Force transmission between synergistic skeletal muscles through connective tissue linkages

Knee movements cause changes in the firing behaviour of muscle spindles located within the mono-articular ankle extensor soleus in the rat

We recently showed that within an intact muscle compartment, changing the length of one muscle affects the firing behaviour of muscle spindles located within a neighbouring muscle. The conditions tested, however, involved muscle lengths and relative positions that were beyond physiological ranges. The aim of the present study was to investigate the effects of simulated knee movements on the firing behaviour of muscle spindles located within rat soleus (SO) muscle. Firing from single muscle spindle afferents in SO was measured intra-axonally for different lengths (static) and during lengthening (dynamic) of the lateral gastrocnemius and plantaris muscles. Also, the location of the spindle within the muscle was assessed. Changing the length of synergistic ankle plantar flexors (simulating different static knee positions, between 45 and 130°) affected the force threshold, but not the length threshold, of SO muscle spindles. The effects on type II afferents were substantially (four times) higher than those on type IA afferents. Triangular stretch-shortening of synergistic muscles (simulating dynamic knee joint rotations of 15°) caused sudden changes in the firing rate of SO type IA and II afferents. Lengthening decreased and shortening increased the firing rate, independent of spindle location. This supports our prediction that the major point of application of forces exerted by connections between adjacent muscles is at the distal end of SO. We conclude that muscle spindles provide the CNS with information about the condition of adjacent joints that the muscle does not span.

Acute effects of foam rolling on ankle dorsiflexion and squat exercise patterns in extreme conditioning program practitioners: A randomized clinical trial

BACKGROUND/OBJECTIVES

Joint and muscle overloads commonly occur in extreme conditioning programs (ECP), which require great physical fitness for their practice. For its execution, good functional performance, mobility and adequate movement patterns are required. The fascial system plays a fundamental role in performance in ECP and one of the techniques used to improve joint mobility and movement pattern is the self-myofascial release using a foam roller (FR). Our objective of this study was to evaluate the effect of FR in ankle dorsiflexion (DF) range of motion (ROM), assessed with the Lunge Test, and also in the squat movement pattern, assessed using the Technique smartphone application, in ECP practitioners.

METHODS

The study was carried out with 18 ECP practitioners who practiced for over four months and had a mean age of 30.94 years. The participants were randomized and allocated into two groups: control and intervention. The FR was self-applied bilaterally in the sural triceps region for 90 seconds. Tests to assess DF ROM and squat movement pattern were applied before and immediately after using FR (intervention group) or after three-minute rest (control group).

RESULTS

The use of the FR promoted an immediate increase in ankle DF ROM during the Lunge Test and during the squat and a decrease in dynamic knee valgus during the squat.

CONCLUSION

The FR can be used as a tool for an acute increase in DF ROM and a decrease in dynamic knee valgus, having a positive impact in improving movement patterns.

Force transmission and interactions between synergistic muscles

The classical view of muscles as independent motors has been challenged over the past decades. An alternative view has emerged in which muscles are not isolated but embedded in a three-dimensional connective tissue network that links them to adjacent muscles and other non-muscular structures in the body. Animal studies showing that the forces measured at the distal and proximal ends of a muscle are not equal have provided undisputable evidence that these connective tissue linkages are strong enough to serve as an extra pathway for muscular force transmission. In this historical review, we first introduce the terminology and anatomy related to these pathways of muscle force transmission and provide a definition for the term epimuscular force transmission. We then focus on important experimental evidence indicating mechanical interactions between synergistic muscles that may affect force transmission and/or influence the muscles' force generating capacity. We illustrate that there may exist different expressions of the highly relevant force-length properties depending on whether the force is measured at the proximal or distal tendon and depending on the dynamics of surrounding structures. Changes in length, activation level or disruption of the connective tissue of neighboring muscles, can affect how muscles interact and produce force on the skeleton. While most direct evidence is from animal experiments, studies on humans also suggest functional implications of the connective tissues surrounding muscles. These implications may explain how distant segments, which are not part of the same joint system, affect force generation at a given joint, and, in clinical conditions, explain observations from tendon transfer surgeries, where a muscle transferred to act as an antagonist continues to produce agonistic moments.

Acute effect of diagonal stretching using the posterior oblique sling system on contralateral ankle dorsiflexion

BACKGROUND

A significant increase in the dorsiflexion range of motion (DFROM) after calf muscle stretching has been widely studied. However, it has been shown that the upper body is connected to the ankle joint by passive connective tissues.

OBJECTIVE

The purpose of this study was to examine the effect of upper-back stretching on the mobility of the contralateral ankle.

METHODS

In the supine position, DFROM in the contralateral leg was measured. In the sitting position with and without trunk rotation, DFROM was measured in both legs. In the sitting position with trunk rotation, dorsiflexion was measured only in the contralateral leg. Static diagonal stretching combining trunk rotation with slight trunk flexion was performed in the sitting position with a neutral pelvis.

RESULTS

After stretching, DFROM in contralateral and ipsilateral legs were measured in the sitting position with a neutral pelvis. In the contralateral leg, significant differences in ΔDFROM were observed between the sitting position with trunk rotation and the supine position and between the sitting position with trunk rotation and the sitting position after stretching.

CONCLUSION

In clinical settings, diagonal stretching of the unilateral posterior trunk causes a significant increase in the DFROM of the contralateral lower limb.

Botulinum Toxin Intervention in Cerebral Palsy-Induced Spasticity Management: Projected and Contradictory Effects on Skeletal Muscles

Spasticity, following the neurological disorder of cerebral palsy (CP), describes a pathological condition, the central feature of which is involuntary and prolonged muscle contraction. The persistent resistance of spastic muscles to stretching is often followed by structural and mechanical changes in musculature. This leads to functional limitations at the respective joint. Focal injection of botulinum toxin type-A (BTX-A) is effectively used to manage spasticity and improve the quality of life of the patients. By blocking acetylcholine release at the neuromuscular junction and causing temporary muscle paralysis, BTX-A aims to reduce spasticity and hereby improve joint function. However, recent studies have indicated some contradictory effects such as increased muscle stiffness or a narrower range of active force production. The potential of these toxin- and atrophy-related alterations in worsening the condition of spastic muscles that are already subjected to changes should be further investigated and quantified. By focusing on the effects of BTX-A on muscle biomechanics and overall function in children with CP, this review deals with which of these goals have been achieved and to what extent, and what can await us in the future.

The short-term effect of a myofascial protocol versus light touch applied to the cervical spine towards the prevention of balance disorders in the elderly: protocol of a randomised controlled trial

Background

Falling is a major trauma that can occur with aging, leading to very significant psychological and physical health effects with financial and societal consequences. It is therefore essential to explore therapeutic treatments that can reduce this risk. Some recognized effective treatments exist, concerning in particular the re-education of the muscles of the lower limbs. However, to our knowledge, none of them focus on the cervical spine although the latter is located at an essential physiological crossroads. Manual therapy, which has already demonstrated its impact on pain and balance parameters in the elderly, could be a painless and non-invasive tool of choice in addressing this problem.

Methods

Interventional study (not related to a health product), monocentric, prospective, controlled, randomized double-blind (patient and evaluator performing the measurements). The experiment will take place over three measurement periods on D0, D7 and D21. On D0 subjects will be randomized in 2 groups: experimental and placebo group. Both groups will be assessed on: Short Physical Performance Battery test score, walking speed, lower limb strength, balance, heart rate variability and cervical spine strength and mobility. Then the experimental group will receive a myofascial release protocol applied to the cervical spine and the placebo group will receive a placebo light touch protocol. The intervention will be followed by the same measurements as before. This schedule will be reproduced on D7. On D21, only one assessment will be done.

Discussion

This study started in 2020 but could not go beyond the inclusion phase due to the COVID pandemic. It is envisaged that recruitment could resume during 2022.

Trial registration: Registered by the Comité de Protection des Personnes—Sud Méditerranée; under the title “Prévention des troubles de l’équilibre chez le senior: influence de la thérapie manuelle appliquée au rachis sur les paramètres statiques et dynamiques», n° 19.12.27.47.259 in date of February 4, 2020.

Registered by ClinicalTrials.gov ID: NCT05475652; under the title « The Influence of Manual Therapy Applied to the Cervical Spine in the Prevention of Balance Disorders in the Elderly (ManEq)”.

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

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

The Nonintuitive Contributions of Individual Quadriceps Muscles to Patellar Tracking

The purpose of this study was to quantify the contribution of the individual quadriceps muscles to patellar tracking. The individual and/or combined quadriceps muscles were activated in rabbits (n = 6) during computer-controlled flexion/extension of the knee. Three-dimensional patellar tracking was measured for the vastus lateralis, vastus medialis, and rectus femoris when activated alone and when activated simultaneously at different frequencies, producing a range of knee extensor torques. Patellar tracking changed substantially as a function of knee extensor torque and differed between muscles. Specifically, when all quadriceps muscles were activated simultaneously, the patella shifted more medially and proximally and rotated and tilted more medially compared with when vastus lateralis and rectus femoris were activated alone (P < .05), whereas vastus medialis activation alone produced a similar tracking pattern to that observed when all quadriceps muscles were activated simultaneously. Furthermore, patellar tracking for a given muscle condition shifted more medially and proximally and rotated and tilted more medially with increasing knee extensor torques across the entire range of knee joint angles. The authors conclude that patellar tracking depends crucially on knee extensor force/torque and that vastus medialis affects patellar tracking in a distinctly different way than vastus lateralis and rectus femoris, which produce similar tracking patterns.

Anatomical study of paratenons and fascia lata connections in the posteromedial knee region

INTRODUCTION

In the last decade, fascia research increased significantly in various aspects such as anatomical and biomechanical features related to epimuscular force transmission.

METHODS

The present anatomic study focuses on macroscopic observations of the potential gracilis and semitendinosus paratenons, as well as fascial surroundings connections in the posteromedial knee region on 17 lower-limbs dissections.

RESULTS

The gracilis and semitendinosus expansions and paratenons were observed in all specimen and further connections with the fascia lata and crural fascia were demonstrated. Contrary to the previously described expansions connected to the tendons, we observed that the expansions were the edges of the paratenon tunnel and that the paratenon structure surrounded the overall muscle. Both paratenons of gracilis and semitendinosus were connected to the crural fascia and, respectively, to the sartorius fascia (part of the fascia lata), to the semimembranosus and the fascia lata. Furthermore, numerous connections between the fascia lata and the neighboring structures in the posteromedial knee region are described.

DISCUSSION-CONCLUSION

The present study describes for the first time gracilis and semitendinosus paratenons and other surrounding fascial connections. Such macroscopic observations may represent a new basis for further characterization of the myofascial pathway of epimuscular force transmission in the knee region.

Association between effective neural drive to the triceps surae and fluctuations in plantar-flexion torque during submaximal isometric contractions

What is the central question of this study? What is the association between the fluctuations in various estimates of effective neural drive to the triceps surae muscles and fluctuations in net plantar-flexion torque during steady submaximal contractions? What is the main finding and its importance? The fluctuations in estimates of effective neural drive to the triceps surae were moderately correlated with fluctuations in net torque at light and moderate plantar-flexion torques. Significant variability was observed in the association between neural drive and torque across participants, trials, short epochs of individual contractions, and varying motor unit number. ABSTRACT: The influence of effective neural drive on low-frequency fluctuations in torque during steady contractions can be estimated from the cumulative spike train (CST) or first principal component (FPC) of smoothed motor unit discharge rates obtained with high-density electromyography. However, the association between these estimates of total neural drive to synergist muscles and the fluctuations in net torque has not been investigated. We exposed the variability and compared the correlations between estimates of effective neural drive to the triceps surae muscles and fluctuations in plantar-flexion torque during steady contractions at 10% and 35% of maximal voluntary contraction (MVC) torque. Both neural drive estimates were moderately correlated with torque (CST, 0.55 ± 0.14, FPC, 0.58 ± 0.16) and highly correlated with one another (0.81 ± 0.1) during the 30-s steady contractions. There was substantial variability in cross-correlation values across participants, trials, and the 1-s and 5-s epochs of single contractions. Moreover, epoch duration significantly influenced cross-correlation values. Motor unit number was weakly associated with cross-correlation strength at 35% MVC (marginal R² 0.09 - 0.11; all p < 2.2×10^-5 ), but not at 10% MVC (all p > 0.37). Approximately one fifth of the variance in the coefficient of variation (CV) for torque was explained by CV for the CST estimate of neural drive (p = 6.6×10^-13 , R² = 0.21). Estimates of total neural drive to the synergistic triceps surae muscles obtained by pooling motor unit discharge times were moderately correlated with fluctuations in net plantar-flexion torque. This article is protected by copyright. All rights reserved.

The Association between Symmetrical or Asymmetrical High-Arched Feet and Muscle Fatigue in Young Women

The foot arches are responsible for proper foot loading, optimal force distribution, and transmission throughout the soft tissues. Since the foot arch is an elastic structure, able to adapt to forces transmitted by the foot, it was reported that low arch is related to excessive foot pronation, while high arched foot is more rigid and inflexible. Therefore, it is also probable, that foot arch alterations may change the force transmission via myofascial chains. The objective of this study was to evaluate the effect of symmetrical and asymmetrical excessive feet arching on muscle fatigue in the distal body parts such as the lower limbs, trunk, and head. Seventy-seven women (25.15 ± 5.97 years old, 62 ± 10 kg, 167 ± 4 cm) were assigned to three groups according to the foot arch index (Group 1—both feet with normal arch, Group 2—one foot with normal arch and the other high-arched, Group 3—both feet with high-arch). The bioelectrical activity of the right and left hamstrings muscles, erector spine, masseter, and temporalis muscle was recorded by sEMG during the isometric contraction lasting for 60 s. The stable intensity of the muscle isometric contraction was kept for all the time during the measurement. Mean frequency difference (%), slope (Hz), and intercept (Hz) values were calculated for muscle fatigue evaluation. No differences were observed in fatigue variables for all evaluated muscles between the right and left side in women with symmetrical foot arches, but in the group with asymmetric foot arches, the higher muscle fatigue on the normal-arched side compared to the high-arched side was noted. Significantly greater values of the semitendinosus—semimembranosus muscle frequency difference was observed on the normal-arched side compared to the high-arched side (p = 0.04; ES = 0.52; −29.5 ± 9.1% vs. −24.9 ± 8.4%). In the group with asymmetric foot arches, a significantly higher value of lumbar erector spinae muscle frequency slope (p = 0.01; ES = 1.32; −0.20 ± 0.04 Hz vs. −0.14 ± 0.05 Hz) and frequency difference (p = 0.04; ES = 0.92; −7.8 ± 3.1% vs. −4.8 ± 3.4%) were observed on the high-arched foot side compared to the side with normal foot arching. The thoracic erector spine muscle frequency slope was significantly larger in women with asymmetrical arches than in those with both feet high-arched (right side: p = 0.01; ES = 1.25; −0.20 ± 0.08 Hz vs. −0.10 ± 0.08 Hz); (left side: p = 0.005; ES = 1,17; −0.19 ± 0.04 Hz vs. −0.13 ± 0.06 Hz) and compared to those with normal feet arches (right side: p = 0.02; ES = 0.58; −0.20 ± 0.08 Hz vs. −0.15 ± 0.09 Hz); (left side: p = 0.005; ES = 0.87; −0.19 ± 0.04 Hz vs. −0.14 ± 0.07 Hz). In the group with asymmetric foot arches, the frequency difference was significantly higher compared to those with both feet high-arched (right side: p = 0.01; ES = 0.87; −15.4 ± 6.8% vs. 10.4 ± 4.3%); (left side: p = 0.01; ES = 0.96; 16.1 ± 6.5% vs. 11.1 ± 3.4%). In the group with asymmetric foot arches, a significantly higher value of the masseter muscle frequency difference was observed on the high-arched side compared to the normal-arched side (p = 0.01; ES = 0.95; 6.91 ± 4.1% vs. 3.62 ± 2.8%). A little increase in the longitudinal arch of the foot, even though such is often not considered as pathological, may cause visible changes in muscle function, demonstrated as elevated signs of muscles fatigue. This study suggests that the consequences of foot high-arching may be present in distal body parts. Any alterations of the foot arch should be considered as a potential foot defect, and due to preventing muscle overloading, some corrective exercises or/and corrective insoles for shoes should be used. It can potentially reduce both foot overload and distant structures overload, which may diminish musculoskeletal system pain and dysfunctions.

Evaluating the Effectiveness of Soft Tissue Therapy in the Treatment of Disorders and Postoperative Conditions of the Knee Joint-A Systematic Review

The term "soft tissue therapy" (STT) refers to mechanical methods of treatment involving passive kneading, pressing and stretching of pathologically tense tissues in supporting the process of recovery after surgery or trauma to the musculoskeletal system. The objective of this study was to review current scientific reports evaluating the effectiveness of the use of STT in patients with diseases or after surgical procedures of the knee joint. A systematic search of the popular scientific databases PubMed, Scopus and Embase was performed from inception to 15 October 2021. Eight articles met eligibility criteria and were included in the review. Six papers were related to disorders of the knee joint, while the remaining two studies were related to dysfunctions associated with the conditions after surgical intervention. The findings presented confirmed the effectiveness of STT in orthopaedic patients who showed an increase in lower limb functional parameters. The research has shown that the use of various methods of STT has a significant impact on increasing muscle activity and flexibility as well as increasing the range of motion in the knee joint. The physiotherapeutic methods used had a significant impact on reducing pain and increasing physical function and quality of life. The techniques used reduced the time to descend stairs in patients with knee osteoarthritis. This review summarises the effectiveness of STT as an important form of treatment for orthopaedic patients with various knee joint dysfunctions.

Muscle architecture and shape changes in the gastrocnemii of active younger and older adults

When muscles contract and change length, they also bulge in thickness and/or width. These shape changes extend the functional range of skeletal muscle by allowing individual muscle fibres to shorten at different velocities than the whole muscle. Age-related differences in muscle architecture and tissue properties influence how older muscles change shape and architecture during contractions, yet this remains unexplored in active older adults. The aim of this study was to quantify and compare in vivo muscle architecture and shape changes in the medial (MG) and lateral (LG) gastrocnemii of active younger and older adults during isometric plantarflexion contractions. Fifteen younger (21 ± 2y) and 15 older (70 ± 3y) participants performed contractions at 20%, 40%, 60%, 80%, and 100% of maximum voluntary contraction (MVC). B-mode ultrasound was used to measure fascicle length, pennation angle and muscle thickness in MG and LG. We found no influence of age on changes in normalized fascicle length and thickness, or absolute change in pennation angle during contractions. With increasing contraction level, MG and LG fascicle shortening (P < 0.001) and rotation (P < 0.001) increased. However, the change in muscle thickness increased at higher contraction levels in LG, and not MG. Similarly, increased changes in pennation angle were associated with increased muscle thickness in LG, but not MG at 80% and 100% MVC. These results suggest that (1) gastrocnemii shape changes are similar in active older and younger adults at matched levels of effort, and (2) the relationship between pennation angle and muscle thickness can differ between synergistics (LG and MG) and across contraction levels.

Detection of epimuscular myofascial forces by Golgi tendon organs

Skeletal muscles embed multiple tendon organs, both at the proximal and distal ends of muscle fibers. One of the functions of such spatial distribution may be to provide locally unique force feedback, which may become more important when stresses are distributed non-uniformly within the muscle. Forces exerted by connections between adjacent muscles (i.e. epimuscular myofascial forces) may cause such local differences in force. The aim of this exploratory study was to investigate the effects of mechanical interactions between adjacent muscles on sensory encoding by tendon organs. Action potentials from single afferents were recorded intra-axonally in response to ramp-hold release (RHR) stretches of a passive agonistic muscle at different lengths or relative positions of its passive synergist. The tendons of gastrocnemius (GAS), plantaris (PL) and soleus (SO) muscles were cut from the skeleton for attachment to servomotors. Connective tissues among these muscles were kept intact. Lengthening GAS + PL decreased the force threshold of SO tendon organs (p = 0.035). The force threshold of lateral gastrocnemius (LG) tendon organs was not affected by SO length (p = 0.371). Also displacing LG + PL, kept at a constant muscle-tendon unit length, from a proximal to a more distal position resulted in a decrease in force threshold of LG tendon organs (p = 0.007). These results indicate that tendon organ firing is affected by changes in length and/or relative position of adjacent synergistic muscles. We conclude that tendon organs can provide the central nervous system with information about local stresses caused by epimuscular myofascial forces.

Negligible epimuscular myofascial force transmission between the human rectus femoris and vastus lateralis muscles in passive conditions

PURPOSE

There have been contradictory reports of the effects of epimuscular myofascial force transmission in humans. This study investigated the transmission of myofascial force to the human vastus lateralis muscle by determining whether vastus lateralis slack angle changed with hip angle. Since the distance between the origin and insertion of the vastus lateralis muscle does not change when hip angle changes, any change in vastus lateralis slack angle with hip position can be attributed to epimuscular myofascial force transmission.

METHODS

Nineteen young adults were tested in hip flexed ([Formula: see text]) and neutral ([Formula: see text]) positions. Ultrasound images of the vastus lateralis muscle were obtained as the knee was passively flexed at [Formula: see text]/s. The knee angle at which vastus lateralis muscle fascicles began to lengthen was used to identify muscle slack angle.

RESULTS

Overall, there was a negligible effect of hip position on vastus lateralis slack angle ([Formula: see text] [[Formula: see text] to 1.9]; mean [95% confidence interval]). However, a small and variable effect was noted in 3/19 participants.

CONCLUSION

This result indicates that, over the range of joint angles tested here, there is little or no epimuscular myofascial force transmission between the vastus lateralis muscle and neighbouring bi-articular structures under passive conditions. More broadly, this result provides additional evidence that epimuscular myofascial force transmission tends to be small and variable under passive conditions in healthy human muscle.

Changes in muscle-tendon unit length-force characteristics following experimentally induced photothrombotic stroke cannot be explained by changes in muscle belly structure

PURPOSE

The aim of this study was to assess the effects of experimentally induced photothrombotic stroke on structural and mechanical properties of rat m. flexor carpi ulnaris.

METHODS

Two groups of Young-adult male Sprague-Dawley rats were measured: stroke (n = 9) and control (n = 7). Photothrombotic stroke was induced in the forelimb region of the primary sensorimotor cortex. Four weeks later, muscle-tendon unit and muscle belly length-force characteristics of the m. flexor carpi ulnaris, mechanical interaction with the neighbouring m. palmaris longus, the number of sarcomeres in series within muscle fibres, and the physiological cross-sectional area were measured.

RESULTS

Stroke resulted in higher force and stiffness of the m. flexor carpi ulnaris at optimum muscle-tendon unit length, but only for the passive conditions. Stroke did not alter the length-force characteristics of m. flexor carpi ulnaris muscle belly, morphological characteristics, and the extent of mechanical interaction with m. palmaris longus muscle.

CONCLUSION

The higher passive force and passive stiffness at the muscle-tendon unit level in the absence of changes in structural and mechanical characteristics of the muscle belly indicates that the experimentally induced stroke resulted in an increased stiffness of the tendon.

Neurobiological tensegrity: The basis for understanding inter-individual variations in task performance?

Bernstein's (1996) levels of movement organization includes tonus, the muscular-contraction level that primes individual movement systems for (re)organizing coordination patterns. The hypothesis advanced is that the tonus architecture is a multi-fractal tensegrity system, deeply reliant on haptic perception for regulating movement of an individual actor in a specific environment. Further arguments have been proposed that the tensegrity-haptic system is implied in all neurobiological perception and -action. In this position statement we consider whether the musculoskeletal system can be conceptualized as a neurobiological tensegrity system, supporting each individual in co-adapting to many varied contexts of dynamic performance. Evidence for this position, revealed in investigations of judgments of object properties, perceived during manual hefting, is based on each participant's tensegrity. The implication is that the background organizational state of every individual is unique, given that no neurobiological architecture (musculo-skeletal components) is identical. The unique tensegrity of every organism is intimately related to individual differences, channeling individualized adaptations to constraints (task, environment, organismic), which change over different timescales. This neurobiological property assists transitions from one stable state of coordination to another which is needed in skill adaptation during performance. We conclude by discussing how tensegrity changes over time according to skill acquisition and learning.

An Investigation of the Association between Transversus Abdominis Myofascial Structure and Activation with Age in Healthy Adults using Ultrasound Imaging

BACKGROUND

Because of their importance in core stability, training the deep abdominal muscles, fascial structures and particularly the transversus abdominis, is a key component of many sport and physical therapy programs. However, there are gaps in knowledge about age-related changes in the structure and activation capacity of these muscles.

HYPOTHESIS/PURPOSE

This study investigated the association between deep abdominal muscles and fascial structures and transversus abdominis activation with age in healthy adults.

STUDY DESIGN

A cross-sectional study.

METHODS

Eighty-six adults aged 18 to 77 participated in this study. An ultrasound image of their transversus abdominis, internal oblique, external oblique and associated fasciae was first captured at rest, then during a contraction of the transversus abdominis. Bivariate correlation analyses and hierarchical analyses were performed (significance level: p < 0.05).

RESULTS

The thickness of these three muscles decreases with age ( ρ = -0.66 for external oblique, -0.51 for internal oblique and -0.58 for transversus abdominis), whereas the thickness of their fasciae increases ( ρ = 0.39 for the fascia of external oblique, 0.54 for the fascia between internal oblique and external oblique, and 0.74 for the fascia between internal oblique and transversus abdominis). Transversus abdominis activation decreases with age (r =-0.44). Age accounts for 19.5% of the variance in transversus abdominis activation.

CONCLUSION

These results demonstrate that normal aging is associated with changes in deep abdominal myofascial structures and transversus abdominis activation. Assessment of these metrics can provide valuable baseline information for physical therapists involved in rehabilitation and strengthening programs targeting older individuals.

LEVEL OF EVIDENCE

Level 2.

Characterization of the Force Production Capabilities of Paralyzed Trunk Muscles Activated With Functional Neuromuscular Stimulation in Individuals With Spinal Cord Injury

Paralysis of the trunk results in seated instability leading to difficulties performing activities of daily living. Functional neuromuscular stimulation (FNS) combined with control systems have the potential to restore some dynamic functions of the trunk. However, design of multi-joint, multi-muscle control systems requires characterization of the stimulation-driven muscles responsible for movement.

OBJECTIVE

This study characterizes the input-output properties of paralyzed trunk muscles activated by FNS, and explores co-activation of muscles.

METHODS

Four participants with various spinal cord injuries (C7 AIS-B, T4 AIS-B, T5 AIS-A, C5 AIS-C) were constrained so lumbar forces were transmitted to a load cell while an implanted neuroprosthesis activated otherwise paralyzed hip and paraspinal muscles. Isometric force recruitment curves in the nominal seated position were generated by inputting the level of stimulation (pulse width modulation) while measuring the resulting muscle force. Two participants returned for a second experiment where muscles were co-activated to determine if their actions combined linearly.

RESULTS

Recruitment curves of most trunk and hip muscles fit sigmoid shaped curves with a regression coefficient above 0.75, and co-activation of the muscles combined linearly across the hip and lumbar joint. Subject specific perturbation plots showed one subject is capable of resisting up to a 300N perturbation anteriorly and 125N laterally; with some subjects falling considerably below these values.

CONCLUSION

Development of a trunk stability control system can use sigmoid recruitment dynamics and assume muscle forces combine linearly.

SIGNIFICANCE

This study informs future designs of multi-muscle, and multi-dimensional FNS systems to maintain seated posture and stability.

Changes in neural drive to calf muscles during steady submaximal contractions after repeated static stretches

KEY POINTS

Repeated static-stretching interventions consistently increase the range of motion about a joint and decrease total joint stiffness, but findings on the changes in muscle and connective-tissue properties are mixed. The influence of these stretch-induced changes on muscle function at submaximal forces is unknown. To address this gap in knowledge, the changes in neural drive to the plantar flexor muscles after a static-stretch intervention were estimated. Neural drive to the plantar flexor muscles during a low-force contraction increased after repeated static stretches. These findings suggest that adjustments in motor unit activity are necessary at low forces to accommodate reductions in the force-generating and transmission capabilities of the muscle-tendon unit after repeated static stretches of the calf muscles.

ABSTRACT

Static stretching decreases stiffness about a joint, but its influence on muscle-tendon unit function and muscle activation is unclear. We investigated the influence of three static stretches on changes in neural drive to the plantar flexor muscles, both after a stretch intervention and after a set of maximal voluntary contractions (MVCs). Estimates of neural drive were obtained during submaximal isometric contractions by decomposing high-density electromyographic signals into the activity of individual motor units from medial gastrocnemius, lateral gastrocnemius and soleus. Motor units were matched across contractions and an estimate of neural drive to the plantar flexors was calculated by normalizing the cumulative spike train to the number of active motor units (normalized neural drive). Mean discharge rate increased after the stretch intervention during the 10% MVC task for all recorded motor units and those matched across conditions (all, P = 0.0046; matched only, P = 0.002), recruitment threshold decreased for motor units matched across contractions (P = 0.022), and discharge rate at recruitment was elevated (P = 0.004). Similarly, the estimate of normalized neural drive was significantly greater after the stretch intervention at 10% MVC torque (P = 0.029), but not at 35% MVC torque. The adjustments in motor unit activity required to complete the 10% MVC task after stretch may have been partially attenuated by a set of plantar flexor MVCs. The increase in neural drive required to produce low plantar-flexion torques after repeated static stretches of the calf muscles suggests stretch-induced changes in muscle and connective tissue properties.

Investigation of the association between human fascia lata thickness and its neighboring tissues' morphology and function using B-mode ultrasonography

The fascia lata is a membrane tissue which envelopes all thigh muscles and connects with the subcutaneous adipose tissues through loose connective tissues. It is presumable that the morphology of the fascia lata is strongly affected by the unique properties of underlying thigh muscles and subcutaneous adipose tissues. We aimed to investigate the relationships between characteristics of the fascia lata and adjoining adipose tissues and underlying muscles. Twenty healthy people were recruited (25 ± 3 years, 167.1 ± 8.5 cm, 62.5 ± 13.2 kg). The thickness of the skeletal muscles (rectus femoris, vastus lateralis, biceps femoris, and semitendinosus), and their overlying fascia lata and subcutaneous adipose tissues were measured by B‐mode ultrasonography. Isometric knee extension and flexion torque during maximal voluntary contraction were also tested. The fascia lata thickness demonstrated site‐dependent differences (vastus lateralis: 0.91 ± 0.20 mm > rectus femoris, biceps femoris, and semitendinosus: 0.56–0.69 mm, p < 0.01). Furthermore, there were large individual variations in the fascia lata thickness even in the same region of the thigh. The fascia lata showed positive simple correlations with height (rectus femoris: r = 0.39 p = 0.01, semitendinosus: r = 0.37 p < 0.05), body mass (rectus femoris: r = 0.59, p < 0.01, vastus lateralis: r = 0.47, p < 0.01, semitendinosus: r = 0.55, p < 0.01), corresponding muscle thickness (rectus femoris: r = 0.39, p < 0.05, semitendinosus: r = 0.74, p < 0.01) and knee extension (rectus femoris: r = 0.52, p < 0.01, vastus lateralis: r = 0.40, p < 0.01) and flexion (semitendinosus: r = 0.41, p < 0.01) torques. After adjusting for the influence of height and/or body mass, the fascia lata thickness showed a partial correlation only with the skeletal muscle thickness at the semitendinosus (r = 0.61, p < 0.01). The present study revealed that the fascia lata has site‐specific differences of the thickness, which positively correlates with the underlying muscle thickness and corresponding joint torque. Furthermore, the fascia lata over the semitendinosus is associated with the underlying muscle characteristics independent of the physical constitution. It is assumed that the fascia lata has the plasticity and changes its thickness, which likely corresponds to the morphology of the neighboring tissues and underlying muscle function.

The fascia lata showed individual differences of its thickness which was positively correlated with its underlying muscle thickness and/or strength. Especially, the fascia lata over the ST reflects the underlying muscle characteristics regardless of the physical constitution.

The Effect of Quadriceps Muscle Length on Maximum Neuromuscular Electrical Stimulation Evoked Contraction, Muscle Architecture, and Tendon-Aponeurosis Stiffness

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

Inhomogeneous and anisotropic mechanical properties of the triceps surae muscles and aponeuroses in vivo during submaximal muscle contraction

This study aimed to identify characteristics of the triceps surae muscles and aponeuroses stiffness in vivo, during graded isometric submaximal plantarflexion efforts. A total of twelve healthy male subjects (age: 27 ± 4 years) participated and were required to stay at rest (0% MVC) and perform isometric submaximal plantar flexion contractions (20%, 40%, 60% of MVC) on a dynamometer. Young's modulus of triceps surae muscles and the adjoining aponeuroses between gastrocnemii and soleus at the proximal and distal sites were obtained in the longitudinal direction (along muscle's line of action) during at rest and submaximal plantar flexions. Additionally, Young's modulus of adjoining aponeuroses in the transverse direction at the distal sites was also calculated. Young's modulus of LG (lateral gastrocnemius), SOL-lat (lateral part of soleus) and LPS (superficial aponeurosis of LG) at the proximal site showed significant (p < 0.001) graded increase response to the submaximal contraction levels. Besides, in the lateral side, significant differences in the Young's modulus of aponeuroses were observed between longitudinal and transverse directions at rest and during contractions (p < 0.002). Changes of aponeuroses length were significantly correlated with Young's modulus changes of the proximal gastrocnemii muscle bellies (r = 0.43-0.45, p = 0.006-0.008) and superficial aponeuroses (r = 0.49-0.60, p < 0.002). The results further indicate that the triceps surae muscles and aponeuroses showed inhomogeneous and anisotropic mechanical properties during submaximal muscle contractions, and the stiffening effect of muscle belly possibly make influence on the mechanical properties of aponeuroses during muscle contractions, especially for the lateral gastrocnemius.

Extracellular matrix at the muscle - tendon interface: functional roles, techniques to explore and implications for regenerative medicine

The muscle-tendon interface is an anatomically specialized region that is involved in the efficient transmission of force from muscle to tendon. Due to constant exposure to loading, the interface is susceptible to injury. Current treatment methods do not meet the socioeconomic demands of reduced recovery time without compromising the risk of reinjury, requiring the need for developing alternative strategies. The extracellular matrix (ECM) present in muscle, tendon, and at the interface of these tissues consists of unique molecules that play significant roles in homeostasis and repair. Better, understanding the function of the ECM during development, injury, and aging has the potential to unearth critical missing information that is essential for accelerating the repair at the muscle-tendon interface. Recently, advanced techniques have emerged to explore the ECM for identifying specific roles in musculoskeletal biology. Simultaneously, there is a tremendous increase in the scope for regenerative medicine strategies to address the current clinical deficiencies. Advancements in ECM research can be coupled with the latest regenerative medicine techniques to develop next generation therapies that harness ECM for treating defects at the muscle-tendon interface. The current work provides a comprehensive review on the role of muscle and tendon ECM to provide insights about the role of ECM in the muscle-tendon interface and discusses the latest research techniques to explore the ECM to gathered information for developing regenerative medicine strategies.

An insight on Drosophila myogenesis and its assessment techniques

Movement assisted by muscles forms the basis of various behavioural traits seen in Drosophila. Myogenesis involves developmental processes like cellular specification, differentiation, migration, fusion, adherence to tendons and neuronal innervation in a series of coordinated event well defined in body space and time. Gene regulatory networks are switched on-off, fine tuning at the right developmental stage to assist each cellular event. Drosophila is a holometabolous organism that undergoes myogenesis waves at two developmental stages, and is ideal for comparative analysis of the role of genes and genetic pathways conserved across phyla. In this review we have summarized myogenic events from the embryo to adult focussing on the somatic muscle development during the early embryonic stage and then on indirect flight muscles (IFM) formation required for adult life, emphasizing on recent trends of analysing muscle mutants and advances in Drosophila muscle biology.

Effect of Vastus Medialis Loss on Rabbit Patellofemoral Joint Contact Pressure Distribution

Vastus medialis (VM) weakness is thought to alter patellar tracking, thereby changing the loading of the patellofemoral joint (PFJ), resulting in patellofemoral pain. However, it is challenging to measure VM force and weakness in human studies, nor is it possible to measure the associated mechanical changes in the PFJ. To obtain fundamental insight into VM weakness and its effects on PFJ mechanics, the authors determined PFJ loading in the presence of experimentally simulated VM weakness. Skeletally mature New Zealand White rabbits were used (n = 6), and the vastus lateralis, VM, and rectus femoris were stimulated individually through 3 custom-built nerve cuff electrodes. Muscle torque and PFJ pressure distribution were measured while activating all muscles simultaneously, or when the vastus lateralis and rectus femoris were activated, while VM was not, to simulate a quadriceps muscle strength imbalance. For a given muscular joint torque, peak pressures were greater and joint contact areas were smaller when simulating VM weakness compared with the condition where all muscles were activated simultaneously. The results in the rabbit model support that VM weakness results in altered PFJ loading, which may cause patellofemoral pain, often associated with a strength imbalance of the knee extensor muscle group.

Estimation of the force-velocity properties of individual muscles from measurement of the combined plantarflexor properties

The force-velocity (F-V) properties of isolated muscles or muscle fibers have been well studied in humans and other animals. However, determining properties of individual muscles in vivo remains a challenge because muscles usually function within a synergistic group. Modeling has been used to estimate the properties of an individual muscle from the experimental measurement of the muscle group properties. While this approach can be valuable, the models and the associated predictions are difficult to validate. In this study, we measured the in situ F-V properties of the maximally activated kangaroo rat plantarflexor group and used two different assumptions and associated models to estimate the properties of the individual plantarflexors. The first model (Mdl1) assumed that the percent contributions of individual muscles to group force and power were based upon the muscles' cross-sectional area and were constant across the different isotonic loads applied to the muscle group. The second model (Mdl2) assumed that the F-V properties of the fibers within each muscle were identical, but because of differences in muscle architecture, the muscles' contributions to the group properties changed with isotonic load. We compared the two model predictions with independent estimates of the muscles' contributions based upon sonomicrometry measurements of muscle length. We found that predictions from Mdl2 were not significantly different from sonomicrometry-based estimates while those from Mdl1 were significantly different. The results of this study show that incorporating appropriate fiber properties and muscle architecture is necessary to parse the individual muscles' contributions to the group F-V properties.

Semimembranosus muscle displacement is associated with movement of the superficial fascia: An in vivo ultrasound investigation

The deep fascia enveloping the skeletal muscle has been shown to contribute to the mechanics of the locomotor system. However, less is known about the role of the superficial fascia (SF). This study aimed to describe the potential interaction between the Hamstring muscles and the SF. Local movement of the dorsal thigh's soft tissue was imposed making use of myofascial force transmission effects across the knee joint: In eleven healthy individuals (26.8 ± 4.3 years, six males), an isokinetic dynamometer moved the ankle into maximal passive dorsal extension (knee extended). Due to the morphological continuity between the gastrocnemius and the Hamstrings, stretching the calf led to soft tissue displacements in the dorsal thigh. Ultrasound recordings were made to dynamically visualize (a) the semimembranosus muscle and (b) the superficial fascia. Differences in and associations between horizontal movement amplitudes of the two structures, quantified via cross-correlation analyses, were calculated by means of the Mann-Whitney U test and Kendal's tau test, respectively. Mean horizontal movement was significantly higher in the muscle (5.70 mm) than in the SF (0.72 mm, p < 0.001, r = 0.82). However, a strong correlation between the tissue displacements in both locations was detected (p < 0.001, r = 0.91). A Direct mechanical relationship may exist between the SF and the skeletal muscle. Deep pathologies or altered muscle stiffness could thus have long-term consequences for rather superficial structures and vice versa.

ACUTE OUTCOMES OF MYOFASCIAL DECOMPRESSION (CUPPING THERAPY) COMPARED TO SELF-MYOFASCIAL RELEASE ON HAMSTRING PATHOLOGY AFTER A SINGLE TREATMENT

BACKGROUND

Myofascial decompression (MFD), or cupping, and self-myofascial release (SMR) are common techniques utilized to treat soft tissue injuries and increase flexibility. MFD is a negative pressure soft tissue treatment technique using suction to manipulate the skin and underlying soft tissues. One method of SMR is a foam roller, where a patient rolls his/her bodyweight over a dense foam cylinder in a self-massaging fashion to mobilize soft tissues for the body part treated.

HYPOTHESIS/PURPOSE

The purpose of this investigation was to examine the acute effects on hamstring flexibility and patient-rated outcome measures comparing two soft tissue treatments, 1) MFD, and 2) a moist heat pack with SMR using a foam roller in patients with diagnosed hamstring pathology.

STUDY DESIGN

Pilot randomized controlled trial study.

METHODS

Seventeen collegiate athletes [13 males (20.6+/- years; 184.9+/-cm; 90.8+/-kg) and 4 females (20.5+/-years; 167.1+/-cm; 62.7+/-kg)] with diagnosed hamstring pathology (mild strain and/or symptoms of tightness, pain, decreased strength, and decreased flexibility) were randomly assigned to receive MFD or SMR. The MFD group (n = 9) received three minutes of static treatment using six plastic-valve suction cups along the hamstrings followed by 20 repetitions of active movement with cups in place. SMR (n = 8) received 10 minutes of heat treatment over the hamstrings followed by 60 seconds of general mobilization over the entire hamstring area, and 90 seconds of targeted foam rolling on the area of most perceived tightness. Passive hamstring flexibility (ROM) and a patient-rated outcome measure [Perceived Functional Ability Questionnaire (PFAQ)] were assessed before and immediately after treatment. The Global Rating of Change measure (GROC) was administered post-intervention.

RESULTS

Passive ROM and subjective PFAQ measures for overall flexibility and flexibility of the hamstrings were significantly different from pre- to post-intervention measurements regardless of the treatment received. A significant difference was found in favor of the MFD group for the GROC values.

CONCLUSION

The findings suggest that both treatments are beneficial in increasing hamstring length. Patients though felt an enhanced treatment effect using MFD over SMR for perceived benefits to hamstring flexibility.

LEVELS OF EVIDENCE

Level 2.

The Structure and Role of Intramuscular Connective Tissue in Muscle Function

Extracellular matrix (ECM) structures within skeletal muscle play an important, but under-appreciated, role in muscle development, function and adaptation. Each individual muscle is surrounded by epimysial connective tissue and within the muscle there are two distinct extracellular matrix (ECM) structures, the perimysium and endomysium. Together, these three ECM structures make up the intramuscular connective tissue (IMCT). There are large variations in the amount and composition of IMCT between functionally different muscles. Although IMCT acts as a scaffold for muscle fiber development and growth and acts as a carrier for blood vessels and nerves to the muscle cells, the variability in IMCT between different muscles points to a role in the variations in active and passive mechanical properties of muscles. Some traditional measures of the contribution of endomysial IMCT to passive muscle elasticity relied upon tensile measurements on single fiber preparations. These types of measurements may now be thought to be missing the important point that endomysial IMCT networks within a muscle fascicle coordinate forces and displacements between adjacent muscle cells by shear and that active contractile forces can be transmitted by this route (myofascial force transmission). The amount and geometry of the perimysial ECM network separating muscle fascicles varies more between different muscle than does the amount of endomysium. While there is some evidence for myofascial force transmission between fascicles via the perimysium, the variations in this ECM network appears to be linked to the amount of shear displacements between fascicles that must necessarily occur when the whole muscle contracts and changes shape. Fast growth of muscle by fiber hypertrophy is not always associated with a high turnover of ECM components, but slower rates of growth and muscle wasting may be associated with IMCT remodeling. A hypothesis arising from this observation is that the level of cell signaling via shear between integrin and dystroglycan linkages on the surface of the muscle cells and the overlying endomysium may be the controlling factor for IMCT turnover, although this idea is yet to be tested.

Skeletal Muscle Shape Change in Relation to Varying Force Requirements Across Locomotor Conditions

Contractions of skeletal muscles to generate in vivo movement involve dynamic changes in contractile and elastic tissue strains that likely interact to influence the force and work of a muscle. However, studies of the in vivo dynamics of skeletal muscle and tendon strains remain largely limited to bipedal animals, and rarely cover the broad spectra of movement requirements met by muscles that operate as motors, struts, or brakes across the various gaits that animals commonly use and conditions they encounter. Using high-speed bi-planar fluoromicrometry, we analyze in vivo strains within the rat medial gastrocnemius (MG) across a range of gait and slope conditions. These conditions require changes in muscle force ranging from decline walk (low) to incline gallop (high). Measurements are made from implanted (0.5–0.8 mm) tantalum spheres marking MG mid-belly width, mid-belly thickness, as well as strains of distal fascicles, the muscle belly, and the Achilles tendon. During stance, as the muscle contracts, muscle force increases linearly with respect to gait–slope combinations, and both shortening and lengthening fiber strains increase from approximately 5 to 15% resting length. Contractile change in muscle thickness (thickness strain) decreases (r² = 0.86; p = 0.001); whereas, the change in muscle width (width strain) increases (r² = 0.88; p = 0.001) and tendon strain increases (r² = 0.77; p = 0.015). Our results demonstrate force-dependency of contractile and tendinous tissue strains with compensatory changes in shape for a key locomotor muscle in the hind limb of a small quadruped. These dynamic changes are linked to the ability of a muscle to tune its force and work output as requirements change with locomotor speed and environmental conditions.

Joint and muscle-tendon coordination strategies during submaximal jumping

Previous research has demonstrated that during submaximal jumping humans prioritize reducing energy consumption by minimizing countermovement depth. However, sometimes movement is constrained to a nonpreferred pattern, and this requires adaptation of neural control that accounts for complex interactions between muscle architecture, muscle properties, and task demands. This study compared submaximal jumping with either a preferred or a deep countermovement depth to examine how joint and muscle mechanics are integrated into the adaptation of coordination strategies in the deep condition. Three-dimensional motion capture, two force plates, electromyography, and ultrasonography were used to examine changes in joint kinetics and kinematics, muscle activation, and muscle kinematics for the lateral gastrocnemius and soleus. Results demonstrated that a decrease in ankle joint work during the deep countermovement depth was due to increased knee flexion, leading to unfavorably short biarticular muscle lengths and reduced active fascicle length change during ankle plantar flexion. Therefore, ankle joint work was likely decreased because of reduced active fascicle length change and operating position on the force-length relationship. Hip joint work was significantly increased as a result of altered muscle activation strategies, likely due to a substantially greater hip extensor muscle activation period compared with plantar flexor muscles during jumping. Therefore, coordination strategies at individual joints are likely influenced by time availability, where a short plantar flexor activation time results in dependence on muscle properties, instead of simply altering muscle activation, while the longer time for contraction of muscles at the hip allows for adjustments to voluntary neural control.

NEW & NOTEWORTHY Using human jumping as a model, we show that adapting movement patterns to altered task demands is achieved differently by muscles across the leg. Because of proximal-to-distal sequencing, distal muscles (i.e., plantar flexors) have reduced activation periods and, as a result, rely on muscle contractile properties (force-length relationship) for adjusting joint kinetics. For proximal muscles that have greater time availability, voluntary activation is modulated to adjust muscle outputs.

Histopathology of Oral Submucous Fibrosis in Third Dimension with an Additional note on Hypothesis of Epithelial Atrophy

Oral submucous fibrosis (OSMF) is a potentially malignant disorder, characterized by progressive fibrosis of the lamina propria and underlying connective tissue. It has high chances of malignant transformation. It is caused by betel nut which is very common habit among Indians. Thus, regular monitoring of histopathological changes is mandatory by physicians, private practitioners, and oral pathologists. Therefore, histopathological changes should be understood by everyone who is into health care. This article is a preliminary report on three-dimensional (3D) images and 3D-animation video of histopathological aspect of OSMF designed by author herself, for better understanding of histopathological aspect, which has never been reported so far. Additional hypothesis on epithelial atrophy have also been proposed.

Vascularization of tissue-engineered skeletal muscle constructs

Skeletal muscle tissue can be created in vitro by tissue engineering approaches, based on differentiation of muscle stem cells. Several approaches exist and generally result in three dimensional constructs composed of multinucleated myofibers to which we refer as myooids. Engineering methods date back to 3 decades ago and meanwhile a wide range of cell types and scaffold types have been evaluated. Nevertheless, in most approaches, myooids remain very small to allow for diffusion-mediated nutrient supply and waste product removal, typically less than 1 mm thick. One of the shortcomings of current in vitro skeletal muscle organoid development is the lack of a functional vascular structure, thus limiting the size of myooids. This is a challenge which is nowadays applicable to almost all organoid systems. Several approaches to obtain a vascular structure within myooids have been proposed. The purpose of this review is to give a concise overview of these approaches.

Fascial organisation of motor synergies: a hypothesis

In the field of biomechanics and motor control understanding movement coordination is paramount. Motor synergies represent the coordination of neural and physical elements embedded in our bodies in order to optimize the solutions to motor problems. Although we are able to measure and quantify the movement made manifested, we do not have confidence in explaining the anatomical bases of its organisation at different levels. It is our contention that the flexible hierarchical organization of movement relies on the fascial structurers to create functional linkages at different levels, and this concept attunes with the neural control of synergies. At the base of movement organization there is a (somatic) equilibrium point that exists on the fascia where the neurologically- and mechanically-generated tensions dynamically balance out. This somatic equilibrium point is at the base of postural control, afferent flow of information to the nervous system about the state of the muscles, and of the coordinative pre-activation of muscular contraction sequences specific for a synergy. Implications are discussed and suggestions for research and clinical applications are made.

Validity of Ultrasound Imaging Versus Magnetic Resonance Imaging for Measuring Anterior Thigh Muscle, Subcutaneous Fat, and Fascia Thickness

The aim of the present study was to determine the validity of ultrasound (US) imaging versus magnetic resonance imaging (MRI) for measuring anterior thigh muscle, subcutaneous adipose tissue (SAT), and fascia thickness. Twenty healthy, moderately active participants (aged 49.1 ± 9.74 (36–64) years), underwent imaging of the anterior thigh, using ultrasound and MRI modalities on the same day. Images were analyzed offline to assess the level of agreement between US and MRI measurements. Pearson’s correlation coefficient showed an excellent relationship between US imaging and MRI for measuring muscle (r = 0.99, p < 0.01), SAT (r = 0.99, p < 0.01), and non-contractile tissue (SAT combined with perimuscular fascia) thickness (r = 0.99, p < 0.01). Perimuscular fascia thickness measurement showed a poor correlation between modalities (r = 0.39, p < 0.01). Intra-class correlation coefficients (ICC3,1) also showed excellent correlation of the measurements with ICC = 0.99 for muscle thickness, SAT, and non-contractile tissue, but not for perimuscular fascia, which showed poor agreement ICC = 0.36. Bland and Altman plots demonstrated excellent agreement between US imaging and MRI measurements. Criterion validity was demonstrated for US imaging against MRI, for measuring thickness of muscle and SAT, but not perimuscular fascia alone on the anterior thigh. The US imaging technique is therefore applicable for research and clinical purposes for muscle and SAT.

Significance of epimuscular myofascial force transmission under passive muscle conditions

In the past 20 yr, force transmission via connective tissue linkages at the muscle belly surface, called epimuscular myofascial force transmission, has been studied extensively. In this article, the effects of epimuscular linkages under passive muscle conditions are reviewed. Several animal studies that included direct (invasive) measurements of force transmission have shown that different connective tissue structures serve as an epimuscular pathway and that these tissues have sufficient stiffness, especially at supraphysiological muscle lengths and relative positions, to transmit substantial passive forces (up to 15% of active optimal force). Exact values of lumped tissue stiffness for different connective tissue structures have not yet been estimated. Experiments using various imaging techniques (ultrasound, MRI, shear wave elastography) have yielded some, but weak, evidence of epimuscular myofascial force transmission for passive muscles in humans. At this point, the functional consequences of epimuscular pathways for muscle and joint mechanics in the intact body are still unknown. Potentially, however, these pathways may affect sensory feedback and, thereby, neuromuscular control. In addition, altered epimuscular force transmission in pathological conditions may also contribute to changes in passive range of joint motion.

A comprehensive and volumetric musculoskeletal model for the dynamic simulation of the shoulder function

We present a volumetric and extensive finite element model of the shoulder usable in the context of inverse control, in which the scapula is left unconstrained on the ribcage. Such a model allows for exploring various shoulder movements, which are essential for making patient-specific decisions. The proposed model consists of 23 volumetric muscles parts modelled using the finite element method. The glenohumeral, acromioclavicular and sternoclavicular joints are modelled with soft ball-socket constraints. The musculoskeletal model can be controlled by a tracking-based algorithm, finding the excitations values in the muscles needed to follow some target points. The moment arms obtained during abduction and rotation are compared with the literature, which includes results from cadaveric data and a fine FE model of the rotator cuff and the deltoid. We simulated the paralysis of serratus anterior, a main reason of scapular winging, and compared it with its physiological counterpart. A deficiency in the range of motion as well as a reduction in upward rotation were observed, which both corroborate clinical observations. This is one of the most comprehensive model of the shoulder, which can be used to study complex pathologies of the shoulder and their impact on functional outcome such as range-of-motion.

Single finger movements in the aging hand: changes in finger independence, muscle activation patterns and tendon displacement in older adults

With aging, hand mobility and manual dexterity decline, even under healthy circumstances. To assess how aging affects finger movement control, we compared elderly and young subjects with respect to (1) finger movement independence, (2) neural control of extrinsic finger muscles and (3) finger tendon displacements during single finger flexion. In twelve healthy older (age 68-84) and nine young (age 22-29) subjects, finger kinematics were measured to assess finger movement enslaving and the range of independent finger movement. Muscle activation was assessed using a multi-channel electrode grid placed over the flexor digitorum superficialis (FDS) and the extensor digitorum (ED). FDS tendon displacements of the index, middle and ring fingers were measured using ultrasound. In older subjects compared to the younger subjects, we found: (1) increased enslaving of the middle finger during index finger flexion (young: 25.6 ± 12.4%, elderly: 47.0 ± 25.1%; p = 0.018), (2) a lower range of independent movement of the index finger (young_middle = 74.0%, elderly_middle: 45.9%; p < 0.001), (3) a more evenly distributed muscle activation pattern over the finger-specific FDS and ED muscle regions and (4) a lower slope at the beginning of the finger movement to tendon displacement relationship, presenting a distinct period with little to no tendon displacement. Our study indicates that primarily the movement independence of the index finger is affected by aging. This can partly be attributed to a muscle activation pattern that is more evenly distributed over the finger-specific FDS and ED muscle regions in the elderly.

Minimal force transmission between human thumb and index finger muscles under passive conditions

It has been hypothesized that force can be transmitted between adjacent muscles. Intermuscle force transmission violates the assumption that muscles act in mechanical isolation, and implies that predictions from biomechanical models are in error due to mechanical interactions between muscles, but the functional relevance of intermuscle force transmission is unclear. To investigate intermuscle force transmission between human flexor pollicis longus and the index finger part of flexor digitorum profundus, we compared finger flexion force produced by passive thumb flexion after one of three conditioning protocols: passive thumb flexion-extension cycling, thumb flexion maximal voluntary contraction (MVC), and thumb extension stretch. Finger flexion force increased after all three conditions. Compared to passive thumb flexion-extension cycling, change in finger flexion force was less after thumb extension stretch (mean difference 0.028 N, 95% CI 0.005 to 0.051 N), but not after thumb flexion MVC (0.007 N, 95% CI -0.020 to 0.033 N). As muscle conditioning changed finger flexion force produced by passive thumb flexion, the change in force is likely due to intermuscle force transmission. Thus, intermuscle force transmission resulting from passive stretch of an adjacent muscle is probably small enough to be ignored.

Myofascial Loads Can Occur without Fascicle Length Changes

Many studies have shown that connective tissue linkages can transmit force between synergistic muscles and that such force transmission depends on the position of these muscles relative to each other and on properties of their intermuscular connective tissues. Moving neighboring muscles has been reported to cause longitudinal deformations within passive muscles held at a constant muscle-tendon unit (MTU) length (e.g., soleus [SO]), but muscle forces were not directly measured. Deformations do not provide a direct measure of the force transmitted between muscles. We combined two different muscle preparations to assess whether myofascial loads exerted by neighboring muscles result in length changes of SO fascicles. We investigated the effects of proximal MTU length changes of two-joint gastrocnemius (GA) and plantaris (PL) muscles on the fascicle length of the one-joint SO muscle within (1) an intact muscle compartment and (2) a disrupted compartment that allowed measurements of fascicle length and distal tendon force of SO simultaneously. SO muscle bellies of Wistar rats (n = 5) were implanted with sonomicrometry crystals. In three animals, connectivity between SO and GA+PL was enhanced. Measurements were performed before and during maximal excitation of all plantar flexor muscles. In both setups, MTU length of GA+PL did not affect the length of SO fascicles, neither during passive nor active conditions. However, lengthening the MTU of GA+PL increased distal tendon force of SO by 43.3-97.8% (P < 0.001) and 27.5-182.6% (P < 0.001), respectively. This indicates that substantial myofascial force transmission between SO and synergistic muscle can occur via a connective tissue network running parallel to the series of SO sarcomeres without substantial length changes of SO fascicles.

Contribution of individual quadriceps muscles to knee joint mechanics

Many attempts have been made to determine the contribution of individual muscles in an agonistic group to the mechanics of joints. However, previous approaches had the limitations that muscles often could not be controlled in a precise manner, that individual muscles in an agonistic group could not be activated individually, and that individual muscle contributions could not be measured in an actively contracting agonistic group. Here, we introduce a surgical approach that allows for controlled activation of individual muscles of an agonistic group. The approach is illustrated for the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) of the rabbit quadriceps femoris group. We provide exemplar results for potential applications of the approach, such as measuring the pressure distribution in the patellofemoral joint, and the torque–angle relationship of VL, VM and RF when activated individually and when the three muscles are activated simultaneously.

Why do muscles lose torque potential when activated within their agonistic group?

Agonistic muscles lose approximately 20% of their individual torque generating capacity when activated with their agonistic muscles compared to when stimulated in isolation. In this study, we (i) tested if this loss in torque was accompanied by a corresponding loss in force, thereby testing the potential role of changes in moment arms between conditions; (ii) removed all inter-muscular connections between the quadriceps muscles, thus determining the potential role of inter-muscular force transmission; and (iii) systematically changed the inter-muscular pressure by performing experiments at different activation/force levels, thereby exploring the possible role of inter-muscular pressure in the loss of torque capacity with simultaneous muscle activation. Experiments were performed in a New Zealand White rabbit quadriceps model (n=5). Torque and force were measured during activation of femoral nerve branches that supply the individual quadriceps muscles while activating these branches simultaneously and in isolation. Regardless of joint angle and inter-muscular connections between muscles, the differences in torque values between the simultaneous and the isolated activation of the quadriceps muscles were also observed for the directly measured force values. Mean differences in simultaneous and isolated muscle activation remained similar between the intact and separated conditions: torque difference (21±5% of maximum isometric torque of intact condition [MICtorque], versus 19±6% MICtorque respectively) and for force (18±3% MICforce versus 19±7% MICforce respectively). The absolute torque loss was independent of the force, and thus presumably the inter-muscular pressures. Based on these results, we conclude that neither moment arm, inter-muscular pressure nor inter-muscular force transmission seems to be the primary cause for the torque deficit observed during simultaneous compared to isolated muscle activation. The mechanisms underlying loss of force capacity during agonistic muscle contraction remain unknown.