Zone 3: The “Comfortably Uncomfortable” Zone

Zone 3: Comfortably Hard (Tempo)

Zone 3 sits between steady aerobic work and threshold. It’s the zone of purposeful discomfort — strong, committed effort you could sustain for around an hour.For triathletes, Zone 3 is race-pace territory for Olympic-distance and strong segments of 70.3.

Why Zone 3 Matters

It builds strength under aerobic load

Zone 3 teaches your body to hold a strong pace without tipping into anaerobic zones.

You get better at managing fatigue

Working here builds mental and muscular resilience.

Your heart and lungs adapt to higher sustained demandsY

ou strengthen your entire aerobic system — like

upgrading the engine and the fuel lines.

Glycogen use becomes more efficient

You learn to handle harder work without blowing through carbohydrate stores too quickly.

What Zone 3 Feels Like

• Breathing deeper, but controlled

• Talking becomes short phrases

• Legs feel loaded but not burning

• A steady, focused grind

You’re working, but you’re not at your limit.

Simple Zone 3 Session

3 × 10 minutes tempo (Zone 3) with 3 minutes easy

Smooth, steady pressure. No surging.

Zone 3 builds the strength that supports race-day speed.