MariposasInterval Training
Interval training alternates between periods of higher-effort work and lower-effort recovery, repeated multiple times within a single session. The core idea is that this structure lets you accumulate more total time at a challenging intensity than you could sustain in one continuous push. Most people assume intervals always mean sprinting until you collapse, but the work-to-rest ratio and intensity level vary enormously depending on the goal. A 20-second all-out effort followed by 40 seconds of rest taxes your anaerobic system and builds short-burst power. A 4-minute hard run followed by 3 minutes of easy jogging hits your aerobic ceiling and improves cardiovascular efficiency in a very different way. The ratio you choose, not just the hard portions, determines what adaptation you actually get from the session.
Example
A runner might do 6 rounds of 2 minutes at a pace that feels genuinely hard but controlled, followed by 90 seconds of slow walking or jogging to let the heart rate drop before the next effort. Over several weeks of this structure, the pace that once felt hard at 2 minutes starts to feel manageable, a sign that aerobic capacity has improved. That progressive shift in perceived difficulty is interval training working as intended.