isotonic devices (leg-press and knee extension chair) were described and discussed. Results from these studies indicate a positive effect of eccentric training on muscle strength and activation, especially in eccentric tests, as well as a significant hypertrophic response. However, conflicting results and gaps observed in the literature encouraged us to perform two original studies to verify: (1) the time course of neural and morphological adaptations to knee extensor eccentric training and their contribution to strength gains (Chapter II); and (2) the specific adaptive responses from synergistic knee extensor muscles: rectus femoris (RF) and vastus lateralis (VL) (Chapter III). Twenty healthy men performed a four-week control period without training, followed by a 12-week eccentric training on an isokinetic dynamometer. Knee extensor evaluations of torque, electromyography and ultrasonography were made every four weeks. A higher strength increase was observed in eccentric tests, followed by isometric and concentric tests. Muscle activation in eccentric and isometric tests increased after four and eight weeks of training, respectively, while the concentric tests presented no change in the electromyographic activity. Muscle thickness, anatomical cross-sectional area and fascicle length values increased after four and eight weeks of training, but did not change between the eighth and twelfth intervention week. Adaptations in RF and VL fascicular geometry were similar throughout the training program. Our findings suggest that: (1) there is a strong specificity effect of eccentric exercise on increases in muscle strength and activation; (2) eccentric and isometric strength gains up to the eighth week of training are related to measurable neural and morphological adaptations, while other mechanisms may be related to strength increase in the last four weeks of intervention; (3) concentric strength gain is not affected by neural adaptations; (4) eccentric training increases fascicle length, but not pennation angle; (5) muscle architecture adaptations may occur in the first weeks of training; and (6) despite the structural and functional differences, RF and VL present similar adaptation levels

Efeito da fototerapia prévia ao exercício isocinético sobre a fadiga e o dano muscular

Desde seu desenvolvimento na década de 60, a fototerapia têm sido utilizada no tratamento de diversas condições patológicas, havendo um considerável corpo de evidências acerca de sua ação regenerativa, analgésica e anti-inflamatória. Tais efeitos terapêuticos podem ser explicados pela capacidade que a energia luminosa possui de ser absorvida pelos tecidos e estimular ou inibir processos intracelulares. Estudos recentes têm apresentado resultados promissores desta terapia também sobre a redução da fadiga e do dano muscular induzido pelo exercício. A fadiga muscular é um fenômeno multifacetado caracterizado por uma progressiva redução da capacidade de produção de força do músculo. O dano muscular, causado principalmente pelas ações excêntricas do exercício, é caracterizado pela desorganização da estrutura microscópica do músculo e redução da capacidade contrátil deste tecido. Assim, o objetivo do presente trabalho foi verificar o efeito da fototerapia aplicada imediatamente antes do exercício sobre: (1) a fadiga muscular de extensores de joelho submetidos a exercício isocinético concêntrico; (2) o dano muscular de extensores de joelho submetidos a exercício isocinético excêntrico. No primeiro estudo, 17 homens saudáveis e fisicamente ativos participaram de um desenho experimental cruzado no qual foram submetidos a 30 repetições concêntricas máximas de flexo-extensão do joelho, precedidas de tratamento com fototerapia ou placebo. A fototerapia foi aplicada através de um equipamento de light emitting diodes therapy (LEDT) composto por 35 diodos infravermelhos de 850 nm e 34 diodos vermelhos de 660 nm. O tratamento foi realizado em três pontos do quadríceps com aplicação de uma dose total de 125,1 J. Mensurações da função muscular dos extensores de joelho foram realizadas antes e imediatamente após o exercício através de contrações voluntárias máximas (CVM) de extensores de joelho a 60º de flexão da articulação. Como resultado, observou-se que os voluntários apresentaram um decréscimo de torque significativamente menor quando tratados com fototerapia em comparação ao tratamento placebo. No segundo estudo, 36 homens saudáveis e fisicamente ativos foram randomizados em grupo fototerapia (n=18) e grupo placebo (n=18), e submetidos a cinco séries de 15 contrações excêntricas máximas de extensores de joelho. Avaliações de dor muscular e níveis séricos das enzimas lactato desidrogenase (LDH) e creatina kinase (CK) foram mensuradas pré-exercício, 24 e 48 horas pós-exercício. Avaliações da função muscular (CVM de extensores de joelho) foram realizadas pré-exercício, imediatamente após, 24 e 48 horas após o exercício. Um equipamento de low level laser therapy (LLLT) composto por cinco diodos infravermelhos de 810 nm foi utilizado para aplicar o tratamento em seis pontos do quadríceps e transmitir uma dose total de 180 J. Como resultado, observou-se que o grupo fototerapia apresentou: (1) menores incrementos de LDH 48 horas após o exercício; (2) menores incrementos de CK 24 e 48 horas após o exercício; e (3) menor decréscimo do torque de extensores de joelho imediatamente após, 24 e 48 horas após o exercício, em comparação ao grupo placebo. Os achados destes estudos permitem concluir que o tratamento com fototerapia foi capaz de atenuar os efeitos da fadiga e do dano muscular induzidos por exercício em dinamômetro isocinético.Since its development in the 60’s, phototherapy has been used in the treatment of several pathological conditions, with a considerable body of evidence with respect to its regenerative, analgesic and anti-inflammatory action. These therapeutic effects may be explained by the capacity that the light energy has of being absorbed by soft tissues and stimulate or inhibit intracellular processes. Recent studies have also shown promising results regarding the reduction of muscle fatigue and exercise induced muscle damage. Muscle fatigue is a multifaceted phenomenon characterized by a progressive reduction in muscle force production capacity. Muscle damage, mainly caused by eccentric exercise, is characterized by the microscopic disorganization of muscle structure and reduction of the contractile capacity of this tissue. Thus, the purpose of this study was to verify the effect of phototherapy applied immediately before exercise on: (1) knee extensors muscle fatigue after isokinetic concentric exercise; (2) knee extensor muscle damage after isokinetic eccentric exercise. In the first study 17 healthy and physically active male subjects participated of a cross-over design trial. Subjects were subjected to 30 maximal concentric repetitions of knee flexion-extension, preceded by placebo or phototherapy treatment. Phototherapy was applied with a light emitting diodes therapy (LEDT) equipment composed by 35 infrared diodes of 850 nm wavelength and 34 red diodes of 660 nm. Treatment was applied in three different points of the quadriceps muscle with a total dose of 125.1 J. Measurements of knee extensor muscle function were obtained before and immediately after exercise by maximal voluntary contractions (MVC) at a knee angle of 60º of joint flexion. Subjects showed a significant smaller decrease in torque when treated with phototherapy compared to placebo treatment. On the second study, 36 healthy and physically active male subjects were randomized into a phototherapy (n=18) and a placebo (n=18) group, and subjected to five series of 15 maximal knee extensor eccentric contractions. Measurements of pain and serum levels of lactate dehydrogenase (LDH) and creatine kinase (CK) enzymes were obtained pre-exercise, 24 and 48 hours postexercise. Evaluations of muscle function (knee extensor MVC) were obtained preexercise, immediately after, and 24 and 48 hours after exercise. A low level laser therapy (LLLT) equipment composed by five infrared diodes of 810 nm wavelength was used to apply the treatment on six different points of the quadriceps muscle with a total dose of 180 J. The phototherapy group showed: (1) smaller increments of LDH 48 hours after exercise; (2) smaller increments of CK 24 and 48 hours after exercise; and (3) smaller decrease on knee extensor torque immediately after, 24 and 48 hours after exercise compared to the placebo group. These findings allow us to conclude that the phototherapy treatment was able to attenuate the effects of fatigue and muscle damage induced by isokinetic exercise