Effects of Renal Failure on Skeletal Muscle

In this cross-sectional study, we examined biopsies from the vastus lateralis muscle of 13 predialytic uremic men (mean age 46 ± 8 years). Their average glomerular filtration rate was 14 ± 7 ml/min×1.73 m2 and their maximal exercise capacity, measured by standardized exercise test on a bicycle ergometer, was 184 ± 45 W (94% of the expected norm). The proportion of type I fibers (type 1%) in the uremic group was similar to that of the reference group (42 ± 11 vs. 41 ± 8% NS). The proportion of type IIA fibers (type IIA%) in the uremic group was higher than in the reference group (44 ± 10 compared to 35 ± 9%, p < 0.05). The proportion of type IIB fibers (type IIB%) was lower than in the reference group (13 ± 8 vs. 21 ± 8%, p < 0.05). Type I fiber area was similar to that of the reference group (4,768 ± 1,033 vs. 4,627 ± 1,112 μm2, NS). Type IIA and type IIB fiber areas tended to be smaller than those of the reference group (type IIA fiber area: 4,515 ± 929 vs. 5,213 ± 1,288 μm2, NS; type IIB fiber area: 3,953 ± 1,066 vs. 4,406 ± 1,582 μm2, NS) with a type IIA area/type I area ratio which was significantly lower than in the reference group. Citrate synthase activity was 0.48 ± 0.08 μkat/g in the uremic group and 0.50 ± 0.08 μkat/g in the reference group, NS. Phosphofructokinase activity was 1.2 ± 0.5 μkat/g in the uremic group and 1.1 ± 0.3 μkat/g in the reference group, NS. Maximal exercise capacity showed a positive correlation to type 1% (r = 0.71, p < 0.01) and a negative correlation to type IIA% (r=-0.73, p < 0.01). In multiple regression analysis, type 1% showed a negative correlation to GFR, when maximal working capacity had been accounted for (r = -0.83, p < 0.005). The observed increase in type IIA% at the expense of type IIB% in conjunction with the negative correlation between type 1% and GFR may indicate a relationship between progressive uremia and muscle fiber composition, which may lead to a reduced exercise capacity.