Physical therapy for acute and sub-acute low back pain: A systematic review and expert consensus.

OBJECTIVE: To review the effectiveness of different physical therapies for acute and sub-acute low back pain supported by evidence, and create clinical recommendations and expert consensus for physiotherapists on clinical prescriptions. DATA SOURCES: A systematic search was conducted in PubMed and the Cochrane Library for studies published within the previous 15 years. REVIEW METHODS: Systematic review and meta-analysis, randomized controlled trials assessing patients with acute and sub-acute low back pain were included. Two reviewers independently screened relevant studies using the same inclusion criteria. The Physiotherapy Evidence Database and the Assessment of Multiple Systematic Reviews tool were used to grade the quality assessment of randomized controlled trials and systematic reviews, respectively. The final recommendation grades were based on the consensus discussion results of the Delphi of 22 international experts. RESULTS: Twenty-one systematic reviews and 21 randomized controlled trials were included. Spinal manipulative therapy and low-level laser therapy are recommended for acute low back pain. Core stability exercise/motor control, spinal manipulative therapy, and massage can be used to treat sub-acute low back pain. CONCLUSIONS: The consensus statements provided medical staff with appliable recommendations of physical therapy for acute and sub-acute low back pain. This consensus statement will require regular updates after 5-10 years.

Myofascial junction: Emerging insights into the connection between deep/muscular fascia and muscle.

Muscles and fasciae are mutually connected and are influenced by force transmission. However, the anatomical connectivity and histological features of these structures remain unclear. The aim of this study was to assess the evidence for connection between muscles and deep/muscular fasciae. We assessed this relationship in different topographical regions of human cadavers and in mice. The results showed that myofascial junctions (MFJ) were made up of collagen I immune-positive structures occupying an average area of 5.11 ± 0.81 µm2, distributed in discrete regions at the interface between muscle and fascia with an average density of 9.7 ± 2.51 MFJ/mm and an average inclination angle of 35.25 ± 1.52°. These specialized structures also showed collagen III and HA immunopositivity and the presence of elastic fibers. The human myofascial junction can be visualized, opening emerging insights into the connection between deep/muscular fascia and muscle.

Quantity and Distribution of Muscle Spindles in Animal and Human Muscles.

Muscle spindles have unique anatomical characteristics that can be directly affected by the surrounding tissues under physiological and pathological conditions. Understanding their spatial distribution and density in different muscles is imperative to unravel the complexity of motor function. In the present study, the distribution and number/density of muscle spindles in human and animal muscles were reviewed. We identified 56 articles focusing on muscle spindle distribution; 13 articles focused on human muscles and 43 focused on animal muscles. The results demonstrate that spindles are located at the nerve entry points and along distributed vessels and they relate to the intramuscular connective tissue. Muscles' deep layers and middle segments are the main topographic distribution areas. Eleven articles on humans and thirty-three articles on animals (totaling forty-four articles) focusing on muscle spindle quantity and density were identified. Hand and head muscles, such as the pronator teres/medial pterygoid muscle/masseter/flexor digitorum, were most commonly studied in the human studies. For animals, whole-body musculature was studied. The present study summarized the spindle quantity in 77 human and 189 animal muscles. We identified well-studied muscles and any as-yet unfound data. The current data fail to clarify the relationship between quantity/density and muscle characteristics. The intricate distribution of the muscle spindles and their density and quantity throughout the body present some unique patterns or correlations, according to the current data. However, it remains unclear whether muscles with fine motor control have more muscle spindles since the study standards are inconsistent and data on numerous muscles are missing. This study provides a comprehensive and exhaustive approach for clinicians and researchers to determine muscle spindle status.

Biochemical and Histological Differences between Longitudinal and Vertical Fibres of Dupuytren's Palmar Aponeurosis and Innovative Clinical Implications.

Dupuytren's disease, a chronic and progressive fibroproliferative lesion of the hand, which affects the palmar fascia, has a recurrence rate after selective aponeurotomy of 20-40% at 5 years. This study focused, for the first time, on the microanatomical and histopathological characteristics of the longitudinal and vertical fibres (usually spared during surgery) in the aponeurosis with Dupuytren's disease, in different stages of the Tubiana's classification. Twelve human samples were collected and analysed by immunostaining, Total Collagen Assay, ELISA Immunoassay, and immunoblotting for the Von Willebrand factor, α-Sma, D2-40, CD-68, Total Collagen, Collagen-I and III, IL1ß, TNF-α to analyse the blood and lymphatic vascularization, the amount and distribution of collagen, and the inflammation. The results show a progressive increase in the arterial vascularization in the vertical fibres (from 8.8/mm2 in the early stage to 21.4/mm2 in stage 3/4), and a parallel progressive decrease in the lymphatic drainage (from 6.2/mm2 to 2.8/mm2), correlated with a local inflammatory context (increase in IL-1ß and TNF-α until the stage 2) in both the longitudinal and vertical fibres. The acute inflammation after stage 2 decreased, in favour of a fibrotic action, with the clear synthesis of new collagen (up to ~83 µg/mg), especially Collagen-I. These results clearly demonstrate the involvement of the septa of Legueu and Juvara in the disease pathology and the modifications with the disease's progression. A greater understanding of the pathology becomes fundamental for staging and the adequate therapeutic timing, to obtain the best morpho-functional result and the lowest risk of complications.

The Impact of Sciatic Nerve Injury on Extracellular Matrix of Lower Limb Muscle and Thoracolumbar Fascia: An Observational Study.

Peripheral nerve injury (PNI) is a complex clinical challenge resulting in functional disability. Neurological recovery does not always ensure functional recovery, as extracellular matrix (ECM) alterations affect muscle function. This study evaluates hyaluronan (HA) and collagen concentration in the gastrocnemius muscle and thoracolumbar fascia (TLF) in unilateral lower limb PNI rats to explore systemic ECM alterations following PNI and their impacts on functional recovery. Eighteen 8-week-old male Sprague-Dawley rats were divided into experimental (n = 12 left sciatic nerve injury) and control (n = 6) groups. After six weeks, motor function was evaluated. Muscle and TLF samples were analysed for HA and collagen distribution and concentrations. SFI and gait analysis confirmed a functional deficit in PNI rats 6 weeks after surgery. HA concentration in both sides of the muscles decreased by approximately one-third; both sides showed significantly higher collagen concentration than healthy rats (12.74 ± 4.83 µg/g), with the left (32.92 ± 11.34 µg/g) significantly higher than the right (20.15 ± 7.03 µg/g). PNI rats also showed significantly lower HA (left: 66.95 ± 20.08 µg/g; right: 112.66 ± 30.53 µg/g) and higher collagen (left: 115.89 ± 28.18 µg/g; right: 90.43 ± 20.83 µg/g) concentrations in both TLF samples compared to healthy rats (HA: 167.18 ± 31.13 µg/g; collagen: 47.51 ± 7.82 µg/g), with the left TLF more affected. Unilateral lower limb PNI induced HA reduction and collagen accumulation in both the lower limb muscles and the TLF, potentially exacerbating motor function impairment and increasing the risk of low back dysfunctions.

Fascial plane blocks: from microanatomy to clinical applications.

PURPOSE OF REVIEW: In the last 20 years, advancements in the understanding of fasciae have significantly transformed anaesthesia and surgery. Fascial plane blocks (FPBs) have gained popularity due to their validated safety profile and relative ease. They are used in various clinical settings for surgical and nonsurgical indications. Growing evidence suggests a link between the microscopic anatomy of fasciae and their mechanism of action. As a result, knowledge of these aspects is urgently needed to better optimise pain management. The purpose of this review is to summarise the different microscopic aspects of deep/muscular fascia to expand our understanding in the performance of FPBs. RECENT FINDINGS: There is ample evidence to support the role of FPBs in pain management. However, the exact mechanism of action remains unclear. Fasciae are composed of various structural elements and display complex anatomical characteristics at the microscopic level. They include various cell types embedded within an extracellular matrix abundant in collagens and hyaluronan. Increasingly, numerous studies demonstrated their innervation that contributes to their sensory functions and their role in proprioception, motor coordination and pain perception. Lastly, the diversity of the cellular and extracellular matrix, with their viscoelastic properties, is essential to understanding the FPBs' mechanism of action. SUMMARY: Physicians must be aware of the role of fascial microscopic anatomy and better understand their properties to perform FPBs in a conscious manner and enhance pain management.

Ultrasound Imaging of Thoracolumbar Fascia: A Systematic Review.

Over the past decade, there has been a notable increase in research focused on ultrasound imaging of thoracolumbar fascia (TLF). Nevertheless, published papers' results about the application of US imaging in TLF examination are still sparse. Background and Objevtives: Hence, this systematic review was performed aiming to firstly investigate the use and the methodology of ultrasound imaging to assess pathologic and healthy TLF. Secondarily, we aim to assess intra- and inter-observer reproducibility of US imaging in TLF assessment. Materials and Methods: The search was done on PubMed and Web of Science database from inception to April 2024. Furthermore, the references of included papers were thoroughly checked to find eligible publications. The MeSH keywords used were: "Thoracolumbar fascia", "Ultrasound Imaging", "Ultrasound", "Ultrasonography", and "Ultrasound examination". Results: Studies were aimed primarily at TLF diagnosis, treatment monitoring, or evaluating movement-related changes, underscoring the diverse clinical applications. The US parameters assessed included TLF thickness, echogenicity, stiffness, deformation, shear strain, and displacement, providing comprehensive insights into TLF features. Conclusions: Advanced US imaging holds promise as a reliable tool in musculoskeletal assessment, offering insights into TLF pathology/disfunction, treatment outcomes, and movement dynamics.

Hearing and Seeing Nerve/Tendon Snapping: A Systematic Review on Dynamic Ultrasound Examination.

Nerve/tendon snapping can occur due to their sudden displacement during the movement of an adjacent joint, and the clinical condition can really be painful. It can actually be challenging to determine the specific anatomic structure causing the snapping in various body regions. In this sense, ultrasound examination, with all its advantages (especially providing dynamic imaging), appears to be quite promising. To date, there are no comprehensive reviews reporting on the use of dynamic ultrasound examination in the diagnosis of nerve/tendon snapping. Accordingly, this article aims to provide a substantial discussion as to how US examination would contribute to 'seeing' and 'hearing' these pathologies' different maneuvers/movements.

Reference centers for tissue and body donations: Compulsory requirements in Italy.

Recent Italian legislation (Law No. 10/2020) establishes the legal, ethical and technical requirements governing how individuals can donate their bodies or tissues post-mortem for study, training, and scientific research purposes. A ministerial working group has recently approved some of the law's implementing rules relating to technical issues. The rules for implementing the new legislation, retrieved from the legal databases and translated into English, are discussed. For the first time in Italy, the law establishes compulsory requirements and minimum characteristics-in terms of logistics, safety, availability of staff, space, and equipment-for institutions to be recognized as reference centers for the conservation and use of bodies and tissues donated post-mortem for study, training and scientific research purposes. This makes it possible to standardize the features of such reference centers nationwide, and to coordinate their activities and potential future development, while ensuring basic operational efficiency and workplace safety, the provision of adequate facilities, buildings and equipment, and staff training. The law and its implementing rules discussed here are the first to establish criteria and compulsory requirements for centers receiving body and tissue donations in Italy. This is a step forward for the whole anatomy community, providing practical guidelines for body donation programs and related facilities in other countries too.

What's old is new again: The anatomical studies of Franklin P. Mall and the fascial-interstitial spaces.

Franklin Mall was one of the foremost scientists of the turn of the 19th century, an exemplary mentor as well as researcher, and his revolutionary contributions are still relevant today. Mall's early training in Leipzig with Wilhelm His and Carl Ludwig provided him with an unusual perspective on the integration of anatomy and physiology, and his interest in the links between structure and function guided the work he carried out after joining the faculty of the new Johns Hopkins University School of Medicine. Mall carried out innovative studies on the one hand using dye injection to trace blood and lymphatic supplies to different organs and on the other hand using "putrefaction" to digest tissues and study the organization of the reticular space, demonstrating that it was the underlying source of support for all the organs. These two studies of Mall's, carried out independently, provide the basis for modern studies integrating the understanding of fascia and interstitial spaces.

Blood supply to the superficial fascia of the abdomen: An anatomical study.

The aim of this study was to examine data demonstrating that Scarpa's fascia, a superficial fascia of the anterior abdominal wall, is a vascularized tissue. Specimens of the fascia of seven volunteers undergoing abdominoplasty surgical procedures at the Plastic Surgery Unit of the University of Padova Medical Center were collected. Fractal analysis and quantitative assessment of the vascular network of the fascia was carried out, exploiting the presence of blood in the vessels. Each sample was divided and processed for histological/immunohistochemical analysis (into 5 micron-paraffin embedded sections and cryo-sectioned free-floating samples) as well as for electron microscopy study. A rich vascular pattern forming a fine, dense meshwork with an area percentage of 6.20% ± 2.10% von Willebrand factor stained vessels was noted in all the specimens of the fascia examined; the area percentage of the αSMA-stained vessels was 2.93% ± 1.80%. The diameters of the vessels fell between the 13 and 65 µm range; the network was composed of arteries, veins, capillaries and lymphatic segments. Topological results showed that the vascular network within Scarpa's fascia is well branched (segments: 6615 ± 3070 and 8.40 ± 3.40 per mm2 ; crossing points: 3092 ± 1490 and 3.40 ± 1.90 per mm2 ). Fractal analysis (fractal dimension = 1.063 ± 0.10; lacunarity = 0.60 ± 0.10) revealed that this particular vascular network has an optimal spatial distribution and homogeneity occupying the entire space of the superficial fascia. These findings could undoubtedly be useful to plastic surgeons as well as to pain management specialists.

From Muscle to the Myofascial Unit: Current Evidence and Future Perspectives.

The "motor unit" or the "muscle" has long been considered the quantal element in the control of movement. However, in recent years new research has proved the strong interaction between muscle fibers and intramuscular connective tissue, and between muscles and fasciae, suggesting that the muscles can no longer be considered the only elements that organize movement. In addition, innervation and vascularization of muscle is strongly connected with intramuscular connective tissue. This awareness induced Luigi Stecco, in 2002, to create a new term, the "myofascial unit", to describe the bilateral dependent relationship, both anatomical and functional, that occurs between fascia, muscle and accessory elements. The aim of this narrative review is to understand the scientific support for this new term, and whether it is actually correct to consider the myofascial unit the physiological basic element for peripheral motor control.

Detection of Mast Cells in Human Superficial Fascia.

The recent findings showed that the superficial fascia is a fibrous layer in the middle of hypodermis, richly innervated and vascularized, and more complex than so far demonstrated. This study showed the presence of mast cells in the superficial fascia of the human abdomen wall of three adult volunteer patients (mean age 42 ± 4 years; 2 females, 1 male), by Toluidine Blue and Safranin-O stains and Transmission Electron Microscopy. Mast cells are distributed among the collagen bundles and the elastic fibers, near the vessels and close to the nerves supplying the tissue, with an average density of 20.4 ± 9.4/mm2. The demonstration of the presence of mast cells in the human superficial fascia highlights the possible involvement of the tissue in the inflammatory process, and in tissue healing and regeneration processes. A clear knowledge of this anatomical structure of the hypodermis is fundamental for a good comprehension of some fascial dysfunctions and for a better-targeted clinical practice.

A New Player in the Mechanobiology of Deep Fascia: Yes-Associated Protein (YAP).

Recent studies have demonstrated that fascial fibroblasts are susceptible to mechanical stimuli, leading to the remodeling of the extracellular matrix (ECM). Moreover, the extensive literature on Yes-associated protein (YAP) has shown its role in cell mechanics, linking cell properties, such as shape, adhesion, and size, to the expression of specific genes. The aim of this study was to investigate the presence of YAP in deep fascia and its activation after a mechanical stimulus was induced via a focal extracorporeal shockwave (fESW) treatment. Thoracolumbar fascia (TLF) samples were collected from eight patients (age: 30-70 years; four males and four females) who had undergone spine elective surgical procedures at the Orthopedic Clinic of University of Padova. YAP was measured in both tissue and TLF-derived fibroblasts through immunoblotting. COL1A1 and HABP2 gene expression were also evaluated in fibroblasts 2, 24, and 48 h after the fESW treatment. YAP was expressed in all the examined tissues. The ratio between the active/inactive forms (YAP/p-YAP) of the protein significantly increased in fascial fibroblasts after mechanical stimulation compared to untreated cells (p = 0.0022). Furthermore, COL1A1 and HABP2 gene expression levels were increased upon treatment. These findings demonstrate that YAP is expressed in the deep fascia of the thoracolumbar region, suggesting its involvement in fascial mechanotransduction processes, remodeling, regeneration, and fibrogenesis. This study indicates, for the first time, that YAP is a "new player" in the mechanobiology of deep fascia.

The transversoclasiotome: a novel instrument for examining the vertebral artery.

Opening the foramen transversarium of the cervical vertebrae is necessary for accessing the vertebral vessels. There are no specialist tools for cutting the anterior lamina of the transverse processes, and alternatives lead to questionable results. A novel tool, the transversoclasiotome, is described and tested. The literature and patent databases were systematically reviewed. A blueprint of the transversoclasiotome was created, and the prototype was tested through autopsy on ten fresh-frozen cadavers within our Body Donation Program. The transversoclasiotome consists of two delicate branches mounted as a scissor, one a cutting jaw and the other a knocker with a rounded tip, both angled 30° to the principal axis. The jaws shut, facing each other in parallel. The cutting jaw corresponds to a slit on the knocker profile without protruding beyond it even when entirely closed. It acts by cutting and wedging. The testing autopsies demonstrated its suitability for its purpose, with an adequate response to the pressure exerted on the bone lamina. The section cut cleanly, without sliding off while closing on the bone. The vertebral vessels were not injured either during instrument insertion or cutting. Their morphological features are described. The transversoclasiotome has been proven appropriate for sectioning the anterior lamina of transverse processes of the cervical vertebrae. It meets the needs of clinical anatomy in teaching and training clinicians or surgeons, forensic clinical anatomy during medico-legal investigation, and research.

Distinct displacement of the superficial and deep fascial layers of the iliotibial band during a weight shift task in runners: An exploratory study.

Motion of the fascial layers of the iliotibial band (ITB), as a reinforcement of the deep fascia lata, is likely to be relevant for its function and mechanical behaviour. This exploratory study aimed to evaluate the ITB fascial layers displacement during a weight shift task. Thirteen pain-free runners performed a 6-second standing weight shift task. B-mode ultrasound imaging using an automated fascicle tracking algorithm was used to measure proximal and distal displacement of superficial and deep ITB layers at the middle region. To study the potential contributors to individual variation of fascial motion, we recorded the activity of five hip/thigh muscles with electromyography (EMG), thigh/pelvis/trunk position with accelerometers, and centre of pressure with a force plate. Linear regressions estimated the relationship between displacement of fascial layers and hip/trunk angles. Independent t-tests or Fisher's exact tests compared EMG and movement-related parameters between participants who demonstrated motion of the fascia in the proximal and distal directions. Thickness of the ITB and the loose connective tissue between its layers were calculated. Proximal displacement was observed in six (-4.1 ± 1.9 mm [superficial]) and two (-6.2 ± 2.0 mm [deep]) participants. Distal displacement was observed for seven participants for each layer (3.1 ± 1.1 mm [superficial]; 3.6 ± 1.3 mm [deep]). Four participants did not show displacement of the deep layer. Trunk lateral flexion and gluteus medius muscle activity were determinants of proximal motion of the superficial layer. Loose connective tissue was thinner in participants without displacement of the deep layer. Displacement of the ITB fascial layers varies between individuals. Variation related to differences in joint movements and muscle activity. This study highlights the complex interaction between fascia and movement.

Elastic Fibres in the subcutaneous tissue: Is there a difference between superficial and muscular fascia? A cadaver study.

BACKGROUND: In last years the role of fascia in proprioception and pain has been confirmed in numerous papers, but the real structure of fasciae is not still entirely known. To date, many studies have evaluated the elastic fibres in arteries, ligaments, lungs, epidermis and dermis, but only two studies exist about the elastic fibres in the fasciae, and they did not distinguish between superficial (in the subcutaneous tissue) and deep/muscular fasciae. The aim of the study was to assess the percentage of elastic fibres between superficial and deep fascia. MATERIALS AND METHODS: Three full thickness specimens (proximal, middle and distal respectively) were taken from each of four regions of the thigh of three non-embalmed cadavers: the anterior (Ant), the lateral (Lat), the posterior (Post) and the medial (Med) aspect. Thus, a total of 12 specimens were collected from each analysed thigh and histological Weigert Van Gieson stains was performed. Three sections per specimen were considered for the morphometric analysis. RESULTS: In all the specimens the superficial and deep fasciae were clearly recognizable. The difference in percentage of elastic fibres between superficial and deep fasciae in same region for all four was highly significant (p < 0.001). They are abundant in the superficial fascia than deep fascia. CONCLUSIONS: In the light of these findings is evident that the superficial (in the subcutaneous tissue) and deep fasciae have different elasticity. This difference may improve grading of fascial dysfunction in dermatological diseases as burns, scars and lymphedema to better plan treatments.

Muscle spindles of the multifidus muscle undergo structural change after intervertebral disc degeneration.

PURPOSE: Proprioceptive deficits are common in low back pain. The multifidus muscle undergoes substantial structural change after back injury, but whether muscle spindles are affected is unclear. This study investigated whether muscle spindles of the multifidus muscle are changed by intervertebral disc (IVD) degeneration in a large animal model. METHODS: IVD degeneration was induced by partial thickness annulus fibrosus lesion to the L3-4 IVD in nine sheep. Multifidus muscle tissue at L4 was harvested at six months after lesion, and from six age-/sex-matched naïve control animals. Muscle spindles were identified in Van Gieson's-stained sections by morphology. The number, location and cross-sectional area (CSA) of spindles, the number, type and CSA of intrafusal fibers, and thickness of the spindle capsule were measured. Immunofluorescence assays examined Collagen I and III expression. RESULTS: Multifidus muscle spindles were located centrally in the muscle and generally near connective tissue. There were no differences in the number or location of muscle spindles after IVD degeneration and only changes in the CSA of nuclear chain fibers. The thickness of connective tissue surrounding the muscle spindle was increased as was the expression of Collagen I and III. CONCLUSION: Changes to the connective tissue and collagen expression of the muscle spindle capsule are likely to impact their mechanical properties. Changes in capsule stiffness may impact the transmission of length change to muscle spindles and thus transduction of sensory information. This change in muscle spindle structure may explain some of the proprioceptive deficits identified with low back pain.

Fascial Innervation: A Systematic Review of the Literature.

Currently, myofascial pain has become one of the main problems in healthcare systems. Research into its causes and the structures related to it may help to improve its management. Until some years ago, all the studies were focused on muscle alterations, as trigger points, but recently, fasciae are starting to be considered a new, possible source of pain. This systematic review has been conducted for the purpose of analyze the current evidence of the muscular/deep fasciae innervation from a histological and/or immunohistochemical point of view. A literature search published between 2000 and 2021 was made in PubMed and Google Scholar. Search terms included a combination of fascia, innervation, immunohistochemical, and different immunohistochemical markers. Of the 23 total studies included in the review, five studies were performed in rats, four in mice, two in horses, ten in humans, and two in both humans and rats. There were a great variety of immunohistochemical markers used to detect the innervation of the fasciae; the most used were Protein Gene Marker 9.5 (used in twelve studies), Calcitonin Gene-Related Peptide (ten studies), S100 (ten studies), substance P (seven studies), and tyrosine hydroxylase (six studies). Various areas have been studied, with the thoracolumbar fascia being the most observed. Besides, the papers highlighted diversity in the density and type of innervation in the various fasciae, going from free nerve endings to Pacini and Ruffini corpuscles. Finally, it has been observed that the innervation is increased in the pathological fasciae. From this review, it is evident that fasciae are well innerved, their innervation have a particular distribution and precise localization and is composed especially by proprioceptors and nociceptors, the latter being more numerous in pathological situations. This could contribute to a better comprehension and management of pain.

The Effects of Aging on the Intramuscular Connective Tissue.

The intramuscular connective tissue plays a critical role in maintaining the structural integrity of the muscle and in providing mechanical support. The current study investigates age-related changes that may contribute to passive stiffness and functional impairment of skeletal muscles. Variations in the extracellular matrix in human quadriceps femoris muscles in 10 young men, 12 elderly males and 16 elderly females, and in the hindlimb muscles of 6 week old, 8 month old and 2 year old C57BL/6J male mice, were evaluated. Picrosirius red, Alcian blue and Weigert Van Gieson stainings were performed to evaluate collagen, glycosamynoglycans and elastic fibers. Immunohistochemistry analyses were carried out to assess collagen I, collagen III and hyaluronan. The percentage area of collagen was significantly higher with aging (p < 0.01 in humans, p < 0.001 in mice), mainly due to an increase in collagen I, with no differences in collagen III (p > 0.05). The percentage area of elastic fibers in the perimysium was significantly lower (p < 0.01) in elderly men, together with a significant decrease in hyaluronan content both in humans and in mice. No significant differences were detected according to gender. The accumulation of collagen I and the lower levels of hyaluronan and elastic fibers with aging could cause a stiffening of the muscles and a reduction of their adaptability.