Skeletal muscle contributions to reduced fitness in cystic fibrosis youth.

Background: Increased maximal oxygen uptake (V̇O2max) 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 V̇O2max, although exact mechanisms remain unknown. This study utilises gold-standard methodologies to control for the residual effects of muscle size from V̇O2max 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 V̇O2max 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 V̇O2max, once mCSA and TMV were controlled for. Results: V̇O2max 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 V̇O2max 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.

Survey of exercise testing and training in cystic fibrosis clinics in the UK: a decade of progress.

OBJECTIVES: Regular exercise testing is recommended for people with cystic fibrosis (pwCF), as is the provision and regular review of exercise training programmes. A previous survey on exercise testing and training for pwCF in the UK was conducted over a decade ago. With the landscape of CF changing considerably during this time, this survey aimed to evaluate UK-based exercise testing and training practices for pwCF a decade on. DESIGN: Cross-sectional, online survey. PARTICIPANTS: A survey was distributed electronically to UK CF clinics and completed by the individual primarily responsible for exercise services. Descriptive statistics and qualitative analyses were undertaken. RESULTS: In total, 31 CF centres participated, representing ~50% of UK specialist clinics. Of these, 94% reported using exercise testing, 48% of which primarily use cardiopulmonary exercise testing. Exercise testing mostly occurs at annual review (93%) and is most often conducted by physiotherapists (62%). A wide variation in protocols, exercise modalities, normative reference values and cut-offs for exercise-induced desaturation are currently used. All centres reportedly discuss exercise training with pwCF; 94% at every clinic appointment. However, only 52% of centres reportedly use exercise testing to inform individualised exercise training. Physiotherapists typically lead discussions around exercise training (74%). CONCLUSIONS: These data demonstrate that the majority of respondent centres in the UK now offer some exercise testing and training advice for pwCF, representing a marked improvement over the past decade. However, continued efforts are now needed to standardise exercise practices, particularly regarding field testing practices and the translation of test results into personalised training programmes for pwCF.

Quantification of thigh muscle volume in children and adolescents using magnetic resonance imaging.

Abstract Estimating muscle volume (MV) using variable numbers of cross-sectional area (CSA) slices obtained from magnetic resonance imaging (MRI) introduces an error that is known in adults, but not in children and adolescents, whereby body sizes differ due to growth and maturation. Therefore, 15 children and adolescents (11 males, 14.8 ± 2.1 years) underwent MRI scans of the right thigh using a 1.5 T scanner to establish this error. A criterion MV was determined by tracing around and summing all CSAs, with MV subsequently estimated using every second, third, fourth and fifth CSA slice. Bland-Altman plots identified mean bias and limits of agreement (LoA) between methods. Error rates between 1.0 and 10.4% were seen between criterion and estimated MV. Additional analyses identified an impact of formulae selection, with a cylindrical formula preferred to a truncated cone. To counter high error between criterion and estimated MV due to the discrepancies in the number of CSA slices analysed, length-matched criterion volumes were established, with reduced error rates (0.5-2.0%) being produced as a result. CSA at 50% thigh-length also predicted MV, producing a high error (13.8-39.6%). Pearson's correlation coefficients determined relationships between error and measures of body size/composition, with all body size/composition measures being correlated (r = -0.78-0.86, p < 0.05) with the error between criterion and estimated MV. To conclude, MV can be accurately estimated using fewer CSA slices. However, the associated error must be considered when calculating MV in children and adolescents, as body size biases estimates.

Scaling the Oxygen Uptake Efficiency Slope for Body Size in Cystic Fibrosis.

PURPOSE: The aim of this study was to describe the relationship between body size and oxygen uptake efficiency slope (OUES) in pediatric patients with cystic fibrosis (CF) and healthy controls (CON), to identify appropriate scaling procedures to adjust the influence of body size upon OUES. METHODS: The OUES was derived using maximal and submaximal points from cardiopulmonary exercise testing in 72 children (36 CF and 36 CON). OUES was subsequently scaled for stature, body mass (BM), and body surface area (BSA) using ratio-standard (Y/X) and allometric (Y/X) methods. Pearson's correlation coefficients were used to determine the relationship between body size and OUES. RESULTS: When scaled using the ratio-standard method, OUES had a significant positive relationship with stature (r = 0.54, P < 0.001) and BSA (r = 0.25, P = 0.031) and significant negative relationship with BM (r = -0.38, P = 0.016) in the CF group. Combined allometric exponents (b) for CF and CON were stature 3.00, BM 0.86, and BSA 1.40. A significant negative correlation was found between OUES and stature in the CF group when scaled allometrically (r = -0.37, P = 0.027). Nonsignificant (P > 0.05) correlations for the whole group were found between OUES and allometrically scaled BM (CF r = -0.25, CON, r = 0.15) and BSA (CF r = -0.27, CON r = 0.13). CONCLUSIONS: Only allometric scaling of either BM or BSA, and not ratio-standard scaling, successfully eliminates the influence of body size upon OUES. Therefore, this enables a more direct comparison of the OUES between patients with CF and healthy controls.