Interval Training: How to Use a Stopwatch to Improve

Always running at the same pace, on the same route, eventually stops making you better. To gain speed and endurance, coaches recommend adding interval training: short, intense efforts separated by recovery periods. For these sessions to work, one tool is essential: the stopwatch. Here's how to structure your sessions and measure your progress, with our online stopwatch and its split times.

What is interval training?

Interval training means alternating high-intensity efforts with recovery phases, either active (jogging) or passive (walking or standing still). Instead of running 30 minutes at a moderate pace, you might run 10 × 1 minute fast, with 1 minute of recovery between each repetition.

This alternation lets you spend more time at high intensity than you could in a continuous effort, where you would tire quickly. It improves cardiovascular fitness, speed and resistance to fatigue. You'll find it in running, cycling, swimming, rowing and many HIIT-style workouts.

A few classic sessions

The 30/30

30 seconds of fast running, 30 seconds of jogging recovery, repeated 8 to 15 times. It's the ideal session to start interval training: the efforts are short, and the recovery lets you keep up the quality.

Track repeats

For example 6 to 10 × 400 meters, with 1 min 30 s of recovery. You time each lap to check that you're holding your target pace, without going out too fast on the first repeats.

The pyramid

Efforts of increasing then decreasing length: 1, 2, 3, 2, 1 minute, with recovery equal to half the effort time. It teaches you to manage different paces in the same session.

Long intervals

For runners preparing a 10K or a half marathon: 3 to 5 × 5 minutes at a sustained pace, with 2 minutes of recovery. The goal is to get used to holding a fast pace for a long time.

In every case, start with at least 15 to 20 minutes of easy jogging to warm up, and finish with a cool-down. One or two interval sessions a week are enough; the rest of your training should stay at an easy pace.

Why the stopwatch is essential

Measuring effort precisely

Without a stopwatch, you tend to cut efforts short when fatigue sets in, and to stretch out recoveries. The stopwatch keeps the session honest: 30 seconds is 30 seconds, even on the tenth repetition.

Checking consistency

The most common mistake in interval training is starting too fast. The first repetition is quick, the last one falls apart. Split times show that gap immediately. A good session is a series of consistent times, or even slightly faster ones at the end. A gap of more than a few seconds between your best and worst repetition usually means your starting pace was too ambitious.

Tracking your progress

By recording your times week after week on the same session, you measure your progress concretely: 400 meters run in 1:52 instead of 1:58 a month earlier, or the same pace held with less recovery. It's also a great source of motivation.

Beyond running

• Core work: time your planks and try to add a few seconds each week, without sacrificing good form.
• Swimming: a full-screen stopwatch, placed by the pool, lets you time each length.
• Circuit training: measure the total time of a circuit and the time spent at each station.
• Coaching a group: a coach or PE teacher can record each student's time with the split times.
• Outside of sport: time a speech, a science experiment or a mental math exercise.

Using our stopwatch for your sessions

Our online stopwatch shows time to the hundredth of a second, on a sweep-hand dial inspired by sports stopwatches and on a digital readout.

1. Click "Start" at the beginning of your session.
2. At the end of each lap or repetition, click "Split time". The table shows the split since the previous time and the total time.
3. Spot your fastest lap, shown in green, and your slowest, in red, at a glance.
4. Click "Stop" to pause timing, then "Start" again to resume without resetting.

The full screen mode displays the stopwatch in large format on a tablet or a gym screen, readable from several meters away.

Tip: for an interval session, click "Split time" at the end of each effort and at the end of each recovery. You'll get a complete breakdown of the session. Remember to write down your times or take a screenshot before closing the page: they aren't saved.

If you'd rather have an alarm at the end of a set duration, for example for a recovery or a plank, use our hourglass timer instead, which rings at the end of the countdown.

A few precautions

Interval training is demanding on the heart, muscles and tendons. Increase intensity and volume gradually, plan recovery days between hard sessions and listen to signs of fatigue or pain. If you're returning to exercise after a long break or have health concerns, ask your doctor before getting started.

In short

Interval training is one of the most effective ways to improve, as long as you're consistent and precise. The stopwatch is its natural ally: it frames the effort, reveals pacing gaps and makes progress visible. Pick a simple session like the 30/30, time each repetition, and compare your times in a few weeks. The numbers will speak for themselves.