Understanding the Relationship between Intrinsic Cardiorespiratory Fitness and Serum and Skeletal Muscle Metabolomics Profile.

Intrinsic cardiorespiratory fitness (iCRF) indicates the CRF level in the sedentary state. However, even among sedentary individuals, a wide interindividual variability is observed in the iCRF levels, whose associated molecular characteristics are little understood. This study aimed to investigate whether serum and skeletal muscle metabolomics profiles are associated with iCRF, measured by maximal power output (MPO). Seventy sedentary young adults were submitted to venous blood sampling, a biopsy of the vastus lateralis muscle and iCRF assessment. Blood serum and muscle tissue samples were analyzed by proton nuclear magnetic resonance (1H NMR) spectroscopy. Metabolites related to iCRF were those supported by three levels of evidence: (1) correlation with iCRF, (2) significant difference between individuals with low and high iCRF, and (3) metabolite contribution to significant pathways associated with iCRF. From 43 serum and 70 skeletal muscle analyzed metabolites, iCRF was positively associated with levels of betaine, threonine, proline, ornithine, and glutamine in serum and lactate, fumarate, NADP+, and formate in skeletal muscle. Serum betaine and ornithine and skeletal muscle lactate metabolites explained 31.2 and 16.8%, respectively, of the iCRF variability in addition to body mass. The results suggest that iCRF in young adults is positively associated with serum and skeletal muscle metabolic levels, indicative of the amino acid and carbohydrate metabolism.

Augmented Anabolic Responses after 8-wk Cycling with Blood Flow Restriction.

INTRODUCTION: Low-intensity endurance training (ET) performed with blood flow restriction (BFR) can improve muscle strength, cross-sectional area (CSA) and cardiorespiratory capacity. Whether muscle strength and CSA as well as cardiorespiratory capacity (i.e., V˙O2max) and underlying molecular processes regulating such respective muscle adaptations are comparable to resistance and ET is unknown. PURPOSE: To determine the respective chronic (i.e., 8 wk) functional, morphological, and molecular responses of ET-BFR training compared with conventional, unrestricted resistance training (RT) and ET. METHODS: Thirty healthy young men were randomly assigned to one of three experimental groups: ET-BFR (n = 10, 4 d·wk, 30-min cycling at 40% of V˙O2max), RT (n = 10, 4 d·wk, 4 sets of 10 repetitions leg press at 70% of one repetition maximum with 60 s rest) or ET (n = 10, 4 d·wk, 30-min cycling at 70% of V˙O2max) for 8 wk. Measures of quadriceps CSA, leg press one repetition maximum, and V˙O2max as well as muscle biopsies were obtained before and after intervention. RESULTS: Both RT and ET-BFR increased muscle strength and hypertrophy responses. ET-BFR also increased V˙O2max, total cytochrome c oxidase subunit 4 isoform 1 abundance and vascular endothelial growth factor mRNA abundance despite the lower work load compared to ET. CONCLUSIONS: Eight weeks of ET-BFR can increase muscle strength and induce similar muscle hypertrophy responses to RT while V˙O2max responses also increased postintervention even with a significantly lower work load compared with ET. Our findings provide new insight to some of the molecular mechanisms mediating adaptation responses with ET-BFR and the potential for this training protocol to improve muscle and cardiorespiratory capacity.