The guide

Is it safe to push hard?

By GyroscopeUpdated November 14, 202611 sources

For most healthy people, yes. See a doctor before hard sessions if exercise brings chest pain, fainting or unusual breathlessness, or if you have known heart, metabolic or kidney disease. If you’ve been mostly sitting, build up with brisk walking first.

If you get chest discomfort during exercise, stop. The same goes for pain in your arms, back, neck, jaw or stomach, shortness of breath, a cold sweat, nausea, a racing or irregular heartbeat, or feeling lightheaded. The American Heart Association says to call 911 for any heart attack warning signs, even if you’re not sure, because it’s almost always the fastest way to get treatment.

Is hard exercise dangerous?

Two stories get told about it. In one, hard exercise is risky, especially after 40, and you hear about someone who collapsed on a run. In the other, anyone can do anything, and a doctor’s visit is a waste of time. Neither is right for everyone.

In 2014 the American College of Sports Medicine brought experts together to look again at who needs a check before exercise. Their 2015 update starts from three findings. Exercise is safe for most people. The heart problems linked to exercise are often preceded by warning signs or symptoms. And the risk gets smaller as people become more active and fit. The panel also found the old rules sent too many people to the doctor, which may have kept some from exercising at all.

Risk factors alone, like your age or your cholesterol, no longer mean you need a doctor’s visit before you start. What decides it is how active you are now, whether you have symptoms or known disease, and how hard you plan to go.

Who should see a doctor first?

See your doctor before hard sessions if any of these is true:

• Exercise brings chest pain or pressure, fainting, or breathlessness that’s out of proportion to what you’re doing.
• You have known heart disease, or a heart condition you’ve been told about.
• You have diabetes or another metabolic disease, or kidney disease.
• You take a beta blocker or another medicine that controls your heart rate.
• You’re pregnant, for anything beyond what you already do.

If you’re active already and none of these applies, you can usually add hard sessions without a visit. If you’ve been mostly sitting and none applies, start with walking and build up. Ask a doctor any time something feels wrong.

A simple way to picture it

Think of a car that’s sat in the garage all winter. You wouldn’t take it straight onto the highway at full speed. You’d drive it around the block, check that nothing’s knocking, and then open it up.

Your body after months of sitting is that car. A few weeks of brisk walking is the drive around the block. And if something knocks, you get it looked at before you push it.

How do you build up from inactive?

1. Weeks 1 to 4: walk. Brisk walks most days, building to 30 minutes, 5 days a week. That’s the 150 minutes the US guideline asks for. In 24 trials, brisk walking alone raised VO2 max in people who had been inactive.
2. Week 5 on: add one harder session. An uphill walk or bike session with four 4-minute efforts at about 16 out of 20 on the effort scale, with 3 easy minutes between.
3. Later: a second hard session, if the first feels fine for a few weeks.

Starting the hard session at week 5 is our own choice, not a rule from a trial. If your joints hurt when you run, the Cooper Institute suggests a walking test instead of a run, and the same goes for the sessions, so use a bike, a rowing machine or a steep walk. The full plan is in how to raise it.

What if you take a beta blocker?

Beta blockers slow your heart, and changing the heart’s output changes VO2 max with it (Bassett and Howley, 2000). That’s why the heart rate zones and the 4x4 band on this site don’t apply to you. Your heart won’t reach those numbers, and chasing them would mean pushing far too hard.

Use the effort scale instead. It runs from 6 (no effort at all) to 20 (the hardest you can imagine). The Generation 100 trial in people aged 70 to 77 used about 16 for the hard minutes and about 13 for the steady sessions. Ask your doctor before you start hard sessions, and never change a dose to train harder.

Your watch’s VO2 max can be off too. Apple says conditions or medicines that limit your heart rate might cause an overestimate. Can I use heart rate zones on a beta blocker? has more.

What about pregnancy?

The US guideline asks for at least 150 minutes a week of moderate activity during pregnancy and after, and says women who already do vigorous exercise, such as running, can continue. It also says to talk to your doctor about whether or how to adjust.

On this site that means no max tests and no new hard plan during pregnancy. Keep doing what your doctor or midwife is happy with.

What about altitude?

Thin air lowers VO2 max. In trained endurance athletes it fell 6.3 percent for every 1,000 meters (3,300 feet) up, starting from as low as 800 meters (about 2,600 feet). The same effort costs more up a mountain, so slow down, and don’t test yourself there and compare it with a test at home.

Is a VO2 max test itself safe?

A lab test pushes you to your limit on purpose, with staff watching. For most healthy people it’s fine. The same screening applies, so symptoms or known disease mean a doctor first. More in is a VO2 max test safe?.

Why get fitter at all?

Being unfit is a risk too. In 122,007 people tested at the Cleveland Clinic, below average fitness for their age, against above average, carried the same extra risk of death as smoking. The safest long-term choice for most people is to get fitter, one step at a time. Why it predicts how long you live has the evidence.

A watch can’t rule out a heart problem. If something feels wrong during exercise, stop, whatever your watch says.