Sprinting vs. running: A few hard minutes may trigger surprisingly big changes in the body

For people who insist they don't have time to exercise, researchers have produced an intriguing answer: You may be able to accomplish quite a lot in just a few very uncomfortable minutes.

A new study from Rockefeller University found that six 30-second, all-out sprints — just three minutes of actual sprinting — produced striking changes in proteins and metabolites circulating in the blood.

The response was much larger than researchers observed after 90 minutes of moderate exercise.

Nearly 25% of the proteins measured changed immediately after sprint exercise, compared with fewer than one-quarter of 1% after 90 minutes of moderate cycling. Moderate treadmill running produced more changes than cycling, but still substantially fewer than sprinting.

Sprinting also changed more than 200 metabolites and triggered increases in proteins involved in blood-vessel growth, tissue remodeling and hormonal signaling.

The peer-reviewed study was published in Cell Reports Medicine.

Three minutes — but not really a three-minute workout

There's an important catch to the attention-grabbing comparison. Participants didn't simply sprint continuously for three minutes and go home.

They performed six 30-second all-out intervals separated by four-minute recovery periods. That makes the session roughly half an hour long, including recovery — although only three minutes involved sprinting.

And "all-out" matters. Sprint interval training is considerably more strenuous than simply running somewhat faster than usual.

Researchers compared the sprint protocol with moderate continuous exercise performed either on a treadmill or bicycle.

The results suggest that exercise intensity itself may be an important signal that causes organs and tissues throughout the body to communicate differently.

Sprinting changed the blood — and the blood changed fat cells

Researchers went a step further.

They exposed human fat cells grown in the laboratory to plasma collected from participants after exercise.

Blood collected after sprinting caused extensive changes in gene activity in the fat cells, including genes involved in processing fuel, responding to hormones and sensing nutrients.

Blood collected immediately after moderate cycling produced much smaller changes.

Moderate exercise wasn't doing nothing, however. Its molecular response appeared to develop more slowly.

About three hours later, researchers detected a wave of fatty acids and proteins released by the liver — the sort of response expected during sustained endurance exercise.

In other words, sprinting and endurance exercise may not simply be stronger and weaker versions of the same thing.

They may cause different biological responses.

Possible connection to diabetes, obesity and heart disease

Researchers then compared the exercise-responsive proteins with health information from more than 53,000 people in the UK Biobank.

Many of the proteins affected by sprinting were associated with lower risks of cardiovascular and metabolic disease.

The difference was particularly striking for metabolic conditions.Researchers identified 33 proteins associated with reduced risk of obesity, type 2 diabetes and related disorders.

Sprinting altered 32 of the 33. Moderate exercise altered only three. More than one-quarter of the proteins were also associated with slower biological aging.

That doesn't prove sprinting caused those health outcomes. But it gives researchers clues about how vigorous exercise might produce some of its benefits.

So is sprinting better than running?

Not necessarily.

The study measured short-term molecular responses, not long-term outcomes such as weight loss, cardiovascular fitness, heart attacks, diabetes or longevity.

A larger molecular response isn't automatically a better one.

Moderate running and other aerobic exercise have decades of evidence behind them and provide benefits that weren't being measured by simply counting proteins immediately after a workout.

Running, brisk walking, swimming and cycling can improve cardiovascular fitness, blood pressure, insulin sensitivity, mood and endurance. They also allow people to exercise considerably longer than they could at maximum intensity.

Sprinting appears to offer something different: an extremely strong physiological stimulus delivered in a very short period of intense effort.

That makes the two forms of exercise potentially complementary rather than competitors.

Sprinting and running aren't the same exercise

A recreational jogger might describe a fast run as a sprint, but physiologically there is a substantial difference.

Moderate running: You can sustain it for many minutes, breathing hard but remaining in control.

High-intensity intervals: Very hard efforts lasting perhaps 30 seconds to several minutes, followed by recovery.

All-out sprinting: Near-maximal effort that can be maintained only briefly.

The Rockefeller experiment was at the extreme end of that spectrum. Participants performed six genuine all-out 30-second efforts.

That's a much different demand on the heart, lungs, muscles and connective tissue than going out for a 30-minute jog.

The injury question

This is also where consumers should be cautious.

Going from a largely sedentary lifestyle directly to repeated all-out sprints is not the exercise equivalent of taking a shortcut.

Sprinting places substantial forces on the hamstrings, calves, Achilles tendons, knees and other tissues. Someone accustomed to walking or jogging may have enough cardiovascular capacity to run fast while lacking the muscle and tendon conditioning needed to do it safely.

Age isn't necessarily a barrier to vigorous exercise, but conditioning, cardiovascular health, medications, previous injuries and other medical conditions can matter.

People who have been inactive or have cardiovascular disease or significant medical problems should talk with a health-care professional before suddenly beginning maximal-intensity exercise.

And beginners don't need to reproduce a laboratory sprint protocol to add intensity.

A brisk uphill walk, short faster-running intervals, harder cycling or brief periods of climbing stairs can increase exercise intensity without requiring someone to run down the street at maximum speed.

What this means

The most useful takeaway isn't "three minutes of sprinting replaces 90 minutes of exercise." It's that exercise intensity may matter more than many people realize.

The body apparently recognizes a few very hard bursts of exercise as a dramatically different physiological event from prolonged moderate activity, setting off rapid communication among muscles, fat tissue, blood vessels and other organs.

That raises the possibility that a practical exercise program doesn't have to choose between long, steady workouts and very short intense ones.

For many people, the better formula may ultimately turn out to be some of both:

Move regularly. Build aerobic endurance. And, if your health and conditioning permit it, occasionally move very fast.

The Rockefeller findings suggest those few hard minutes may be doing considerably more inside the body than anyone watching the clock would suspect.

But be sure to avoid the “three-minute workout” trap. The actual protocol was six 30-second maximal efforts with four-minute recoveries, so we're talking about roughly a half-hour session, not three minutes from sneakers-on to shower. And the cohorts were tiny — fewer than 20 people in each group and predominantly male.

Want to try sprint intervals? Start gradually

The new research makes sprinting sound enticing: a few very hard efforts produced much larger immediate molecular changes than prolonged moderate exercise.

But don't go from the couch to six all-out 30-second sprints.

Sprinting puts much greater forces on muscles and tendons than jogging does, particularly the hamstrings. A gradual progression lets those tissues adapt to high-speed running.

A safer way to begin

• Build a base first. Be comfortable walking briskly, jogging, cycling or doing another aerobic activity regularly before adding very hard intervals.
• Warm up. Spend 10 to 15 minutes walking or jogging easily, followed by dynamic movements such as leg swings and progressively faster short runs. Don't make your first fast effort your first movement of the day.
• Don't start at 100%. For the first few sessions, try short accelerations at perhaps 60% to 70% of what feels like maximum speed rather than an all-out sprint.
• Keep the intervals short. Beginners might start with four to six faster efforts lasting 10 to 20 seconds, with plenty of easy walking or jogging between them.
• Increase speed gradually. Over several weeks, move toward harder efforts only if you're recovering comfortably and aren't experiencing pain.
• Allow recovery. Sprint training doesn't need to be done every day. Muscles and connective tissues need time to recover from unusually intense loading.
• Strengthen your legs. Hamstring and other lower-body strengthening can help prepare muscles for high-speed running. Research has found particularly strong injury-prevention benefits from eccentric hamstring exercises.
• Stop if something hurts. Sudden hamstring, calf, Achilles tendon, knee or chest pain isn't something to "run through."

You don't have to sprint

There's no requirement to run at maximum speed to benefit from interval training.

People who aren't runners can increase intensity with fast uphill walking, cycling, swimming, an elliptical machine or stair climbing. A short interval that leaves you breathing hard can provide vigorous exercise without the impact and peak forces of an all-out running sprint.

Who should be especially cautious?

People who have been sedentary, have known cardiovascular or significant medical conditions, take medications that affect exercise response, or have a history of serious muscle, tendon or joint injuries should consider talking with a health-care professional before beginning maximal-intensity exercise.

And remember what the new study actually found: sprinting produced unusually large short-term molecular responses. It did not prove that sprinting is safer, healthier or a substitute for regular aerobic exercise.

The sensible takeaway is simpler:

Keep moving — and if you're healthy and conditioned enough for it, adding a little speed may provide benefits that steady exercise alone doesn't.