Non-Muscular Structures Can Limit the Maximal Joint Range of Motion during Stretching

Do the fasciae of the soleus have a role in plantar fasciitis?

Plantar fasciitis is a chronic, self-limiting, and painful disabling condition affecting the inferomedial aspect of the heel, usually extending toward the metatarsophalangeal joints. There is compelling evidence for a strong correlation between Achilles tendon (AT) loading and plantar aponeurosis (PA) tension. In line with this, tightness of the AT is found in almost 80% of patients affected by plantar fasciitis. A positive correlation has also been reported between gastrocnemius-soleus tightness and heel pain severity in this condition. Despite its high prevalence, the exact etiology and pathological mechanisms underlying plantar heel pain remain unclear. Therefore, the aim of the present paper is to discuss the anatomical and biomechanical substrates of plantar fasciitis with special emphasis on the emerging, though largely neglected, fascial system. In particular, the relationship between the fascia, triceps surae muscle, AT, and PA will be analyzed. We then proceed to discuss how structural and biomechanical alterations of the muscle-tendon-fascia complex due to muscle overuse or injury can create the conditions for the onset of PA pathology. A deeper knowledge of the possible molecular mechanisms underpinning changes in the mechanical properties of the fascial system in response to altered loading and/or muscle contraction could help healthcare professionals and clinicians refine nonoperative treatment strategies and rehabilitation protocols for plantar fasciitis.

Acute effect of static stretching on non-muscular tissue stiffness and joint flexibility: a comparative study between older and young men

PURPOSE

Non-muscular tissue stiffness is assumed to have a negative impact on joint flexibility, and a reduction in non-muscular tissue stiffness may be important, especially in older adults. The present study aimed to compare the acute effects of static stretching on non-muscular tissue stiffness between older and young adults and to investigate whether a decrease in tissue stiffness improves joint flexibility.

METHODS

Twenty older (62-83 years) and 20 young (21-24 years) males participated. Ankle dorsiflexion static stretching (five sets of 90 s each) was performed, and before and after stretching, the ankle dorsiflexion range of motion (RoM), passive ankle joint stiffness, and shear wave speed (SWS) (an index of stiffness) of the sciatic nerve, tibial nerve, and posterior thigh fascia were measured.

RESULTS

Stretching led to an increase in RoM and a decrease in passive joint stiffness in both groups (P < 0.001) with no significant between-group differences (P ≥ 0.055). The between-group difference in the effect of stretching on SWS was evident only for the sciatic nerve, and a decline in sciatic nerve SWS was only observed in the older adult group (pre-stretching: 2.5 ± 0.3 m/s; post-stretching: 2.3 ± 0.4 m/s; P = 0.027). A significant positive repeated-measures correlation was observed between the sciatic nerve SWS and passive joint stiffness (P = 0.014, rrm = 0.540).

CONCLUSION

The reduction in sciatic nerve stiffness by stretching was noticeable in older men and led to improved joint flexibility. These findings may provide insight into tissue adaptation by stretching and may be used to explore effective exercises for improving joint flexibility in older adults.

Sustained versus repetitive standing trunk extension results in greater spinal growth and pain improvement in back pain:A randomized clinical trial

BACKGROUND

McKenzie standing trunk extension exercises have been used for the management of low back pain (LBP). However, no study to date has investigated the effect of standing trunk extension postures on spinal height and clinical outcomes.

OBJECTIVE

To evaluate in subjects with LBP following a period of trunk loading how spinal height, pain, symptoms' centralization and function outcome measures respond to two standing postures interventions: (1) repetitive trunk extension (RTE) and (2) sustained trunk extension (STE).

METHODS

A consecutive sample of convenience of people with LBP were recruited to participate in 2-session physical therapy using either RTE or STE in standing.

RESULTS

Thirty participants (18 women) with a mean age of 53 ± 17.5 years completed the study. The first session resulted in spinal height increase (spinal growth) of 2.07 ± 1.32 mm for the RTE intervention and 4.54 ± 1.61 mm for the STE group (p< 0.001; ES = 1.67), while the second session (2-week following the first session) resulted in spinal growth of 2.39 ± 1.46 mm for the RTE group and 3.91 ± 2.06 mm for the STE group (p= 0.027; ES = 0.85). The STE group presented with the larger reduction in most pain from 6 to 2 as compared to the RTE group from 6 to 4 between Session 1 and Session 2 (p< 0.001). There was no difference between the groups in Modified Oswestry score and symptoms centralization (p= 0.88 and p= 0.77, respectively).

CONCLUSION

People with LBP experienced greater spine growth and improvements of pain during standing STE as compared to RTE. People with LBP could use such postures and movements to alleviate their LBP and improve spine height while in a weight bearing position.

Acute Effects of Stretching Exercises on Posterior Chain: Analysis of Shear Modulus by Elastography SSI

The posterior chain muscles of the lower limb include the hamstrings and triceps surae, along with the Achilles tendon. This study aimed to investigate the acute effects of static stretching exercises commonly used in clinical and training settings on the shear modulus (µ) of these muscles and tendon using Supersonic Shear-Wave Imaging (SSI) elastography. Fifteen healthy adults participated in the study, performing stretching exercises for hamstrings and triceps surae. Shear modulus and joint range of motion (ROM) were measured before and after the stretching protocols. The hip and ankle mean ROM significantly increased by 19.27% and 24.10%, respectively. However, the stretching protocol did not significantly alter in µ of the hamstrings, the gastrocnemius muscles, and the Achilles tendon. K-means clustering analysis identified a group where the subjects with lower initial ROM showed higher amplitude gains and a significant decrease in the semimembranosus stiffness after stretching. These findings suggest that the stretching protocol was effective in improving joint mobility but not sufficient to elicit immediate mechanical changes in muscle and tendon stiffness. Neural adaptations and nonmuscular structures might contribute to increased ROM. The study highlights the importance of considering individual initial ROM and subsequent responses when evaluating the effects of stretching exercises on muscle and tendon properties.

Response to Mechanical Properties and Physiological Challenges of Fascia: Diagnosis and Rehabilitative Therapeutic Intervention for Myofascial System Disorders

Damage to the fascia can cause significant performance deficits in high-performance sports and recreational exercise and may contribute to the development of musculoskeletal disorders and persistent potential pain. The fascia is widely distributed from head to toe, encompassing muscles, bones, blood vessels, nerves, and internal organs and comprising various layers of different depths, indicating the complexity of its pathogenesis. It is a connective tissue composed of irregularly arranged collagen fibers, distinctly different from the regularly arranged collagen fibers found in tendons, ligaments, or periosteum, and mechanical changes in the fascia (stiffness or tension) can produce changes in its connective tissue that can cause pain. While these mechanical changes induce inflammation associated with mechanical loading, they are also affected by biochemical influences such as aging, sex hormones, and obesity. Therefore, this paper will review the current state of knowledge on the molecular level response to the mechanical properties of the fascia and its response to other physiological challenges, including mechanical changes, innervation, injury, and aging; imaging techniques available to study the fascial system; and therapeutic interventions targeting fascial tissue in sports medicine. This article aims to summarize contemporary views.

Suggesting a mechanism for acupuncture as a global percutaneous needle fasciotomy that respects tensegrity principles for treating fibromyalgia

Acupuncture is a minimally invasive therapeutic method that uses small caliber needles while inserting them through the skin into various areas of the body. Some empirical studies find evidence to support the use of acupuncture as a treatment for certain medical conditions, however, this peculiar practice is widely considered as the domain of alternative and non-evidence-based medicine. Several mechanisms have been suggested in an attempt to explain the therapeutic action of acupuncture, but the way in which acupuncture alleviates chronic non-cancer pain or psychosomatic and psychiatric disorders is not fully understood. A recent study suggested a theoretical model (coined "Fascial Armoring") with a cellular pathway to help explain the pathogenesis of myofascial pain/fibromyalgia syndrome and functional psychosomatic syndromes. It proposes that these syndromes are a spectrum of a single medical entity that involves myofibroblasts with contractile activity in fascia and aberrant extracellular matrix (ECM) remodeling, which may lead to widespread mechanical tension and compression. This can help explain diverse psycho-somatic manifestations of fibromyalgia-like syndromes. Fascia is a continuous interconnected tissue network that extends throughout the body and has qualities of bio-tensegrity. Previous studies show that a mechanical action by needling induces soft tissue changes and lowers the shear modulus and stiffness in myofascial tissue. This hypothesis and theory paper offers a new mechanism for acupuncture therapy as a global percutaneous needle fasciotomy that respects tensegrity principles (tensegrity-based needling), in light of the theoretical model of "Fascial Armoring." The translation of this model to other medical conditions carries potential to advance therapies. These days opioid overuse and over-prescription are ubiquitous, as well as chronic pain and suffering.

Mechanical Linkage between Achilles Tendon and Plantar Fascia Accounts for Range of Motion of Human Ankle-Foot Complex

PURPOSE

The human ankle-foot complex possesses a passive range of motion (ROM) through changes in tibiocalcaneal ( θcal ) and foot arch ( θarch ) angles. Based on the anatomical linkage between the Achilles tendon (AT) and plantar fascia (PF), we hypothesized that AT and PF with different mechanical properties conjointly modulate the passive ROM of the human ankle-foot complex. We examined the association of AT and PF stiffness with passive ankle-foot ROM and further addressed differences between sexes.

METHODS

A series of sagittal magnetic resonance images of the foot and passive ankle plantar flexion torque were obtained for 20 men and 20 women with their ankle-foot passively rotated from 30° of plantar flexion to 20° of dorsiflexion. Based on the measured changes in AT and PF lengths, θcal , θarch , and passive torque, AT and PF stiffness were determined.

RESULTS

Upon passive ankle dorsiflexion, AT and PF were lengthened; their length changes were inversely correlated. Men showed a stiffer AT, more compliant PF, less calcaneal rotation, and greater foot arch deformation compared with women. Furthermore, we found inverse correlations between AT stiffness and ROM of θcal , and between PF stiffness and ROM of θarch in men and women.

CONCLUSIONS

Passive AT and PF extensibility counter each other. AT and PF stiffness and passive ROM of ankle-foot components were countered between sexes; however, associations between stiffness and passive ROM of the ankle-foot complex were consistent between sexes. Our findings support the notion that the balanced mechanical interaction between the AT and PF can account for the passive ROM of the human ankle-foot complex in vivo , and the differences between sexes.

Scoping review and interpretation of myofascial pain/fibromyalgia syndrome: An attempt to assemble a medical puzzle

BACKGROUND

Myofascial Pain Syndrome (MPS) is a common, overlooked, and underdiagnosed condition and has significant burden. MPS is often dismissed by clinicians while patients remain in pain for years. MPS can evolve into fibromyalgia, however, effective treatments for both are lacking due to absence of a clear mechanism. Many studies focus on central sensitization. Therefore, the purpose of this scoping review is to systematically search cross-disciplinary empirical studies of MPS, focusing on mechanical aspects, and suggest an organic mechanism explaining how it might evolve into fibromyalgia. Hopefully, it will advance our understanding of this disease.

METHODS

Systematically searched multiple phrases in MEDLINE, EMBASE, COCHRANE, PEDro, and medRxiv, majority with no time limit. Inclusion/exclusion based on title and abstract, then full text inspection. Additional literature added on relevant side topics. Review follows PRISMA-ScR guidelines. PROSPERO yet to adapt registration for scoping reviews.

FINDINGS

799 records included. Fascia can adapt to various states by reversibly changing biomechanical and physical properties. Trigger points, tension, and pain are a hallmark of MPS. Myofibroblasts play a role in sustained myofascial tension. Tension can propagate in fascia, possibly supporting a tensegrity framework. Movement and mechanical interventions treat and prevent MPS, while living sedentarily predisposes to MPS and recurrence.

CONCLUSIONS

MPS can be seen as a pathological state of imbalance in a natural process; manifesting from the inherent properties of the fascia, triggered by a disrupted biomechanical interplay. MPS might evolve into fibromyalgia through deranged myofibroblasts in connective tissue ("fascial armoring"). Movement is an underemployed requisite in modern lifestyle. Lifestyle is linked to pain and suffering. The mechanism of needling is suggested to be more mechanical than currently thought. A "global percutaneous needle fasciotomy" that respects tensegrity principles may treat MPS/fibromyalgia more effectively. "Functional-somatic syndromes" can be seen as one entity (myofibroblast-generated-tensegrity-tension), sharing a common rheuma-psycho-neurological mechanism.

Modulation in the Stiffness of Specific Muscles of the Quadriceps in Patients With Knee Osteoarthritis and Their Relationship With Functional Ability

Deficits in the flexibility of the quadriceps are one of the risk factors for developing knee joint disorders. No studies have investigated the changes in the stiffness of the quadriceps muscle among patients with knee osteoarthritis (OA). Therefore, the purpose of this study was to investigate changes in the stiffness of specific-muscle of the quadriceps in patients with knee OA and their relationship with functional ability. Twenty-five patients with knee OA and 25 healthy, asymptomatic subjects were recruited in this study. The stiffness of the vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) in all participants was evaluated using MyotonPRO at 60° and 90° flexion of the knee joint. The results of this study showed a greater VL stiffness in patients with knee OA than in healthy subjects at both 60° and 90° of knee flexion (p &lt; 0.05). Significant differences in VL, VM and RF stiffness were obtained at different knee joint angles in individuals with and without knee OA (p &lt; 0.05). In addition, there was a positive correlation between VL stiffness and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores in patients with Knee OA (60° of knee flexion: r = 0.508, p = 0.010; 90° of knee flexion: r = 0.456, p = 0.022). These results indicate that there is an increase in VL stiffness in patients with knee OA compared with healthy, asymptomatic subjects, and the quadriceps stiffness was increased with knee flexion in both healthy subjects and patients with knee OA. VL stiffness is associated with WOMAC scores in patients with knee OA.

Effects of Self-Myofascial Release Using a Foam Roller on the Stiffness of the Gastrocnemius-Achilles Tendon Complex and Ankle Dorsiflexion Range of Motion

Increased muscle stiffness can contribute to reduced range of motion (ROM) and impaired function. Reduced ankle dorsiflexion ROM has been associated with increased injury risk in the ankle. Self-myofascial release (SMR) has been widely used in clinical and sports settings, but the effects of SMR on gastrocnemius and Achilles tendon (AT) stiffness are unclear. Therefore, we investigated the effects of self-myofascial release using a foam roller (FR) on the stiffness of the gastrocnemius–AT complex and ankle dorsiflexion ROM. Fifty healthy, untrained, and non-sedentary participants (age=22.5±2.6years) were randomly divided into an intervention group (FR group) and a control group. The subjects in the intervention group received a single foam roller intervention (three sets of 1min), while the subjects in the control group performed a 5-min sedentary rest. Stiffness of the gastrocnemius–AT complex was evaluated using MyotonPRO and the ankle dorsiflexion ROM was assessed using the weight-bearing lunge test. For the foam roller and control groups, the between-group analysis revealed a statistically significant difference in gastrocnemius stiffness and ankle dorsiflexion ROM after intervention (p<0.05). Within-group analysis revealed a significant increase in ROM and a significant decrease in medial and lateral gastrocnemius (LG) stiffness for the foam roller group after the intervention (p<0.05). In addition, further analysis of the preintervention data revealed a significant negative correlation between ankle dorsiflexion ROM and AT stiffness (r=−0.378 and p=0.007). These results suggest that self-myofascial release using a foam roller on the calf is an effective method for decreasing the stiffness of the gastrocnemius and increasing ankle dorsiflexion ROM.

Altered Triceps Surae Muscle-Tendon Unit Properties after 6 Months of Static Stretching

INTRODUCTION

This study examined the effects of 24 wk of daily static stretching of the plantarflexors (unilateral 4 × 60-s stretching, whereas the contralateral leg served as a control; n = 26) on joint range of motion (ROM), muscle-tendon unit morphological and mechanical properties, neural activation, and contractile function.

METHODS

Torque-angle/velocity was obtained in passive and active conditions using isokinetic dynamometry, whereas muscle-tendon morphology and mechanical properties were examined using ultrasonography.

RESULTS

After the intervention, ROM increased (stretching, +11° ± 7°; control, 4° ± 8°), and passive torque (stretching, -10 ± 11 N·m; control, -7 ± 10 N·m) and normalized EMG amplitude (stretching, -3% ± 6%; control, -3% ± 4%) at a standardized dorsiflexion angle decreased. Increases were seen in passive tendon elongation at a standardized force (stretching, +1.3 ± 1.6 mm; control, +1.4 ± 2.1 mm) and in maximal passive muscle and tendon elongation. Angle of peak torque shifted toward dorsiflexion. No changes were seen in tendon stiffness, resting tendon length, or gastrocnemius medialis fascicle length. Conformable changes in ROM, passive dorsiflexion variables, tendon elongation, and angle of peak torque were observed in the nonstretched leg.

CONCLUSIONS

The present findings indicate that habitual stretching increases ROM and decreases passive torque, altering muscle-tendon behavior with the potential to modify contractile function.

Muscle Architectural and Functional Adaptations Following 12-Weeks of Stretching in Adolescent Female Athletes

This study examined the effects of high-volume static stretching training on gastrocnemius muscle architecture, ankle angle and jump height in 21 female adolescent volleyball players. Static stretching of the plantar flexors of one leg (STR) was performed five times/week for 12 weeks, in addition to volleyball training, with the contra-lateral leg used as control (CON). Total duration of stretching per session increased from 540 s (week 1) to 900 s (week 12). At baseline, week 12 and after 3 weeks of detraining, muscle architecture at the middle and the distal part of both gastrocnemius heads (medialis and lateralis) and ankle angle were examined at rest and at maximum dorsiflexion. At the same time-points gastrocnemius cross-sectional area (CSA) was also assessed, while jumping height was measured at baseline and week 12. Following intervention, ankle dorsiflexion increased in both legs with a greater increase in STR than CON (22 ± 20% vs. 8 ± 17%, p < 0.001). Fascicle length at the middle part of gastrocnemius medialis increased only in the STR, at rest (6 ± 7%, p = 0.006) and at maximum dorsiflexion (11 ± 7%, p < 0.001). Fascicle length at maximum dorsiflexion also increased at the distal part of gastrocnemius lateralis of STR (15 ± 13%, p < 0.001). A greater increase in CSA (23 ± 14% vs. 13 ± 14%, p < 0.001) and in one-leg jumping height (27 ± 30% vs. 17 ± 23%, p < 0.001) was found in STR than CON. Changes in ankle angle, fascicle length and CSA were maintained following detraining. High-volume stretching training for 12 weeks results in ankle dorsiflexion, fascicle length and muscle cross sectional area increases in adolescent female volleyball players. These adaptations may partly explain improvements in jump performance.

Effects of Warm-up on Hamstring Stiffness, Stress-Relaxation, Flexibility and Knee Proprioception in Young Soccer Players

CONTEXT

Nerves or fascia may limit motion in young soccer players, thereby contributing to frequent hamstring injuries. Nerve gliding exercises and self-myofascial release techniques may enhance the range of motion.

OBJECTIVE

The aim of this study was to compare the acute effect of foam rolling (FR) and neurodynamic nerve gliding (NDNG) on hamstring flexibility, passive stiffness, viscoelasticity and proprioception during the warm-up of soccer players.

DESIGN

Crossover study design.

SETTING

Research laboratory.

PARTICIPANTS

Fifteen male soccer players on the same team (age 18.0 ± 1.4 years, body mass 76.9 ± 7.8 kg, height 183 ± 6 cm).

INTERVENTION

FR and NDNG included six sets of 45 s with 15 s rest between each set. Over a two-week period subjects performed NDNG and FR on two separate occasions.

MAIN OUTCOME MEASURE(S)

Hip flexion angle (SLR), knee extension range of motion (ROM), knee joint position sense (AKJPS), hamstring passive resistance torque (PRT), stiffness (STFmax and STF80%) and viscoelasticity (stress-relaxation test (SRT)).

RESULTS

A significant interaction between time and intervention was found for knee ROM (p = 0.017), PRT (p = 0.044), and STFmax (p = 0.042). NDNG induced an increase in ROM (p = 0.011), PRT (p = 0.008), and STFmax (p = 0.030). Both NDNG and FR induced an increase in SLR (p < 0.001). No interaction or main effects was found for SRT and AKJPS.

CONCLUSION

The inclusion of NDNG in the warm-up routine increased the ROM more in comparison with FR and may be of benefit to soccer players.

Associations between Range of Motion and Tissue Stiffness in Young and Older People

Supplemental digital content is available in the text.

Purpose

The purpose of this study was to investigate differences in the associations between passive ankle dorsiflexion range of motion (ROM) and stiffness of the triceps surae, sciatic nerve, and deep fascia located in the posterior leg between young and older people.

Methods

Twenty young and twenty older males were recruited and were placed in a prone position with their hip and knee fully extended. Passive ankle dorsiflexion ROM was determined based on the onset of pain during passive dorsiflexion at 1°·s⁻¹ using an isokinetic dynamometer. Shear wave speeds (as a stiffness index) of the triceps surae, the sciatic nerve, and the deep fascia in the posterior leg were evaluated by ultrasound shear wave elastography.

Results

The shear wave speeds of the medial and lateral gastrocnemius measured at 15° dorsiflexion correlated negatively with passive ROM in young but not in older participants. The shear wave speed of the sciatic nerve measured at 15° dorsiflexion correlated negatively with passive ROM only in older participants. No association was observed between passive ROM and shear wave speed of the deep fascia in the posterior leg. For data measured at maximal dorsiflexion angle (as an index of stretch tolerance), shear wave speeds of the triceps surae and passive joint torque correlated positively with passive ROM in both groups.

Conclusion

These results suggest that the tissues limiting passive ankle dorsiflexion ROM are muscle and nerve for young and older people, respectively, whereas stretch tolerance influences passive ROM for both groups. This implies that the relative contribution of nonmuscular tissues to joint flexibility become stronger than that of muscles with age.

Peripheral Nerve Responses to Muscle Stretching: A Systematic Review

Stretching is commonly used to increase range of motion and flexibility. Therefore, investigations are usually oriented towards the muscle-tendon unit. Limited evidence exists regarding potential effects of stretching on peripheral nerves which lie within muscles. The objective of this investigation will be to elucidate the responses of peripheral nerves to stretching. A literature search was performed using the following databases: Scopus, NLM Pubmed and ScienceDirect. Studies regarding the effects of stretching protocols on responses of peripheral nerves were retrieved for investigation. The NHLBI tool was used for quality assessment. Outcomes included nerve stiffness, nerve displacement, pain pressure thresholds and resistive torque. A total of 10 studies were considered eligible and were included in this investigation. The quality assessment of the studies revealed an overall "fair to good" methodological quality across the included studies. All studies except for one involved healthy participants. High heterogeneity of stretching protocols was retrieved. As a consequence of stretching, nerve stiffness (-15.6%) and pain pressure thresholds (-1.9kg) increased. Nerve displacements on each movement plane for all the considered nerves and nerve deformation were also frequently observed. Peripheral nerve responses to muscle stretching include decreased nerve stiffness and increased pain pressure thresholds. Nerve displacement also frequently occurs. It is still unclear if reduced nerve displacement may lead to clinical outcomes. There is a lack of longitudinal studies regarding peripheral nerve adaptations to stretching.

Ultrasound Imaging of Crural Fascia and Epimysial Fascia Thicknesses in Basketball Players with Previous Ankle Sprains Versus Healthy Subjects

Background: Fascial layers may play an important role in locomotor mechanics. Recent researches have revealed an association between increases of fascia thickness and reduced joint flexibility in patients with chronic pain. The purpose of this study was to measure and compare, through the use of ultrasound imaging, the thickness of the deep/crural fascia in different points of the leg as well as the epimysial fascia thickness at level 2 of anterior compartment of leg, in male basketball players with history of recurrent ankle sprain and in healthy participants. Methods: A cross-sectional study has been performed using ultrasound imaging to measure deep/crural fascia thickness of anterior, lateral and posterior compartment of the leg at different levels with a new protocol in a sample of 30 subjects, 15 basketball players and 15 healthy participants. Results: Findings of fascial thickness revealed statistically significant differences (p < 0.01) in epimysial fascia thickness and in deep/crural fascia thickness between levels/compartments of the same group and between two groups. Moreover, Post 3 deep/crural fascia thicknesses (p < 0.001) were decreased showing statistically significant difference for the basketball players group respect the healthy participants group. Conclusions: These findings suggested that the posterior compartment was thicker than anterior compartment, probably due to a postural reason in both groups. Moreover, they showed an increase of thickness of the epimysial fascia in basketball players with previous ankle sprains. This variability underlines the importance to assess the fasciae and to make results comparable.

Fascial or Muscle Stretching? A Narrative Review

Stretching exercises are integral part of the rehabilitation and sport. Despite this, the mechanism behind its proposed effect remains ambiguous. It is assumed that flexibility increases, e.g., action on muscle and tendon, respectively, but this is not always present in the stretching protocol of the exercises used. Recently, the fasciae have increased popularity and seems that they can have a role to define the flexibility and the perception of the limitation of the maximal range of motion (ROM). Deep fascia is also considered a key element to transmit load in parallel bypassing the joints, transmitting around 30% of the force generated during a muscular contraction. So, it seems impossible dividing the action of the muscles from the fasciae, but they have to be considered as a “myofascial unit”. The purpose of this manuscript is to evaluate the mechanical behavior of muscles, tendons, and fasciae to better understand how they can interact during passive stretching. Stress-strain values of muscle, tendon and fascia demonstrate that during passive stretching, the fascia is the first tissue that limit the elongation, suggesting that fascial tissue is probably the major target of static stretching. A better understanding of myofascial force transmission, and the study of the biomechanical behavior of fasciae, with also the thixotropic effect, can help to design a correct plan of stretching.

Can Static Stretching Reduce Stiffness of the Triceps Surae in Older Men?

Purpose

The purpose of this study was to investigate reductions of muscle stiffness induced by static stretching in older and younger men.

Methods

Twenty older (62–83 yr) and 20 younger (21–24 yr) men were recruited. Ankle dorsiflexion static stretching was consisted of 90 s × 5 repetitions. Before and after the stretching, the dorsiflexion range of motion (RoM), passive plantar flexion torque, and shear modulus (an index of stiffness) of the medial (MG) and lateral gastrocnemius and the soleus were measured.

Results

RoM, passive torque, and shear modulus of the triceps surae measured at the maximal dorsiflexion angle before stretching were significantly lower for the older group than the younger group. This suggests a weak stretching intensity for older compared with younger people. The stretching significantly improved RoM for both groups. For the older group, a significant reduction in passive torque was only observed at a 15° dorsiflexion angle, and the shear modulus was significantly decreased only for the distal region of MG. For the younger group, passive torque was significantly reduced for the entire RoM, and a significant decrease in shear modulus was found for the central and distal regions of MG and lateral gastrocnemius. A significant correlation between the muscle shear modulus measured at the maximal dorsiflexion angle before stretching and a stretching-induced decrease in muscle shear modulus was observed for older and younger participants. This indicates that the higher stretching intensity can reduce more muscle stiffness.

Conclusion

Static stretching can reduce muscle stiffness regardless of age, although the stretching effect on muscle stiffness was limited for older people. This might be due to a lower stretching intensity for older than younger people.

Chronic effects of muscle and nerve-directed stretching on tissue mechanics

Tissue-directed stretching interventions can preferentially load muscular or nonmuscular structures such as peripheral nerves. How these tissues adapt mechanically to long-term stretching is poorly understood. This randomized, single-blind, controlled study used ultrasonography and dynamometry to compare the effects of 12-wk nerve-directed and muscle-directed stretching programs versus control on maximal ankle dorsiflexion range of motion (ROM) and passive torque, shear wave velocity (SWV; an index of stiffness), and architecture of triceps surae and sciatic nerve. Sixty healthy adults were randomized to receive nerve-directed stretching, muscle-directed stretching, or no intervention (control). The muscle-directed protocol was designed to primarily stretch the plantar flexor muscle group, whereas the nerve-directed intervention targeted the sciatic nerve tract. Compared with the control group [mean; 95% confidence interval (CI)], muscle-directed intervention showed increased ROM (+7.3°; 95% CI: 4.1-10.5), decreased SWV of triceps surae (varied from -0.8 to -2.3 m/s across muscles), decreased passive torque (-6.8 N·m; 95% CI: -11.9 to -1.7), and greater gastrocnemius medialis fascicle length (+0.4 cm; 95% CI: 0.1-0.8). Muscle-directed intervention did not affect the SWV and size of sciatic nerve. Participants in the nerve-directed group showed a significant increase in ROM (+9.9°; 95% CI: 6.2-13.6) and a significant decrease in sciatic nerve SWV (> -1.8 m/s across nerve regions) compared with the control group. Nerve-directed intervention had no effect on the main outcomes at muscle and joint levels. These findings provide new insights into the long-term mechanical effects of stretching interventions and have relevance to clinical conditions where change in mechanical properties has occurred.NEW & NOTEWORTHY This study demonstrates that the mechanical properties of plantar flexor muscles and sciatic nerve can adapt mechanically to long-term stretching programs. Although interventions targeting muscular or nonmuscular structures are both effective at increasing maximal range of motion, the changes in tissue mechanical properties (stiffness) are specific to the structure being preferentially stretched by each program. We provide the first in vivo evidence that stiffness of peripheral nerves adapts to long-term loading stimuli using appropriate nerve-directed stretching.

Immediate effects of neurodynamic nerve gliding versus static stretching on hamstring neuromechanical properties

PURPOSE

We investigated the immediate effects of neurodynamic nerve gliding (ND) on hamstring flexibility, viscoelasticity, and mechanosensitivity, compared with traditional static stretching (ST).

METHODS

Twenty-two physically active men aged 21.9 ± 1.9 years were divided randomly into two equal intervention groups using ST or ND. An isokinetic dynamometer was used to measure the active knee joint position sense, perform passive knee extension, record the passive extension range of motion (ROM) and the passive-resistive torque of hamstrings. Stiffness was determined from the slope of the passive torque-angle relationship. A stress relaxation test (SRT) was performed to analyze the viscoelastic behavior of the hamstrings. The passive straight leg raise (SLR) test was used to evaluate hamstring flexibility.

RESULTS

A significant interaction was observed for ROM and passive ultimate stiffness, reflected by an increase in these indicators after ND but not after SD. SLR increased significantly in both groups. After ST, a significantly faster initial stress relaxation was observed over the first 4 s. than after ND. There was no significant change in the active knee joint position sense.

CONCLUSIONS

ND provided a slightly greater increase in hamstring extensibility and passive stiffness, possibly by decreasing nerve tension and increasing strain in connective tissues than ST. The ST mostly affected the viscoelastic behavior of the hamstrings, but neither intervention had a significant impact on proprioception.

Phase angle associated with different indicators of health-related physical fitness in adults with obesity

In obese populations, the exacerbated increase in adipose tissue results in a significant reduction of health-related physical fitness and can affect the phase angle (PhA), a promising health indicator of cell health and integrity. The aim of this study was to investigate the association of PhA with health-related physical fitness indicators in obese adults. This cross-sectional study had a non-probabilistic sample and was conducted from April to June 2018. The PhA was obtained by a bioelectrical impedance analysis, and the health-related physical fitness indicators evaluated were percentage of body fat (%BF), lower- and upper-body maximal strength, cardiorespiratory fitness (relative V̇O2peak), and flexibility. Pearson and Spearman´s linear correlations, crude and adjusted linear regression analyses were performed. A total of 69 obese adults (60.8% female; BMI = 33.5 ± 2.8 kg/m²) with a mean age of 34.6 ± 7.1 years were studied. The PhA means were 5.8 (±0.6º) and had an inverse correlation with %BF (r=-0.74; p<0.001) and positive correlation with V̇O2peak (r=0.50; p<0.001), lower- and upper-body maximal strength (r=0.65; r=0.70; p<0.001, respectively). After adjustment, %BF (β=-0.065, adjusted R²=0.53; p<0.001), lower- and upper-body maximal strength (β=0.004; adjusted R²=0.46; p<0.001, and β=0.024; adjusted R²=0.50; p<0.001, respectively) were predictors of PhA. Our results suggest the favorable role of PhA as a clinically viable tool to screen and identify the physical fitness variables and functional status of obese adults.

The effects of 6 weeks of constant-angle muscle stretching training on flexibility and muscle function in men with limited hamstrings' flexibility

PURPOSE

The aim of the present study was to evaluate the effects of 6 weeks of a constant-angle hamstring muscle flexibility training on muscle-tendon stiffness and the range of motion (ROM) in young men with limited hamstring ROM.

METHODS

13 participants performed unilateral stretching training (EL), while the contralateral limb acted as control (CL). ROM, relative and peak passive torque, passive stiffness, dynamic knee flexion strength, and active optimum joint angle were assessed before and after the last training session. In addition, participants were tested during the first and last training sessions for first stretch sensation during the stretching procedure only in the EL.

RESULTS

Straight-leg raise and isokinetic knee ROM tests (both p < 0.0001; from 59.4 ± 8.1 to 70.3 ± 9.8, from 28.3 ± 7.6 to 18.5 ± 5.2, respectively) and peak passive torque (p = 0.001; from 53.1 ± 11.7 to 64.9 ± 12.3) increased only in EL and no changes in relative passive torque, passive stiffness, dynamic knee flexion strength, and active optimum joint angle (p > 0.05) were observed. At the point of first stretch sensation, significant increases in passive torque (p = 0.004) and angle (p < 0.001) were found from pre- to post-training.

CONCLUSION

The flexibility training induced significant increases in ROM alongside increases in peak passive torque (stretch tolerance) and the ROM at which stretch was first perceived. However, this occurred without changes in muscle-tendon mechanical properties or transfer to the untrained limb (CL). These results suggest that limb-specific ROM increases were underpinned by neural adaptations.

Fascia thickness, aging and flexibility: is there an association?

The morphology of the connective tissue may play an important role in locomotor mechanics. Recent research has revealed an association between increased fascia thickness and reduced joint flexibility in patients with chronic pain. The present study aimed to examine the relationship of both factors in healthy individuals, additionally testing the hypothesis that older subjects display a higher fascia thickness. Young (n = 18, 22 ± 1 years) and old (n = 17, 69 ± 4 years) healthy females were recruited for a quasi-experimental, cross-sectional trial. All participants underwent standardized ultrasound-based thickness measurements of the deep fasciae of the trunk and lower limb. Flexibility was assessed using sit and reach testing (hamstring extensibility) and the Schober test (lumbar flexion and extension). Systematic between-group differences of fascia thickness and variable associations (i.e. fascia thickness and flexibility) were detected using non-parametric data analyses. Young adults exhibited higher fascia thickness of the anterior and posterior lower leg, anterior thigh and abdominal wall (+12.3-25.8%, P < 0.05). Conversely, older participants showed higher thickness in the lumbar spine (+40.0-76.7%, P < 0.05). Correlations of both body mass and fascia thickness (τ = 0.45-0.75, P < 0.05), as well as flexibility and fascia thickness (τ = 0.38-0.42, P < 0.05) were found. Age-related changes in fascia thickness may be a contributing factor of restrictions in joint range of motion. Further study delineating the cause-effect triangle of body mass index, flexibility and fascia thickness is necessary.

The potential role of sciatic nerve stiffness in the limitation of maximal ankle range of motion

It is a long held belief that maximal joint range of motion (ROM) is restricted by muscle tension. However, it exists indirect evidence suggesting that this assumption may not hold true for some joint configurations where non-muscular structures, such as the peripheral nerves, are stretched. Direct evidences are lacking. This study aimed to determine whether a static stretching aiming to load the sciatic nerve without stretch within plantar flexors is effective to: (i) alter nerve stiffness; and (ii) increase the ankle’s maximal ROM. Passive maximal ankle ROM in dorsiflexion was assessed with the hip flexed at 90° (HIP-flexed) or neutral (HIP-neutral, 0°). Sciatic nerve stiffness was estimated using shear wave elastography. Sciatic nerve stretching induced both a 13.3 ± 7.9% (P < 0.001) decrease in the nerve stiffness and a 6.4 ± 2.6° increase in the maximal dorsiflexion ROM assessed in HIP-flexed. In addition, the decrease in sciatic nerve stiffness was significantly correlated with the change in maximal ROM in dorsiflexion (r = −0.571, P = 0.026). These effects occurred in the absence of any change in gastrocnemius medialis and biceps femoris stiffness, and ankle passive torque. These results demonstrate that maximal dorsiflexion ROM can be acutely increased by stretching the sciatic nerve, without altering the muscle stiffness.

Associations of passive muscle stiffness, muscle stretch tolerance, and muscle slack angle with range of motion: individual and sex differences

Joint range of motion (ROM) is an important parameter for athletic performance and muscular injury risk. Nonetheless, a complete description of muscular factors influencing ROM among individuals and between men and women is lacking. We examined whether passive muscle stiffness (evaluated by angle-specific muscle shear modulus), tolerance to muscle stretch (evaluated by muscle shear modulus at end-ROM), and muscle slack angle of the triceps surae are associated with the individual variability and sex difference in dorsiflexion ROM, using ultrasound shear wave elastography. For men, ROM was negatively correlated to passive muscle stiffness of the medial and lateral gastrocnemius in a tensioned state and positively to tolerance to muscle stretch in the medial gastrocnemius. For women, ROM was only positively correlated to tolerance to muscle stretch in all muscles but not correlated to passive muscle stiffness. Muscle slack angle was not correlated to ROM in men and women. Significant sex differences were observed only for dorsiflexion ROM and passive muscle stiffness in a tensioned state. These findings suggest that muscular factors associated with ROM are different between men and women. Furthermore, the sex difference in dorsiflexion ROM might be attributed partly to that in passive muscle stiffness of plantar flexors.

Can chronic stretching change the muscle-tendon mechanical properties? A review

It is recognized that stretching is an effective method to chronically increase the joint range of motion. However, the effects of stretching training on the muscle-tendon structural properties remain unclear. This systematic review with meta-analysis aimed to determine whether chronic stretching alter the muscle-tendon structural properties. Published papers regarding longitudinal stretching (static, dynamic and/or PNF) intervention (either randomized or not) in humans of any age and health status, with more than 2 weeks in duration and at least 2 sessions per week, were searched in PubMed, PEDro, ScienceDirect and ResearchGate databases. Structural or mechanical variables from joint (maximal tolerated passive torque or resistance to stretch) or muscle-tendon unit (muscle architecture, stiffness, extensibility, shear modulus, volume, thickness, cross-sectional area, and slack length) were extracted from those papers. A total of 26 studies were selected, with a duration ranging from 3 to 8 weeks, and an average total time under stretching of 1165 seconds per week. Small effects were seen for maximal tolerated passive torque, but trivial effects were seen for joint resistance to stretch, muscle architecture, muscle stiffness, and tendon stiffness. A large heterogeneity was seen for most of the variables. Stretching interventions with 3- to 8-week duration do not seem to change either the muscle or the tendon properties, although it increases the extensibility and tolerance to a greater tensile force. Adaptations to chronic stretching protocols shorter than 8 weeks seem to mostly occur at a sensory level.