What principle of exercise training is illustrated by a woman noticing increased muscular endurance without significant strength gain after consistent running?

The principle of specificity is illustrated in this scenario, as it describes how the body adapts to the specific demands of the exercise performed. In this case, the woman is experiencing increased muscular endurance from her consistent running. This enhancement occurs because running predominantly targets and develops the aerobic energy systems and the muscular endurance of specific muscle groups used during the activity, rather than leading to significant increases in maximal strength.

Specificity indicates that training adaptations, such as greater endurance, occur in direct response to the type of exercise performed. Therefore, the woman's improvement in endurance reflects her body’s adaptation to the particular stress placed upon it through running, demonstrating how different forms of exercise can lead to specific physical enhancements. This concept is critical in designing training programs that are intended to achieve particular fitness goals, indicating that if one wants to improve strength, they would need to focus on strength training exercises rather than endurance activities.