Determining Changes in Electromyography Indices when Measuring Maximum Acceptable Weight of Lift in Iranian Male Students.

BACKGROUND: In spite of the increasing degree of automation in industry, manual material handling (MMH) is still performed in many occupational settings. The aim of the current study was to determine the maximum acceptable weight of lift using psychophysical and electromyography indices. METHODS: This experimental study was conducted among 15 male students recruited from Tehran University of Medical Sciences. Each participant performed 18 different lifting tasks which involved three lifting frequencies, three lifting heights and two box sizes. Each set of experiments was conducted during the 20 min work period using free-style lifting technique and subjective as well as objective assessment methodologies. SPSS version 18 software was used for descriptive and analytical analyses by Friedman, Wilcoxon and Spearman correlation techniques. RESULTS: The results demonstrated that muscle activity increased with increasing frequency, height of lift and box size (P<0.05). Meanwhile, MAWLs obtained in this study are lower than those in Snook table (P<0.05). In this study, the level of muscle activity in percent MVC in relation to the erector spine muscles in L3 and T9 regions as well as left and right abdominal external oblique muscles were at 38.89%, 27.78%, 11.11% and 5.55% in terms of muscle activity is more than 70% MVC, respectively. The results of Wilcoxon test revealed that for both small and large boxes under all conditions, significant differences were detected between the beginning and end of the test values for MPF of erector spine in L3 and T9 regions, and left and right abdominal external oblique muscles (P<0.05). The results of Spearman correlation test showed that there was a significant relation between the MAWL, RMS and MPF of the muscles in all test conditions (P<0.05). CONCLUSION: Based on the results of this study, it was concluded if muscle activity is more than 70% of MVC, the values of Snook tables should be revisited. Furthermore, the biomechanical perspective should receive special attention in determining the standards for MMH.

Mechanisms of muscular electrophysiological and mitochondrial dysfunction following exposure to malathion, an organophosphorus pesticide.

Muscle dysfunction in acute organophosphorus (OP) poisoning is a cause of death in human. The present study was conducted to identify the mechanism of action of OP in terms of muscle mitochondrial dysfunction. Electromyography (EMG) was conducted on rats exposed to the acute oral dose of malathion (400 mg/kg) that could inhibit acetylcholinesterase activity up to 70%. The function of mitochondrial respiratory chain and the rate of production of reactive oxygen species (ROS) from intact mitochondria were measured. The bioenergetic pathways were studied by measurement of adenosine triphosphate (ATP), lactate, and glycogen. To identify mitochondrial-dependent apoptotic pathways, the messenger RNA (mRNA) expression of bax and bcl-2, protein expression of caspase-9, mitochondrial cytochrome c release, and DNA damage were measured. The EMG confirmed muscle weakness. The reduction in activity of mitochondrial complexes and muscular glycogen with an elevation of lactate was in association with impairment of cellular respiration. The reduction in mitochondrial proapoptotic stimuli is indicative of autophagic process inducing cytoprotective effects in the early stage of stress. Downregulation of apoptotic signaling may be due to reduction in ATP and ROS, and genotoxic potential of malathion. The maintenance of mitochondrial integrity by means of artificial electron donors and increasing exogenous ATP might prevent toxicity of OPs.

Modulation of the ipsilateral and contralateral H reflexes following ipsilateral mechanical pressure of the foot in normal subjects.

OBJECTIVE: Mechanoreceptors from the foot sole likely contribute in the reflex regulations. Therefore, it was hypothesized that repetitive low threshold afferents stimulation would have an inhibitory effect on the soleus H-reflexes. METHODS: Sixteen normal subjects voluntarily, participated in the study and were randomly allocated. Subjects were remained in prone position. The Cutaneous Mechanical Pressure (CMP equal to 50% of leg and foot weight) was applied to the ipsilateral lateral and Medial plantar surface by a designed instrument through a square plate (30 x 30 mm). H reflex as an indicator for excitability of motoneurones was bilaterally elicited before and after the application of the CMP. The H-reflex parameters were estimated. RESULTS: Mechanical pressure significantly depressed soleus H-reflex excitability in ipsilateral and contralateral feet in all subjects. CONCLUSION: The demonstration of a decrease in H-reflex excitability as a result of applied pressure to the foot sole suggests that the change in reflex excitability is the result of a common spinal mechanism. The results highlight the modulatory effects that natural stimulation of afferents can have on reflex excitability. SIGNIFICANCE: The placement of a small flat plate, in order to apply pressure to the plantar eminence, may be useful for modulation of muscle tone. In addition, these findings might be useful for reducing spasticity; because spasticity is at least partially caused by hyperexcitability of the motorneuron pool.

Functional assessment of knee joint position sense following anterior cruciate ligament reconstruction.

CONTEXT: The anterior cruciate ligament (ACL) has both mechanical and proprioceptive (sensory) functions. Knee-joint proprioception has been assessed using either reproduction of position or threshold to detect passive motion in non-weight-bearing positions. It has been suggested that a more functional and dynamic/active assessment of proprioception might clarify the effects of injury and reconstruction on the proprioceptive function of ACL at the knee joint. OBJECTIVE: To assess knee joint position sense (JPS) following ACL reconstruction in functional positions. SUBJECTS: Twelve male patients who had undergone ACL reconstruction and 12 male healthy control subjects participated in the study. METHODS AND MAIN OUTCOME MEASURES: JPS was evaluated by reproduction of the angles in weight-bearing position with limb movement into flexion and extension. The dominant knee of healthy subjects and both (reconstructed and uninjured) knees of the patients were tested. Absolute angular error was used as a dependent variable. RESULTS: There was no significant difference between the operated and uninjured knees of patients or between patients and healthy controls (p>or=0.05). These results were measured during two tasks of limb movement into flexion and extension. CONCLUSION: We found no evidence of impaired JPS in weight-bearing positions in subjects with ACL reconstruction at a mean follow-up of 11 months after surgery compared with subjects with healthy knees.

Is there any relationship between the Modified Ashworth Scale scores and alpha motoneuron excitability indicators?

The purpose of this study was to investigate the relationship between the modified Ashworth scale (MAS) scores and alpha motoneuron excitability indicators. Thirty-one post-stroke patients were assessed for this object. The main outcome measures were the MAS and electro physiologic assessments. The latter was performed using both conventional (Hmax/Mmax) and new (Hslope/Mslope) measures of spinal excitability. Data on thirty-one adult subjects with hemiplegia (twenty-five men and six women) were analysed. The soleus Hmax/Mmax ratio appeared to correlate directly with the MAS scores (r = 0.36; P < 0.05). Correlation between the MAS scores and either Hslope/Mslope ratio or H-reflex latency was not significant (P > 0.05). In seventeen patients whose H-reflex could be evoked bilaterally, spinal excitability indicators showed significant difference between the affected and non-affected sides (P < 0.05). Based on the results of this study, there is no relationship between the MAS scores and the preferred measure of alpha motoneuron excitability. This research suggests that the MAS could not distinguish between the reflexive and non-reflexive components of the hypertonicity in ankle plantar flexors.

The effect of transcutaneous electrical nerve stimulation on sympathetic skin response.

The aim of present study was to determine whether combination of transcutaneous electrical nerve stimulation (TENS) and acupuncture inhibits sympathetic nerve activity in healthy humans. Multiunit efferent postganglionic sympathetic activity was recorded with Toennies set. In this study, the aim was to obtain latency, amplitude and duration of sympathetic skin response (SSR) and skin temperature (ST) from both hands in 15 healthy subjects. Subjects randomly assigned and everybody participated in all the three groups [Control Group (CG), Acupuncture Group (AG) and Nerve Stimulation Group (NSG)]. TENS (2 Hz, 250 microsecond) was applied over the median nerve of the right elbow in NSG for 20 min, either, TENS was applied over (HE-7) point of the right hand in CG (TENS off) and AG (TENS on) for 20 min. SSR (lat, amp, dur) and ST data was recorded before TENS and for immediate, 5 min and 10 min post--TENS. ST was recorded in distal phalanx of index finger of both hands and SSR was recorded from both hands. TENS in CG did not affect ST and SSR following stimulation. TENS applied at AG and NSG caused a significant increase in ST (P = 0.001), significant increase in latency of SSR (P = 0.001), significant decrease in amplitude of SSR (P = 0.001) and no significant changes were observed in duration of SSR (P > 0.05). Then statistical analysis showed differences between both of groups (AG & NSG) for ST and SSR post--TENS. Transcutaneous electrical nerve stimulation inhibits sympathetic nerve activity in healthy humans.