The ability of metabolically active tissue (e. g. muscle) to change energy sources from fat to carbohydrates (and vice versa) is termed

The ability of metabolically active tissue (e.g. muscle) to change energy sources from fat to carbohydrates (and vice versa) is termed: Metabolic flexibility.

Explanation:

The human body primarily uses two sources of energy, glucose and fat. Glucose is found in the bloodstream and stored as glycogen in muscles and the liver, and fat in adipose tissue and in fatty acids. Metabolic flexibility is the ability of the body to alternate between the different energy substrates according to the circumstances of each moment. People with good metabolic flexibility will find it easier to use body fat and perform better physically. At lower intensity during exercise, more fat is consumed and at higher intensity, more glucose. If that high intensity is maintained, glycogen stores will be depleted. So then, how much energy is stored, how much is needed and how it will be delivered, is part of the reading that our body performs. This cellular adaptation to the requirements is known as metabolic flexibility.