How much cardio do you need? Easy cardio and the talk test

Short answer: US guidelines ask adults for 150 to 300 minutes a week of moderate activity, such as brisk walking, or half as much vigorous activity. You can judge your effort by how easily you can talk. If you're starting from little or nothing, begin with what feels comfortable and add a few minutes at a time over weeks.

How much cardio the guidelines recommend

The Physical Activity Guidelines for Americans (2nd edition, 2018) recommend:

150 to 300 minutes a week of moderate activity, or
75 to 150 minutes a week of vigorous activity, or
a mix of the two. As a rule of thumb, one vigorous minute counts about the same as two moderate minutes.

The guidelines also say some activity is better than none, and going past 300 minutes brings more benefit. If you're inactive now, start well below these numbers and build up gradually.

The talk test

You don't need a heart-rate monitor to judge your effort. The talk test uses something you already know: how easily you can speak.

What talking feels like	Effort	Examples
You can talk in full sentences comfortably	Easy	A walk, an easy bike ride, easy rowing
You can talk, but only a few words at a time	Brisk	Steady cycling or rowing, jogging
You can't get out more than a word or two	Hard	Sprints, intervals, Tabata

There's research behind this. In healthy adults, the point where talking first gets difficult lines up closely with the point where your breathing starts to speed up sharply because the effort is getting hard. In one study of 16 people, that held on both a treadmill and a stationary bike, and talking was clearly uncomfortable above that point (Persinger and colleagues, 2004). In another, the talk test moved with that point as people's fitness changed, and the authors judged it good enough to set exercise effort (Foster and colleagues, 2008). These were lab studies of healthy people, so treat the talk test as a good guide, not a measurement.

To try it, say a sentence out loud during your walk or ride. If it comes out smoothly, you're at easy effort. If you have to break it up to breathe, you're at brisk. If you can't get it out, you're working hard.

Why easy cardio matters

Easy cardio builds your heart, lungs and endurance, and you recover from it quickly. So you can do a lot of it without hurting your strength training.

A pooled analysis of combined strength and cardio training found that the cost to strength gains depended on the type and amount of cardio. Running led to clear losses where cycling didn't, and longer and more frequent cardio sessions cost more (Wilson and colleagues, 2012). Walking wasn't tested, but easy walking and easy cycling are sensible choices if you also lift.

How to build up

Find your starting point. How long can you walk, ride or row while still holding a conversation? Ten minutes is a fine start. So is 45.
Do that a few times a week.
Add five minutes after two sessions in a row that you finished comfortably, with no pain.
Take five minutes off if a session was too hard, or you slept badly and feel run down.

The guidelines say to increase gradually over weeks to months, without giving an exact rate. Small, regular steps are the safe choice.

Sample weeks

Starting from little or nothing

Four 15-minute easy walks: 60 minutes
Add five minutes to each walk every week or two
Reach 150 minutes over a couple of months

Already walking regularly

Three 30-minute walks and one 45-minute bike ride: 135 minutes
Add one 20-minute session to pass 150

Short on time

Two 30-minute easy walks: 60 minutes
Two 20-minute brisk bike rides: 40 minutes that count about as much as 80 moderate minutes
Total: about 140 moderate minutes from 100 minutes of exercise

Common mistakes

Making every session hard. If every walk leaves you out of breath, you'll recover slowly and skip more. Most of your cardio should be easy.
Thinking easy doesn't count. A brisk walk you can talk through is exactly the moderate activity the guidelines count.
Adding too much at once. Going from nothing to an hour a day is how sore joints happen. Add five minutes at a time.
Counting your lifting as cardio. A strength session raises your heart rate, but it doesn't replace steady cardio. A circuit with little rest, like an EMOM, can count for some of both.

If you have heart disease or another health condition, or you get chest pain or unusual breathlessness when you exercise, check with your doctor before you start.

Where hard cardio fits

Short, hard workouts like REHIT or Tabata can improve fitness in little time. They work best on top of an easy base, not instead of it. Keep them to one or two a week, after lifting or at least four hours before a heavy leg session.

How Axial Fit does it

You choose your cardio. A main option and others you'd also do, from what your equipment allows: walk, incline walk or hills, cycle, row, elliptical, jog, stair machine, swim, ruck or jump rope.
It starts where you are. It asks how long you can do your main option and still hold a conversation, and your first session starts there. Without an answer, a walk starts at 20 minutes.
Five minutes at a time. On a goal that grows, two full easy sessions in a row at your current length add five minutes, up to a cap for each option. A brisk session asks, "Could you have kept going at that pace?" Yes counts toward a step up, Maybe holds, and two No answers in a row take a step back.
A weekly target that grows. Your target starts at the minutes you said you can give, at least 60. Each week you meet it, it goes up by 30, 45 or 60 minutes, depending on the pace you chose, up to a ceiling of 150 to 300 minutes set by your goal.
Brisk counts double. A brisk minute counts as two, following the guidelines' rule of thumb. Brisk is offered once you've answered the health questions and either said you already do harder cardio or logged two good easy sessions. It suggests at most three brisk sessions a week, not on back-to-back days.
The talk test after circuits. After an EMOM, Tabata or Intervals, one optional question, "How was your breathing?", sets whether its minutes count as easy, brisk or hard. No answer counts as easy.
Honest minutes. Strength sessions don't count toward your cardio minutes.

Sources

US Department of Health and Human Services, 2018. Physical Activity Guidelines for Americans, 2nd edition. odphp.health.gov
Persinger R, Foster C, Gibson M, Fater DC, Porcari JP, 2004. Consistency of the talk test for exercise prescription. Medicine and Science in Sports and Exercise, 36(9), 1632-1636. PubMed 15354048
Foster C, Porcari JP, Anderson J, Paulson M, Smaczny D, Webber H, Doberstein ST, Udermann B, 2008. The talk test as a marker of exercise training intensity. Journal of Cardiopulmonary Rehabilitation and Prevention, 28(1), 24-30. doi:10.1097/01.HCR.0000311504.41775.78
Wilson JM, Marin PJ, Rhea MR, Wilson SM, Loenneke JP, Anderson JC, 2012. Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. Journal of Strength and Conditioning Research, 26(8), 2293-2307. doi:10.1519/JSC.0b013e31823a3e2d