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The results of the application of a computerized method for the estimation of motor unit numbers in the human extensor digitorum brevis are presented. In patients with Duchenne and limb-girdle and facioscapulohumeral muscular dystrophies, motor unit numbers are within the normal range, but are significantly reduced in myotonic muscular dystrophy.

Twenty-five patients with congenital idiopathic clubfoot, aged 1 day to 22 months, were studied electromyographically. No myopathic or neurogenic changes were found in tibialis anterior, peroneus, gastrocnemius, extensor digitorum brevis, and abductor hallucis brevis muscles of the leg and foot. Maximum motor nerve conduction velocities for the peroneal and tibial nerves were normal. It is concluded that conventional electromyographic techniques were unable to demonstrate abnormalities suggesting neuropathic or myopathic changes in idiopathic clubfoot.

A detailed electrophysiological study has been made of the extensor digitorum brevis, thenar, hypothenar and soleus muscles in one patient with myotubular or centronuclear myopathy. The main finding was a noticeable reduction in the population of active motor units in all the investigated muscles. The remainer units showed normal sizes. The experimental observations have been interpreted in terms of a neuropathic process. Un estudio electrofisiológico detallado fué hecho en los músculos extensor corto de los dedos, de la eminencia tenar, de la eminencia hipotenar y soleo en un paciente con el diagnóstico de miopatía miotubular o centronuclear. El hallazgo principal fué una notoria reducción en el número de unidades motoras activas en todos los músculos investigados, en tanto que las unidades remanentes mostraron tamaño conservado. Las observaciones hechas se han interpretado como favoreciéndo la génesis neurógena en el desarrollo de este proceso.

The central program for activation of different hindlimb muscles during ‘fictive locomotion’ in immobilized thalamic cats, expressed in the time structure of motor discharges in nerves to different muscles, was investigated. For the majority of hindlimb muscles this program was quite simple and consisted of alternating appearance of bursts of discharges in the nerves to flexors and extensors. The level of activity within individual bursts of discharges in the nerves to flexors and extensors was changed in time in an unpredictable manner. Correlation analysis of activity which appeared in the same phase in the nerves to flexors (or, respectively, extensors) showed that the maximum dependence between two concurrent bursts was observed at zero time shift. These data support Brown's hypothesis about the existence in each part of the spinal cord of two half-centers operating alternately during locomotion—one for the flexors and another for the extensors—which activate the motoneurones of the corresponding muscles. Activity in the nerves to biarticular muscles (m. semitendinosus, m. posterior biceps, m. tenuissimus) and in the nerves to m. extensor digitorum brevis and m. peroneus tertius was of a more complex nature. The central program of activation of these muscles depended on the intensity of ‘fictive locomotion’. A suggestion was made that the motor nuclei of these muscles are connected with the half-centers in a more complex manner.

The innervation of the right M. extensor digitorum brevis was investigated in 52 subjects with the aid of stimulation electromyography. In 13 cases (25%) a particular branch of the superficial branch of the peroneal nerve, the accessory deep peroneal nerve, could be identified. In 1 case it alone, and in 12 cases, together with the deep peroneal nerve, innervated the M. ext. dig. brevis. The significance of the awareness of this anomalous innervation is pointed out.

Summary The variation of the extensor digitorum brevis (EDB) muscle was examined in 113 hindlimbs of dogs. Four types were discriminated in this muscle. Of the three heads of the muscle, the medial head went to the 2nd digit in types I and II, and to the 2nd and 3rd digits in types III and IV. The middle head went to the 3rd digit in types I and IV, and to the 3rd and 4th digits in types II and III. The lateral head went to the 4th digit in all the types. Type II was the most common of the four (78.76 %). Type III was found in 8.85%, type 1 in 973% and type IV in 2.66%.

Thompson’s free muscle grafts were performed on 8 patients with unilateral facial palsy, and their results were assessed regarding the effects on closure of the eyelids and elevation of the drooped corner of the mouth.

A short account is given of the different feedback signals that control the central pattern generators for locomotion. Particular attention is given to the feedback signals that are elicited by static hip position and by dynamic hip movements.

SUMMARY:Electrophysiological studies have been carried out on five patients with neuropathies of different etiologies. In each patient serial estimates were made of the numbers of functioning motor units in various muscles. It was found that the intensity of the neuropathic process and the rate of recovery differed in a consistent way among the motoneuron pools investigated. The lesion was more severe in extensor digitorum brevis neurons than in thenar neurons, while the hypothenar ones were least affected. A stage of partial synaptic failure has been recognized in which a motoneuron appears to be no longer able to excite a muscle fiber, but still capable of maintaining certain trophic activities. By comparing the number of functioning motor units with the size of the maximum evoked muscle response it has been possible to detect the adoption of denervated muscle fibers by axonal sprouts from ‘healthy’ surviving neurons (collateral reinnervation). Lastly, in some muscles it appears that the adopted muscle fibers may subsequently be recaptured by the original motoneurons following recovery of the latter from the neurotoxic insult.

Single unit recordings have been made from the muscle spindles of the extensor digitorum brevis I muscle of the chelonian emys orbicularis. The responses to ramp-type mechanical stretches (up to 5 mm s−1 velocity and up to 1.6 mm extension) were compared to those of spindles from other groups. It is found that the spindles have lower rates of firing than those from the other groups with the exception of the snake spindles. Generally the spindles behaved like the secondary ending of mammalian spindles or the tonic type of snake spindle in terms of their response to the velocity of stretch. The results are consistent with the view that the tonic response arises from intrafusal muscle fibres in which the sensory region has a structure which is fairly uniform and similar to that of the polar regions and not interrupted by accumulations of nuclei.

Golgi tendon organs from human, cat and rat extensor digitorum brevis muscles are compared in structural design. Microscopic studies reveal that these receptors appear to be very similar in structure, suggesting close functional similarities even though they are largest in man, intermediate size in cats and smallest in rats. This contrasts with similar observations on the structure of muscle spindles which show strong differences in respect to the insertion of intrafusal muscle fibers thereby implying species specialization of response characteristics to intramuscular tensions and pressures. Reconstructive drawings of human tendon organs from serial sections suggest how sensory endings may be affected by tensions at the musculotendinous junctions due to stretch or contraction of motor units. Finely divided collagen bundles appear to compress and distort nerve endings lying between them, thus inducing the generation of spike discharges.

Histochemical investigations upon intrafusal muscle fibers of spindles in the extensor digitorum brevis 1 muscle of the tortoise have been carried out. The localization of phosphorylase, succinic dehydrogenase and adenosine activities together with the demonstration of lipids by the propylene glycol-Sudan method all failed to produce results which could be used to categorize the intrafusal fibers into more than one type. From these results and from previous histologic investigations it is suggested that the tortoise muscle spindle contains just one kind of intrafusal muscle fiber.

Samples of the extensor digitorum brevis muscle (EDB) obtained at necropsy from 26 subjects without known neuromuscular disease were examined histologically and histochemically. In the two youngest subjects, aged 2 months and 8 years, a mosaic distribution of type I and type II fibres was present. From the second decade onwards, increasing with age, the mosaic pattern was gradually replaced by groups of type I and type II fibres and areas of grouped fibre atrophy appeared. It is suggested that these findings may be explained by a slow process of denervation and reinnervation. This process does not seem to occur to the same extent in three other distal limb muscles from which specimens were also examined.

In patients with various types of chronic motor denervation, the numbers of surviving motor units have been compared with the twitch tensions developed by the same muscle (extensor digitorum brevis). It was found that functional compensation in partially denervated muscles was often marked; in most patients abnormally small twitches occurred only when fewer than 10% of motor axons remained. The factors responsible for this compensation are considered. The twitch speeds of partially denervated muscles differed markedly, even among patients with the same disorder; there was evidence to suggest that the twitches of some motor units might become slower than those found in normal muscles.

Necropsy material from 8 previously normal subjects aged from 8 to 42 years, dying suddenly as a result of trauma or acute illness, was used to collect data on fibre type distribution in the deltoid, biceps brachii, rectus femoris, gastrocnemius and extensor digitorum brevis. In every specimen “enclosed fibres” were counted in 10 areas, each area comprising 150–200 fibres. A muscle fibre was considered to be enclosed when it was surrounded on all sides by fibres of its own histochemical type. The extensor digitorum brevis was different from the other limb muscles, due to extensive grouping of type I and type II fibres. A mosaic pattern was present in the other muscles. A variation in the fibre type distribution within the framework of the mosaic pattern was shown to occur in different parts of the deltoid, biceps brachii and rectus femoris of two subjects. The most superficial portions of these muscles contained a higher percentage of type II fibres than the deeper portions. Figures on fibre type distribution derived from specimens obtained from the superficial parts of limb muscles may not, therefore, necessarily apply to the whole muscle. The percentage of type I fibres was higher than 50 in the deltoid and gastrocnemius, lower than 50 in the rectus femoris and about 50 in the biceps brachii. In these four muscles clusters of up to 13 enclosed fibres, or groups of 30–40 fibres of uniform histochemical type, were found and such groups are therefore presumed to be within the normal range. Even larger clusters may occasionally occur in muscles (e.g. deltoid) in which one fibre type predominates. In striated muscles with fibre type predominance it will be difficult to draw a clear distinction between normal clusters of the predominant fibre type and pathological “type-grouping” of fibres of the same type. Nevertheless, there is a close adherence to the normal mosaic pattern in the aforementioned four limb muscles. Clusters of different fibre types comprising three enclosed fibres are beyond the normal range if they occur frequently within each other's vicinity. While in deltoid it is not possible to say that a uniform group of fibres containing, say, 50 fibres (with 25 enclosed fibres) is necessarily abnormal, it is very uncommon in such normal muscles to find clusters (with 3 or more enclosed fibres) of both histochemical types lying in close relationship to one another. Nevertheless this study indicates the need for caution in concluding that large groups of muscle fibres of one histochemical type in human limb muscles necessarily indicate denervation and subsequent reinnervation.

In an effort to determine more accurately the physical characteristics of human tendon, stress-strain and tensile strength studies were performed on tendons removed from amputated lower limbs. The tendons of M. extensor digitorum longus, M. extensor digitorum brevis, M. extensor hallucis longus, M. flexor digitorum longus and M. flexor hallucis longus were used in the studies. Tensile strength of the extensor tendons averaged 13,392 psi while that of the flexor tendons was less, with an average of 10,944 psi. These results indicate that, of the tendons tested, the extensors are about 20 per cent stronger than the flexors. The stress-strain data were analyzed by a computerized statistical method utilizing a multiple-regression analysis employing as many as 8 variables. All stress-strain curves shown were derived by this method. The difference in stiffness previously reported to exist between embalmed flexor and extensor tendons was not manifest in the present study. However, in the range from 0 to 3·0 per cent strain, thought by many to be the normal physiologic range, extensors and flexor tendons were seen to react differently to stress. The flexors initially exhibited greater strain per unit stress and gradually became stiffer, the stress-strain curves exhibiting an upward concavity. The extensors were initially stiffer, gradually responding with more strain per unit stress, and the stress-strain curve was slightly concave downward. The stress-strain curves of unembalmed flexor and extensor tendons as calculated in the present study are reminiscent of the curves previously reported for embalmed extensor tendons.

Hereditary aspects in the anomalous innervation of the extensor digitorum brevis muscle by the accessory deep peroneal nerve, were investigated. Utilizing electrophysiological techniques, 22% of 100 healthy unrelated individuals demonstrated this variation in innervation of one or both extensor digitorum brevis muscles. The study of family members of five of these subjects with the variation showed that 78% of relatives also had this anomalous innervation. These data suggest that hereditary factors may be significant in the occurrence of this variation and a dominant mode of inheritance may be the case.

In Reply.— Dr. Montero is correct that the electromyographic (EMG) findings were in the extensor digitorum brevis muscles of the lower extremity. The finding of EMG abnormalities in distal muscles in a patient with proximal muscle weakness illustrates again that EMG and clinical findings may not always correlate. The upper extremities were involved in the patient's generalized neuromuscular disease, but not enough, evidently, to cause wringing hands. In fact, because of her failure to respond to any treatment, most of the hand wringing was done by her physicians.

Two healthy females and twelve healthy males, aged 19-24 yr, underwent strength training for periods of 9-21 wk. The muscles trained included extensor digitorum brevis (N = 3), soleus (N = 7), brachioradialis (N = 4), and the hypothenar muscles (N = 3). The effect of training on motoneuron excitability was measured as the degree to which two reflex responses (V1 and V2) were potentiated by voluntary effort. Strength training was found to increase V1 and V2 potentiation by 49.7 and 38.9%, respectively, (P less than 0.01) for pooled muscle comparisons with the exception of the soleus V2 wave, which was rarely seen and excluded from this analysis. There was a positive correlation (r = 0.83, P less than 0.01) between the change in the V1 and V2 potentiation. It was argued that strength training may cause an increased ability to raise motoneuron excitability during voluntary effort.