The all-important final meters: the sprint


Almost always a cycling race ends in a sprint. If it’s not a bunch sprint, it’s a leading group that sprints for the flowers or a classic sprint à deux that decides who gets the kisses. Even the most gruesome mountain stages end in a sprint(s) more than once. So if you, as a cyclist, want to keep insisting that you can’t sprint, your chances seem to be almost gone and you’d better start playing checkers. Of course it’s a bit crazy that races of more than 200 km are only decided in the last 200 meters, but it’s however the truth. Which components actually determine whether you can ride a good sprint and can you improve on that? In this article we will try to answer these questions.

The importance of peak power

With the rise of the power meters, we now get a very nice glimpse into the produced sprinting capacities of the pro peloton. Often the maximum produced peak power is pointed out. Power equals the delivered energy in a certain time frame and is expressed in Watts. The shorter this time frame is chosen, the larger the power output, or the so-called peak power. Because a sprint can last up to 20 seconds, the delivered peak power of 1 second does not say a lot. However, the peak power can say something about the acceleration and this is very important in sprinting. To go deeper into this, we first have to look at which resistance have to be overcome in sprinting.

Which resistances work on a cyclist?

The sum of all forces acting on a sprinter equals the mass of the sprinter (plus the bike) times the acceleration. This is nothing but Newton’s second law and you can always steal the show with it on drinks and parties. It follows that it takes more power to give something heavy the same acceleration as something light. The forces that play a role in a sprint are in the first place the force that the sprinter delivers on the pedals and then the opposing forces namely the air resistance, the rolling resistance, and when the road goes up gravity. When the force delivered by the sprinter is greater than the counteracting forces, the sprinter continues to accelerate. When the sprinter delivers exactly the same amount of force as the other forces working against him or her, he or she keeps cycling at a constant speed.

What is the most important resistance?

Gravity is a constant counteracting force depending on the weight of the cyclist. As far as rolling resistance is concerned, a lighter cyclist also has an advantage and it matters what kind of tyres you have fitted and, of course, the tyre pressure. But by far the most important counteracting force is the air resistance, at least on the flat and that is where most sprints are decided.

What is the effect of frontal surface and drag?

In the first place, the harder you go, the more air resistance you try to slow down. Two factors are particularly important here, and that is the size of the frontal surface and the so-called drag coefficient. With a small frontal surface you need to move less air when you want to go through it and the drag is smaller. The drag coefficient is a measure of the extent to which the displaced air ‘sticks’ to the cyclist. Closely related to this is the turbulence or ‘wake’ that occurs behind the cyclist and ideally is as small as possible.

What are good power numbers in a cycling sprint?

To give an insight in how these resistances and wattages relate to each other, we take the data of an ‘unknown’ sprinter who wins the bunch sprint in a grand tour. This data is from a study that does not want to reveal the name of the sprinter. The peak power of this sprinter was only 1097 Watts. On the other hand, he manages an average of 926 Watt for 14 seconds, after a ride of more than five and a half hours during which the last three minutes he had to deliver an average of 490 Watt to keep up with the pace and in the last 64 seconds he even delivered more than 600 Watt. That’s quite impressive.
In 14 seconds the sprinter manages to accelerate from 58.5 km/h to 65 km/h. The power output of 926 Watt can be divided into 6% to overcome rolling resistance (54 Watt), 74% (688 Watt) to defy air resistance and 20% (184 Watt) to accelerate. This shows how important it is to sprint as aerodynamically as possible.

What is better; sitting or standing sprinting?

For example, research has shown that standing sprinting can increase the power on the pedals by 8 % to 12 %. However, this increases the frontal surface area and thus the air resistance. At really high speeds the increase in the available power can therefore sometimes be less than the increase in air resistance, so it’s better to sit down again quickly. Track sprinters that regularly reach 80 km/h, often sit down again quickly after the first acceleration. The extra power released during standing sprints comes from the upper body, which is transferred over the hip joint. This indicates that for sprinting the upper body should be well trained. This is in line with the observation that track sprinters are generally muscled guys. However, in road cycling you often first have to overcome 200 km over hilly terrain, where you don’t want to carry this extra muscle mass. That’s why professional cyclists are actually all well-trained endurance athletes, of whom some just do a little better in a time trial, or sprinting or uphill.

Which muscle fiber types do you need in a sprint?

Besides aerodynamics, success in a sprint is largely determined by muscle volume and muscle fiber type. Research has shown that thigh size can explain 70 % of the variation in peak power of different cyclists. It is therefore worthwhile to keep a close eye on your competitor’s thighs. In addition, the distribution in muscle fibre type is important. Roughly speaking, two muscle fiber types can be distinguished: the slow-twitch type I fiber and the fast-twitch type II fiber. The main distinction between both types of fibres is that type I fibres have a lower optimal contraction rate and produce less power than type II fibres. On the other hand, type I fibres can sustain an effort much longer. Type I fibres are namely well-blooded and rich in glycogen and aerobic enzymes. These fibres produce relatively little strength, but can keep that up for a long time by aerobic combustion. Type II fibres work on mainly anaerobic energy, that is to say without the presence of oxygen. With the formation of lactate, these muscles will not last as long, but they can contract up to 5 times more vigorously (per muscle mass unit). It should be noted that through training, part of the type II fiber can be tuned into muscle fibers with mainly type I properties. However, there is also a part that cannot be ‘tuned’ by training, and the extent to which you have these powerful fibres is innate. In sprinting, therefore, there is big piece of genetics involved.

What is the ideal cadence and crank length in a sprint?

The extent to which you have both types of muscle fibres and the distribution of type of muscle fibres determines the optimum pedal speed to produce as much power as possible. The pedal speed is determined by the crank length and the pedalling frequency. Someone with mainly type II fibers has a preference for a higher contraction speed and thus a higher pedal speed than someone with a lot of type I fibers. Research with track sprinters shows that on average most power is produced at 120 to 140 revolutions per minute. For more endurance-trained athletes this number will be somewhat lower, but it is important to note that the chosen resistance must in any case last until at least 110 to 120 rpm. If you choose a too heavy gearing, the powerful type II fibres will not be able to use their full power. Research has shown that the crank length to be chosen makes little difference in the maximum peak power produced. There are no significant differences in peak power between the commercially available crank lengths (from 165mm to 180mm).

What is the effect of good positioning in a sprint?

But the most important factor in sprinting on the road turns out to be positioning. As explained earlier, by far the biggest resistance to overcome is air resistance. By positioning behind a teammate or competitor this resistance can be reduced by up to 25%. The point is of course that when you start from someone’s wheel you have to overcome two more meters. If you come from the tenth position you have to deal with terrible slow sprinters if you want to have some chance of winning. From a mathematical model it can be calculated that if you take two sprinters that can both produce exactly the same amount of power as the professional cyclist in the example. The sprinter that starts from the wheel will overtake the sprinter in front within 8 seconds and eventually win with 1.05 meters difference over a sprint distance of 236 meters. The sprinter who starts the sprint in third place will have to settle for third place with the same amount of power.
In summary, sprinting is quite a complex affair. An important factor that determines the success in sprinting is the aerodynamic resistance that has to be overcome. In addition, issues such as standing or sitting sprinting, pedalling frequency, muscle mass, muscle fibre type and especially positioning play an important role. Finally, a very important tip: never put your hands in the air too early.
For working on your sprint you can take a look at our JOIN Cycling application. It contains a database with more than 500 interval trainings for cyclists. You can find a sample of those workouts here. Before you can set your zones, doing an exercise test is essential. More information can be found here