Reflex control of posterior shoulder muscles from arm afferents in healthy people

In order to position the hand during functional tasks, control of the shoulder is required. Heteronymous reflexes from the upper limb to shoulder muscles are used to assist in this control. To investigate this further, the radial and ulnar nerves were stimulated at elbow level whilst surface electromyographic activity of posterior deltoid, infraspinatus and latissimus dorsi muscles were recorded. In addition, the cutaneous branch of the radial nerve and the skin of the fifth digit were stimulated in order to investigate any cutaneous contribution to reflex activity. Reflexes were evoked in all three of these shoulder muscles from hand and/or forearm afferents. However, the reflexes differed; whereas both excitatory and inhibitory reflexes were evoked in posterior deltoid and infraspinatus, the reflexes in latissimus dorsi were mainly excitatory. Cutaneomuscular reflexes were seldom evoked here, but when they were present they were generally evoked at longer latencies than the reflexes evoked by mixed nerve stimulation. The results suggest a role for reflexes originating from the forearm and/or hand in the control of the shoulder.     

The effects of an isometric knee extension with hip adduction (KEWHA) exercise on selective VMO muscle strengthening

We investigated the effects of four weeks of training using a knee extension with hip adduction (KEWHA) exercise in asymptomatic participants. In addition, we compared different methods of electromyographic (EMG) onset-time detection. Eighteen participants who achieved earlier activation of the vastus lateralis (VL) muscle compared to that of the vastus medialis obliquus (VMO) muscle performed the isometric KEWHA exercise in the sitting position for four weeks. A 15° hip adduction was added to the existing knee extension in the KEWHA exercise. EMG onset times were detected using a computer-analyzed system and evaluated using two methods in which the thresholds for activity onset were set at two and three standard deviations (SDs) of the mean baseline activity. No significant difference in the EMG onset-time for the VMO muscle was observed compared to that of the VL muscle between the pre- and post-tests (p > 0.05) when data at 2 SDs of the mean baseline activity were analyzed. However, a significant difference in the onset times for the VMO muscle and VL muscle was found between the pre- and post-tests (p < 0.05) when data at 3 SDs of the mean baseline activity were analyzed. In addition, less variation was observed in data analyzed at 3 SDs compared to that of the data at 2 SDs. The normalized VMO:VL muscle ratio was not significantly different between the pre- and post-tests. These findings show that the KEWHA exercise may decrease the difference between the onset times of VMO and VL muscles. In addition, we suggest that task-specific EMG onset-time detection methods are required to minimize variations in the data obtained during the recording of muscle activation.     

Kinematic and electromyographic analyses of a karate punch

The aims of this study were: (i) to present the kinematic and electromyographic patterns of the choku-zuki punch performed by 18 experienced karatekas from the Portuguese team, and (ii) to compare it with the execution of 19 participants without any karate experience. The kinematic and electromyographic data were collected from the arm and forearm during the execution of the specific punch. A two-way analysis of variance (ANOVA) was used with significant level set at p ? 0.05. We found that the kinematic and neuromuscular activity in this punch occurs within 400 ms. Muscle activities and kinematic analysis presented a sequence of activation bracing a near-distal end, with the arm muscles showing greater intensity of activation than muscles in the forearm. In the skill performance, the arm, flexion and internal rotation, and the forearm extension and pronation movements were executed with smaller amplitude in the karate group. Based on the results of this study, the two groups’ presented distinct kinematic and electromyographic patterns during the performance of the choku-zuki punch.     

Daily muscle vibration amelioration of neural impairments of the soleus muscle during 2 weeks of immobilization

V-wave, F wave and H-reflex responses of soleus were used to determine neural adaptations to 2-week immobilization and whether muscle vibration intervention during immobilization would attenuate the negative adaptations induced by immobilization. Thirty subjects were divided into the ankle immobilization group and the immobilization with muscle vibration group. Mechanical vibrations with constant low amplitude (0.3 mm) were applied (12 × 4 min daily) with a constant frequency of 100 Hz on the soleus muscle of the subjects in vibration group during the ankle immobilization period. Soleus maximal M-wave (Mmax) and H-reflex (Hmax) were evoked at rest. F-wave was recorded by supramaximal stimulation delivered at rest and V-wave during maximum voluntary contraction (MVC). The EMG during MVC was represented by its root-mean-square (RMS) value. Each subject was examined before and after 2 weeks of immobilization. Results showed that following 2 weeks of immobilization, Mmax, Hmax and F wave all did not change with immobilization in either group (P > 0.05). After 2 weeks of immobilization, significant reductions in V/Mmax (of 30.78%) (P < 0.01) and EMG RMS (24.82%) (P < 0.001) were found in the immobilization group. However, no significant changes occurred in the immobilization with muscle vibration group. Such findings suggested that 2 weeks of immobilization resulted in neural impairments as evidenced by the reduction in EMG and V wave, and that such decrease was prevented by the intervention of muscle vibration during the immobilization period.     

Effect of severity of knee osteoarthritis on the variability of gait parameters

Gait analysis has provided important information concerning gait patterns and variability of gait in patients with knee osteoarthritis (OA) of varying severity. The objective of this study was to clarify how the variability of gait parameters is influenced by the severity of knee OA. Gait analysis was performed at three different controlled walking speeds in three groups of subjects with varying degrees of knee OA (20 healthy subjects with no OA and 90 patients with moderate or severe OA). The variability of gait parameters was characterized by the coefficient of variance (CV) of spatial-temporal parameters, as well as by the mean coefficient variance (MeanCV) of angular parameters. Based on our results, we conclude that the complexity of gait decreases if the walking speed differs from the self-selected speed. In patients with knee OA, the decreased variability of angular parameters on the affected side represents decreased joint flexibility. This leads to decreased consistency in movements of the lower limbs from stride-to-stride, as shown by increased variability of spatial-temporal parameters. Decreased joint flexibility and consistency of movement can be associated with decreased complexity of movement. Other joints of the kinetic chain, such as joints of the non-affected side and the pelvis, play an important role in compensation and adaptation of step-by step motion and in the ability of secure gait. Results suggest that the variability of gait associated with knee osteoarthritis is gender-dependent. During rehabilitation, particular attention must be paid to improving gait stability and proprioception and gender differences should be taken into account.     

Muscle fatigue induced by two different resistances: Elastic tubing versus weight machines

Elastic tubes are devices relatively inexpensive, easy to use, portable and safe, which are claimed to provide advantages with respect to training with free weights or weight machine. The aim of this work was to assess neuromuscular modification induced by the use of two different muscle contraction modalities (elastic versus weight resistances) until exhaustion. Fourteen healthy physically active male students (age: 28 ± 6 years; body mass 72.1 ± 11.0 kg; height: 173.5 ± 6.9 cm) were recruited. They were requested to reach exhaustion with dynamic contraction at 70% of their own One Repetition Maximal (1RM) using, in two different days and in random order, Thera Band® tubes or traditional weight plates on an arm machine designed and built for those tasks. Before and after such contractions a standardized fatiguing isometric test (3 Maximal Voluntary Contractions, MVC plus 60 s at 60% MVC) was requested to assess differences induced by the exhaustion sessions. During fatiguing tests surface EMG signals were recorded from biceps brachii muscle with linear arrays of eight electrodes (silver bars 10 mm apart, 5 mm long, and 1 mm diameter) in single differential configuration. Initial values and rates of change of Average Rectified Value (ARV), MeaN power Frequency (MNF) and muscle fiber Conduction Velocity (CV) were calculated to compare the effects of the two contraction modalities. No differences were found between “elastic session” and “weight session” PRE MVCs (31.9 ± 8.8 and 29.9 ± 8.3 nm, respectively) and endurance times (28 ± 6 and 26 ± 7 s, respectively). The same was observed for POST values. During the post-contraction isometric fatigue test, the only parameters influenced by the contraction modality were the initial CV and the rate of change in CV which were 12% and 37% greater (p < 0.05) respectively after contractions performed with elastic resistance compared to free weights. These findings confirm others for which contractions done with the use of elastic band seem to require greater muscle activation; moreover, they highlight a sort of “muscle conditioning” after that specific contraction modality which requires the use of faster motor units. It is thus possible to consider the practical use of such elastic devices to increase the neuromuscular activation, for instance in specific rehabilitation settings where slow movements with minimal risk of injury are requested (post surgery rehabilitation, physical activity with elderly people or children).     

Muscle co-contraction after anterior cruciate ligament reconstruction: Influence of functional level

Background

ACL reconstruction is recommended to improve function in subjects with ligament injuries. However, after surgery, some individuals are not able to return to their pre-injury functional level. The mechanisms related to this incapacity are not well understood.

Study design

Cross-sectional study.

Methods

Co-contraction levels were assessed in individuals who returned to their pre-injury functional level and in 10 individuals who were not able to return to full activity after unilateral ACL reconstruction. Electromyography of the vastus lateralis and biceps femoris muscles before and after sudden perturbations applied during the stance phase of walking was used to calculate co-contraction.

Results

The involved limb had lower co-contraction pre-perturbation than the non-involved limb in both groups (p = 0.049). The co-contraction level post-perturbation was significantly higher in the limited return group than in the full return group (p = 0.03).

Conclusion

Decreased co-contraction in the involved limb before perturbation may be caused by sensorial changes resulting from surgery or injury. Increased co-contraction levels observed in the limited return group after perturbation may be a compensatory mechanism to make up for possible decreased intrinsic stability of the knee joint.

Clinical relevance

Increased co-contraction after perturbation does not contribute to knee stability.     

Spectral properties of electromyographic and mechanomyographic signals during dynamic concentric and eccentric contractions of the human biceps brachii muscle

The purpose of this study was to describe and examine the variations in recruitment patterns of motor units (MUs) in biceps brachii (BB) through a range of joint motion during dynamic eccentric and concentric contractions. Twelve healthy participants (6 females, 6 males, age = 30 ± 8.5 years) performed concentric and eccentric contractions with constant external loading at different levels. Surface electromyography (EMG) and mechanomyography (MMG) were recorded from BB. The EMGs and MMGs were decomposed into their intensities in time–frequency space using a wavelet technique. The EMG and MMG spectra were then compared using principal component analysis. Variations in total intensity, first principal component (PCI), and the angle θ formed by first component (PCI) and second component (PCII) loading scores were explained in terms of MU recruitment patterns and elbow angles. Elbow angle had a significant effect on dynamic concentric and eccentric contractions. The EMG total intensity was greater for concentric than for eccentric contractions in the present study. MMG total intensity, however, was lower during concentric than during eccentric contractions. In addition, there was no significant difference in θ between concentric and eccentric contractions for both EMG and MMG. Selective recruitment of fast MUs from BB muscle during eccentric muscle contractions was not found in the present study.     

Molecular origin of the sequence-dependent kinetics of reactions between cisplatin derivatives and DNA

Experimental and theoretical studies related to the kinetics of interactions between cisplatin derivatives and DNA are critically reviewed. The reaction between DNA and cisplatin is a multistep reaction, consisting of aquation, electrostatic preassociation, nucleophilic substitution of one aqua ligand by a DNA guanine, and crosslink formation. If the reacting platinum complex is cis-[PtCl(NH₃)₂(H₂O)]⁺, the monoadduct bears one chlorido ligand, and the crosslink formation is preceded by a second aquation step. The kinetics of all these steps, including that of the monoadduct aquation, is significantly modulated by the flanking bases. In the case of the cisplatin derivatives carboplatin and oxaliplatin, recent work has clearly shown that the opening of the dicarboxylate chelate ring is faster than cisplatin hydrolysis; however, the even much faster ring closure keeps the concentration of the ring-opened species very low. Correlation of data from reactions with nucleotides on the one hand and from those with DNA on the other hand indicates that in vitro, the reactions with DNA proceed with the intact dicarboxylates as the reacting species. Thus, for carboplatin and oxaliplatin, the species reacting with DNA are electroneutral, while for cisplatin, the reactive species are cationic. The fact that nevertheless the in vitro sequence-selectivities appear similar for all three complexes suggests that hydrogen bonding between platinum leaving groups and DNA residues is not a factor determining the sequence-selective binding to GG and AG sequences.This review focuses at the studies designed to quantify and explain the physical origin of the influence of DNA sequence on the reaction kinetics.