Fig. 1

Myocardiogenic and skeletal myogenic determinants of reduced exercise tolerance in type 2 diabetes. Schematic representation of two pathophysiological hypotheses explaining the alterations observed in type 2 diabetes mellitus through cardiopulmonary exercise testing. Central and peripheral (efferent fibers to lungs, heart, conduit vessels, muscle arterioles are represented on the right, while afferent fibers of muscle metaboreflex and cardiac sympathetic reflex are represented on the left of the picture) nervous system, the baroreceptor, lungs, heart, conduit vessels, muscular vasculature, oxygen diffusion from capillaries to muscle, skeletal muscle and muscle cells are schematically represented. In each hypothesis, the organ/system that is primarily impaired is colored in grey and is marked with a black cross, whilst the other organs maintain their colors. Secondary involvement of other organs/systems is indicated with vertical grey arrows indicating stimulation (arrow facing up) or inhibition (arrow facing down) through known physiological mechanisms, which are represented as grey dotted lines with captions. On top of the figure, the grey text panel explains the primary involvement of the organ/system identified with the black cross and grey shadowing; the text panel beneath the figure shows a list of the altered cardiopulmonary exercise test variables observed in type 2 diabetes mellitus that may be explained by the pathophysiological hypothesis here shown. a Myocardiogenic determinants: an insufficient cardiac output adjustment reduces muscle perfusion, force production, and thus exercise tolerance. b Skeletal myogenic determinants: reduced skeletal muscle aerobic capacity or early fatigue can account for the reduced oxygen uptake, peripheral oxygen extraction, whilst a reduced cardiac output may be secondary to an enhanced baroreflex activation (see main text for full description)