Cardio for lifters

The WHO guideline for adults is 150 to 300 minutes of moderate aerobic activity a week, or 75 to 150 minutes of vigorous activity, or a mix, plus regular muscle-strengthening work ^[1]. The ACSM's guidance is similar: at least 150 minutes of moderate or 75 minutes of vigorous cardio, alongside resistance training on two to three days ^[2].

Lifting covers the strength half. A practical minimum for the aerobic half is two or three sessions of 20 to 40 minutes. Some is much better than none, and brisk walking counts.

Zone 2 is the popular name for steady, easy cardio: an effort of about 3 to 4 out of 10 where you can hold a conversation in full sentences. Heart-rate formulas are rough; the talk test is a good enough guide.

What it's good for: it builds an aerobic base, adds to your weekly activity total, and is easy to recover from, which matters when your legs also have to squat.

What the evidence doesn't support: the claim that zone 2 is uniquely effective. A 2025 review concluded that current evidence does not show zone 2 to be the optimal intensity for improving mitochondrial or fat-burning capacity in the general population, and that higher intensities matter for cardiometabolic benefits, particularly when total training time is low ^[3].

The fair reading: easy cardio is useful because you can do a lot of it without wrecking your lifting, not because it's special. If you have 60 minutes a week for cardio, include some harder work. If you have several hours, most of it can be easy.

Intervals alternate hard efforts with easy recovery. Both steady training and intervals produce large improvements in VO2max, with intervals a little ahead: about 1.2 mL/kg/min more in a meta-analysis of controlled trials, with longer work intervals doing somewhat better ^[4].

Two formats that work:

• Short: 6 to 8 rounds of 30 seconds hard (8 to 9 out of 10), 30 to 60 seconds easy.
• Long: 4 rounds of 3 to 4 minutes hard (7 to 8 out of 10, breathing heavily but sustainable), 2 to 3 minutes easy.

One or two interval sessions a week is plenty alongside lifting. Hard intervals are demanding; if you have a heart condition, high blood pressure or other health concerns, talk to your GP first, and build up from easy work over a few weeks.

The interference effect is the idea that endurance training blunts strength and muscle gains. Here's the state of the evidence.

Muscle size: no meaningful interference. A 2022 meta-analysis covering 43 studies found concurrent training did not compromise hypertrophy (effect size −0.01) or maximal strength (−0.06) compared with lifting alone ^[5].

Explosive strength: some interference. The same analysis found a small reduction in gains in explosive strength (−0.28), mainly when cardio and lifting were done in the same session; when sessions were separated by at least three hours the effect was no longer significant ^[5].

Trained lifters: more sensitive. In a meta-analysis split by training status, concurrent training reduced lower-body strength gains in trained people (−0.35) but not in untrained or moderately trained people. Again, the effect showed up only when both were done in the same session (−0.66 same session versus −0.10 separate sessions) ^[6].

HIIT: small lower-body effect. Adding HIIT to lifting didn't affect hypertrophy or upper-body strength, but lower-body strength gains were slightly smaller (−0.25) ^[7].

Mode and dose: mixed. An older meta-analysis found running, but not cycling, reduced strength and size gains, and that interference grew with the frequency and duration of endurance work ^[8]. The newer analysis did not find a difference between running and cycling ^[5]. Treat the mode question as unsettled and the dose question as plausible: marathon training and maximal leg strength compete; three moderate sessions and a lifting program mostly don't.

• Separate when you can. Put cardio on non-lifting days, or at least three hours from lifting ^[5]. This matters most for trained lifters chasing lower-body strength ^[6].
• If same session, lift first. Strength improves most in what you do while fresh ^[9]. A short finisher after lifting is fine.
• Keep hard leg cardio away from heavy leg days. Hard intervals the day before squats will cost you reps. Pair intervals with upper-body days, or after a leg session with a rest day following.
• Choose low-impact modes if your legs are beaten up. Cycling, rowing and incline walking produce less muscle soreness than running for most people who aren't used to running. That's coaching practice, and consistent with the older running-versus-cycling finding ^[8].
• Eat for the extra work. More activity means more energy needed. Under-eating is a more common cause of stalled lifting than cardio itself.
• Add gradually. Start with one or two sessions and build over a month.

Lifting three days (full body):

• Mon, Wed, Fri: lift
• Tue: 30–40 min easy
• Sat: intervals, or a longer easy session

Lifting four days (upper/lower):

• Mon upper, Tue lower, Thu upper, Fri lower
• Mon or Thu: ten-minute finisher after lifting
• Wed or Sat: 30–45 min easy

If strength is the absolute priority for a block, drop to two easy sessions and hold intervals at one short session. If conditioning is the priority, do the reverse and keep lifting at a maintenance dose; even a single hard set of 6 to 12 reps per lift, two or three times a week, has been shown to keep building strength in trained lifters, though less than higher volumes ^[10].