Restoration of motor function of the deep fibular (peroneal) nerve by direct nerve transfer of branches from the tibial nerve: an anatomical study

Traction injuries of the common fibular (peroneal) nerve frequently result in significant morbidity due to tibialis anterior muscle paralysis and the associated loss of ankle dorsiflexion. Because current treatment options are often unsuccessful or unsatisfactory, other treatment approaches need to be explored. In this investigation, the anatomical feasibility of an alternative option, consisting of nerve transfer of motor branches from the tibial nerve to the deep fibular nerve, was studied. In ten cadaveric limbs, the branching pattern, length, and diameter of motor branches of the tibial nerve in the proximal leg were characterized; nerve transfer of each of these motor branches was then simulated to the proximal deep fibular nerve. A consistent, reproducible pattern of tibial nerve innervation was seen with minor variability. Branches to the flexor hallucis longus and flexor digitorum longus muscles were determined to be adequate, based on their branch point, branch pattern, and length, for direct nerve transfer in all specimens. Other branches, including those to the tibialis posterior, popliteus, gastrocnemius, and soleus muscles were not consistently adequate for direct nerve transfer for injuries extending to the bifurcation of the common fibular nerve or distal to it. For neuromas of the common fibular nerve that do not extend as far distally, branches to the soleus and lateral head of the gastrocnemius may be adequate for direct transfer if the intramuscular portions of these nerves are dissected. This study confirms the anatomical feasibility of direct nerve transfer using nerves to toe-flexor muscles as a treatment option to restore ankle dorsiflexion in cases of common fibular nerve injury.     

Intramuscular distribution of nerves supplying the soleus muscle in the chimpanzee

The human soleus muscle is considered a specialized muscle in terms of its origin, insertion and muscle fibre architecture (especially with regard to the existence of the bipenniform part). Its peculiarities have been understood as results of erect posture and bipedal walking (Frey, 1913). Sekiya (1991) pointed out that another feature of the human soleus muscle the nerve supply, i.e. the muscle received two kinds of nerves, the anterior branch (R. anterior) and the posterior branch (R. posterior); the former supplied the bipenniform part at the anterior surface of the muscle and communicated with the R. posterior within the muscle. In nonhuman primates, the soleus muscle has no bipenniform part and the nerve, identical with the R. anterior to the human soleus muscle, is unknown. The purpose of the present study is to clarify the pattern of the nerve supply to the soleus muscle in the chimpanzee, with special reference to the intramuscular distribution of the nerves and to discuss the origin of the R. anterior to the human soleus muscle from a comparative anatomical point of view. Six soleus muscles from three chimpanzees (Pan troglodytes) were examined under a stereomicroscope to clarify the intramuscular distribution of nerves supplying these muscles. The nerves supplying the soleus muscle were classified into three types according to the sites of their entry into the muscle. The first group nerve was the thickest of all nerves innervating the muscle, entered the muscle at the posterior surface of the proximal third and was considered as homologous with the R. posterior in the human.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spatial relationships between masticatory muscles and their innervating nerves in man with special reference to the medial pterygoid muscle and its accessory muscle bundle

The relationships between the positional arrangement of the surrounding and innervating nerves of the muscles supplied by the mandibular nerve, in particular those medial to the main trunk of the nerve, were examined in 24 head halves from 12 Japanese cadavers by dissection from the inside after removal of the bony elements except for the mandible. In ten sides of five heads, the lingual nerve pierced the medial pterygoid muscle, and the bundle lateral to the nerve was found to be separated as an accessory muscle bundle. The accessory bundle was frequently attached to the mylohyoid muscle. In addition, the inferior alveolar nerve and the lingual nerve frequently communicated, and in four specimens a branch from the lingual nerve entered the mylohyoid to communicate with the proper nerve. The innervation pattern indicated that the medial pterygoid muscle consists of the anteromedial and the posterolateral main parts, and sometimes has an accessory bundle. Based on the present findings and the previous studies of the positional relationships between the muscles and nerves by our research group, we propose that the muscles innervated by the mandibular nerve could be classified as an inner group (the lateral pterygoid) and an outer group (the other muscles). A possible scheme of the positional relationships between the muscles and nerves is presented.     

Electrophysiologic response recorded in the first dorsal interosseous muscle with stimulation of the tibial and deep fibular nerves

Foot intrinsic muscle innervation may demonstrate some variability. The first dorsal interosseous muscle (FDI) is innervated by the deep branch of the lateral plantar nerve (LPN) from the main trunk of the tibial nerve. Contribution from the deep fibular nerve (DFN) may also play a role in the supply of the FDI. Thirty healthy adult volunteers were studied to determine the presence and type of response in the FDI with stimulation of the tibial nerve/deep branch of the LPN and DFN. Both nerves were stimulated at the ankle and knee with a surface and needle recording from the FDI. Latency, amplitude, and conduction values were recorded for each nerve. The incidence of DFN supply to the FDI was 16.6% with a mean ankle amplitude of 152 microV. The incidence of tibial nerve/deep branch of the LPN supply to the FDI was 100%, with a mean ankle amplitude of 5.11 mV. The superficial branch of the LPN is most often studied when evaluating for tarsal tunnel syndrome because the standard recording site is the abductor digiti minimi (ADM). Recording from the ADM, however, frequently produces a less than desirable waveform, and the technical challenges encountered with this site make tarsal tunnel syndrome assessment difficult. It is also possible that selective involvement of the deep branch of the LPN may occur, and if so, recording from the FDI may prove valuable.     

Reinnervation of fast and slow mammalian muscles by a superfluous number of motor axons

In this study peripheral nerves from flexor digitorum longus, (alien nerve) as well as the deep branch of the muscle's own lateral popliteal nerve were cut and connected to the distal stump of the lateral popliteal nerve. Extensor digitorum longus and tibialis anterior muscles then became reinnervated to a similar extent by either nerve, showing no preference for its own nerve. A significant proportion of the endplates in these muscles remained permanently supplied by more than one axon, and a proportion of the muscle fibres was supplied by both nerves. No ectopic endplates were formed on fast muscle fibres. The same two nerves were also connected to the slow soleus muscle and this muscle became preferentially reinnervated by the nerve to flexor digitorum longus. In contrast to fast muscles, endplates of soleus muscle fibres were only rarely contacted by more than one axon, and ectopic endplates were often found in this muscle. In both types of muscles that had an excess of motor nerves, extensive sprouting persisted for many months. Thus, identical motor nerves induce different patterns of innervation in slow and fast muscles, and muscle fibres do not show a preference for their own nerve.     

A morphological study on the coracobrachialis muscle

The musculocutaneous nerve (MC) usually pierces the coracobrachialis muscle (cbr) in man. However in rare cases it does not pierce the muscle but runs downward adhering to the median nerve. Although this unusual course of MC is well noted in the literature, there has been no satisfactory explanation given for its derivation. The present author thought that cbr was a composite muscle innervated by at least two different nerves and a change in composition of the muscle parts might have something to do with the change in the course of MC. Therefore MC, cbr and its nerve supply were observed in 240 human arms. The nerve fiber analysis of MC and the branches to cbr were made in 27 arms, specially selected from them. Additionally, to correlate the results of humans and other mammals, the same analysis was performed using 4 prosimian arms (3 species). The results were as follows: 1. The nerve branches innervating human cbr could be classified into three groups. The first group branches were those constant in appearance, arising from MC and usually innervating the largest area of cbr. The author designated these branches Rmc (branches of MC). The second group consisted of a branch which arose from the middle trunk of the brachial plexus (the seventh cervical nerve), passed dorsal to MC and supplied the proximal deep part of cbr situated dorsal to the course of MC. This branch was also constant in appearance and called Rp (deep branch). The third group branched off from the ventral surface of the middle trunk (the seventh cervical nerve), passed ventral to MC and supplied the proximal ventral part of cbr situated ventral to the course of MC. This branch (called Rs, superficial branch) appeared in only 5 out of 27 cases. 2. The change in the course of MC was closely correlated with the change in the ratio of the part innervated by Rmc to the part innervated by Rp. In the case where the part innervated by Rmc was larger and the part innervated by Rp was smaller than usual, the ratio was larger than ordinary and MC pierced the deeper part of cbr. On the contrary, in the case where the part supplied by Rmc was smaller and the part supplied by Rp was larger than usual, the ratio was smaller and MC pierced the more superficial part. In extreme cases where the part supplied by Rmc was very slight, MC did not pierce cbr. 3. In prosimians, cbr was composed of two muscular parts.(ABSTRACT TRUNCATED AT 400 WORDS)     

Lateromedial and dorsoplantar borders among supplying areas of the nerves innervating the intrinsic muscles of the foot.

The branching patterns of nerves supplying the intrinsic muscles of the foot were analyzed as a basis to confirm the muscle layer structure. Thirty-eight feet of 20 Japanese cadavers were examined in detail in this study. The first dorsal interosseus was innervated by a branch from the deep peroneal nerve as well as a branch of the lateral plantar nerve in 92.1%, the second dorsal interosseus in 10. 5% and the third dorsal interosseus in 2.6%. In three specimens, branches from the deep peroneal nerve innervated the oblique head of the adductor hallucis or the lateral head the flexor hallucis brevis. In addition, branches from the medial and lateral plantar nerves and the deep peroneal nerve formed communication loops in three specimens. The first dorsal interosseus, the oblique head of the adductor hallucis and the lateral head of the flexor hallucis and their innervating nerve branches are closely related within the first intermetatarsal space. Since the tibial part of the first interosseus muscle primordium is occupied in the space during development, the variations of innervation patterns and formation of the communicating nerve loops may be explained by various combinations of the part and the other muscle primordia.     

Improved functional recovery of denervated skeletal muscle after temporary sensory nerve innervation

Prolonged muscle denervation results in poor functional recovery after nerve repair. The possible protective effect of temporary sensory innervation of denervated muscle, prior to motor nerve repair, has been examined in the rat. Soleus and gastrocnemius muscles were denervated by cutting the tibial nerve, and the peroneal nerve was then sutured to the transected distal tibial nerve stump either immediately or after two, four or six months. In half of the animals with delayed repair, the saphenous (sensory) nerve was temporarily attached to the distal nerve stump. Muscles were evaluated three months after the peroneal-to-tibial union, and were compared with each other, with unoperated control muscles and with untreated denervated muscles. After four to six months of sensory "protection", gastrocnemius muscles weighed significantly more than unprotected muscles, and both gastrocnemius and soleus muscles exhibited better preservation of their structure, with less fiber atrophy and connective tissue hyperplasia. The maximum compound action potentials were significantly larger in gastrocnemius and soleus muscles following sensory protection, irrespective of the delay in motor nerve union. Isometric force, although less than in control animals and in those with immediate nerve repair, remained reasonably constant after sensory protection, while in unprotected muscles there was a progressive and significant decline as the period of denervation lengthened. We interpret these results as showing that, although incapable of forming excitable neuromuscular junctions, sensory nerves can nevertheless exert powerful trophic effects on denervated muscle fibers. We propose that these findings indicate a useful strategy for improving the outcome of peripheral nerve surgery.     

The innervation of deep muscles of the human forearm extensors]

The innervation of four deep muscles of the human forearm extensors (the abductor pollicis longus, the extensor pollicis brevis, the extensor pollicis longus, and the extensor indicis muscles) were investigated in 24 bodies (48 sides) from those used in the 1989 and 1990 student courses in gross anatomy dissection at the Iwate Medical University School of Medicine. The forearm extensor muscles and the deep branch of the radial nerve were dissected intensively in the student courses in gross anatomy and were removed afterwards. The four deep muscles of the human forearm extensors and the nerves innervating the muscles were observed while they were immersed in the water and with use of a stereomicroscope--with the assistance of which they were drawn. In six sides the intramuscular nerve supply was also examined carefully and drawn. The results were as follows. 1. The nerves to the four deep muscles of the forearm extensors arose usually from the deep branch of the radial nerve after emerging the supinator muscle and sending branches to superficial forearm extensors. In some cases a nerve or nerves to the superficial forearm extensors were observed arising from the deep branch of the radial nerve after sending one or more branches to the deep forearm extensor muscles, or from the branches to the deep muscles themselves. However they were split easily from the deep branch of the radial nerve and from the branches to the four deep forearm extensors proximally near to the emerging of the deep branch from the supinator muscle. Therefore, it was considered to be constant that the nerves to the four deep forearm extensors arose from the deep branch of the radial nerve after branching to the superficial forearm extensors. 2. The radial group of the deep forearm extensors (the abductor pollicis longus and the extensor pollicis brevis muscles) was innervated usually by one branch that arose from the deep branch of the radial nerve just after emerging from the supinator and giving off branches to the superficial forearm extensors. This branch ran on the dorsal (extensor) surface of the abductor pollicis longus muscle distally, sending many twigs to this muscle, and entered into the muscle at various distances from the origin (Figs. 1-6). The abductor pollicis brevis muscle was innervated by some twigs that ran usually inside but occasionally outside of the abductor pollicis longus muscle (Figs. 7-10).(ABSTRACT TRUNCATED AT 400 WORDS)     

Site-dependent differences in density of sympathetic nerve fibers in muscle-innervating nerves of the human head and neck

The autonomic nerve supply of skeletal muscle has become a focus of interest because it is closely related to the adaptation of energy metabolism with aging. We have performed an immunohistochemistry study on tyrosine hydroxylase (TH) and neuronal nitric oxide synthase (nNOS) using specimens obtained from ten selected elderly cadavers (mean age 83.3 years) in which we examined muscle-innervating nerves (abbreviated “muscle-nerves” hereafter) of ten striated muscles (soleus, infraspinatus, extra-ocular inferior rectus, lateral rectus, superior obliquus, temporalis, orbicularis oculi, posterior cricoarytenoideus, trapezius and genioglossus) and, as a positive control, the submandibular ganglion. We found that the extra-ocular muscles received no or very few TH-positive nerve fibers. Muscle-nerves to the other head and neck muscles contained a few or several TH-positive fibers per section, but their density (proportional area of TH-positive fibers per nerve cross-section) was one-half to one-third of that in nerves to the soleus or infraspinatus. We did not find nNOS-positive fibers in any of these muscle-nerves. In the head and neck muscles, with the exception of those of the tongue, there appeared to be very few TH-positive nerve fibers along the feeding artery. Consequently, the head and neck muscles seemed to receive much fewer sympathetic nerves than limb muscles. There was no evidence that nNOS-positive nerves contributed to vasodilation of feeding arteries in striated muscles. This site-dependent difference in sympathetic innervation would reflect its commitment to muscle activity. However, we did not find any rules determining the density of nerves according to muscle fiber type and the mode of muscle activity.     

Reexamination of the communicating branch between the sural and tibial nerves

Reexamination of communicating branches between the sural and tibial nerves ventral to the calcanean tendon was carried out on 52 legs of 26 Japanese cadavers which were used for ordinary dissection practices at the Niigata University School of Medicine. Communicating branches were found in 7 out of 52 dissections (13.5% of cases). In three of the 7 specimens, the communicating branch, the sural nerve and the tibial nerve with the deep crural fascia were removed from the legs and demonstrated by a modified Sihler's staining technique. Three types of communicating branches, Y, U and N, were distinguished on the basis of their shapes. In type Y, a medial branch from the sural nerve and a branch from the tibial nerve joined in Y-shape and become one terminal branch. In type U, the both branches formed a loop between the sural and tibial nerves. The type N communicating branch ran obliquely and medially to reach the tibial nerve distally. Only the Y type appeared in 5 specimens. Both the Y and U type and the Y and N types occurred in one specimen each. We assume that the communicating branch of the N type contains motor fibers which are derived from the sural nerve and innervate some plantar muscles, because this type is correspond to the communication type of some animals in which motor fibers have been demonstrated. Therefore, if the sural nerve biopsy is performed to examine a pure sensory nerve, removal of the more distal part of the sural nerve than a diverging point of a communicating branch is recommended. This study also indicated that the modified Sihler's staining technique is useful to examine distributions of cadaveric peripheral nerves after medical students' dissection course.     

Lateromedial and dorsoplantar borders among supplying areas of the nerves innervating the intrinsic muscles of the foot

The branching patterns of nerves supplying the intrinsic muscles of the foot were analyzed as a basis to confirm the muscle layer structure. Thirty‐eight feet of 20 Japanese cadavers were examined in detail in this study. The first dorsal interosseus was innervated by a branch from the deep peroneal nerve as well as a branch of the lateral plantar nerve in 92.1%, the second dorsal interosseus in 10.5% and the third dorsal interosseus in 2.6%. In three specimens, branches from the deep peroneal nerve innervated the oblique head of the adductor hallucis or the lateral head the flexor hallucis brevis. In addition, branches from the medial and lateral plantar nerves and the deep peroneal nerve formed communication loops in three specimens. The first dorsal interosseus, the oblique head of the adductor hallucis and the lateral head of the flexor hallucis and their innervating nerve branches are closely related within the first intermetatarsal space. Since the tibial part of the first interosseus muscle primordium is occupied in the space during development, the variations of innervation patterns and formation of the communicating nerve loops may be explained by various combinations of the part and the other muscle primordia. Anat Rec 255:465–470, 1999. © 1999 Wiley‐Liss, Inc.     

An anatomic study of structure and innervation of the serratus anterior muscle

Background

The structure and function of the serratus anterior muscle are partitioned into three parts. If the morphological characteristics in each part can be demonstrated in more detail, the cause of dysfunction will probably be identifiable more accurately. The purpose of this study was to demonstrate the details of the structure and innervation in each part of the serratus anterior muscle.

Materials and methods

This macroscopic anatomic study was conducted using ten sides from five cadavers. The structure and innervation in each part of this muscle were examined.

Results

In the superior part, the independent branch was divided from a branch innervating the levator scapulae muscle. In the middle part, the long thoracic nerve descended on one-third of the anterior region between the origin and insertion. In the inferior part, the long thoracic nerve which ramified into many branches and branches from the intercostal nerves were distributed on all sides.

Conclusion

This study demonstrated that the innervation of the serratus anterior muscle was different in each part. The difference indicates that the superior part has an intimate relation with the levator scapulae muscle while the middle and inferior parts could be the actual serratus anterior muscle. Moreover, the distribution of branches from the intercostal nerves shows that the inferior part has a connection with some trunk elements. Understanding these characteristics of innervation is useful to identify the cause of dysfunction. In addition, we assert that the constant distribution of branches from the intercostal nerves is significant for the morphology.     

Histochemical differentiation of fibers in the rat slow and fast twitch muscles.

Wistar male rats were sacrificed at 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, and 21 days, and at 5 and 10 weeks of age. The histochemical differentiation of slow twitch soleus and fast twitch plantaris muscle fibers was examined from the enzyme activities of adenosine triphosphatase (slow- or fast-contracting), succinate dehydrogenase (high- or low-oxidative), and alpha-glycerophosphate dehydrogenase (high- or low-glycolytic). The soleus muscle fibers differentiated into slow-contracting (S) and fast-contracting (F) fibers at 7 days of age. In the plantaris muscle, differentiation into S and F fibers in the deep portion occurred earlier (9 days) than in the superficial portion (11 days). Thereafter, fiber type shifts between S and F were observed in both muscles. Differentiation into fast-contracting oxidative glycolytic (FOG), fast-contracting glycolytic (FG), and slow-contracting oxidative (SO) fibers occurred in both muscles at 15 and 17 days of age. After subdivision into the three fiber types, a type shift from FOG to FG was observed in both the deep and superficial portions of the plantaris muscle.     

Skeletal muscle atrophy in old rats: differential changes in the three fiber types.

This study was undertaken to reevaluate the effects of ageing on skeletal muscle mass and on mitochondrial and glycolytic enzyme levels in the different types of skeletal muscle in rats. It was found that some muscles atrophy with ageing, while others do not, in male rats. Atrophy appears to occur in weight-bearing muscles, and is most marked in those with a high proportion of type IIb fibers. The muscles that did not atrophy are non-weight-bearing, and include the epitrochlearis (predominantly type IIb fibers) and the adductor longus (predominantly type I fibers). The average cross-sectional area of muscle fibers in the plantaris muscles of 28-30-month-old rats was approximately 30% smaller than that of 9-10-month-old animals, providing evidence that the approximately 30% lower weight of the plantaris in the old group was entirely due to fiber atrophy. The proportion of type IIa fibers was decreased and the proportion of type I fibers was increased in the plantaris of the old rats. The respiratory capacity of the soleus muscle (predominantly type I fibers), and the glycolytic capacity of the superficial, white (type IIb) and deep, red (predominantly type IIa) portions of the vastus lateralis, were reduced in the old rats. Our results provide evidence that ageing has differential effects on the three types of skeletal muscle fiber, and on weight-bearing and non-weight-bearing muscles, in the rat.     

小鱼际肌肌内神经和肌梭密度分布

目的揭示小鱼际肌肌内神经和肌梭密度的分布规律。方法对成年20具尸体(40例)小鱼际标本用改良Sihler肌内神经染色法和苏木精-伊红(HE)染色法。结果小鱼际肌肌外神经干长0.49～1.64 cm,从肌起端深面入肌。小指展肌内尺侧和桡侧有独立的神经支配,可分为两个神经肌亚部;小指短屈肌的肌内神经干斜行穿越肌实质中央;小指对掌肌内神经吻合形式多样,"U"型吻合更明显。3块肌的桡侧部神经分支分布密集。小指对掌肌肌梭密度最高为(19.33±2.72)个/g;小指短屈肌其次,有(15.79±1.33)个/g;小指展肌最少,为(12.86±1.69)个/g。结论三块肌桡侧部更多地参与精细调节;肌块越小,肌梭密度越高。     

经后外侧入路治疗胫骨平台后外侧骨折的解剖学研究及应用

目的为经膝关节后外侧入路治疗胫骨平台后外侧骨折提供解剖学基础。方法 (1)福尔马林浸泡的防腐成人下肢标本20例,解剖观察并测量与膝关节后外侧入路相关的主1要血管、神经的走行特点,膝关节后外侧主要肌肉、韧带的分布。(2)新鲜冷藏下肢标本4例,按照设计的入路进行模拟手术,评估该入路的可行性。(3)在解剖学研究的基础上,临床应用12例,观察该入路的临床效果。结果膝关节后外侧入路的手术切口全长均不经过腓总神经主干;深层经腓肠肌外侧头外侧和比目鱼肌肌间隙分离,保护了内侧的血管神经束;胫前血管在腓骨头下方(4.15±0.36)cm处自腘动脉发出,影响了远端的显露,但足够复位固定简单的后外侧骨折。临床应用12例,均取得了满意的疗效。结论经膝关节后外侧入路治疗简单的胫骨平台单纯后外侧骨折具有安全,损伤小,暴露充分,临床效果良好等优点,有一定的推广价值。     

Motor unit numbers,motor unit sizes and innervation of single muscle fibres in hyperinnervated adult mouse soleus muscle

The sural and the lateral plantar nerves were implanted simultaneously into the denervated soleus muscle of adult mice. Each of these nerves contained approximately the normal number of soleus motor axons. This procedure therefore allowed a study of how an initial excessive number of motor axons provided by two different, foreign nerves and terminating into the soleus muscle affected the final pattern of muscle innervation. In muscles examined two months or more after the implantation of the foreign nerves all muscle fibres were innervated. The fraction of the muscle innervated by either nerve varied widely from one preparation to another. However, all the motor axons which were implanted into the muscle appeared to make permanent synapses. Moreover, the distribution of motor unit sizes of each foreign nerve relative to the total number of muscle fibres innervated by that nerve was similar to the distribution of motor unit sizes in muscles cross-innervated by that nerve alone, although the absolute motor unit sizes were reduced. Estimated by intracellular recording, 20–30% of the muscle fibres were polyneuronally innervated. A similar fraction of teased muscle fibres stained for acetylcholinesterase had more than one endplate.     

Synaptic connections from large muscle afferents to motoneurones in human lower limbs

OBJECTIVES: Our study was undertaken to investigate reciprocal inhibition in humans both from ankle flexors to extensors and from ankle extensors to flexors. METHODES: Changes in the firing probability of single motor units in response to electrical stimulation of muscle nerves (the peristimulus time histogram technique) were used to derive the reciprocal projections of muscle spindle Ia afferents to the motoneurones of ankle muscles. Discharges of units in ankle flexors (the tibialis anterior muscle [TA]) and extensors (soleus [SOL] and medial gastrocnemius [MG] muscles) were investigated respectively after stimulation of the posterior tibial (PTN) and common peroneal (CPN) nerves (predominantly on the deep branch). In eight normal subjects aged 24 to 40 years, one motor unit per each muscle was studied. RESULTS: CPN stimulation produced reciprocal Ia inhibition in the SOL of 5 of 7 of them and in the MG of 3 of 5, whereas PTN stimulation produced reciprocal Ia inhibition in the TA of only 2 of 6 subjects. CONCLUSIONS: These findings suggest that at low level contraction reciprocal Ia inhibition from ankle flexors to extensors may be stronger than that from ankle extensors to flexors.