Sprint training for adults, how to start running fast without getting hurt
Sprinting is the most rewarding thing a runner can add and the easiest to overdo. How many fast efforts a week is safe, why the last rep is the dangerous one, what a stress fracture feels like before it hurts, and a first month that works.
Updated 2 September 2026 · by the makers of SpeedRun
Why this guide comes first
The person who built SpeedRun broke a bone doing what the app measures. Not in a race, in an ordinary session, weeks after the hard block that actually caused it. That is how bone injuries work, and it is why the app opens its coaching library with the risks rather than the technique. Speed is the best thing you can add to your running. It also has a dose, and almost nobody is told what it is.
Sprinting is a different sport from jogging
When you jog, the load is spread over minutes and the bones that carry it are the ones you have been loading for years. When you sprint, you are up on the front of the foot, your hamstrings are producing force while being stretched at speed, and the forces per step are several times higher. Your heart and lungs adapt to that in weeks. Tendons and bones take months. The gap between the two is where most sprint injuries live, and the fitter you are aerobically, the more tempting it is to run into that gap.
The dose: how many fast efforts a week
Easy running is measured in minutes. Sprinting is not. The number that matters is how many efforts you ran close to your maximum, and the research on this is unusually clean.
In practice that is two, at most three, genuine speed sessions a week, each with three to six all-out efforts, each ending while you are still fast. Forty-eight hours between them, seventy-two after a big one. The watch counts your sprints for you and shows how many you have done this week, so the number is never a guess.
The last rep is where it happens
Hamstring strains cluster when athletes are tired and push past the signal to ease off. The tired foot rolls differently and loads the second metatarsal harder. Every injury pattern in the sprint literature points the same way: the dangerous rep is the one you add because the numbers were nice.
A good rule: stop the session when your form goes, not when your legs give out. If a rep is slower than the one before it, you are done for the day. The watch shows you each rep's speed the moment it ends, which makes the rule easy to keep.
The injury that gives no warning
Muscle tells you the same day. Bone does not tell you at all until late.
If you have a spot that hurts under one fingertip and it is moving up that ladder, that is a stop and get seen, not a manage it. None of this is a diagnosis, and no app can see inside a bone. What you can do is notice a spot, notice which rung it is on, and act early, because one rung is roughly a month of running.
A first month that works
This is the shape of a start, not a prescription. Move one thing at a time, and skip a step rather than force it.
Week one. Two easy runs and one session of strides: after a ten-minute jog, run four to six efforts of about 60 m, building to fast but not all out, walking back between them. No sprints yet.
Week two. Same, but the strides become three sprints. Tap SPRINT, take the countdown, run through 100 m, walk back, wait until you feel completely recovered. Note the speed. Stop after three.
Week three. Two sprint days, three to four reps each, at least two days apart. Keep the easy runs. This is the week to add a 10-20-30 session on the other hard day if you want an interval workout.
Week four. Hold the volume. Do not add reps. Look at the records screen and compare week four with week two. If the number went up with the same dose, the training is working, and that is the signal to trust.
Then keep the pattern. Two or three hard days, easy days between, sprints ending while they are still crisp. The people who stay fast for years are not the ones who sprinted most. They are the ones who never had to stop.
Warm up more than you think
A cold hamstring strains at speeds a warm one shrugs off. Ten minutes of easy jogging, then a few strides, then the first sprint. The watch knows you are still warming up and will not count a fast warm-up stride as a sprint unless you ask it to.
Strength, and the base underneath
The research keeps coming back to two protective factors: a base of easy running under the speed work, and strength in the calf, foot and hamstring. The easy runs are not filler. They are the reason the fast work is safe.
If you have had a stress fracture before
The single best predictor of a stress fracture is having had one, and coming back badly is how people collect the second. Come back the way the clinical literature describes: distance before speed, one change at a time, no symptoms during, after or the next day. Speed is the last thing to come back, not the first thing to test yourself with.
