Clinical anatomy and biomechanics of the ankle in dance.
The ankle is an important joint to understand in the context of dance because it is the connection between the leg and the foot that establishes lower extremity stability. Its function coordinates with the leg and foot and, thus, it is crucial to the dancer's ability to perform. Furthermore, the ankle is one of the most commonly injured body regions in dance. An understanding of ankle anatomy and biomechanics is not only important for healthcare providers working with dancers, but for dance scientists, dance instructors, and dancers themselves. The bony architecture, the soft tissue restraints, and the locomotive structures all integrate to allow the athletic artistry of dance. Yet, there is still much research to be carried out in order to more completely understand the ankle of the dancer.
Ankle injuries account for a large percentage of all musculoskeletal conditions suffered by participants in a variety of physical activities, (1) and are the most common of all injuries in many sports. (2) Some athletic activities require extremes of ankle motion (e.g., soccer and gymnastics). However, classical ballet alone necessitates the combination of moving the ankle into absolutely maximum dorsiflexion (when a ballerina stands in the demiplie position) and into absolutely maximum plantar flexion (when she stands in the en pointe position). The very nature of these positions and the repetition with which they are practiced predispose the classical ballet dancer to a host of potential musculoskeletal stresses in the ankle. (3-10)
Dancers clearly are athletes, (11-14) sustain extreme physical stresses like athletes, (15) and experience high injury rates during dance participation. (3-6,16-25) Various studies place the incidence of ankle injuries between 4.7% and
(22.) 2% of all injuries suffered by dancers.
(3-5,18,20,21) This review article presents the anatomical and biomechanical principles of the ankle that are relevant to clinicians, scientists, and educators who work with dancers.
Normal Joint Anatomy and Mechanics Normal Bony Anatomy
The ankle, or talocrural joint, is a trochoid synovial joint. Though it is often considered a hinge, or ginglymus joint, (26,27) several authors indicate that its axis is more complicated than a simple uniaxial hinge. (28-33) The distal tibia and fibula form the joint's boxlike mortise; this is an area rather than a specific anatomical structure. The three articular surfaces of the ankle mortise are:
1. Medial: the lateral portion of the medial malleolus,
2. Superior: the tibial plafond, and
3. Lateral: the medial surface of the lateral malleolus.
The mortise contains the superior portion of the talus. This includes its articular surface, which is also called the trochlea, or dome. The talar trochlea is wedge-shaped when viewed from the superior direction. (34-36) It is usually more narrow posteriorly than anteriorly,
(37) although Barnett and Napier reported that a number of their talar specimens exhibited parallel sides (i.e., the anterior and posterior trochlear widths were equal). (28)
The talar dome sometimes is described as a truncated cone lying sideways, with the smaller circumference forming the medial edge of the dome and the larger circumference forming the lateral edge. (38) Barnett and Napier suggested that the articular surface of the talus is even more complex. They identified the arcs of three circles of different radii that demarcate the edges of the dome: one for the lateral edge, one for the anterior one-third of the medial edge, and a third arc for the posterior two-thirds of the medial edge. The smallest of these three is the arc of the anterior medial edge, and the largest is the arc of the posterior medial edge. (28) They compared the configuration to two truncated cones lying side-by-side.
The anatomy of the ankle joint, then, precludes the axis of the ankle lying in any of the three cardinal planes (sagittal, coronal, transverse). It is oblique to these planes, due largely to the architecture of the talar dome. A generalized single axis runs through the tips of the malleoli. (39) Singh and colleagues reported a single axis running just distal to the tips of the malleoli, but they found sizeable variations in its location among ankles. (40) Barnett and Napier identified two separate axes in the ankle: one for dorsiflexion and one for plantar flexion. (28) Hicks reproduced these findings the following year (1953) and reported that movement of the ankle cannot occur around both of these axes simultaneously. (29) More than 35 years later Lundberg's work, using roentgen stereophotogrammetry (a method utilizing x-rays taken in two planes to obtain three-dimensional information about the skeletal system), further developed the observations of Barnett and Napier and Hicks. (30-32) As seems obvious, dorsiflexion occurs around the dorsiflexion axis and plantar flexion occurs around the plantar flexion axis. (28,29) These two axes cross in the interior of the talar trochlea. At or near this same point the axes for ankle pronation, supination, medial rotation, and lateral rotation also intersect, (30,32) a spot Lundberg refers to as a "hub, around which the ankle joint has more freedom of movement than is often assumed." (32)
Normal Ligamentous Anatomy and Mechanics
The ankle joint receives its primary support from an array of ligaments that lie medially, laterally, posteriorly, and superiorly to the joint. The medial ligament complex is termed the deltoid ligament, a fan-shaped group of four ligaments comprising the anterior talotibial, calcaneotibial, tibionavicular, and posterior talotibial ligaments. (41) These four portions of the deltoid are combined into a substantial expansion of the medial joint capsule. (42) Siegler and associates noted the relative strength of the deltoid, in spite of their discovery that its calcaneotibial portion could only resist negligible forces before it failed. (43) Therefore they disregarded the calcaneotibial ligament in their study, concluding that it is not an important supporting structure of the medial ankle, even though overall the deltoid is quite strong. According to both Siegler and coworkers (43) and Attarian and colleagues (44) the strongest of the main ligaments in the ankle is the deep portion of the deltoid, the anterior and posterior talotibial complex.
The ligament support on the lateral side is not nearly as strong, and this is well known to be the most commonly injured ankle region. (45,46) The anterior talofibular ligament sits horizontally when the ankle is in anatomical position, running from the anterior edge of the lateral malleolus to the lateral aspect of the neck of the talus. (42,47) When the ankle is plantar flexed the anterior talofibular ligament moves downward toward a nearly vertical position and tightens (45,47); this results because its talar insertion moves downward. Attarian and associates evaluated several ankle bone-ligament-bone in vitro preparations for their capacity to resist force loading. (44) They found that the anterior talofibular is the weakest of all the ankle ligaments, a conclusion corroborated by other authors. (42,43,47) The calcaneofibular ligament attaches to the distal tip of the lateral malleolus (46,48) and the lateral tubercle of the calcaneus. (35,46) (Sarrafian states specifically that this ligament originates from the anterior aspect of the fibular tip. (35)) The ligament sits obliquely when the ankle is in anatomical position and becomes vertical, or closely parallel to the fibula, in dorsiflexion. (47) During plantar flexion its distal attachment moves rearward, which relaxes the ligament and places it into a horizontal position. (42,47)
Three other ligaments also are important to overall ankle stability: the posterior talofibular ligament, the anterior inferior tibiofibular ligament, and the posterior inferior tibiofibular ligament. The posterior talofibular is a very strong, horizontal ligament that runs between the inside of the posterior lip of the lateral malleolus and the posterolateral tubercle of the talus. (47) The anterior and posterior inferior tibiofibular ligaments support the syndesmosis of the distal tibia and fibula. Thus, they are proximal to the ankle joint and are significant because the integrity of the mortise is largely dependent on these two ligaments and the interosseous membrane. (49)
In 1950 Bonnin identified the relative weakness of the anterior talofibular ligament and the relative moderate strength of the calcaneofibular ligament. (42) Makhani suggested that the calcaneofibular ligament "is the most important component of the lateral ligament." (47) He further indicated that various portions of the lateral ligamenture demonstrate changing orientations and tension forces while the ankle moves through its range of motion, a finding consistent with more recent studies. (50-53) In the often-injured lateral ligament complex, it is interesting to consider the characteristics of these ligaments in the positions of demi-plie and en pointe. According to the authors cited above, it is expected that in demi-plie the anterior talofibular ligament will relax and the calcaneofibular ligament will be under tension. The opposite is expected when en pointe. Although no studies to date have examined the ankle ligaments under the extreme position of en pointe, it is clear that strain (a measure of deformation) in the anterior talofibular increases with increasing plantar flexion. (50-54) Cawley and France (54) and Bahr and colleagues (50) further concluded that the increase in anterior talofibular strain is accentuated during compressive loading through the ankle joint. Maximum plantar flexion en pointe places the anterior talofibular ligament parallel to the fibula; when in this position it functions as the primary stabilizing ligament of the lateral ankle. (50) Furthermore, based on the observations of the cited researchers, the fully plantar flexed en pointe position presumably places the anterior talofibular ligament at particular risk because it is the weakest ankle ligament, it is at its longest length, and it is under its maximum tension force. Figure 1 shows the anticipated positions of the anterior talofibular and calcaneofibular ligaments at three points in ankle range of motion seen in ballet.
[FIGURE 1 OMITTED] (35,41,42,45-48,77)
Motion at the Ankle Joint Range of Dorsiflexion and Plantar Flexion
Dorsiflexion of the ankle is usually described as a uniaxial motion in the sagittal plane. It is the movement of the dorsum of the foot upward toward the leg. This movement places the ankle into its most stable position, when the trochlea of the talus and the articular surfaces of the tibia and fibula are "close-packed." (55) The opposite motion, plantar flexion, is usually described as a uniaxial movement of the plantar surface of the foot in an inferior direction (i.e., pointing the foot). (26) Parenthetically, the dorsi-flexion and plantar flexion labels are preferred because confusion exists when assigning the terms flexion and extension to ankle movements. For instance, some authors use flexion to mean plantar flexion and extension to mean dorsiflexion. (27,56) Conversely, others give extension as an alternate name for plantar flexion and flexion as an alternate for dorsiflexion. (26)
Reporting the range of motion of the ankle is subject to various technical considerations. Clinical range of motion measurement uses the anatomical landmarks of the midlines of the fibular shaft and fifth metatarsal and an axis at the lateral malleolus. (57) Considering anatomical position--or ankle neutral position--as zero, in non-dancers normal active clinical dorsiflexion is 20[degrees] and normal active clinical plantar flexion is 50[degrees]. (26,27,36,55,57) However, goniometry of the ankle joint necessarily encompasses movements in joints of the foot, (31,33,42,58) so that, in fact, accurate clinical measurement of tibiotalar motion alone is not possible. (59)
Lundberg and associates found that as much as 40% of plantar flexion motion occurred in the joints of the midfoot, but the relative amounts attributable to each of these joints varied widely among individuals. They reported mean talocrural motion (i.e., angular motion between the tibia and the talus only) as 23[degrees] of dorsiflexion and 28[degrees] of plantar flexion. (30,31)
Backer and Kofoed compared passive ankle range of motion using a manual goniometer with active weightbearing ankle range of motion using a perpendicular pendulum goniometer. Their results for passive motion were 15[degrees] of dorsiflexion and 44[degrees] of plantar flexion; for active weightbearing motion they measured 38[degrees] of dorsiflexion and 50[degrees] of plantar flexion. (60)
True ankle joint motion between the tibia and talus is typically measured by x-ray. Bonnin suggested that radiography is the only accurate measurement tool for talocrural motion. (42) He demonstrated that the arc of the articular surface of the talar dome subtends an angle of 90[degrees] to 105[degrees], and that 50[degrees] to 55[degrees] of this is taken up by the tibial plafond's congruence with the talus. According to his measurements a maximum of 55[degrees] is left for total movement of the tibia on the talus, with an additional 5[degrees] available if the posterior edge of the tibial articular surface passes the posterior edge of the talar articular surface. (42) Backer and Kofoed noted a significant difference between radiographic and clinical measurements in plantar flexion, attributing the difference to the former measuring tibiotalar motion and the latter measuring motion between the leg and the foot. (61) Using an x-ray method, Sammarco and coworkers reported the mean ranges of motion of the ankle in weightbearing as 21[degrees] [+ or -] 7[degrees] for dorsiflexion and 23[degrees] [+ or -] 8[degrees] for plantar flexion in non-dancers. (33) Their non-weightbearing findings were 23[degrees] [+ or -] 8[degrees] for dorsiflexion and 23[degrees] [+ or -] 10[degrees] for plantar flexion. The discrepancy in these plantar flexion values when compared to those obtained by clinical goniometry reflects the difference between true tibiotalar range of motion and ankle motion that includes tibiotalar range of motion plus segmental motion between pairs of tarsals and metatarsals.
Weseley and colleagues also studied weightbearing ankle range of motion radiographically. (56) In their series of 50 ankles maximum tibiotalar dorsiflexion values fell between 0[degrees] and 23[degrees], and maximum tibiotalar plantar flexion values fell between 10[degrees] and 51[degrees]. Their comparative clinical measurements among ankles ranged from a low of 0[degrees] to a high of 30[degrees] for dorsiflexion, and from a low of 60[degrees] to a high of 85[degrees] for plantar flexion. This again highlights the difference between clinical range of motion that includes motion at joints in the foot and true ankle range of motion between the tibia and talus.
Assessment of plantar flexion can be technically challenging, (58) particularly in ballet dancers. This is partly due to the extreme clinical range seen in dancers. Hamilton and associates evaluated 14 female and 14 male professional dancers on a variety of musculoskeletal characteristics that included ankle range of motion. (62) They found plantar flexion in females to be 113[degrees] from anatomical position and 107[degrees] in males. Wiesler and coworkers measured ankle range of motion in 119 female and 29 male dancers. (63) Their reported plantar flexion values were 101[degrees] [+ or -] 2.5[degrees] (left) and 96[degrees] [+ or -] 2.7[degrees] (right) in female ankles. For males their results were 99[degrees] [+ or -] 6.9[degrees] (left) and 97[degrees] [+ or -] 7.3[degrees] (right). Dorsiflexion values reported by these investigators were 77[degrees] [+ or -] 2.2[degrees] (left) and 78[degrees] [+ or -] 2.3[degrees] (right) for females and 62[degrees] [+ or -] 6.1[degrees] (left) and 63[degrees] [+ or -] 5.9[degrees] (right) for males.
Novella described a method for assessing maximal plantar flexion in dancers that identifies the angular difference between the dorsal border of the talus and navicular and the anterior border of the tibia using a gravity goniometer (inclinometer). (64) In his series of 811 dancers he found this mean difference to be 8[degrees] [+ or -] 3[degrees] in females and 5[degrees] [+ or -] 2.5[degrees] in males. Calculations from his technique indicate that relative to the tibia the talus plantar flexes 98[degrees] from anatomical position in female dancers and 95[degrees] in male dancers. This stands in stark contrast to other authors' findings in non-dancers.
Lin and associates measured ankle plantar flexion in university ballet dancers en pointe using video analysis.
(65) Mean plantar flexion for the right ankle was 52[degrees] [+ or -] 4.3[degrees]; for the left ankle it was 54[degrees] [+ or -] 6.0[degrees]. The proximity of these values to the maximum plantar flexion seen in non-dancers
(50[degrees]) suggests that the placement of the anatomical markers on their subjects could not approximate the anatomical landmarks used in ankle goniometry. Supporting this point is the authors' description of the markers' placements: on the mid-shank, the lateral malleolus, the heel, and the dorsum of the foot between the second and third metatarsophalangeal joints (with the subject wearing pointe shoes). Even accounting for differences between weightbearing and non-weightbearing measurement of range-of-motion, their protocol could not have measured tibiotalar motion, and it likely underestimated the clinical range of motion in these ballerinas when compared to the work of other authors. (62-64)
Muscles Acting on the Ankle
The muscles that act on the ankle to produce dorsiflexion and plantar flexion can be categorized into primary and secondary movers. Muscles that produce ankle movement also have other, and often primary, functions. They are all extrinsic muscles, meaning that their contractile portions lie outside the ankle itself--in the leg--and the tendons of those muscles insert on bones of the foot in such a way that ankle motion is elicited when the muscles contract. These leg muscles are divided into four compartments bounded by fascial septa: the superficial posterior compartment, the deep posterior compartment, the lateral compartment, and the anterior compartment. The muscles contained in each compartment are listed in Table 1.
The primary plantar flexors are the two calf muscles: gastrocnemius and soleus. (26) These are sometimes referred to as "triceps surae" because of their three origins, or heads: two of the gastrocnemius and one of the soleus. The gastrocnemius is a two-joint muscle that also flexes the knee. (26) A third, yet weaker, plantar flexor is the plantaris; it is of less practical consequence in plantar flexion because it is relatively small compared to the triceps surae muscles. It is also somewhat difficult to study because of its location under the gastrocnemius and its variability of morphology and tendon insertion. (66) Plantaris is absent in nearly 7% of individuals; one-third of these have bilateral absence. (66)
Secondary plantar flexors include muscles whose primary actions are inversion, eversion, or toe flexion. An invertor that assists with plantar flexion is the tibialis posterior. (26,27) Evertors that help plantar flex the ankle are peroneus brevis and peroneus longus. (26,27) Finally, two toe flexors also contribute to plantar flexion: the flexor hallucis longus and flexor digitorum longus. (26,27)
The primary dorsiflexor of the ankle is the tibialis anterior. (26) However, the two extrinsic toe extensor muscles--extensor hallucis longus and extensor digitorum longus--also contribute significantly to dorsiflexion because of their course across the anterior aspect of the ankle. Peroneus tertius, sometimes thought of as an offshoot of extensor digitorum longus, also should be considered an assistor of dorsiflexion, (27) though it is absent in (10.) 5% of individuals. (67) Table 2 summarizes the various functions of the extrinsic leg muscles in the context of plantar flexion and dorsiflexion.
Certain muscles not required for gross movement in a particular dance maneuver may play a role in balance. Although electromyographical studies of dancers are scarce, the first of two investigations by Trepman and colleagues explored first position standing posture and demi-plie. (68) They found the lateral and medial heads of the gastrocnemius--a plantar flexor--displayed a variety of EMG patterns during demi-plie by professional dancers. Since the demi-plie movement does not require plantar flexion, they suggested the gastrocnemius likely contracts as necessary to preserve balance. Other muscles in which they found similar contractile variability during demi-plie were the tibialis anterior, gluteus maximus, the hamstring group, and the adductor group.
These authors also discovered in their first study that the tibialis anterior increases its contractility at the point of changing from lowering to raising in the demi-plie. (68) In their second study, (69) the tibialis anterior contracted isometrically during the portions of grand-plie when the heel was not in contact with the ground. Thus, the tibialis anterior may stabilize the ankle for proper execution of either maneuver. The real value of the work by Trepman and colleagues is much broader than muscle function in the lower extremity during specific actions. That is, their investigations highlight an interesting and necessary area of future research because it appears that many assumptions about how muscles contract as movers and stabilizers to produce dance movements may need to be re-evaluated. (68,69)
Mechanical Levers in Ankle Movement
Motion at the ankle--in dance or any other activity--depends on how forces are applied to the levers of the skeleton. In mechanics there are three types of levers: first, second, and third class. All three types are seen about the ankle; the class depends on what motion is being performed and whether or not the lower extremity is weightbearing. The ankle is a second class lever system when performing releve. (26) In a second class lever, the resistance (body weight) is between the fulcrum and the applied force. Therefore, in releve the fulcrum is the metatarsophalangeal region on the floor, the resistance is the body weight exerted through the talocrural joint, and the force of action is exerted by the triceps surae inserted at the posterior calcaneus via the Achilles' tendon (Fig. 2A). Remaining on the toes requires isometric contraction of the musculature while maintaining the center of gravity over the foot's area of contact with the floor. (70)
Dorsiflexion while weightbearing creates a fulcrum where the heel rests on the floor. This also is a second class lever system because the force of the dorsiflexors is exerted forward of the resistance (which is again the force of the body weight through the talocrural joint). Note that as in plantar flexion, here the resistance is between the fulcrum and the applied force. This system is shown in Figure 2B.
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
One more mechanical observation about the lever system of the ankle is worth mentioning because it pertains to ankle strengthening and rehabilitation. Consider the situation of using an elastic resistance band to develop plantar flexion strength. The band passes across the plantar surface of the forefoot, with the dancer holding both ends while plantar flexing against the resistance of the band. In this case the ankle operates as a first class lever. In such a lever--for example, a see-saw--the fulcrum is positioned between the resistance and the acting force. Thus, the fulcrum is the talocrural joint, the resistance is applied on the plantar forefoot, and the force of the triceps surae acts on the calcaneus. This is shown in Figure 3A.
Conversely, strengthening the dorsiflexors would require the elastic band to pass across the dorsal surface of the forefoot with the free ends of the band secured by an assistant or a piece of apparatus. In this scenario the ankle is a third class lever system, because the force application provided by the dorsiflexors is between the fulcrum (the talocrural joint) and the resistance on the forefoot. Figure 3B illustrates this.
Compression of Joint Surfaces at Extremes of Ankle Motion
Stormont and coworkers suggest that articular surface contact between the tibia and talus provides a sizeable amount of ankle stability to valgus and varus movement between 15[degrees] of dorsiflexion and 20[degrees] of plantar flexion in the absence of the ligaments. (71) Clearly the tibiotalar motion of a ballerina moving from demi-plie to en pointe moves through a substantially greater range of motion than this. However, no studies replicate Stormont and coworkers' findings at the extremes of ankle motion seen in ballet. When the ankle is in maximum plantar flexion during demi-pointe or pointe the posterior edge of the tibial plafond articulates with the talus and calcaneus. In spite of the seemingly reduced contact area of the articular surfaces of the tibia and talus (because of the narrower posterior portion of the talus moving into the mortise), standing en pointe is a bony "locked" position of the ankle and subtalar joints (7,72,73) from which ankle sprains are unlikely. (7)
Brown and Micheli express an alternate opinion, suggesting that in extreme plantar flexion "... only the narrow portion of the talus remains in the mortise--affording only limited bony stability while placing increasing demands on the soft-tissue restraints...." (74) Certainly the contours of the ankle's articular surfaces, the forces transmitted from the tibia through the ankle to the foot and then the floor, the mechanics of the subtalar joint, and the tension forces applied to the ankle and foot by the ligaments and muscles and tendons all play a role in ankle stability en pointe, and represent topics for future research.
In the forced dorsiflexion of demiplie an anterior fulcrum is created if the anterior edge of the tibial plafond contacts the dorsal neck of the talus. (75) The resulting lever system stretches the posterior ankle soft tissues, and posterior distraction of the joint then removes the normally parallel congruence of the tibial and talar articular surfaces. This is a radiographic finding associated with dancers with anterior bony impingement. (75) Anterior impingement is exacerbated when exostoses either extend the anterior edge of the tibia, raise the dorsum of the talar neck, or both. (76)
A properly functioning ankle is fundamental to success in dance. While the ankle injury rate in dance is high, it may be surprising that it is not even higher given the long hours of rehearsing and performing. Studying clinically-oriented anatomy and biomechanics of the ankle will help dance medicine practitioners, dance scientists, dance instructors, and dancers understand the intricacies of the ankle in this art form. The bones, ligaments, muscles, and tendons, along with the nervous and cardiovascular systems, provide the functional framework for the beauty, artistry, and athleticism of the various genres of dance. There is ample fertile ground for future research into the ankle function of dancers. Particularly in classical ballet, the only physical activity in the world requiring repetitive movement from maximum forced dorsiflexion to maximum forced plantar flexion, there is much knowledge still to be gained beyond the currently available investigations of the ankle in non-dancers and sports participants.
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Jeffrey A. Russell, M.S., A.T.C., Islay M. McEwan, M.Sc., M.C.S.P., Yiannis Koutedakis, Ph.D., and Matthew A. Wyon, Ph.D.
Jeffrey A. Russell, M.S., A.T.C., is from the University of Wolverhampton School of Sport, Performing Arts and Leisure, Walsall, United Kingdom. Islay M. McEwan, M.Sc., M.C.S.P., is from the Department of Exercise and Sport Science, Manchester Metropolitan University, United Kingdom. Yiannis Koutedakis, Ph.D., is from the Department of Sport and Exercise Sciences, Thessaly University, Trikala, Greece; and the School of Sport, Performing Arts and Leisure, Wolverhampton University, United Kingdom. Matthew A. Wyon, Ph.D., is from the University of Wolverhampton School of Sport, Performing Arts and Leisure, Walsall, United Kingdom.
Correspondence: Jeffrey A. Russell, M.S., A.T.C., P.O. Box 1649 Brentwood, Tennessee 72024; email@example.com.
Table 1 Muscle Compartments of the Leg Muscle Compartment Muscles Superficial Posterior Gastrocnemius Soleus Plantaris Deep Posterior Flexor hallucis longus Flexor digitorum longus Tibialis posterior Lateral Peroneus longus Peroneus brevis Anterior Extensor hallucis longus Tibialis anterior Peroneus tertius (when present) Table 2 Muscles Acting on the Talocrural Joint (adapted from Floyd and Thompson (26) and Magee (27)) Primary or Secondary Additional Actions Action Muscles Acting Mover of Muscle Plantar Gastrocnemius P Knee flexion flexion Soleus P Plantaris S Knee flexion Flexor hallucis S Flexion of great longus toe; Inversion Flexor digitorum S Flexion of toes longus 2-5; Inversion Tibialis posterior S Inversion Peroneus longus S Eversion Peroneus brevis S Eversion Dorsiflexion Tibialis anterior P Inversion Extensor hallucis S Extension of great longus toe; Inversion Extensor digitorum S Extension of toes longus 2-5; Eversion Peroneus tertius S Eversion
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|Author:||Russell, Jeffrey A.; McEwan, Islay M.; Koutedakis, Yiannis; Wyon, Matthew A.|
|Publication:||Journal of Dance Medicine & Science|
|Date:||Jul 1, 2008|
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