Does Cardio
Kill Gains?Zone 2 Cardio, Lifting and the Interference Effect

You've finally built a lifting routine, and now your feed is full of zone 2 cardio (searches for it are up about 22% over the past year). Half the videos say it's the key to longevity and fat loss. The other half say any cardio will "eat your gains" and undo the muscle you're working so hard for. So you're left wondering whether that Saturday run or spin class is quietly sabotaging your progress.

It's a reasonable worry. For decades, coaches talked about an "interference effect": the idea that endurance training blunts strength and muscle gains. Some early research did point that way. But the research has grown a lot since then, and the newer picture is much more reassuring for anyone who lifts for strength, health and how they feel.

We went through the main evidence: a 2012 meta-analysis that shaped the "cardio kills gains" idea, a larger 2022 update, a 2026 umbrella review of all the meta-analyses on combining cardio and lifting, and a 2025 expert consensus on what zone 2 actually is. Below we cover what zone 2 means, what the interference effect really affects, whether running or cycling matters, how to order your sessions, how much cardio makes sense, and sample weeks that combine both.

What is zone 2 cardio?

This section explains the term, because "zone 2" gets used loosely online.

Zone 2 is a steady, moderate cardio intensity: hard enough that you're clearly working, easy enough that you could keep going for a long time. A 2025 expert consensus in the International Journal of Sports Physiology and Performance, based on a panel of 14 sport scientists and coaches, described it as training just below the first lactate or ventilatory threshold: roughly the point where your breathing starts to pick up noticeably.

Those thresholds are measured in a lab, which isn't practical for most people. The simplest everyday guide is the talk test from the US Centers for Disease Control and Prevention (CDC):

Heart-rate formulas and wearable "zones" are other ways to estimate it, but they vary between people and devices. If you can hold a conversation in full sentences but would struggle to sing, you're in the right range.

One more point from the expert consensus: the adaptations people credit to zone 2, like a stronger heart and better endurance, aren't unique to zone 2. Slightly easier or slightly harder cardio produces many of the same benefits. Zone 2 is a useful, sustainable intensity, not a magic one.

Does cardio kill gains? What the research says

This is the main question. Here's how the evidence has evolved.

The 2012 meta-analysis that started the worry

A 2012 meta-analysis in the Journal of Strength and Conditioning Research by Wilson and colleagues pooled 21 studies comparing strength training alone with strength plus endurance training. Concurrent training still built muscle and strength, but somewhat less than strength training alone, and power was clearly reduced. The interference grew with more frequent and longer cardio sessions, and in that analysis it showed up with running but not cycling.

This paper is a big reason "cardio kills gains" became gym wisdom.

The 2022 update: muscle and strength are fine

A larger 2022 meta-analysis in Sports Medicine by Schumann and colleagues included 43 studies of healthy adults training for at least four weeks. Compared with strength training alone, adding aerobic training:

• Did not reduce muscle growth. The difference was essentially zero.
• Did not significantly reduce maximal strength, such as how much you can lift for one rep.
• Did reduce explosive strength (jumping and fast, powerful movements) by a small amount.

The explosive-strength drop was larger when cardio and lifting were done in the same session, and not significant when they were at least three hours apart. Cycling versus running, training more or fewer than five times a week, being untrained or active, and being younger or older than 40 didn't change the results.

The 2026 umbrella review: same conclusion

A 2026 umbrella review in Sports Medicine by Held and colleagues pulled together all the existing meta-analyses on combining endurance and resistance training. Compared with lifting alone, strength was largely similar, muscle growth was essentially unaffected, and power was similar too. Concurrent training also improved aerobic fitness, which lifting alone didn't. Most participants were recreationally active adults training for about 10 weeks, so the findings fit typical gym-goers better than elite athletes.

Why the old warnings still circulate

If the newer evidence is reassuring, why do people still say cardio ruins progress? A few reasons are worth knowing, because they point to the real limits.

• Very high cardio volumes are a different story. The 2012 analysis found interference grew with the frequency and duration of endurance training, and the 2026 review noted that high endurance volumes may impair resistance adaptations. Training for a marathon and trying to build maximum muscle at the same time is genuinely harder than adding 2 or 3 moderate sessions.
• Elite athletes are underrepresented. Most studies used recreational exercisers over a few months. Highly trained strength or power athletes may see more trade-offs.
• Fatigue is real even when muscle gains aren't affected. A hard run right before squats will make your squats feel worse that day, even if it doesn't change your long-term muscle growth.
• Food matters. Lots of extra cardio without eating more can leave you underfueled, which makes building muscle harder regardless of what the training studies show.

Running vs cycling: does the type of cardio matter?

This section covers a question the research hasn't fully settled.

The 2012 meta-analysis found that running, but not cycling, was linked to smaller gains in muscle and strength. One common explanation is that running involves more impact and muscle damage in the legs. But the 2022 meta-analysis found no significant difference between cycling and running, and the 2026 umbrella review noted that some individual studies actually suggested cycling reduced lower-body gains more than running.

So the honest answer is that the evidence is mixed, and modality probably matters much less than how much cardio you do and how you schedule it.

Practical takeaways

• Pick the cardio you enjoy and will keep doing. Walking, cycling, rowing, swimming, the elliptical and easy jogging all count.
• If your legs feel beaten up for lifting, try lower-impact options like cycling, swimming, the elliptical or incline walking, at least on the days before leg sessions.
• Mix it up if you like. There's no evidence you need to stick to one type.

Cardio before or after weights?

If you do both in one session, order is the next question.

The 2026 umbrella review found a trend toward greater strength and muscle gains when lifting came before endurance training, though the authors described it as a trend rather than a confirmed effect, and the advantage in individual studies was small. Order didn't affect aerobic fitness.

On spacing: the 2022 meta-analysis found the drop in explosive strength mainly appeared when both were done in the same session, not when they were at least three hours apart. The 2026 review mentions a suggestion of at least three hours between sessions, especially after hard cardio, but notes that the ideal gap is still largely unknown.

Putting it into practice

Remember that these are sensible defaults based on small effects. Doing cardio first because that's when the bike is free won't erase your progress.

How much cardio should you do if you lift?

This section covers how much is enough for health without crowding out your strength training.

The US Physical Activity Guidelines recommend at least 150 minutes a week of moderate aerobic activity (or 75 minutes of vigorous activity, or a mix), plus muscle-strengthening activity on at least 2 days a week. That's the baseline for health, and it pairs well with a typical lifting routine.

Walking counts. If you already walk a lot during the day, some of your weekly cardio is already done.

Why cardio is worth doing even if muscle is your goal

It's easy to frame cardio only as a threat to gains. It's also one of the most useful things you can do for your health and your training.

• It improves aerobic fitness. The 2026 umbrella review found concurrent training improved aerobic capacity as much as endurance training alone, and more than lifting alone.
• It supports overall health. Regular moderate aerobic activity is a core part of the US Physical Activity Guidelines for good reason.
• It can make lifting sessions easier to recover from between sets. Many lifters find better fitness helps them handle longer sessions, though this is a common coaching observation rather than a directly tested finding.
• It's flexible. A walk, a bike ride or a swim can fit into days when a full lifting session doesn't.

Put it together: your week

Here's how to combine lifting and zone 2 cardio with food, sleep and energy in mind.

Option A: 2 lifting days + 3 cardio sessions

Option B: 3 lifting days + 2 cardio sessions

Making it work day to day

• Eat enough. Adding cardio raises your energy needs. Keep protein steady (about 1.2 to 1.6 g per kg of body weight a day for most women who lift) and don't let more cardio turn into under-eating.
• Use cardio as a flexible day. Slept badly or feel run down? A gentle zone 2 session or walk is often a better fit than heavy lifting.
• Protect your leg days. Avoid a long or hard run the day before heavy squats or deadlifts if your legs feel it.
• Check progress after 6 to 8 weeks. If your lifts are still going up and your energy is good, your mix is working.

Frequently asked questions

Does cardio kill gains?

For most people, no. A 2022 meta-analysis of 43 studies found that adding aerobic training to strength training didn't reduce muscle growth or maximal strength. Explosive power was slightly reduced, mainly when cardio and lifting were done in the same session.

Is zone 2 cardio good for building muscle?

Zone 2 doesn't build much muscle on its own, but it doesn't appear to interfere with the muscle you build from lifting. It improves aerobic fitness and supports overall health, which makes it a good partner for strength training.

Should I do cardio before or after weights?

If strength or muscle is your priority, lifting first is a sensible default. A 2026 umbrella review found a small trend toward better strength and muscle gains with lifting first. If you can, separating the two by a few hours is even better, especially for power.

Is running or cycling better for lifters?

The research is mixed. An older meta-analysis linked running, but not cycling, to smaller gains, while a larger 2022 analysis found no difference. Choose the type you enjoy, and switch to lower-impact options if running leaves your legs too tired to lift.

How do I know if I'm in zone 2?

Use the talk test. You should be able to speak in full sentences but not sing. If you can only get out a few words before needing a breath, you're working harder than zone 2.

How much cardio can I do without losing muscle?

Around 150 minutes of moderate cardio a week, alongside at least two lifting sessions, is unlikely to affect muscle gains. Very high cardio volumes, like training for an endurance event, make interference more likely, especially if you don't eat enough.

Conclusion

So, does cardio kill gains? For most people who lift, it doesn't. Recent research shows that adding cardio doesn't reduce muscle growth or maximal strength, and the small cost to explosive power mostly shows up when both are squeezed into one session. Zone 2 is a sustainable, talk-but-not-sing pace that fits easily into a lifting week.

Lift first or space sessions apart when you can, choose cardio you enjoy, aim for about 150 minutes a week, and eat enough to support both. You don't have to choose between being strong and being fit.

This article is for general education and isn't medical advice.

If you want help putting this into your own week, Wellio is an AI coach that sees the whole picture: it builds your plan around your workouts, meals, sleep and energy, and guides you day by day as life changes. Log your lifting sessions, bring in your workouts and steps from Apple Health, and get a week that fits strength and cardio together. Join the Wellio waitlist.

Sources

1. Schumann M, Feuerbacher JF, Sünkeler M, et al. Compatibility of concurrent aerobic and strength training for skeletal muscle size and function: an updated systematic review and meta-analysis. Sports Medicine, 2022.lida.sport-iat.de
2. Wilson JM, Marin PJ, Rhea MR, et al. Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. Journal of Strength and Conditioning Research, 2012.search.pedro.org.au
3. Held S, Wolf L, Rappelt L, et al. Maximizing Adaptations in Concurrent Training: An Umbrella Review of Meta-analyses. Sports Medicine, 2026.fisiologiadelejercicio.com
4. What Is "Zone 2 Training"?: Experts' Viewpoint on Definition, Training Methods, and Expected Adaptations. International Journal of Sports Physiology and Performance, 2025.zaguan.unizar.es
5. Centers for Disease Control and Prevention. How to Measure Physical Activity Intensity.cdc.gov
6. Centers for Disease Control and Prevention. Physical Activity Guidelines for Adults.cdc.gov
7. Rising Trends. Top Fitness Trends (September 2026).risingtrends.co