Exercise Frequency During Endurance Training: Cardiorespiratory, Hematological, and Muscle Oxidative Adaptations

The goal of this interventional study is to compare training for different numbers of days each week in healthy, young individuals. The main questions it aims to answer are: * Does exercising less often improve endurance fitness as much as exercising more often? * Are endurance fitness improvements caused by improvements in the muscle and blood? Participants will train on a stationary bike for eight weeks. Researchers will measure the participants endurance fitness, as well as muscle and blood characteristics, before and after training to look for improvements from the training protocols. Researchers will compare low-frequency exercise (two times per week) and high-frequency exercise (four times per week) to see if they each improve endurance fitness.