25 and 42.83 μm for type I fibers and between 26.45 and 39.12 μm for type II fibers; mean values for area were ranging from 972.1 to 2,680.2 μm2 for type I fibers and between 651.0 and 1,720.3 μm2 for type II fibers. In the OA group, the mean fiber diameter was between 35.2 and 50.34 μm for type I fiber and between 33.49 and 53.69 μm for type II fibers; the mean fiber area was between 1,532.8 and 2,792.5 μm2 for type I fiber and between 1,644.0 and 2,857.8 μm2 for type II fibers. Fig. 1 Analysis of muscle fiber atrophy. a In osteoporosis, vastus lateralis muscle biopsy

reacted for ATPase pH 4.2 shows a preferential type II muscle fiber (light fibers) atrophy. b Mega-histogram comparing fiber diameter distribution in OP and OA. Type II fibers in the OP group have a higher degree of deviation from the normal distribution toward the atrophic range. c Linear regression graph showing in OP an ABT-888 selleck chemical inverse correlation between selleck type II fiber atrophy and BMD The analysis of the mega-histogram showed that fiber diameters in the OP group had a higher degree of deviation from the normal distribution toward the atrophic range, compared to OA. This deviation

was slight for type I fibers and very prominent for type II fibers (Fig. 1b). In the OA group, 8.25 % of type I fibers and 12.5 % of type II fibers were atrophic. In the OP group, atrophy was more prominent and involved preferentially type II fibers: in fact, 11.67 % of type I fibers and 36.86 % of type II fibers were atrophic. In both groups, type II fiber atrophy was significantly

more frequent than type I fiber (p value <0.01), with a threefold ratio in OP and only a 1.5-fold ratio in OA. On the basis of these raw data, in order to take into account the fact that large deviations from the normal range are more important than small ones, we calculated the atrophy factor (AF) for the different fiber types in both groups, as previously described [15–17]. This analysis showed that the AF for type I fiber was 155 in OP and 110 in OA (normal threshold value, 100). The AF for type II fibers was 451 in OP and 185 in OA (normal threshold value, 200), thus confirming that type II atrophy is a prominent feature in OP only. Correlation analysis To verify if there was a correlation between percentage of muscle atrophy found in these two groups of patients and severity of disease, Atazanavir we performed the Pearson product–moment correlation test. The statistical analysis showed that in OP, the percentage of type II fiber atrophy correlated with neck and total femoral BMD values (correlation coefficient r = −0.6 and p value <0.05) (Fig. 1c), but not with type I fiber atrophy, patient’s age, and BMI. In OA, type I and type II fiber atrophy were highly correlated with each other (correlation coefficient r = 0.875, p value <0.0001) and with disease duration (correlation coefficient r = 0.664 and 0.655, respectively; p value <0.