Myofascial Connections Research Articles

Paraspinal Muscle Stiffness during Hamstring Exercise Using Shear-Wave Elastography.

Soccer teams integrate specific exercises into their typical workout programs for injury prevention. This study examined the effects of hamstring exercise on paraspinal and hamstring stiffness. These findings can inform training and rehabilitation programs to improve muscle health and prevent injuries. Fifteen young, healthy males performed passive and active (submaximal) knee flexion efforts from 0°, 45°, to 90° angle of knee flexion from the prone position. Using shear-wave elastography (SWE) and surface electromyography, we measured the elastic modulus and root mean square (RMS) signal of the erector spinae (ES), multifidus (MF), semitendinosus (ST), and semimembranosus (SM) during different knee flexion angles. Passive SWE modulus at 0° was 12.44 ± 4.45 kPa (ES), 13.35 ± 6.12 kPa (MF), 22.01 ± 4.68 kPa (ST), and 21.57 ± 5.22 kPa (SM) and it was greater (p < 0.05) compared to 45° and 90°. The corresponding values during knee flexion contractions at 0° increased to 18.99 ± 6.11 kPa (ES), 20.65 ± 11.31 kPa (MF), 71.21 ± 13.88 kPa (ST), and 70.20 ± 14.29 kPa (SM) and did not differ between angles (p > 0.05). Compared to rest, the relative increase in the SWE modulus during active contraction had a median value (interquartile range) ranging from 68.11 (86.29) to 101.69 (54.33)% for the paraspinal muscles and it was moderately to strongly correlated (r > 0.672) with the corresponding increase of the hamstring muscles [ranging from 225.94 (114.72) to 463.16 (185.16)%]. The RMS signal was greater during active compared to passive conditions, and it was lower at 90° compared to 45° (for SM/ST) and 0° (for all muscles). The association between paraspinal and hamstring passive muscle stiffness indicates a potential transmission of forces through myofascial connections between the lumbar spine and the lower limbs. In this laboratory setting, hamstring exercises affected the stiffness of the paraspinal muscles.

Описательный обзор соматических дисфункций, ассоциированных с мышечно-фасциальной хронической тазовой болью

Myofascial pelvic pain is a major component of the chronic pelvic pain that is often not properly diagnosed by health care professionals. To fully understand the nature and function of the pelvic floor, it must be studied it in its most global aspect, taking into account numerous activities other than urological, gynecological, and intestinal ones: pelvic stabilization, participation in breathing, walking. It is necessary to consider the pelvic floor as a muscular-fascial unit with synergistic and antagonistic activity of muscle bundles, including more or less intertwined ones, with multiple functions, and not only with the function of closing the pelvic cup. Also, the pelvic floor muscles are connected to distant parts of the body, such as the feet and neck, through myofascial connections. Therefore, functional disorders in distant sites, such as flat feet, spasm of the respiratory diaphragm, or tension of the dura mater of the spinal cord, can lead to pelvic floor dysfunctions and musculofascial pain. In turn, pelvic floor dysfunctions will also affect the statics and dynamics of the body.

The Most Common Functional Disorders and Factors Affecting Female Pelvic Floor.

The pelvic floor (PF) is made of muscles, ligaments, and fascia, which ensure organ statics, maintain muscle tone, and are involved in contractions. This review describes the myofascial relationships of PF with other parts of the body that determine the proper functions of PF, and also provides insight into PF disorders and the factors contributing to them. PF plays an important role in continence, pelvic support, micturition, defecation, sexual function, childbirth, and locomotion, as well as in stabilizing body posture and breathing, and cooperates with the diaphragm and postural muscles. In addition, PF associates with distant parts of the body, such as the feet and neck, through myofascial connections. Due to tissue continuity, functional disorders of muscles, ligaments, and fascia, even in the areas that are distant from PF, will lead to PF disorders, including urinary incontinence, fecal incontinence, prolapse, sexual dysfunction, and pain. Dysfunctions of PF will also affect the rest of the body.

Myofiber stretch induces tensile and shear deformation of muscle stem cells in their native niche

Muscle stem cells (MuSCs) are requisite for skeletal muscle regeneration and homeostasis. Proper functioning of MuSCs, including activation, proliferation, and fate decision, is determined by an orchestrated series of events and communication between MuSCs and their niche. A multitude of biochemical stimuli are known to regulate MuSC fate and function. However, in addition to biochemical factors, it is conceivable that MuSCs are subjected to mechanical forces during muscle stretch-shortening cycles because of myofascial connections between MuSCs and myofibers. MuSCs respond to mechanical forces in vitro, but it remains to be proven whether physical forces are also exerted on MuSCs in their native niche and whether they contribute to the functioning and fate of MuSCs. MuSC deformation in their native niche resulting from mechanical loading of ex vivo myofiber bundles was visualized utilizing mT/mG double-fluorescent Cre-reporter mouse and multiphoton microscopy. MuSCs were subjected to 1 h pulsating fluid shear stress (PFSS) with a peak shear stress rate of 6.5 Pa/s. After PFSS treatment, nitric oxide, messenger RNA (mRNA) expression levels of genes involved in regulation of MuSC proliferation and differentiation, ERK 1/2, p38, and AKT activation were determined. Ex vivo stretching of extensor digitorum longus and soleus myofiber bundles caused compression as well as tensile and shear deformation of MuSCs in their niche. MuSCs responded to PFSS in vitro with increased nitric oxide production and an upward trend in iNOS mRNA levels. PFSS enhanced gene expression of c-Fos, Cdk4, and IL-6, whereas expression of Wnt1, MyoD, Myog, Wnt5a, COX2, Rspo1, Vangl2, Wnt10b, and MGF remained unchanged. ERK 1/2 and p38 MAPK signaling were also upregulated after PFSS treatment. We conclude that MuSCs in their native niche are subjected to force-induced deformations due to myofiber stretch-shortening. Moreover, MuSCs are mechanoresponsive, as evidenced by PFSS-mediated expression of factors by MuSCs known to promote proliferation.

Surgical Mobilization of Skeletal Muscles Changes Functional Properties—Implications for Tendon Transfers

Tendon transfer surgery restores function by rerouting working muscle-tendon units to replace the function of injured or paralyzed muscles. This procedure requires mobilizing a donor muscle relative to its surrounding myofascial connections, which improves the muscle's new line of action and increases excursion. However, the biomechanical effect of mobilization on a donor muscle's force-generating function has not been previously studied under invivo conditions. The purpose of this study was to quantify the effect of surgical mobilization on active and passive biomechanical properties of 3 large rabbit hind limb muscles. Myofascial connections were mobilized stepwise from the distal end to the proximal end of muscles (0%, 25%, 50%, and 75% of muscle length) and their active and passive length-tension curves were measured after each degree of mobilization. Second toe extensor, a short-fibered muscle, exhibited a 30% decline in peak stress and 70% decline in passive stress, whereas extensor digitorum longus, a short-fibered muscle, and tibialis anterior, a long-fibered muscle, both exhibited similar smaller declines in active (about 18%) and passive stress (about 65%). The results highlight 3 important points: (1) a trade-off exists between increasing muscle mobility and decreasing force-generating capacity; (2) intermuscular force transmission is important, especially in second toe extensor, because it was able to generate 70% of its premobilization active force although most fibers were freed from their native origin; and (3) muscle architecture is not the major influence on mobilization-induced force impairment. These data demonstrate that surgical mobilization itself alters the passive and active force-generating capacity of skeletal muscles. Thus, surgical mobilization should not be viewed simply as a method to redirect the line of action of a donor muscle because this procedure has an impact on the functional properties of the donor muscle itself.

The Five Diaphragms in Osteopathic Manipulative Medicine: Myofascial Relationships, Part 1.

Working on the diaphragm muscle and the connected diaphragms is part of the respiratory-circulatory osteopathic model. The breath allows the free movement of body fluids and according to the concept of this model, the patient's health is preserved thanks to the cleaning of the tissues by means of the movement of the fluids (blood, lymph). The respiratory muscle has several systemic connections and multiple functions. The founder of osteopathic medicine emphasized the importance of the thoracic diaphragm and body health. The five diaphragms (tentorium cerebelli, tongue, thoracic outlet, thoracic diaphragm and pelvic floor) represent an important tool for the osteopath to evaluate and find a treatment strategy with the ultimate goal of patient well-being. The two articles highlight the most up-to-date scientific information on the myofascial continuum for the first time. Knowledge of myofascial connections is the basis for understanding the importance of the five diaphragms in osteopathic medicine. In this first part, the article reviews the systemic myofascial posterolateral relationships of the respiratory diaphragm; in the second I will deal with the myofascial anterolateral myofascial connections.

The Five Diaphragms in Osteopathic Manipulative Medicine: Myofascial Relationships, Part 2.

The article continues the anatomical review of the anterolateral myofascial connections of the five diaphragms in osteopathic manipulative medicine (OMM), with the most up-to-date scientific information. The postero-lateral myofascial relationships have been illustrated previously in the first part. The article emphasizes some key OMM concepts; the attention of the clinician must not stop at the symptom or local pain but, rather, verify where the cause that leads to the symptom arises, thanks to the myofascial systems. Furthermore, it is important to remember that the human body is a unity and we should observe the patient not as a series of disconnected segments but as multiple and different elements that work in unison; a dysfunction of tissue will adversely affect neighboring and distant tissues. The goal of the work is to lay solid foundations for the OMM and the five-diaphragm approach showing the myofascial continuity of the human body.

EFFECTS OF LOWER EXTREMITY AND TRUNK KINETIC CHAIN RECRUITMENT ON SERRATUS ANTERIOR MUSCLE ACTIVATION DURING FORWARD PUNCH PLUS EXERCISE ON STABLE AND UNSTABLE SURFACES

The stabilizing action of the serratus anterior (SA) muscle is vital in maintaining normal scapulothoracic rhythm. This warrants investigation of exercises to discern which are best to activate the SA muscle. Recruitment of the muscles in the trunk and lower extremity kinetic chain during exercises has demonstrated increased SA activation due to the myofascial connections between various segments of the body. Variation of surfaces during an exercise has also been shown to alter the muscle recruitment patterns. The primary purpose was to determine the effects of trunk and lower extremity kinetic chain muscle recruitment on the SA muscle activity while on an unstable surface. The secondary purpose was to determine if the SA muscle activity would change when the surface stability during the exercises was reduced. Descriptive, within-subject repeated measures. Surface electromyographic activity of the SA, latissimus dorsi (LD), external oblique (EO) on the dominant, and femoral adductor (FA) muscles on the non-dominant side and gluteus maximus bilaterally was analyzed during forward punch plus (FPP) and two of its' variations: FPP with closed chain serape (CS), FPP with open chain serape (OS) on stable and unstable surface in twenty-one healthy males. A two-way repeated measure ANOVA was used to determine the difference in the muscle activation between exercises, surfaces, and interaction between these two variables. A separate one-way repeated measures ANOVA with Sidak post hoc test was used for comparisons between stable and unstable surfaces. (p≤0.05). Muscle activity was statistically significantly higher for the CS and the OS exercises compared to the FPP for all the muscles except for the LD within the same surface. There was no significant difference in muscle activity for any of the muscles when compared between stable and unstable surfaces. Incorporating the trunk and lower extremity kinetic chain during the FPP exercise increased the SA activation on both stable and unstable surfaces. However, the type of surface did not influence the activation of any muscle across exercises. The results of this study further strengthen the benefit of the kinetic chain exercises but also caution that adding an unstable surface to an exercise does not always imply higher muscle activation. 2b.

Can the Use of Unstable Surfaces and Instruction for Conscious Abdominal Contraction Increase the EMG Activity of the Periscapular Muscles During the Dynamic Push-Up?

It is believed that conscious abdominal contraction (CAC) during exercise encourages greater periscapular activation through existing myofascial connections. On the other hand, it is postulated that the use of unstable surfaces would promote greater neuromuscular demand. To analyze the effect of CAC on periscapular muscle activity during push-up plus exercise on stable and unstable surfaces and to evaluate the correlation between electromyographic (EMG) activity of the serratus anterior (SA) and abdominal oblique muscles. Repeated-measures design in a single group, pre-post CAC. Biomechanics laboratory. Twenty-three male volunteers without a history of lesions in the upper limbs participated in the study. Five repetitions of push-ups on stable and unstable surfaces were performed with and without instruction for CAC. The normalized amplitude of the EMG activity was obtained from the muscles of the upper, middle, and lower trapezius, SA upper (SA_5th) and lower (SA_7th) portions, external oblique (EO), and internal oblique. CAC increased the activity of the EO, internal oblique, middle trapezius, and SA (P < .05) in both surfaces. The use of the unstable surface increased the EMG activity of the EO, SA_7th, and middle trapezius and decreased the EMG activity of the SA_5th. However, all changes observed in EMG signals were of low magnitude, with effect sizes lower than 0.45. There was a weak correlation between the EMG activity of the EO and SA_5th (r = .24) and a strong correlation between the EO and SA_7th (r = .70). The isolated use of CAC or unstable surface during push-up seems to present no practical relevance, but the combined use of these strategies may increase activation of the SA_7th and middle trapezius muscles.

Activity patterns of extrinsic finger flexors and extensors during movements of instructed and non-instructed fingers

The fingers of the human hand cannot be controlled fully independently. This phenomenon may have a neurological as well as a mechanical basis. Despite previous studies, the neuromechanics of finger movements are not fully understood. The aims of this study were (1) to assess the activation and coactivation patterns of finger specific flexor and extensor muscle regions during instructed single finger flexion and (2) to determine the relationship between enslaved finger movements and respective finger muscle activation. In 9 healthy subjects (age 22–29), muscle activation was assessed during single finger flexion using a 90 surface electromyography electrode grid placed over the flexor digitorum superficialis (FDS) and the extensor digitorum (ED). We found (1) no significant differences in muscle activation timing between fingers, (2) considerable muscle activity in flexor and extensor regions associated with the non-instructed fingers and (3) no correlation between the muscle activations and corresponding movement of non-instructed fingers. A clear disparity was found between the movement pattern of the non-instructed fingers and the activity pattern of the corresponding muscle regions. This suggests that mechanical factors, such as intertendinous and myofascial connections, may also affect finger movement independency and need to be taken into consideration when studying finger movement.

Limited mechanical effects of intermuscular myofascial connections within the intact rat anterior crural compartment

Skeletal muscles of the rat anterior crural compartment are mechanically connected by epimuscular myofascial connections, but the relevance for mechanical muscle function within physiological ranges of joint motion is unclear. We evaluated the net effect at the ankle joint of epimuscular myofascial connections between tibialis anterior (TA) and extensor digitorum longus (EDL) muscles in the rat (n=8) and determined which anatomical structures may mediate such epimuscular mechanical interactions. We assessed (1) effects of knee angle (i.e. changes in EDL length and position relative to TA) and interactions of knee angle with fasciotomy and proximal EDL tenotomy on TA ankle moment and (2) the effect of knee angle on TA and EDL ankle moment summation. Knee angle was varied between 60° and 130°. Ankle angle was kept constant (90°). TA and EDL were excited individually and simultaneously (TA&EDL). The mathematical sum of individual TA and EDL moments was compared with the moment exerted by TA&EDL to assess the extent of non-additive ankle moment summation. Magnitude of TA ankle moment was not affected by knee angle, but frontal plane moment direction was. However, dissections indicated that this was not caused by the compartmental fascia or EDL length changes. Moment summation was non-additive in magnitude (+1.1±1.1% mean±s.d.) and frontal plane direction. The latter was affected by knee angle and ranged from +0.2±0.3° at 60° to +1.1±0.6° at 130°. As the net effects found were very limited, we conclude that myofascial connections between muscles in the anterior crural compartment have limited mechanical relevance during normal movement.

Changes in muscle spindle firing in response to length changes of neighboring muscles.

Skeletal muscle force can be transmitted to the skeleton, not only via its tendons of origin and insertion but also through connective tissues linking the muscle belly to surrounding structures. Through such epimuscular myofascial connections, length changes of a muscle may cause length changes within an adjacent muscle and hence, affect muscle spindles. The aim of the present study was to investigate the effects of epimuscular myofascial forces on feedback from muscle spindles in triceps surae muscles of the rat. We hypothesized that within an intact muscle compartment, muscle spindles not only signal length changes of the muscle in which they are located but can also sense length changes that occur as a result of changing the length of synergistic muscles. Action potentials from single afferents were measured intra-axonally in response to ramp-hold release (RHR) stretches of an agonistic muscle at different lengths of its synergist, as well as in response to synergist RHRs. A decrease in force threshold was found for both soleus (SO) and lateral gastrocnemius afferents, along with an increase in length threshold for SO afferents. In addition, muscle spindle firing could be evoked by RHRs of the synergistic muscle. We conclude that muscle spindles not only signal length changes of the muscle in which they are located but also local length changes that occur as a result of changing the length and relative position of synergistic muscles.

No functionally relevant mechanical effects of epimuscular myofascial connections between rat ankle plantar flexors.

Triceps surae muscles are mechanically connected by the shared Achilles tendon and by epimuscular myofascial connections. We aimed to assess the effects of proximal lengthening of gastrocnemius and plantaris muscles, imposed by changes in knee angle, on the magnitude and direction of the 3D ankle moment exerted by the soleus muscle and the mechanical interaction between ankle plantar flexor muscles during co-activation of gastrocnemius muscle, in the rat (N=9). Ankle angle was kept constant (90 deg), whereas knee angle was varied between 60 deg and 130 deg. At each knee angle, the soleus muscle was excited individually as well as simultaneously with the gastrocnemius muscle (SO+GA). The mathematical sum of individual soleus and gastrocnemius ankle moments was compared with the ankle moment exerted by SO+GA to assess nonlinear summation. Knee angle did not affect the magnitude of the soleus ankle moment (P=0.695). Moment directions in the transverse (P=0.050) and frontal (P=0.008) planes were affected by knee angle, but dissection indicated that this was not caused by length changes of the two-joint synergistic muscles. Nonlinear summation was found in the magnitude (-1.4 ± 1.9%, mean ± s.d., P<0.001) and in the frontal plane vector direction of the ankle moment (0.13 ± 0.23 deg, P=0.003); however, the extent did not change with knee angle. Although contraction of SO+GA increased the length of the Achilles tendon compared with its length at rest, this was not dependent on the knee angle (P=0.649). Despite the fact that intermuscular force transmission per se cannot be excluded, we conclude that, in vivo, the mechanical effects of epimuscular myofascial connections between rat ankle plantar flexors are not functionally relevant.

Effects of knee joint angle on global and local strains within human triceps surae muscle: MRI analysis indicating in vivo myofascial force transmission between synergistic muscles

PurposeMechanical interactions between muscles have been shown for in situ conditions. In vivo data for humans is unavailable. Global and local length changes of calf muscles were studied to test the hypothesis that local strains may occur also within muscle for which global strain equals zero.MethodsFor determination of globally induced strain in m. gastrocnemius in dissected human cadavers several knee joint angles were imposed, while keeping ankle joint angle constant and measuring its muscle–tendon complex length changes. In vivo local strains in both gastrocnemius and soleus muscles were calculated using MRI techniques in healthy human volunteers comparing images taken at static knee angles of 173° and 150°.ResultsImposed global strains on gastrocnemius were much smaller than local strains. High distributions of strains were encountered, e.g. overall lengthened muscle contains locally lengthened, as well as shortened areas within it. Substantial strains were not limited to gastrocnemius, but were found also in synergistic soleus muscle, despite the latter muscle–tendon complex length remaining isometric (constant ankle angle: i.e. global strain = 0), as it does not cross the knee. Based on results of animal experiments this effect is ascribed to myofascial connections between these synergistic muscles. The most likely pathway is the neurovascular tract within the anterior crural compartment (i.e. the collagen reinforcements of blood vessels, lymphatics and nerves). However, direct intermuscular transmission of force may also occur via the perimysium shared between the two muscles.ConclusionsGlobal strains imposed on muscle (joint movement) are not good estimators of in vivo local strains within it: differing in magnitude, as well as direction of length change. Substantial mechanical interaction occurs between calf muscles, which is mediated by myofascial force transmission between these synergistic muscles. This confirms conclusions of previous in situ studies in experimental animals and human patients, for in vivo conditions in healthy human subjects.

In muscle lengthening surgery multiple aponeurotomy does not improve intended acute effects and may counter-indicate: an assessment by finite element modelling

The goal was to assess the effects of multiple aponeurotomy on mechanics of muscle with extramuscular myofascial connections. Using finite element modelling, effects of combinations of the intervention carried out at a proximal (P), an intermediate (I) and a distal (D) location were studied: (1) Case P, (2) Case P-I, (3) Case P-D and (4) Case P-I-D. Compared to Case P, the effects of multiple interventions on muscle geometry and sarcomere lengths were sizable for the distal population of muscle fibres: e.g. at high muscle length (1) summed gap lengths between the cut ends of aponeurosis increased by 16, 25 and 27% for Cases P-I, P-D and P-I-D, respectively, (2) characteristic substantial sarcomere shortening became more pronounced (mean shortening was 26, 29, 30 and 31% for Cases P, P-I, P-D and P-I-D, respectively) and (3) fibre stresses decreased (mean stress equalled 0.49, 0.39, 0.38 and 0.33 for Cases P, P-I, P-D and P-I-D, respectively). In contrast, no appreciable effects were shown for the proximal population. The overall change in sarcomere length heterogeneity was limited. Consequently, the effects of multiple aponeurotomy on muscle length–force characteristics were marginal: (1) a limited reduction in active muscle force (maximal ‘muscle weakening effect’ remained between 5 and 11%) and (2) an even less pronounced change in slack to optimum length range of force exertion (maximal ‘muscle lengthening effect’ distally was 0.2% for Case P-I-D) were shown. The intended effects of the intervention were dominated by the one intervention carried out closer to the tendon suggesting that aponeurotomies done additionally to that may counter-indicated.

Myofascial Force Transmission via Extramuscular Pathways Occurs between Antagonistic Muscles

Most often muscles (as organs) are viewed as independent actuators. To test if this is true for antagonistic muscles, force was measured simultaneously at: (1) the proximal and distal tendons of the extensor digitorum muscle (EDL) to quantify any proximo-distal force differences, as an indicator of myofascial force transmission, (2) at the distal tendons of the whole antagonistic peroneal muscle group (PER) to test if effects of EDL length changes are present and (3) at the proximal end of the tibia to test if myofascially transmitted force is exerted there. EDL length was manipulated either at the proximal or distal tendons. This way equal EDL lengths are attained at two different positions of the muscle with respect to the tibia and antagonistic muscles. Despite its relatively small size, lengthening of the EDL changed forces exerted on the tibia and forces exerted by its antagonistic muscle group. Apart from its extramuscular myofascial connections, EDL has no connections to either the tibia or these antagonistic muscles. Proximal EDL lengthening increased distal muscular forces (active PER ΔF ≈ +1.7%), but decreased tibial forces (passive from 0.3 to 0 N; active ΔF ≈ –5%). Therefore, it is concluded that these antagonistic muscles do not act independently, because of myofascial force transmission between them. Such a decrease in tibial force indicates release of pre-strained connections. Distal EDL lengthening had opposite effects (tripling passive force exerted on tibia; active PER force ΔF ≈ –3.6%). It is concluded that the length and relative position of the EDL is a co-determinant of passive and active force exerted at tendons of nearby antagonistic muscle groups. These results necessitate a new view of the locomotor apparatus, which needs to take into account the high interdependence of muscles and muscle fibres as force generators, as well as proximo-distal force differences and serial and parallel distributions of sarcomere lengths that are consequences of such interaction. If this is done properly, the effects of integrating a muscle fibre, muscle or muscle group into higher levels of organisation of the body will be evident.

Myofascial force transmission between antagonistic rat lower limb muscles: Effects of single muscle or muscle group lengthening

Effects of lengthening of the whole group of anterior crural muscles (tibialis anterior and extensor hallucis longus muscles (TA + EHL) and extensor digitorum longus (EDL)) on myofascial interaction between synergistic EDL and TA + EHL muscles, and on myofascial force transmission between anterior crural and antagonistic peroneal muscles, were investigated. All muscles were either passive or maximally active. Peroneal muscles were kept at a constant muscle tendon complex length. Either EDL or all anterior crural muscles were lengthened so that effects of lengthening of TA + EHL could be analyzed. For both lengthening conditions, a significant difference in proximally and distally measured EDL passive and active forces, indicative of epimuscular myofascial force transmission, was present. However, added lengthening of TA + EHL significantly affected the magnitude of the active and passive load exerted on EDL. For the active condition, the direction of the epimuscular load on EDL was affected; at all muscle lengths a proximally directed load was exerted on EDL, which decreased at higher muscle lengths. Lengthening of anterior crural muscles caused a 26% decrease in peroneal active force. Extramuscular myofascial connections are thought to be the major contributor to the EDL proximo-distal active force difference. For antagonistic peroneal complex, the added distal lengthening of a synergistic muscle increases the effects of extramuscular myofascial force transmission.