The purpose of the study was to investigate the relationship between muscle fiber composition and the rate of force development (RFD) in well-trained individuals with different training background. Thirty-eight young males with different training background participated: 9 endurance runners, 10 power-trained, 9 strength-trained, and 10 sedentary. They performed maximal isometric leg press for the measurement of RFD. Body composition (dual x-ray absorptiometry) and vastus lateralis fiber type composition was also evaluated. When all participants were examined as a group, moderate correlations were found between the percent of type II muscle fibers and RFD between 100-600ms (r: 0.321 - 0.497, p<0.05). The correlation coefficients were higher for the cross-sectional area (CSA) and the %CSA of type II and IIx muscle fibers (r: 0.599 - 0.847, p<0.001). For the power group, RFD up to 250ms was highly correlated with % type IIx muscle fibers and type IIx fiber CSA (r: 0.670 - 0.826, p<0.05), as well as with %CSA of type IIx fibers (r: 0.714 - 0.975, p<0.05). Significant correlations were found between the relative RFD (·kg lower extremities lean mass) and CSA-%CSA of type II and IIx fibers for the power group (r: 0.676 - 0.903, p<0.05). No significant correlations were found between muscle morphology and RFD for the other groups. In conclusion, the present data suggest that there is a strong link between the type IIx muscle fibers and early RFD and relative RFD in power-trained participants. Type II fibers seem to be moderately linked with RFD in non-power-trained individuals.
The interaction of phosphatidyl choline-cholesterol liposomes incorporating dihexadecyl phosphate as recognizable lipid with complementary guanidinylated diaminobutane poly(propylene imine) dendrimers of the fourth and fifth generation afforded liposome-dendrimer aggregates which were redispersed by the addition of an excess of a phosphate buffer. The higher generation dendrimeric derivative proved more effective when interacted with liposomes. This behavior was attributed to multivalent effects, which, as generally established, enhance the reactivity of multifunctional particles. Turbidimetry, atomic force microscopy (AFM) and optical microscopy were used for investigating the interaction of the complementary particles while the redispersion of the aggregates was studied by transmission electron microscopy (TEM). Liposomal membrane stability in the collapse and redispersion processes was assessed by the calcein fluorescence method, TEM, and AFM.
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