No pain, no gain, no idea what half these terms mean.
A heart rate training zone where you exercise at a moderate intensity that feels suspiciously easy, which is exactly why it's effective and exactly why gym bros refuse to do it. It's the fitness equivalent of being told to slow down and actually enjoy the journey.
The highest heart rate training zone at 90-100% of maximum heart rate, reserved for short bursts of maximum effort. Where your lungs burn, your legs scream, and your Garmin judges you.
The moderate-intensity training zone between comfortable aerobic work and hard threshold efforts, also known as 'no man's land' because it's allegedly too hard for easy days and too easy for hard days. Every endurance athlete's accidental default pace.