The effectiveness of how much energy your muscles use for a given movement varies depending on your calorie intake. TEA (Thermic Effect of Activity) refers to how much energy your muscles use for a given activity.
In a caloric deficit your muscles become more energy efficient to save energy, burning LESS calories during your workout. In a caloric surplus your muscles are metabolically LESS effective and thereby use MORE calories in your workout.
Your body is thus constantly trying to counteract changes you make in your calorie intake, using MORE energy when you eat too much and using LESS energy when you eat too little. This “balancing” principle is known as homeostasis. Some people have more effective homeostasis than others, explaining why some people are “hardgainers” who need to add much more calories to their diet to gain weight.
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Source: Goldsmith R. Effects of experimental weight perturbation on skeletal muscle work efficiency, fuel utilization, and biochemistry in human subjects. AM J Physiol Regul Integr Comp Physiol. 2010 Jan;298(1):R79-88.