The Cardio You Keep Skipping: How Much You Actually Need Alongside Your Lifts

You walk past the rowing machines on the way to the squat rack every single session. You tell yourself you'll do ten minutes on the bike at the end. You never do.

If that's you, you're in good company — most people who lift weights seriously develop a quiet allergy to the cardio kit. The avoidance isn't pure laziness, though: it usually comes from a genuine worry that aerobic work will eat into the gains you've worked hard to build. That worry is understandable, but for most lifters the trade-off is far more favourable than gym-floor folklore suggests.

Why Lifters Quietly Sidestep Cardio

The "cardio kills gains" idea has had a long run. It's the kind of thing that gets said confidently between sets and never really questioned. There's a real phenomenon behind it — the interference effect, where endurance training can blunt strength or muscle growth — but what the gym-floor version leaves out is that the effect is heavily shaped by how much you do, what kind, and when.

The quiet cost of skipping it entirely? Your cardiovascular base slowly erodes. Recovery between heavy sets slows down. A few flights of stairs leave you breathing harder than they should. None of that shows up on a maxes board, but it chips away at training quality in ways that compound over months.

Does Cardio Kill Your Gains?

Let's deal with this head-on. Research looking at what happens when you add aerobic training alongside resistance work has found that the effect on muscle hypertrophy is real — but modest, and manageable with sensible programming, Concurrent training & hypertrophy meta-analysis, 2022. An umbrella review drawing together the broader concurrent training literature confirms that adaptation in both strength and endurance is achievable: the variables that matter most are intensity, volume, and scheduling, Concurrent training umbrella review, 2025.

Translation: a couple of cardio sessions a week won't hollow out your squats. Sprinting to exhaustion before a heavy leg session will.

Zone 2 vs HIIT: Which One Works Best Alongside Lifting

Two to three cardio sessions a week, each around 20 to 30 minutes, is a sensible starting target for most lifters. The question is which type.

Zone 2 (steady, conversational effort) — a brisk walk, a gentle cycle, or a controlled row where you could still hold a conversation — sits at an intensity that's unlikely to meaningfully interfere with strength adaptations. It builds your aerobic base, improves recovery between sets, and takes a lighter toll on your system overall. For most lifters, Zone 2 is the easiest cardio to slot in without feeling the cost elsewhere in your training.

HIIT earns its place too, but it demands more respect. Research comparing concurrent training modalities has flagged that high-intensity aerobic work carries a greater interference risk alongside strength training than lower-intensity alternatives, Concurrent training modalities, 2016. HIIT also creates more residual fatigue, which bleeds into your next heavy session if the timing is off. That's not a reason to bin it — it's a reason to earn it. One well-scheduled HIIT session a week is a reasonable addition once a base is built.

One practical point: rowing, cycling, and walking distribute effort differently from running. If your programme is quad-heavy — squats, lunges, leg press — rowing or cycling creates less cumulative lower-body fatigue than a running session does. Varying modalities is a simple way to protect your lifts.

Timing It Right

Most interference problems aren't caused by the combination of cardio and lifting — they're caused by the sequencing.

HIIT immediately before heavy legs is the pairing that reliably bites back. Your nervous system arrives taxed and your muscles pre-fatigued, which undermines performance in the lifts that matter most. Research into the molecular basis of the interference effect has highlighted that high-intensity concurrent work creates a specific conflict with strength adaptation pathways, Interference effect mechanisms, 2014. This isn't abstract — you'll feel it in your squat numbers.

What tends to work better:

• Cardio after lifting: your strength work gets your full, rested focus. Zone 2 tacked on at the end of a session is fine; HIIT after a demanding lift is probably too much total stress in one slot.
• Cardio on separate days: the cleanest option when your schedule allows. Zone 2 on rest days sits neatly between lifting sessions without interfering with either.
• Low-intensity cardio before upper-body sessions: minimal interference risk, and it doubles as an effective warm-up.

How to Use This in the Gym

Adding cardio doesn't mean overhauling your entire week. Here's how to bolt it on without the drama:

• Start with one session: a single 20-minute Zone 2 session — rowing, cycling, or a brisk walk — on a day you're not lifting. Run that for a fortnight before adding a second.
• Choose a non-competing modality: if you squat and deadlift two to three times a week, default to rowing or cycling rather than running to reduce lower-body overlap.
• Schedule HIIT away from legs: if HIIT is in your week, place it after an upper-body session, or on a day with a comfortable gap from your heavy lower-body work.
• Track your lifts: the real test is whether your training performance holds. If your key lifts are still moving well after two weeks, the cardio is working. If they drop, scale back before removing cardio entirely.
• Count what you're already doing: a 20-minute commute cycle or an active job contributes to your weekly aerobic work. You may need less formal cardio than you think.

What a Realistic Week Looks Like

Minimal schedule (3 training days) Mon: Lift — Wed: Lift — Fri: Lift + 20 min Zone 2 after

Moderate schedule (4 training days) Mon: Lift — Tue: 25 min Zone 2 — Thu: Lift — Fri: Lift — Sat: Lift + optional Zone 2

Squeezed (weekday evenings only) Mon: Lift — Wed: Lift + 20 min Zone 2 after upper body — Thu: 20 min Zone 2 standalone — Sat: Lift

None of these require extra hours you don't have. They just redirect a fraction of the time you're already spending.

You Don't Have to Choose

The most capable gym-goer isn't the one who can only lift or only run — it's the one whose engine can sustain quality training over years. Your cardiovascular base is part of that engine.

Two or three short sessions a week, scheduled sensibly around your lifts, keeps that engine turning without meaningful cost to your strength work. Zone 2 first, HIIT later — and never immediately before heavy legs.

Want sessions that take the scheduling headache away entirely? Browse SmartGyms classes that blend strength and cardio in one slot — no planning required.

When to Get Professional Advice

If you notice unusual breathlessness, chest tightness, or fatigue during cardio that is new for you, speak to your GP before adding more aerobic work. If you are managing a joint issue, returning from injury, or haven't done any sustained cardio in a long time, start with short low-impact sessions and consider checking in with a physiotherapist or qualified fitness professional first.

This article is general information, not medical advice. If you have a health condition or are new to exercise, check in with a qualified professional before making big changes.

If you're training around pain or a current injury, get it assessed by a physiotherapist or GP before pushing on.