Training zones explained

The 5-Zone System

Norvin uses the British Rowing 5-zone framework to define training intensity. Each zone produces a specific physiological adaptation — training at the wrong intensity means you're building the wrong thing, or worse, accumulating fatigue without the fitness gains to justify it.

The five zones are:

• UT2 — Easy, conversational effort. You could hold a full conversation. This is pure aerobic foundation work: teaching your body to use fat as fuel, building capillary density, and developing cardiac efficiency. Most athletes underestimate how valuable this zone is.
• UT1 — Steady state. Comfortably sustainable for long efforts. Breathing is deeper but controlled. This is the workhorse zone for endurance development.
• AT — Threshold. Comfortably hard. You're at or near your lactate threshold — the intensity at which lactate production starts to outpace clearance. Improving this zone raises your sustainable race pace.
• TR — Speed endurance and VO2max intervals. Hard efforts that are only sustainable for minutes at a time. These develop your aerobic ceiling.
• AN — Anaerobic. All-out efforts lasting seconds to a couple of minutes. Maximum power, maximum oxygen debt.

How Norvin Calculates Your Zones

Your zones are calculated from your 2K Pace — the average Split Time from an all-out 2000m test. The 2K is the gold standard benchmark in rowing: it taxes both aerobic and anaerobic systems and gives a reliable picture of current fitness.

From that single number, Norvin derives percentage-based thresholds for each zone. As your fitness improves and your 2K pace gets faster, all your training zones shift accordingly.

Why the Distribution Matters

Research consistently supports a Polarized approach: roughly 80% of training volume in UT2 and UT1, with the remaining 20% in AT and above. This balance maximizes aerobic adaptation while leaving enough recovery capacity to absorb the high-intensity work.

Training too much in the middle — not easy enough to recover, not hard enough to drive adaptation — is one of the most common mistakes endurance athletes make.