Setting Your Training Zones

Training zones are the translator between a plan and what you actually do. If the plan says "60 minutes base", it has to be clear how fast that is — otherwise it turns into a stroll or a tempo run depending on the day.

Every zone system rests on the same idea: there is an intensity you can hold for roughly an hour, and everything else is measured against it. That intensity has a different name in each discipline.

The threshold in each discipline

Cycling: FTP. Functional Threshold Power is the power in watts you can sustain for about an hour. It is usually measured with a 20-minute test: after a solid warm-up, ride 20 minutes as evenly hard as you can and subtract 5 percent from the average. A ramp test is the gentler alternative and slightly less precise.

Running: threshold pace and LTHR. Threshold pace is the pace you can hold for roughly an hour — broadly 10 km race pace for well-trained runners, and closer to a one-hour race pace for slower ones. The matching heart rate is LTHR, lactate threshold heart rate. A practical test: run 30 minutes alone, evenly, as hard as you can hold; the average heart rate of the final 20 minutes is a good LTHR estimate.

Swimming: CSS. Critical Swim Speed comes from two time trials, typically 400 and 200 metres. The difference in times divided by the difference in distance gives the pace per 100 metres you can hold for an extended effort.

Why 220 minus age is useless

The best-known formula for maximum heart rate is also the worst. It comes from a rough summary of older studies and carries a standard deviation of roughly 10 to 12 beats — for a 40-year-old the real maximum plausibly sits anywhere between 160 and 200.

Zones calculated on that basis are not imprecise, they are arbitrary. Train by them and, depending on your deviation, you are either permanently too easy or constantly too hard.

There is a second problem on top. Maximum heart rate is the weaker reference point anyway. It says little about your metabolic state, is barely trainable and is hard to establish cleanly in everyday training. Threshold is the better quantity — it moves with training, and it is precisely what you are trying to improve.

Five zones, and what they are for

Zone systems come with three, five, seven or eight steps. The split is convention; what matters is that you use it consistently. A common five-zone model, referenced to threshold heart rate:

• Zone 1, recovery (below 85 percent of LTHR): active recovery. It feels too slow. It is not.
• Zone 2, base (85 to 89 percent): the bulk of your training. Conversation in full sentences is possible. This is where the aerobic foundation is built.
• Zone 3, tempo (90 to 94 percent): brisk but controlled. Useful in moderation, and the zone where too many amateurs spend too much time.
• Zone 4, threshold (95 to 99 percent): around threshold. Hard, but manageable in intervals. The most important stimulus for threshold performance.
• Zone 5, VO2max (100 percent and above): short, very hard intervals. Effective and expensive in recovery terms.

How much of what

Distribution matters more than the exact boundaries. Two approaches that hold up in practice:

Polarised training. Around 80 percent of sessions easy in zones 1 and 2, around 20 percent hard in zones 4 and 5, with the middle largely avoided. The reasoning: easy work costs little recovery and delivers aerobic adaptation, hard work provides the stimulus. The middle costs nearly as much as hard and returns nearly as little as easy.

Volume caps after Jack Daniels. As a share of weekly volume, certain intensities should stay bounded: threshold work at most around 10 percent, VO2max intervals at most 8 percent, very short fast repetitions at most 5 percent. What is counted is time inside the interval, not the duration of the whole session.

Both approaches say the same thing in different words: most of your training is easy, and the hard part is sparingly dosed and genuinely hard.

When to re-measure

Thresholds move — upwards when training works, downwards after longer breaks. Keep using old values and you increasingly train in the wrong place, and every training load calculation is distorted on top.

A test every six to eight weeks makes sense, typically at the end of a recovery week when you are rested. Additionally after any break longer than two weeks, and after any race that produced new bests.

Further reading

• Understanding training load
• Building a triathlon training plan
• FTP calculator