Every cyclist who has ever blown up a time trial knows the feeling: the first 10 minutes felt great, the middle was manageable, and then the wheels fell off. The post-ride data shows exactly what happened — power output was 15–20% too high in the opening third. The question is why experienced riders keep making this mistake, and what the science of pacing strategy actually prescribes.
Time trial pacing research consistently shows that the parabolic deceleration profile — high effort early, progressive slowdown — is the most common pattern among recreational and sub-elite athletes, and consistently the slowest strategy available. The fastest times come from even splits or, in some conditions, a negative split — slightly slower in the first half, faster in the second.
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Abbiss and Laursen's 2008 comprehensive review of pacing strategies in Sports Medicine examined the physiological mechanics behind each pattern. The key insight: aerobic metabolism, which provides 85–95% of energy for time trials lasting more than 4–5 minutes, requires a ramp-up period — typically 60–120 seconds — to reach its maximal contribution. Starting at full power demands immediate anaerobic compensation via the phosphocreatine and glycolytic systems. This anaerobic "overcost" in the opening minute creates a biochemical debt that the aerobic system must then service throughout the remainder of the effort, raising effective RPE and heart rate for any given power output compared to a steady-state equivalent.
The critical power (CP) model formalises this mechanically. Above CP — the highest power sustainable without progressive fatigue — the athlete is drawing down their finite anaerobic W-prime (W') capacity. Every second spent above CP depletes W'. Once W' is fully depleted, power drops precipitously. Starting above CP for even 60–90 seconds in a 20-minute TT can reduce the power sustainable for the remainder of the effort by 3–5 watts — a difference that accumulates to 15–30 seconds of finish time.
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The negative split strategy exploits the interaction between aerobic ramp-up and pacing reserve. By starting at 97–99% of target average power, the athlete allows oxygen delivery and cardiovascular output to reach steady state without anaerobic overspend. Heart rate rises steadily to its target zone. As the effort progresses, the athlete — now aerobically primed — can increase power in the final third by 3–5% while maintaining the same RPE, because the cardiovascular system is now operating at full efficiency.
In practice, a negative split on a flat 20-minute TT might look like: minutes 1–7 at 97% of target average power, minutes 8–14 at 100%, minutes 15–20 at 103–105%. The final surge is not a sprint from depleted reserves — it is the strategic release of a neuromuscular reserve that was protected by disciplined early pacing. Noakes' central governor model supports this: the brain maintains a protective reserve throughout an effort; disciplined pacing allows that reserve to be accessed at the end rather than wasted at the beginning.
Environmental conditions modify the optimal pacing profile. On an uphill finish, a slight positive split (faster on the climb) can be faster overall due to aerodynamic considerations — at lower speeds, the relative cost of air resistance drops and power-to-speed conversion improves. On a headwind-out, tailwind-back course, a slight positive split (harder into the headwind) is mathematically faster for a given average power. These are second-order adjustments to the fundamental principle, not exceptions to it.
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Knowledge of your FTP is the practical foundation of TT pacing. Without an accurate FTP estimate, target power cannot be set, and pacing discipline collapses to feel — which is reliably too aggressive in the first third for most athletes. FTP also determines where your CP sits, and therefore how much W-prime buffer you have against early-effort anaerobic overspend.
The free calculator at winsport.uk/tools/cycling/ftp-calculator estimates your FTP from recent test data, enabling precise power target setting for any TT duration. With a calibrated FTP, you can set a power ceiling for the first seven minutes of your next TT — and discover whether the disciplined negative split approach produces a faster finish time than your usual approach.
What's your current pacing tendency in time trials — do you go out too hard, or have you learned to trust a conservative opening?