Background: Increased maximal oxygen uptake (V̇ O2max) is beneficial in children
with cystic fibrosis (CF) but remains lower compared to healthy peers. Intrinsic
metabolic deficiencies within skeletal muscle (muscle “quality”) and skeletal
muscle size (muscle “quantity”) are both proposed as potential causes for the
lower V̇ O2max, ...
Background: Increased maximal oxygen uptake (V̇ O2max) is beneficial in children
with cystic fibrosis (CF) but remains lower compared to healthy peers. Intrinsic
metabolic deficiencies within skeletal muscle (muscle “quality”) and skeletal
muscle size (muscle “quantity”) are both proposed as potential causes for the
lower V̇ O2max, although exact mechanisms remain unknown. This study utilises
gold-standard methodologies to control for the residual effects of muscle size
from V̇ O2max to address this “quality” vs. “quantity” debate.
Methods: Fourteen children (7 CF vs. 7 age- and sex-matched controls) were
recruited. Parameters of muscle size – muscle cross-sectional area (mCSA) and
thigh muscle volume (TMV) were derived from magnetic resonance imaging,
and V̇ O2max obtained via cardiopulmonary exercise testing. Allometric scaling
removed residual effects of muscle size, and independent samples t-tests and
effect sizes (ES) identified differences between groups in V̇ O2max, once mCSA
and TMV were controlled for.
Results: V̇ O2max was shown to be lower in the CF group, relative to controls, with
large ES being identified when allometrically scaled to mCSA (ES = 1.76) and TMV
(ES = 0.92). Reduced peak work rate was also identified in the CF group when
allometrically controlled for mCSA (ES = 1.18) and TMV (ES = 0.45).
Conclusions: A lower V̇ O2max was still observed in children with CF after
allometrically scaling for muscle size, suggesting reduced muscle “quality” in CF
(as muscle “quantity” is fully controlled for). This observation likely reflects
intrinsic metabolic defects within CF skeletal muscle.