Your training plan has weeks labelled "base," "build," and "peak." It looks logical on paper. But your body has no idea what week it is.
The traditional periodisation model assumes adaptation follows a predictable, linear path. You lay an aerobic foundation first. You add intensity second. You sharpen for the race last. It is tidy, intuitive, and for most age-group athletes, it is the wrong approach.
The Problem with Phases
Traditional periodisation was designed for athletes who can dedicate 20 or more hours per week to training, with full control over their recovery environment. Professional athletes can justify spending eight weeks on pure aerobic base before transitioning to a build phase. They have the volume to make each phase productive and the lifestyle to absorb the transitions.
Age-group athletes do not. Most train between five and ten hours per week, balanced around a full-time job, family, and everything else life demands. When your training window is that small, spending two months on a purely aerobic block means two months with minimal threshold stimulus. That is not a base phase. That is a missed opportunity.
The deeper problem is that the calendar assumes your physiology will be at a predictable point at a predictable time. It assumes that by week nine, your aerobic system will be "ready" for the next block. But your body does not follow a schedule. Some adaptations take weeks. Others take years. The rate depends on your metabolic profile, your training history, your recovery, and a dozen other variables that no template can account for.
What Testing Reveals That a Calendar Cannot
The Norwegian triathlon programme does not follow traditional periodisation. Arild Tveiten, head coach of the programme, has said explicitly that he does not believe in the base-build-peak model. Instead, the programme tests athletes every six to eight weeks and adjusts training based on what the data reveals, not what the calendar dictates.
If testing shows that an athlete's aerobic capacity needs development, training shifts toward longer sub-threshold sessions regardless of the time of year. If the gap between the first and second threshold is too narrow, the focus moves to broadening it. The prescription follows the physiology.
Olav Bu has made the point simply: if you ran the same programme year-round, you would stagnate. Variation is essential. But the variation should respond to what your body is telling you, not to what a spreadsheet decided twelve weeks ago. The Norwegian programme runs aerobic and threshold training year-round. They were doing threshold sessions two weeks before the Olympics. What shifts is the emphasis, driven by what testing reveals as the current limiter.
This is not a luxury reserved for professional athletes with lab access and sports scientists. The principle applies at every level. The testing tools change, but the logic does not.
How Testing Replaces the Calendar
The power-duration curve is the decision-making tool that makes this approach practical for age-group athletes. Multi-duration testing every six to eight weeks builds the athlete's curve across efforts from short surges to sustained threshold work. The shape of the curve, and the ratios between different durations, reveals what the athlete needs next.
A curve that is steep at shorter durations and falls away sharply over longer efforts points to underdeveloped aerobic infrastructure. That athlete needs more time in Zones 1 and 2, with structured Zone 3 work to grow the area between their first and second threshold. A flat curve that sits low across all durations suggests a strong aerobic base but insufficient ceiling. That athlete needs more Zone 4 and Zone 5 work to raise the top end.
The critical distinction: the next training block is not decided by a template. It is decided by what the athlete's physiology is doing right now. Test-driven training produces better outcomes because it removes the guesswork that calendar-based periodisation relies on.
Why This Matters More When Time Is Limited
Professional athletes have the volume and frequency to push through suboptimal programming. Even a poorly timed training phase will produce some adaptation when you train 30 hours per week. For an age-group athlete training eight hours per week, every session carries more weight. Spending six weeks on a training focus your body does not currently need is a significant opportunity cost when you only have six sessions in a week to begin with.
The calendar model also assumes a clean, uninterrupted run at each phase. Age-group life rarely cooperates. A week lost to illness, a business trip that disrupts key sessions, or a stretch of poor sleep shifts where you are physiologically. Your body runs a single stress budget, and a rigid plan cannot adjust when non-training stress changes the equation. Testing does.
This is also why aerobic development and threshold training should not live in separate boxes. They develop on different timescales, and both respond to consistent, year-round stimulus. Restricting threshold work to a "build" block, or restricting easy volume to a "base" phase, creates artificial scarcity of the stimulus your body needs to keep progressing.
The Shift
Test regularly. Let the results guide what you train next. Maintain both aerobic development and threshold training year-round, adjusting the balance based on what the data shows. Stop following a calendar that was designed for someone with a different physiology, different history, and different life.
Your body does not care what week your plan says it is. It only knows what you gave it, what it adapted to, and what it still needs. Train accordingly.
The best training plan is the one that changes when your body does.