Learn the road bike sprint: why standing gives about 13 % more peak power, how to choose gear, timing and line, and when a sprint is too risky.
The honest answer: in a sprint you reach higher peak power standing than seated. A study with eleven recreational riders measured how much: in a 14-second sprint they averaged 1175 watts standing and 1042 watts seated [2]. That is a good eighth more, a difference of about 130 watts. So a sprint is not a question of willpower but of position, gear and timing.
A second measurement backs this up. Twelve college cyclists did 30-second Wingate tests, once seated and once standing. Peak power in the first second was 19.4 watts per kilogram standing and 17.9 seated, the 30-second average 11.0 versus 10.4 [1]. The authors concluded that cyclists should rather be tested standing because they stand up in competition anyway [1].
The sprint is not won in the legs but in the first stroke: gear, position, timing.
Important upfront: studies measure on an ergometer or under controlled conditions, not in traffic. And a sprint is a high-risk situation. Realistically it takes a few weeks until your acceleration is clean before you raise speed and pull (experience value).
Ride in easily and do two or three short build-ups. For the acceleration choose a medium-heavy gear, not the hardest. If the gear is too easy you spin out, if it is too hard you cannot get up to speed (practice).
Milestone: you know your acceleration gear without the chain skipping.
Ride off briskly, about the pace where you usually pedal hard seated. A sprint from standstill with a gear that is too heavy costs time. Stay seated until you choose the moment.
Stand up on the downstroke, take the bars firmly and pull them towards you while pushing the pedal down. Your upper body goes low and far forward. This is the technique in which standing gives the higher power according to measurements [1][2].
Milestone (practice): 5 accelerations of 6 seconds each where the bike does not weave.
Pedal, pull, eyes forward on the line. If you notice cadence collapsing, shift one gear harder, not earlier. With a "forward standing" position the riders in the study reached peak power comparable to classic standing [2]. Whether it works better for you, you test yourself.
Do not brake abruptly after the sprint: keep pedalling lightly, then let it roll out. Only sit down once speed has dropped.
Milestone (practice): you reach the line in a straight track and then come to a controlled roll.
In cycling most injuries happen in competition, not in training. A season-long study of 47 professionals found an injury rate of 4.14 per 1000 hours in racing and 1.23 per 1000 hours in training; the risk ratio was around 10 [3]. In other words, per hour racing is about ten times more dangerous than training. The sprint at the end is the key moment where many riders are packed closely.
A video analysis of 128 head impacts in professional cycling found that 88 percent occurred in road races and predominantly in collisions involving several riders [4]. That suggests your biggest risk in a sprint is the other riders. Train sprints alone or in an agreed group on a free road, hold your line and avoid contact. This guide explains and motivates, it does not replace supervised training.
Train the acceleration in short, hard efforts instead of long sprints: six to ten seconds all-out, then five minutes easy rolling, four to six repetitions (experience value). That protects muscles and tendons and trains exactly what you need in a race: a hard first pull, not endurance in the sprint.
Standing gives the higher peak power: in a study eleven recreational riders averaged 1175 watts standing and 1042 watts seated [2], and in Wingate tests peak power was also higher standing [1]. You only sprint seated if after a long effort you want to add a short push.
A medium-heavy gear in which every stroke has resistance but the crank still gets up to speed. There is no fixed measured value; it is practice standard. Try different gears on a free road.
Studies measure sprints of 14 seconds [2] or 30 seconds [1]. In competition a finish sprint usually lasts only a few seconds. How long you can hold the peak depends on training and can only be tested individually.
Legally, the normal traffic rules apply. In practice a sprint does not belong in traffic, because the risk per hour in racing is about ten times higher than in training [3]. Practise on a free road.
Descending on a Road Bike: Ride Downhill with Margin Instead of Risk