This is an 8-week aerobic base building program with three modality variations — running, cycling, and low-impact (rowing, elliptical, or swimming). All three follow the same weekly structure and progression logic. The goal is building the aerobic foundation that supports everything else — more mitochondria, better fat oxidation, improved cardiac efficiency, and faster recovery from all types of training. Pick the modality that fits your body, your access, and your preferences. The programming adapts.