Build Phase
The build phase is the 6–10 week block after base training in which specific, race-like sessions turn aerobic foundation into race performance.
Definition
The “build phase” is the block in which the foundation laid during base training is converted into race-specific performance. It follows base training, typically lasts 6–10 weeks and ends with the taper.
Volume stays at the level of the final base weeks or drops slightly, while the share of intense and race-like sessions rises clearly. Threshold work, intervals above VT2, brick sessions and workouts at planned race pace define this phase.
Why it matters
Aerobic endurance alone does not make you fast. The ability to hold race pace for the full race duration has to be trained specifically, and for that the body needs stimuli close to the target load. The build phase delivers them without throwing away the base.
At the same time, it is the phase with the highest risk of injury and overtraining. Intensity costs more recovery than volume, and anyone who keeps both high at once breaks down. The skill lies in lowering volume just far enough for the intensity to fit.
Structure and signals
| Feature | Typical value |
|---|---|
| Duration | 6–10 weeks |
| Volume | 85–100% of the base maximum, falling slightly |
Intensity Z1/Z2/Z3 | 70/10/20 |
| Key sessions | 2 per week, plus one long session with a race-pace segment |
| Rhythm | 2:1 or 3:1, unloading week at −40% volume |
Signs the phase is working: output at VT2 rises, race-pace segments get longer at the same heart rate, and recovery between two key sessions is sufficient. HRV stays within the range of the base phase.
Signs it has gone on too long: interval performance stagnates or drops over two weeks, morning resting heart rate sits 5+ beats above baseline for days, HRV falls over seven days, or sleep and appetite deteriorate. That calls for an unloading week, not another hard one.
How obseed measures it
obseed assigns every interval and tempo session to the zones derived from your metabolic diagnostics. This matters most in the build phase: a threshold estimated from a field test can sit 5–8% off the measured VT2, and that is exactly the range where an interval either trains you or overreaches you.
obseed also tracks the weekly share of Z3, the ratio ACWR = load last 7 days / avg load last 28 days, and resting heart rate and HRV from your wearable. If ACWR climbs above 1.3 or HRV falls several days in a row, obseed flags it before the next key session is due.
Example
Build week of a triathlete preparing for a half distance, 12 hours, sixth week of the phase:
| Day | Session | Duration | Zone |
|---|---|---|---|
| Mon | Easy swim, technique | 1 h | Z1 |
| Tue | Bike intervals 4 × 8 min at VT2 | 1.5 h | Z3 |
| Wed | Easy run | 1 h | Z1 |
| Thu | Swim 10 × 100 m race pace, strength | 1.5 h | Z2/Z3 |
| Fri | Rest day | – | – |
| Sat | Bike 3.5 h with 2 × 30 min race pace, brick run 30 min | 4 h | Z1/Z2 |
| Sun | Long run 1.5 h with 3 × 10 min race pace, easy swim 1.5 h | 3 h | Z1/Z2 |
Distribution 70/12/18. After two such weeks comes an unloading week of 7 hours. The phase ends with a peak week, after which the taper begins.
References
- Bompa, T. O. & Buzzichelli, C. (2018). Periodization: Theory and Methodology of Training, 6th ed. Human Kinetics.
Categories
- Trainingsphasen