Cross education of muscular strength during unilateral resistance training and detraining

Abstract. The purpose of the present study was to examine the changes in maximum voluntary isometric contraction (MVC) in the contralateral untrained limb during unilateral resistance training and detraining, and to examine the factors inducing these changes by means of electrophysiological techniques. Nine healthy males trained their plantar flexor muscles unilaterally 4 days·week^–1 for 6 weeks using 3 sets of 10–12 repetitions at 70–75% of one-repetition maximum a day, and detrained for 6 weeks. Progressive unilateral resistance training significantly (P<0.05) increased MVC, integrated electromyogram (iEMG), and voluntary activation in the trained and contralateral untrained limbs. The changes in MVC after training were significantly correlated with the changes in iEMG in both limbs. No significant changes occurred in MVC, voluntary activation, and iEMG in the contralateral limb after detraining. The changes in MVC after detraining did not correlate with the changes in voluntary activation or iEMG in either limb. Training and detraining did not alter twitch and tetanic peak torques in either limb. These results suggest that the mechanisms underlying cross education of muscular strength may be explained by central neural factors during training, but not solely so during detraining. Electronic Publication     

Compartmentalization of single muscle units in cat lateral gastrocnemius

Summary The distribution of muscle fibers in single muscle units in cat lateral gastrocnemius (LG) muscle was analyzed using the method of glycogen depletion. Single, type FF motor units in LG were identified by stimulation of dissected ventral rootlets and then activated to produce depletion of glycogen in their innervated muscle fibers. Serial histological sections were made of the entire triceps surae muscles and then reacted for the demonstration of glycogen. Projected tracings of the sections were used to compare the distribution of glycogen depleted muscle fibers to the heads of the LG muscle. Results of analysis of single muscle units indicate that the muscle fibers innervated by single cat LG type FF motor units are distributed to the same regions of muscle which are innervated by primary branches of the nerve to the LG muscle. The single units are thus compartmentalized. These results support the hypothesis that each of the neuromuscular compartments of LG contains a unique population of motor units. It is suggested that compartmentalization of muscles about primary branches of their muscle nerves may from a major organizational principle in the design of skeletal muscles.     

Dynamic relationship between EMG and torque at the human ankle: Variation with contraction level and modulation

Stochastic system identification techniques were used to determine the dynamic relationship between the electromyogram (EMG) and torque in the ankle muscles of normal human subjects. EMG and torque were recorded while subjects modulated ankle torque by tracking a computer-generated stochastic waveform. Nonparametric impulse response functions (IRFs) relating EMG to ankle torque were computed and parameterised by determining the parameters of the second-order system which provided the best least-squares fit. Two sets of experiments were carried out. In the first, the mean level of torque was varied from 5 per cent of the maximum voluntary contraction (MVC) to 30 per cent MVC while the depth of modulation was held constant at ±5 per cent of MVC. In the second series of experiments the mean torque was held constant at 25 per cent MVC while the depth of modulation was varied from ±2.5 per cent to ±25 per cent. The major findings were: (1) A second-order, low-pass filter provided a good quasilinear model of the EMG/force dynamics under all conditions; (2) The model parameters depended only weakly on the mean level of torque; (3) In contrast, the model parameters depended strongly on the amplitude with which the contraction was modulated; the natural frequency increased significantly with the depth of modulation.     

To what extent is the tibia-calcaneum angle a reliable measurement of the triceps surae length? Radiological correction of the torque-angle curve (III)

Summary Previous papers gave some methods for the reliable measurement of the tibia-calcaneum angle. It is of common use to evaluate the physical properties of triceps surae on the basis of torque-angle curves. However this method is reliable only if each tibia-calcaneum angle corresponds to a defined distance between the insertions of the muscle in subjects of the same height. Evidence is given by radiological measurements that this correspondance is correct in normal children. However, this is no longer true in certain cerebral palsied children because of abnormal translation of the calcaneum and/or abnormal ratio of bone sizes. In this case the torque-angle curves do not define properly the torque-length curves. A method of correction is given. This correction may be as high as 15.MaÎtre de Recherche INSERM (Paris), grant No. 7411766 and U.E.R. Paris-Ouest     

Comprehensive review of surgical approaches to the elbow

The choice of the most suitable surgical approach to the elbow forms the foundation of any successful elbow surgery. The surgical approach is based on the injury or pathology to be addressed and therefore specific anatomical details need to be considered. The surgeon must be comfortable with the bony, ligamentous and neurovascular anatomy of the elbow to consider and execute the best approach for each problem. This is an imperative to avoid iatrogenic injury.This article provides a detailed analysis, valuable technical tips, advantages and disadvantages of the most common approaches to the elbow. The lateral approaches include the Kocher, Kaplan and Extensor Digitorum Communis (EDC) Split approaches, the medial approaches include the Hotchkiss, Flexor carpi ulnaris (FCU) splitting approach, the Taylor and Scham approach. The anterior approach includes the anterior neurovascular interval approach and the posterior approaches include the Olecranon osteotomy, triceps sparing, triceps reflecting approach and finally the Boyd interval approach. The text and illustrations will provide a structured overview for the practicing surgeon.     

Assessment of plantar flexors activation capacity: nerve versus muscle stimulation by single versus double pulse

This study was designed to investigate if the relationship between the interpolated twitch-torque (IT) and voluntary torque (VT) is affected by the number of electrical stimuli (single vs. double) and the stimulation site (nerve trunk vs. muscle). The results showed that the IT–VT relationship of the plantar flexors is appropriately described by a composite (linear + curvilinear) model. Indeed, whatever the stimulation method, the IT–VT relationship was linear between approximately 25 and 75% of the maximal voluntary torque (MVT) and curvilinear for higher contraction intensities. The four stimulation conditions are equivalent in assessing the maximal voluntary activation (VA% range 96.2 ± 5.0 to 98.5 ± 3.1%) as well as in determining the true maximal torque expected for total twitch occlusion (MT_exp range 171.4 ± 21.2 to 179.0 ± 26.8 Nm). The gap between the MVT and MT_exp should be viewed as an index of muscle inactivation. This gap was comparable for the four stimulation methods (2–6%) and close to the deficit in VA% (2–4%). No pulse-number effect was found on the IT–VT relationship when the nerve was stimulated but an effect on the concavity of the composite relationship was observed when the stimulation was applied over the muscle. Even though the four stimulation techniques are equivalent in assessing the maximal activation capacity our results demonstrate that the neural stimulation method is the most consistent as it guarantees the same motor pool recruitment independently from the number of pulses.     

Overcoming abnormal joint torque patterns in paretic upper extremities using triceps stimulation

The goal of this research project was to quantitatively assess whether transcutaneous triceps stimulation can overcome the expression of abnormal torque patterns in the paretic upper limb of subjects with hemiparetic stroke. Abnormal torque patterns consist of strong coupling between shoulder abduction (SAB) and elbow flexion (EF) or between elbow extension (EE) and shoulder adduction (SAD) torques. Both patterns reduce the active range of motion during arm movements. Eight chronic stroke subjects with moderate to severe (Fugl-Meyer assessment scores of 21/66-36/66) upper limb motor impairment participated in this study. Shoulder and elbow joint torques were measured with a 6-degrees-of-freedom load cell under isometric conditions, while the triceps muscle was stimulated to generate EE torques. At the same time the subjects were asked to lift up their arm to generate different SAB torque levels. The obtained isometric results showed that electrical stimulation can overcome abnormal torque patterns in chronic stroke subjects while generating SAB. This is likely to have potential benefits to increase the reaching workspace of the paretic arm.