Therefore, fasted training should be carried out at low intensity at a steady-state (aerobic activity, below the aerobic threshold) In fact, during fasting, the levels of the hormone insulin are kept low, consequently, there will be, in contrast, a high level of glucagon, a hormone that elevates the levels of blood sugar (glycemia), but also of the receptors at the level of the adipocytes, favouring the lipolysis (demolition of body fat for energy purposes).
But the glucagon, unlike the adrenaline generated by the HIIT, can not affect the intramuscular glycogen storage, so it's not catabolic.
Furthermore, a low-intensity workout does not increase the cortisol level as much as a high-intensity workout. This indicates that low-intensity workout are less catabolic. Why this? Because when performing a HIIT workout, as is not being pure aerobic, it evokes the secretion of adrenaline, which in addition to stimulating lipolysis, is also a muscular glycogenolytic, which then decreases the muscle glycogen storage (linked to catabolic processes.
Therefore, it is discouraged to train at high intensity when fasted. And what does a state of catabolism entail? The loss of muscle mass causes chronic fatigue because it decreases the levels of intracellular potassium that regulate the neural exchanges. So always pay attention of what you do, how you do it and why you do it.
Matteo Cigala
Founder & Head Coach
