Which of the following is not one of the five principles of fitness development?

Muscle Isolation is not recognized as one of the five main principles of fitness development. The five principles typically include Progressive Overload, Specificity, Reversibility, Individualization, and Variety.

Progressive Overload refers to gradually increasing the intensity, duration, or frequency of exercise to stimulate muscle growth and improve fitness. Specificity emphasizes that training should be relevant and appropriate to the goals of the individual, ensuring that the type of training is aligned with the desired performance or outcome. Reversibility highlights that fitness levels can decline if training ceases. While these principles guide effective workout regimens, Muscle Isolation does not fit within these foundational concepts. It may refer to specific exercises targeting particular muscle groups, but it lacks the broader application of principles guiding comprehensive fitness development.