Discussion
skeletal muscle glucose, insulin-stimulated skeletal muscle
Preclinical studies have shown that treatment with a selective βIn the current study, an acute dose of clenbuterol (20 µg), as well as prolonged clenbuterol treatment, led to a significant increase in resting energy expenditure in comparison with placebo. Although the exact mechanisms through which selective βAcute administration of βPreviously, several in vitro and preclinical studies have highlighted the ability of βGiven that clenbuterol is infamous for its repartitioning effects upon high doses (i.e., increasing lean mass whilst reducing fat mass)An alternative mechanism by which clenbuterol could affect skeletal muscle glucose uptake is through increased tissue perfusion. More specifically, selective βAlthough the exact underlying molecular mechanisms remain elusive, the improvements in glucose homeostasis upon selective βSeveral limitations can be identified in our study. Firstly, only male participants were included in our study. It is therefore important that future studies within this field are performed with both men and women to investigate if similar effects occur in both sexes. Secondly, we did not measure urinary nitrogen to accurately assess whole-body protein oxidation, but for the calculation of substrate metabolism instead assumed protein oxidation to be a fixed percentage of energy expenditure. However, this assumption might not hold true in situations of enhanced energy expenditure (i.e., clenbuterol treatment), during which variable protein oxidation can occur. Important differences in substrate oxidation could therefore be missed. Thirdly, we recognize that the sample size in this study was limited, which could potentially explain the lack of findings with respect to GLUT4 translocation or mTORC2 activation. Lastly, our muscle biopsies were taken in the overnight fasted, unstimulated state, whereas glucose uptake was elevated upon insulin stimulation. In other words, analysis of insulin-stimulated skeletal muscle material upon βIn conclusion, we here demonstrate that a two-week treatment with the selective β