Pursuit sprint start: the first 15 seconds that define the 4 minutes

Start01 Jun 20267 min readDr. Borja Alfaraz

Anyone who has timed an IP knows that the first 250 metres are 5% of the race but decide 40% of the time. A clean start lets you cruise with W' intact. A chaotic start subtracts 6,000 J in 15 seconds and dooms kilometre 3. Boillet (2024) measured exactly what world-class does in those 15 seconds.

The profile to copy

The Boillet study analysed the instantaneous power profile at start on 34 male pursuiters of world class. The mean curve has three identifiable landmarks:

Pmax: absolute peak power, between 1,400 and 1,900 W, depending on the rider's neuromuscular power.
t_peak: time from pedal-start to Pmax, between 5 and 7 seconds.
Decay phase: from Pmax to cruise power (400-480 W), another 8-10 seconds.

The full profile is an asymmetric bell: fast up, slower down. Modelling it correctly is essential to simulate the pursuit. A model that assumes constant power from second zero overestimates spent W' by 15%.

Boillet's equation for the start

P(t) = P_cruise + (P_max − P_cruise) · exp(−((t − t_peak) / τ)²)

With τ = 4-5 s. This Gaussian model fits real curves with R² > 0.94 in 90% of subjects. It's the basis of AthletePro's start simulation: power is not assumed to instantly stabilise, it is modelled as an explicit bell curve.

Fig. 1 Gaussian power profile of the first 30 s of an IP start (Boillet 2024 model). The peak arrives at 6 s and decays over 15 s to cruise power.

How much W' the start costs

Integrating (P(t) − CP) over the first 15 s for a pursuiter with CP = 400 W, Pmax = 1,600 W, t_peak = 6 s:

0-6 s (rise): 5,400 J above CP
6-15 s (fall): 2,800 J above CP
Total: 8,200 J, roughly 36% of total available W'

That expense is not optional. It's the physical cost of accelerating 78 kg (bike + rider) from 0 to 16 m/s. Ignoring it in pacing means reserving W' for cruise that is no longer there.

The "start soft to save W'" mistake

A rider deciding to start with "only" 1,200 W peak and 8 s to Pmax spends less W' on start (about 5,500 J in 15 s), but pays another price: it takes 3-4 seconds more to reach cruise speed. In a race decided by tenths, those 3-4 seconds are an immediate net loss. And the W' saved doesn't compensate: you don't get to use it well because cruise now demands a power the rider hadn't planned for.

Rule: start with the Pmax you can execute cleanly. Not more (spends W' without gaining speed) and not less (arrive late at cruise).

The technique of the first two pedal strokes

An elite pursuiter starting from the starting gate delivers the first two pedal strokes at 55-70 rpm cadences, against a gearing that at cruise speed demands 110 rpm. That low-cadence max-torque start is pure alactic anaerobic and uses phosphocreatine, not W'. It's an independent resource from the metabolic pool.

That is why riders who include short sprint work in their training plan (10 reps of 8 s max on track) improve their start without touching aerobic power. They are training the phosphagen system, not W'.

Differences by discipline

Event	Typical Pmax	t_peak	Start W' cost
Men's 4 km IP	1,600 W	6 s	8,000 J
Women's 3 km IP	1,200 W	5 s	6,200 J
Men's kilo	2,100 W	7 s	14,000 J
Women's 500 m	1,500 W	6 s	10,500 J
Team pursuit initial leader	1,550 W	7 s	8,800 J

Simulate your start with Boillet 2024

AthletePro models the start bell with tunable Pmax and t_peak. See exactly how much W' the sprint costs you and how much is left for cruise.

Start free trial

References: Boillet A. et al. (2024), Sci. Rep.. Corbett J. (2009), IJSPP. Craig N. P. & Norton K. I. (2001), Sports Med.. Broker J. P. et al. (1999), Med Sci Sports Exerc..