The present study was carried out to search whether organophosphate pesticides affect the mechanical properties of the thoracic aorta. Wistar female rats (aged 6-8 weeks) were assigned randomly to a control group and groups treated with either dichlorvos or chlorpyriphos for 90 days at a dose of 5 mg/kg/day. After that period, animals were killed and thoracic aorta strips in longitudinal direction were isolated. The stress, strain and elastic modulus were obtained from the strips. Our results showed that chronic administration of chlorpyriphos and dichlorvos caused downward shift of the stress-strain relations compared to the control curve. The elastic modulus-stress curve revealed distinct characteristics in the low and high stress regions. A power function was used to simulate the low stress region while a line was fit to the high stress region. Curve fitting procedure illustrated that both pesticides influenced mainly the high stress region, but they had diverse effects at the low stress region. The results also imply that chlorpyriphos and dichlorvos decrease the strength of the aorta and therefore might influence the response of the aorta to mechanical loading induced by blood pressure.

Stretching exercises are known for reduction of musculoskeletal stiffness and elongation of electromechanical delay (EMD). However, computing a change in stiffness by means of time delays, detected between onset of electromyographic (EMG), mechanomyographic (MMG) and force signals, can reveal changes in subcomponents (Delta tEMG-MMG and Delta tMMG-FORCE) of EMD after stretching. In our study, the effect of stretching was investigated while quadriceps femoris (QF) muscle performed isometric contractions. The EMG, MMG, and Force signals were recorded from rectus femoris (RF) and vastus medialis (VM) during five voluntarily isometric contractions at 15 degrees, 30 degrees, and 45 degrees of knee flexion angle, while the leg was positioned on a custom-made device. Subjects in both intervention and control groups underwent same recording procedure before and after stretching. No difference between the baseline repeated contractions (before stretching) was ensured by ANOVA for repeated measures while a difference between PRE and POST was analyzed and concluded based on the effect size results. The EMD did not change; however, subcomponents (Delta tEMG-MMG and Delta tMMG-FORCE) showed differences within RF and VM muscles after stretching. The 30 degrees knee flexion angle appears to be a position where isometric contraction intensity needs to be carefully monitored during rehabilitation period.

The purpose of this study is to obtain distinguishing features of the surface EMG (sEMG) generated by the rectus femoris (RF) and vastus medialis (VM) under maximum voluntary contractions by using the fractal analyses method and compare their dynamic behavior. 15 healthy subjects were requested to produce 5 consecutive maximum voluntary isometric contractions of quadriceps muscle, each lasting 5 seconds with a resting period of 10 seconds between contractions at a knee flexion angle of 15 ^o . Force produced by quadriceps muscles and sEMG from RF and VM were recorded. Correlation dimension and root mean square (rms) values of stationary part of each sEMG were computed. Two-way ANOVA analysis for repeated measures reveled that the mean of the correlation dimension was 1.388±0.004 for RF and 1.376±0.007 for VM. There was a significant main effect for muscle (p = 0.027) whereas there was not a significant effect for time (p = 0.918). The means of the rms of the sEMG signals from RF and VM were not significantly different. It was concluded that the processes in producing sEMG in RF are more complex than that in VM and the correlation dimension can be used as a distinguishing feature of RF and VM.