Westerterp (2017), in European Journal of Clinical Nutrition, analysed data showing that activity-induced energy expenditure (AEE) can vary by more than 500–800 kcal/day between training and rest days in active adults. He noted that while basal metabolic rate (BMR) remains relatively stable, AEE accounts for up to 30–50% of total daily energy expenditure — the most variable component. The study also highlighted compensatory mechanisms such as reduced spontaneous movement or improved efficiency after heavy training, which can offset part of the calorie burn. This demonstrates that static daily calorie targets fail to reflect real-world fluctuations.