The effect of hip and knee joint angles on the muscle-tendon unit during electrical stimulation

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Ceilândia, Programa de Pós-Graduação em Ciências da Reabilitação, 2020.Introdução: O comprimento muscular é um dos principais determinantes da capacidade de geração de força das fibras musculares. O torque varia expressivamente com a manipulação do ângulo articular. Alguns estudos relatam que o ângulo articular influencia o torque evocado e a eficiência da corrente (torque/amplitude da corrente) durante a estimulação elétrica neuromuscular (EENM). Tipicamente, o torque extensor do joelho é maior em ~60o de flexão em uma posição sentada. A arquitetura muscular (i.e., espessura, ângulo de penação [θp] e comprimento do fascículo [Cf]) e o deslocamento do complexo tendão-aponeurose (DCTA) têm sido estudados para explicar mecanismos da geração de torque durante a manipulação do comprimento muscular. No entanto, até o momento, não foram estudados os efeitos dos ângulos do quadril e do joelho durante a EENM no comportamento da unidade miotendínea dos constituintes do quadríceps femoral (QF): o biarticular reto femoral (RF) e os monoarticulares vasto lateral (VL), vasto medial (VM) e vasto intermédio (VI). Até onde sabemos, existe apenas um estudo crônico que trata da EENM em diferentes ângulos articulares, o qual mostrou melhores resultados para a EENM realizada em um maior comprimento muscular. No entanto, uma posição estendida do joelho foi previamente recomendada, apesar do pequeno tamanho de efeito relatado. Vários estudos têm aplicado a EENM do QF escolhendo aleatoriamente o ângulo articular, como sentado ou deitado, com os joelhos estendidos ou flexionados em diferentes ângulos, ou mesmo sem descrição completa. Os clínicos devem estar cientes da configuração articular a fim de otimizar as respostas musculares aos programas de exercícios isométricos. Objetivos: O objetivo principal deste estudo foi investigar o efeito dos ângulos do joelho (60o ou 20o) e do quadril (0o ou 85o) no torque evocado e na eficiência da corrente da EENM. Nós também avaliamos a arquitetura muscular (θp e Cf) em repouso e durante contração e o DCTA de cada componente do QF para investigar a contribuição deles. Hipóteses: Nossa hipótese inicial foi que durante a EENM seria obtido maior torque extensor com o joelho a 60o na posição sentada, porém com amplitude de corrente proporcionalmente menor, portanto, melhor eficiência da corrente. Também levantamos a hipótese de que o θp seria menor e o Cf seria maior quando o joelho estivesse em 60o para todos os componentes do quadríceps (RF, VL, VM e VI), mas para o RF, o quadril em 0o diminuiria o θp e aumentaria o Cf ainda mais. Além disso, esperávamos que o TACD fosse mais pronunciado em posições com maior torque. Métodos: Vinte homens hígidos com idade 24,0 ± 4,6 participaram de cinto sessões separadas por sete dias entre cada uma delas: uma sessão de familiarização e quatro sessões experimentais para testar quatro combinações diferentes de ângulos do quadril e do joelho durante EENM: quadril a 85o (sentado) e joelho a 60o (SJ60); quadril a 85o e joelho a 20o (SJ20); quadril a 0o (deitado) e joelho a 60o (DJ60); e quadril a 0o e joelho a 20o (DJ20). Oito contrações evocadas foram necessárias para realizar a ultrassonografia dos quatro componentes do QF (duas contrações para cada um). Os participantes foram questionados sobre condições de saúde e foi realizada a caracterização demográfica e antropométrica. Na familiarização foi verificado se os participantes toleravam amplitude de corrente suficiente para gerar um torque evocado ≥ 30% da contração voluntária máxima (CVM). Os valores de CVM, torque evocado, eficiência da corrente, amplitude da corrente, espessura muscular, θp, Cf, e DCTP foram reportados por meio de média ± desvio padrão. Para o θp e o Cf, as analyses foram realizadas com os valores de repouso e em contração, bem como com a mudança relativa (%). A ANOVA unidirecional de medidas repetidas com fator “posicionamento” (DJ60, SJ60, DJ20, SJ20) foi aplicada para verificar diferenças entre posições para a CVM, o torque evocado, a eficiência da corrente, a amplitude da corrente e o DCTA. A ANOVA bidirecional (“posicionamento” [4 níveis: DJ60, SJ60, DJ20, and SJ20] versus “intensidade” [2 níveis: repouso and contração evocada]) com medidas repetidas no fator posicionamento foi aplicada para verificar diferença entre posições para o θp e o Cf. Quando uma diferença significativa foi detectada, o teste post-hoc de Tukey foi aplicado. O limiar de significância foi estabelecido em P < 0,05. Todas as análises foram realizadas usando o STATISTICA 23.0 (STATSOFT Inc., Tulsa, Oklahoma, EUA) e o software GRAPHPAD PRISM 8.3.0 (San Diego, CA, EUA) foi utilizado para o design gráfico. Resultados: O torque evocado e a eficiência da corrente foram maiores para o DJ60 e o SJ60 em comparação com o DJ20 e o SJ20 (p <0,001). O QF (média de todos os músculos), o VL e o VM apresentaram menor θp e maior Cf em DJ60 e SJ60, enquanto o reto femoral demonstrou influência do ângulo do quadril, uma vez que em DJ60 houve menor θp e maior Cf do que em todas as outras posições (p < 0,001 – 0,05). O vasto intermédio se comportou semelhante aos demais vastos (p < 0,001), exceto pela falta de diferença no θp entre SK60 em comparação com DJ20 e SJ20 (p = 0,25 e 0,30, respectivamente). A TACD foi maior para o SJ60 em comparação com o DJ60 (p <0,001), apesar do mesmo torque. Discussão: Os principais achados deste estudo foram: 1) o torque evocado extensor do joelho e a eficiência da corrente foram maiores em 60o de flexão do joelho comparado com em 20o, sem diferença de acordo com o ângulo do quadril; 2) O QF teve menor θp and greater Cf em 60o de flexão de joelho. 3) O DCTA foi menor em DJ60 comparado com SJ60 apesar do mesmo torque. Estes novos achados são importantes para ajudar fisioterapeutas e treinadores físicos a desenvolverem estratégias mais efetivas quando aplicarem EENM. Nossos resultados estão de acordo com relatos anteriores que encontraram maior torque evocado a 60o de flexão do joelho em comparação com posições mais estendidas. Um ângulo articular escolhido com cautela permite atingir o torque alvo com menor amplitude de corrente e, com isso, com menos desconforto sensorial. Apenas dois estudos avaliaram a arquitetura de todos os constituintes do QF in vivo, mas eles não aplicaram ENM ou avaliaram diferentes ângulos articulares. Nosso principal achado foi que o QF demonstrou um padrão em que as posições com o joelho a 60o apresentavam θp menor e maior Cf quando comparadas às posições com o joelho a 20o. Assim, sugere-se que em DJ60 e o SJ60 o QF foi colocado em uma melhor configuração para geração de torque, ou seja, melhor aproveitamento da força muscular e comprimento ideal do sarcômero. O QF apresentou um DCTA menor em DJ60 comparado com SJ60, apesar do mesmo torque evocado, indicando que o aumento da tensão passiva em DJ60 limitou o alongamento tendíneo durante a contração. O aumento da tensão do complexo tendão-aponeurose em condições de alongamento permite contrações mais fortes com menor esforço devido à melhor transmissão de força do músculo para o osso. Conclusão: A EENM gera um torque maior a 60o de flexão do joelho, comparado a 20o, independentemente do ângulo do quadril. A arquitetura de cada constituinte do quadríceps demonstrou um comportamento único de acordo com o ângulo do quadril e do joelho, mas predominaram um menor θp e um maior Cf nas posições com maior torque (SJ60 e DJ60). Uma posição mais alongada enrijece o complexo tendão-aponeurose, como demonstrado por um DCTA menor em DJ60 em comparação com SJ60, o que provavelmente contribuiu para uma transmissão otimizada da força e um torque ligeiramente mais alto para o DJ60. Clínicos devem preferencialmente usar NMES em DJ60 ou DJ60 para fins de fortalecimento.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Distrito Federal (FAP-DF)Neuromuscular electrical stimulation (NMES) is recommended to counteract muscle atrophy and for strengthening. However, the influence of hip and knee angles during quadriceps femoris (QF) NMES is poorly investigated. We aimed to investigate the effect of knee and hip angle on NMES-evoked torque and current efficiency. We secondarily assessed the QF architecture at rest and during contraction, and the tendon-aponeurosis complex displacement (TACD). Twenty men aged 24.0 ± 4.6 years received NMES in four positions: hip at 85o (seated) and knee at 60o (SK60); hip at 85o and knee at 20o (SK20); hip at 0o (lying) and knee at 60o (LK60); and hip at 0o and knee at 20o (LK20). NMES- evoked torque and current efficiency (evoked torque/current amplitude) were recorded. Ultrasonography of the QF was performed to measure pennation angle (θp), fascicle length (Lf), and TACD. Evoked torque and current efficiency were greater for LK60 and SK60 compared to LK20 and SK20 (p < 0.01). The QF (all muscles), vastus lateralis, and medialis showed lower θp and higher Lf at LK60 and SK60, while rectus femoris demonstrated influence of hip angle, since in LK60 there was lower θp and higher Lf than in all other positions (p < 0.05). The vastus intermedius was similar to the other vasti, except for a lack of difference in θp between SK60 compared to LK20 and SK20. TACD was greater for SK60 compared to LK60 (p < 0.001) despite the same torque. These findings suggest that clinicians should apply NMES preferably at 60o of knee flexion

Analysis of expiratory muscle strength and spontaneous breathing of individuals on mechanical ventilation: a cross-sectional study

Os músculos da expiração têm funções em todo o ciclo respiratório, mas não são frequentemente avaliados no desmame da ventilação mecânica. Assim, revisões e consensos não mencionam a pressão expiratória máxima (PEmáx) e o treino expiratório. Objetivou-se investigar a relação da força muscular expiratória com a respiração espontânea de indivíduos ventilados mecanicamente. Trata-se de um estudo transversal com participantes de 18 a 79 anos de idade. Foram formados os grupos PEmáx satisfatória (GPES) e PEmáx baixa (GPEB) conforme o ponto de corte de 55cmH2O e comparados a parâmetros de desmame. O GPES (n=9) teve desempenho superior ao do GPEB (n=21) no índice de respiração rápida e superficial (IRRS) (40,6±17,6rpm/L e 75,3±44,1rpm/L, respectivamente; p=0,022) e na frequência respiratória (f) (19,1±6,2rpm e 26,1±9,4rpm; p=0,044). A prevalência de PEmáx satisfatória foi pequena, observada no tamanho dos grupos. Além disso, embora a PEmáx percentual do valor predito tenha sido menor no GPEB, como esperado (67,2±15,4% vs. 45,8±14,7%; p=0,001), a pressão inspiratória máxima percentual não diferiu significantemente (82,4±21,8% vs. 67,8±18,4%; p=0,077). A PEmáx se correlacionou moderadamente com o IRRS (r=–0,406; p=0,026) e com a f (r=–0,426; p=0,017). Conclui-se que a PEmáx≥55cmH2 O esteve associada à melhores valores no IRRS e na f, e que a redução da força muscular expiratória foi mais prevalente e severa que a da força muscular inspiratória.| Los músculos de la espiración tienen funciones en todo el ciclo respiratorio, sin embargo, no son frecuentemente evaluados en el desmame de la ventilación mecánica. Así, revisiones y consensos no mencionan la tensión espiratoria máxima (PEmáx) y el entreno espiratorio. Se ha objetivado investigar la relación de la fuerza muscular espiratoria con la respiración espontánea de los individuos ventilados mecánicamente. Se trata de un estudio transversal con participantes de 18 a 79 años de edad. Han sido hechos los grupos PEmáx satisfactoria (GPES) y PEmáx baja (GPEB) de acuerdo con el punto de corte de 55cmH2O y han sido comparados a parámetros de destete. El GPES (n=9) ha tenido el desempeño superior al del GPEB (n=21) en el índice de respiración rápida y superficial (IRRS) (40,6±17,6rpm/L y 75,3±44,1rpm/L, respectivamente; p=0,022) y en la frecuencia respiratoria (f) (19,1±6,2rpm y 26,1±9,4rpm; p=0,044). La prevalencia de PEmáx satisfactoria ha sido pequeña, ha sido observada en el tamaño de los grupos. Además de eso, aunque la PEmáx porcentual del valor predicho haya sido menor en el GPEB, como ha sido esperado (67,2±15,4% vs. 45,8±14,7%; p=0,001), la presión inspiratoria máxima porcentual no ha diferido significantemente (82,4±21,8% vs. 67,8±18,4%; p=0,077). La PEmáx se ha correlacionado moderadamente con el IRRS (r=–0,406; p=0,026) y con la f (r=–0,426; p=0,017). Se concluye que la PEmáx≥55cmH2O ha estado asociada a los mejores valores en el IRRS y en la f, y que la reducción de la fuerza muscular espiratoria ha sido más prevalente y severa que la de la fuerza muscular inspiratoria.The expiratory muscles have functions throughout the respiratory cycle, but they are not often evaluated in the weaning from mechanical ventilation. Thus, reviews and consensus do not mention the maximal expiratory pressure (MEP) and the expiratory training. The aim of this study was to investigate the relationship of expiratory muscle strength with the spontaneous breathing of individuals on mechanical ventilation. This is a cross-sectional study with participants aged between 18 and 79 years. The groups satisfactory MEP (SMEPG) and low MEP (LMEPG) were formed according to the cut-off point of 55 cmH2 O and compared to weaning parameters. The SMEPG (n=9) had better performance than LMEPG (n=21) in the rapid shallow breathing index (RSBI) (40.6±17.6 bpm/L and 75.3±44.1 bpm/L, respectively; p=0.022) and in the respiratory rate (RR) (19.1±6.2 bpm and 26.1±9.4 bpm; p=0.044). Prevalence of satisfactory MEP was low, as observed in the size of groups. In addition, although the MEP percentage of the predicted value was lower in LMEPG, as expected (67.2±15.4% vs. 45.8±14.7%; p=0.001), the percentage for maximal inspiratory pressure was not significantly different (82.4±21.8% vs. 67.8±18.4%; p=0.077). The MEP was moderately correlated with the RSBI (r=−0.406; p=0.026) and with the RR (r=−0.426; p=0.017). It was concluded that MEP≥55 cmH2 O was associated with better values in RSBI and RR and that the reduction of expiratory muscle strength was more prevalent and severe than that of inspiratory muscle strength

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

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

Health promotion initiatives at school related to overweight, insulin resistance, hypertension and dyslipidemia in adolescents: a cross-sectional study in Recife, Brazil

Abstract Background The emergence of diseases such as dyslipidemia, systemic arterial hypertension, insulin resistance and metabolic syndrome in children and adolescents has brought about a change in the epidemiologic profile of the pediatric population. As action to promote health in the school environment is a useful tool for changing the pattern of health/disease in the young population, the present study aimed to identify schools that promote healthy eating and physical activity and to study the relationship between these practices and the prevalence of overweight, hypertension, insulin resistance and hypercholesterolemia in adolescents. Methods A cross-sectional population-based study was conducted with 2400 adolescents aged from 12 to 17 years old and participating in the “Study of Cardiovascular Risk in Adolescents” (ERICA – Estudo de Riscos Cardiovasculares em Adolescente). The association between dependent (overweight, insulin resistance, hypertension and dyslipidemia) and independent variables (implementation of health promoting initiative in schools) was investigated using the chi-square test and prevalence ratio (PR) with a confidence index (CI) of 95%. Results The unsatisfactory implementation of a “health promoting environment” (PR = 1.02; CI 95%: 1.0; 1.04) and “partnerships with the health sector” (PR = 1.03; CI 95%: 1.01; 1.05) were linked to a high prevalence of overweight in adolescents. Hypercholesterolemia was found to be higher in the schools with unsatisfactory implementation of “healthy eating and health on the scholar curriculum” (PR = 1.71; CI 95%: 1.22; 2.44) and those lacking a “healthy-eating promoting environment” (PR = 1.29; CI 95%: 1.10; 1.54). Schools with unsatisfactory implementation of a “health-eating promoting environment” (PR = 1.36; CI 95%: 1.04; 1.79) and those lacking “partnership with the health sector” (PR = 2.12; CI 95%: 1.38; 3.24) had more adolescents with insulin resistance. There was no association between hypertension and any other component studied. Conclusion Schools which have implemented adequate health promotion in their curriculums showed a lower prevalence of overweight, insulin resistance and hypercholesterolemia in adolescents

Effect of muscle length on maximum evoked torque, discomfort, contraction fatigue, and strength adaptations during electrical stimulation in adult populations: A systematic review

International audienceNeuromuscular electrical stimulation (NMES) can improve physical function in different populations. NMES-related outcomes may be influenced by muscle length (i.e., joint angle), a modulator of the force generation capacity of muscle fibers. Nevertheless, to date, there is no comprehensive synthesis of the available scientific evidence regarding the optimal joint angle for maximizing the effectiveness of NMES. We performed a systematic review to investigate the effect of muscle length on NMES-induced torque, discomfort, contraction fatigue, and strength training adaptations in healthy and clinical adult populations (PROSPERO: CRD42022332965). We conducted searches across seven electronic databases: PUBMED, Web of Science, EMBASE, PEDro, BIREME, SCIELO, and Cochrane, over the period from June 2022 to October 2023, without restricting the publication year. We included cross-sectional and longitudinal studies that used NMES as an intervention or assessment tool for comparing muscle lengths in adult populations. We excluded studies on vocalization, respiratory, or pelvic floor muscles. Data extraction was performed via a standardized form to gather information on participants, interventions, and outcomes. Risk of bias was assessed using the Revised Cochrane risk-of-bias tool for cross-over trials and the Physiotherapy Evidence Database scale. Out of the 1185 articles retrieved through our search strategy, we included 36 studies in our analysis, that included 448 healthy young participants (age: 19–40 years) in order to investigate maximum evoked torque (n = 268), contraction fatigability (n = 87), discomfort (n = 82), and muscle strengthening (n = 22), as well as six participants with spinal cord injuries, and 15 healthy older participants. Meta-analyses were possible for comparing maximal evoked torque according to quadriceps muscle length through knee joint angle. At optimal muscle length 50° - 70° of knee flexion, where 0° is full extension), there was greater evoked torque during nerve stimulation compared to very short (0 – 30°) (p<0.001, CI 95%: -2.03, -1.15 for muscle belly stimulation, and -3.54, -1.16 for femoral nerve stimulation), short (31° - 49°) (p = 0.007, CI 95%: -1.58, -0.25), and long (71° - 90°) (p<0.001, CI 95%: 0.29, 1.02) muscle lengths. At long muscle lengths, NMES evoked greater torque than very short (p<0.001, CI 95%: -2.50, -0.67) and short (p = 0.04, CI 95%: -2.22, -0.06) lengths. The shortest quadriceps length generated the highest perceived discomfort for a given current amplitude. The amount of contraction fatigability was greater when muscle length allowed greater torque generation in the pre-fatigue condition. Strength gains were greater for a protocol at the optimal muscle length than for short muscle length. The quality of evidence was very high for most comparisons for evoked torque. However, further studies are necessary to achieve certainty for the other outcomes. Optimal muscle length should be considered the primary choice during NMES interventions, as it promotes higher levels of force production and may facilitate the preservation/gain in muscle force and mass, with reduced discomfort. However, a longer than optimal muscle length may also be used, due to possible muscle lengthening at high evoked tension. Thorough understanding of these physiological principles is imperative for the appropriate prescription of NMES for healthy and clinical populations

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 (θ p ) and fascicle length ( L f ), 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 θ p and higher L f at SUP60 and SIT60, while for the rectus femoris, in SUP60 there were lower θ p and higher L f than in all positions. The vastus intermedius had a similar pattern to the other vastii, except for lack of difference in θ p 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 L f and lower θ p 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. Clinical Trial Registration www.ClinicalTrials.gov , identifier NCT03822221

Hip and Knee Joint Angles Determine Fatigue Onset during Quadriceps Neuromuscular Electrical Stimulation

International audienceNeuromuscular electrical stimulation (NMES) has been used to increase muscle strength and physical function. However, NMES induces rapid fatigue, limiting its application. To date, the effect of quadriceps femoris (QF) muscle length by knee and hip joint manipulation on NMES-induced contraction fatigability is not clear. We aimed to quantify the effects of different muscle lengths on NMES-induced contraction fatigability, fatigue index, and electromyographic (EMG) activity for QF muscle. QF maximum evoked contraction (QMEC) was applied in a 26 min protocol (10 s on; 120 s off; 12 contractions) in 20 healthy participants ( 24.0 ± 4.6 years old), over 4 sessions on different days to test different conditions. The tested conditions were as follows: 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). Contraction fatigability (torque decline assessed by maximal voluntary contraction [MVC] and during NMES), fatigue index (percentage reduction in MVC), and EMG activity (root mean square [RMS] and median frequency) of the superficial QF’ constituents were assessed. After NMES, all positions except SUP20 had an absolute reduction in MVC ( p < .001 ). Fatigue index was greater in SIT20 than in SIT60 ( p < .001 ) and SUP20 ( p = .01 ). There was significant torque reduction across the 12 QMEC in SUP60 and SIT60, up to 10.5% ( p < .001 – .005 ) and 9.49% ( p < .001 – .033 ), respectively. There was no torque reduction during NMES in SUP20 and SIT20. Fatigue was accompanied by an increase in RMS ( p = .032 ) and a decrease in median frequency for SUP60 ( p < .001 ). Median frequency increased only in the SUP20 condition ( p = .021 ). We concluded that QF NMES-induced contraction fatigability is greater when the knee is flexed at 60° compared to 20°. In addition, a supine position promotes earlier fatigue for a 60° knee flexion, but it delays fatigue onset for a 20° knee flexion compared to the seated position. These results provide a rationale for lower limb positioning during NMES, which depends on training objectives, e.g., strengthening or task-specific functionality training