Exercise and Tendon Remodeling Mechanism

Tendons connect muscles to bones and transmit the force exerted by the corresponding muscle to the skeleton and, therefore, are key components for locomotion. They are responsive to mechanical factors, which are essential for cellular functioning, tendon development, homeostasis, and repairing. Mechanical signals are transduced via molecular signaling pathways which trigger tendon adaptive responses. Previous data have already shown that exercise training promotes physiological adaptive responses, such as morphological properties and biomechanical and biochemical adaptations

Effects of Resistance Training on Muscle Quality Index, Muscle Strength, Functional Capacity, and Serum Immunoglobulin Levels between Obese and Non-obese Older Women

International Journal of Exercise Science 14(7): 707-726, 2021. Considering the negative impact of obesity on neuromuscular and immune systems, we sought to compare the effects of a 10-week resistance training (RT) program on muscle quality index (MQI), muscle strength, functional capacity, and immunoglobulins in older women with and without obesity. Thirty-nine older women participated in the present study (age: 69.02 ± 6.16, fat (%): 38.80% ± 6.28) and underwent a linear RT program performed on two non-consecutive days of the week. Body composition, functional tests, immunoglobulins, muscle quality of upper and lower limbs and absolute muscular strength of the upper and lower limbs were measured. Both groups displayed an increased statistically significant difference in MQI between pre-post training, however obese participants showed a lower field and laboratory MQI when compared to non-obese participants at the same time-points. Obese participants displayed an increased statistically significant 30-second chair stand test, with no differences for non-obese participants. Obese participants showed a higher statistically significant difference for immunoglobulin M when compared to the non-obese group at post-training. Finally, both groups displayed an increased statistically significant difference in muscle strength between pre-post-training. However, obese participants showed a statistically significant lower 10-RM low row score when compared to non-obese participants at post-training. Obese older women showed a lower field and laboratory MQI when compared to non-obese post-training, besides a lower 10-RM low row score which reinforces that obesity blunts the beneficial effects of RT on muscle quality and strength

Adipose tissue extracellular matrix remodeling in response to dietary patterns and exercise : molecular landscape, mechanistic insights, and therapeutic approaches

The extracellular matrix (ECM) is a 3-dimensional network of molecules that play a central role in differentiation, migration, and survival for maintaining normal homeostasis. It seems that ECM remodeling is required for adipose tissue expansion. Despite evidence indicating that ECM is an essential component of tissue physiology, adipose tissue ECM has received limited attention. Hence, there is great interest in approaches to neutralize the harmful effects of ECM enlargement. This review compiles and discusses the current literature on adipose tissue ECM remodeling in response to different dietary patterns and exercise training. High-calorie diets result in substantial adipose tissue ECM remodeling, which in turn could lead to fibrosis (excess deposition of collagens, elastin, and fibronectin), inflammation, and the onset of metabolic dysfunction. However, combining a nutritionally balanced diet with exercise is a remarkable potential strategy for lipolytic activity, preventing rapid ECM expansion in different adipose tissue depots. Despite the distinct exercise modalities (aerobic or resistance exercise) reversing adipose tissue fibrosis in animal models, the beneficial effect on humans remains controversial. Defining molecular pathways and specific mechanisms that mediate the positive effects on adipose tissue, ECM is essential in developing optimized interventions to improve health and clinical outcomes

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

Identification of risk factors for falls in people with multiple sclerosis : a systematic review of prospective studies

O objetivo deste estudo foi identificar, a partir de uma revisão sistemática, variáveis clínicas, instrumentais e demográficas associadas com maior risco de queda em indivíduos com esclerose múltipla (EM), com base em dados prospectivos. A pesquisa foi conduzida nas bases de dados Medline, Web of Science, Bireme e CINAHL, utilizando os descritores “esclerose múltipla”, “quedas”, “quedas acidentais”, “risco de quedas”, “controle postural” e “equilíbrio”, seguido de buscas manuais. Foram considerados elegíveis estudos de coorte prospectivos, com período mínimo de acompanhamento das quedas de três meses, que avaliassem a associação de determinada variável demográfica, clínica ou instrumental em relação a maior risco de queda em indivíduos com EM. A escala de Newcastle-Ottawa modificada foi utilizada para avaliação da qualidade metodológica dos estudos incluídos. Foram identificados 357 estudos, 12 dos quais foram incluídos na revisão sistemática, com total de 1.270 pacientes incluídos. Destes, 740 (58,26%) pacientes apresentaram um ou mais episódios de queda, 396 (31,18%) apresentaram episódios de queda recorrentes (2≥quedas no período estipulado), e 530 (41,74%) não apresentaram nenhum episódio. Com exceção da espasticidade e do impacto da dupla tarefa na velocidade da marcha, todas as variáveis investigadas apresentaram resultados conflitantes quanto às suas associações a maior risco de quedas. São necessários mais estudos que apresentem homogeneidade dos fenótipos clínicos de indivíduos com EM, além da utilização de instrumentos de avaliação validados, a fim de estabelecer uma associação robusta de outras variáveis clínicas, instrumentais e demográficas com maior risco de queda.The objective of this study was to identify demographic, clinical, and instrumental variables associated with falls in people with multiple sclerosis (MS), via systematic review, based on prospective data. The search was conducted in these databases: Medline, Web of Science, Bireme e CINAHL via a search strategy that combined the descriptors “multiple sclerosis”, “falls”, “accidental falls”, “fall risk”, “postural control” and “balance”, followed by manual search. Eligibility criteria were prospective cohort studies with a minimum 3-month follow-up of falls that assessed the association of a demographic, clinical or instrumental variable in relation to a higher fall risk in people with MS. The modified Newcastle-Ottawa Quality Assessment Scale was used for study quality assessment. A total of 357 studies were identified, of which 12 were included in the systematic review and 1,270 patients were included. In this study, 740 (58.26%) patients were classified as fallers, 396 (31.18%) patients had recurrent falls (2≥falls within the stipulated period) and 530 patients (41.74%) were classified as non-fallers. Except for spasticity and dual task cost in gait speed, all investigated variables showed conflicting results regarding their association with a higher fall risk. More studies with clinical homogeneity phenotypes of MS individuals and using validated assessment instruments are necessary to establish a robust association of other clinical, instrumental, and demographic variables with a higher fall risk.El objetivo de este estudio fue identificar, a partir de una revisión sistemática, variables clínicas, instrumentales y demográficas asociadas con un mayor riesgo de caída en individuos con esclerosis múltiple (EM), con base en datos prospectivos. La búsqueda se realizó en las bases de datos: Medline, Web of Science, Bireme y CINAHL, utilizando los descriptores “esclerosis múltiple”, “caídas”, “caídas accidentales”, “riesgo de caídas”, “control postural” y “equilibrio”, seguido de búsquedas manuales. Se consideraron elegibles los estudios de cohorte prospectivos con un período de seguimiento mínimo de caídas de tres meses, que evaluaron la asociación de una variable demográfica, clínica o instrumental en relación con el mayor riesgo de caídas en individuos con EM. La escala modificada de Newcastle-Ottawa se utilizó para evaluar la calidad metodológica de los estudios incluidos. Se identificaron 357 estudios, 12 de los cuales se incluyeron en la revisión sistemática, con un total de 1.270 pacientes incluidos. De estos, 740 (58,26%) pacientes tuvieron uno o más episodios de caída, 396 (31,18%) presentaron episodios de caída recurrentes (2≥caídas en el período estipulado), y 530 (41,74%) no presentaron ningún episodio. Con excepción de la espasticidad y del impacto de la doble tarea en la velocidad de la marcha, todas las variables investigadas presentaron resultados conflictivos en cuanto a sus asociaciones a mayor riesgo de caídas. Se requieren más estudios que presenten homogeneidad de los fenotipos clínicos de pacientes con EM, además del uso de instrumentos de evaluación validados, para establecer una asociación robusta de otras variables clínicas, instrumentales y demográficas con mayor riesgo de caída

Calcaneal tendon plasticity following gastrocnemius muscle injury in rat

Cross-talk between skeletal muscle and tendon is important for tissue homeostasis. Whereas the skeletal muscle response to tendon injury has been well-studied, to the best of our knowledge the tendon response to skeletal muscle injury has been neglected. Thus, we investigated calcaneal tendon extracellular matrix (ECM) remodeling after gastrocnemius muscle injury using a rat model. Wistar rats were randomly divided into four groups: control group (C; animals that were not exposed to muscle injury) and harvested at different time points post gastrocnemius muscle injury (3, 14, and 28 days) for gene expression, morphological, and biomechanical analyses. At 3 days post injury, we observed mRNA-level dysregulation of signaling pathways associated with collagen I accompanied with disrupted biomechanical properties. At 14 days post injury, we found reduced collagen content histologically accompanied by invasion of blood vessels into the tendon proper and an abundance of peritendinous sheath cells. Finally, at 28 days post injury, there were signs of recovery at the gene expression level including upregulation of transcription factors related to ECM synthesis, remodeling, and repair. At this time point, tendons also presented with increased peritendinous sheath cells, decreased adipose cells, higher Young’s modulus, and lower strain to failure compared to the uninjured controls and all post injury time points. In summary, we demonstrate that the calcaneal tendon undergoes extensive ECM remodeling in response to gastrocnemius muscle injury leading to altered functional properties in a rat model. Tendon plasticity in response to skeletal muscle injury merits further investigation to understand its physiological relevance and potential clinical implications

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

Resistance training modulates the matrix mtalloproteinase-2 activity in different trabecular bones in aged rats

Background: Aging decreases osteogenic ability, inducing harmful effects on the bone extracellular matrix (ECM), while exercise training has been indicated as a tool to counteract bone disorders related to advancing age. The modulation of bone ECM is regulated by several types of matrix metalloproteinase (MMP); however, MMP-2 activity in different trabecular bones in response to resistance training (RT) has been neglected. Remodeling differs in different bones under the application of the same mechanical loading. Thus, we investigated the effects of 12 weeks of RT on MMP-2 activity in the lumbar vertebra (L6), tibia, and femur of young (3 months) and older rats (21 months). Methods: Twenty Wistar rats were divided into four groups (five animals per group): young sedentary or trained and older sedentary or trained. The 12-week RT consisted of climbing a 1.1-m vertical ladder three times per week with progressive weights secured to the animals’ tails. The animals were killed 48 h after the end of the experimental period. The MMP-2 activity was assessed by the zymography method. Results: The aging process induced lower MMP-2 activity in the lumbar vertebrae and tibia (p=0.01). RT upregulated pro, intermediate, and active MMP-2 activity in the tibia of young rats (p=0.001). RT also upregulated pro and active MMP-2 activity in the lumbar vertebrae and tibia with advancing age (p=0.01). There was no significant difference (p> 0.05) between groups for MMP-2 of the femur, regardless of age and RT. Conclusion: The aging process impairs MMP-2 activity, but RT is a potential therapeutic approach to minimize the deleterious effects of ECM degeneration in different aged bones. Distinct MMP-2 responses to exercise training may result in specific remodeling processes