11 % of your anaerobic reserve burns in the opening lap: train the fast start, manage your W′ budget and pace the race smartly — backed by race data.
"How do I train for the fast start of an XC race?" The honest answer starts with an uncomfortable number: in the opening lap, racers burn 11 percent of their anaerobic reserve W′ — in later laps it is only 3–5 percent.
So the start is disproportionately expensive, and it is not an accident but the race format: average heart rate around 180, a mean of 76 percent of critical power, 40 percent of the time above it. Add roughly 334 efforts above maximal aerobic power per race, averaging just over 4 seconds — over 300 short flat-out stabs in ninety minutes.
Race preparation therefore means: train the fast start deliberately, manage your W′ budget — and treat the 27 percent of non-pedalling time as a technique reserve. Welcome to race mode.
An XCO race lasts 96 ± 7 minutes and the field rides it at an average heart rate of 180 — for long stretches beyond 90 percent of maximal heart rate, effectively pinned. The opening lap tops everything: 11 percent W′ expenditure, because start position and the first singletrack entry decide half the race.
Arrive unprepared and you pay twice — first with position, then with recovery. Your first step is analysis: pull the power data from your recent race starts and check how deep your W′ balance really was after lap one.
Simulate it — as a whole, not in fragments. A proven practice-based drill derived from the race data: 30–90 seconds near all-out from a standing start, then without pause straight into 10–15 minutes of race intensity at threshold.
Exactly this transition — from full-gas start to "merely very hard" — is the ability that is missing in races if you never rehearsed it. Twice a week of intensity is enough: research recommends 2–3 intense, intermittent sessions per week in total, and the start simulation is one of them, not an extra.
Think of your anaerobic reserve as a battery: above critical power it discharges, below it slowly recharges. In a race you distribute 40 percent of the time above CP across hundreds of short bouts of about 8 seconds at roughly 120 percent of CP.
The consequence for your pacing: not every gap is worth closing, and not every passing move pays for itself. Before the race, define two or three points on the course where an attack is worth it — and ride the rest with discipline just above or below CP instead of torching the budget in prestige duels.
The race does not test one single spike, it tests hundreds — with lactate values around 6.5 mmol/L as a steady state, the zone where the legs burn continuously. You train repeatability with the proven tools: HIIT intervals of 4–6 minutes cut race time by 5 percent, sprint intervals of 30 seconds by 3 percent.
In race preparation you shift the character towards race-specific: shorter spikes, incomplete recoveries, ideally on a climb with a technical counter-section — the profile of the 5–10-second bouts sends its regards.
27 percent of race time is spent not pedalling — in descents and corners it is not your engine that decides, but your braking behaviour. And that correlates measurably with ride time: brake later, shorter and harder and you are faster through the off-road corner.
For race preparation this means: recon the course, fix brake points and lines for the key sections and ride them in repeatedly. Every second you gain downhill without watts is W′ you do not have to re-inject uphill.
Start simulations and position-fight drills belong on wide, open tracks — not in the first singletrack with oncoming traffic. Ride the key sections of the racecourse first with strength left and full concentration before repeating them under fatigue: loss of control on an empty tank is the classic crash cause.
And respect the total load: race preparation replaces your intense weekly sessions, it does not stack on top. Grind yourself into race week and you will stand at the start line tired.
Occasionally ride your start simulation with training partners as a real position fight: shoulder to shoulder on the straight, bottleneck after 200 metres, first one in wins. The fast start is not just physiology, it is chaos management — line choice, drafting, elbows.
No interval programme in the world teaches that, but it decides whether your 11 percent of W′ was an investment or a write-off.
Simulate it as a whole: 30–90 seconds near-maximal from a standing start, then straight into 10–15 minutes at threshold pace — the transition is the real skill. The race data justifies it: 11 percent W′ expenditure in the opening lap versus 3–5 percent later. Once or twice a week within your 2–3 intense sessions.
By critical-power analysis: 40 percent of race time above CP and 26 percent above maximal aerobic power, spread across bouts of about 8 seconds. In addition, race analysis counts around 334 efforts above MAP per race. Pacing therefore means: manage spikes, not hold an average.
In race preparation the rule still holds: 2–3 intense or intermittent sessions per week — only their character becomes more race-specific: start simulations, short spikes with incomplete recoveries, key-section repeats. More hard days do not make you faster, they make you tired on race weekend.
For racing, the mix counts: an aerobic base as foundation, plus HIIT (proven: −5 % race time) and SIT accents — and in the final weeks race-specific building blocks such as fast-start simulations and course recon. Do not forget technique: 27 percent of race time is spent not pedalling, and that is where you gain time without watts.
MTB: Biomechanics and Movement Analysis