Debunking The Concurrent Training Myth: Why Cardio and Weights Belong Together

Can you build muscle and improve endurance at the same time? For years, fitness experts warned against the interference effect – a phenomenon where combining cardio and weights was thought to blunt strength, power, and muscle gains compared to lifting alone.

However, modern sports science paints a completely different picture. Today’s hybrid athletes are proving that smart concurrent training – a structured regimen featuring both strength and aerobic training – won’t ruin your gains.

In fact, when programmed correctly, combining lifting with cardio can optimise your health, performance, and body composition.

READ MORE | Cardio, weights, or both?

Going to extremes

The latest research confirms that the interference effect only happens at the extreme elite level. Unless you’re an Olympic marathoner or a pro bodybuilder, your body is perfectly capable of building muscle while you increase your fitness.

The reality for recreational athletes, especially those who compete in HYROX, is that lifting improves running economy, and improved cardiovascular fitness can help you lift more.

As far back as 2016, sports scientists were drawing attention to the oversimplification of a complex phenomenon.

In a study published in The Journal of Physiology¹, the researchers explained that telling athletes they must lift and run on completely different days to avoid cancelling the training effect is an old-school gym myth.

READ MORE | The cardio conundrum: Which approach is best for conditioning?

Plotting the paths

The myth stems from two cellular signalling pathways that are seemingly opposed to each other.

• mTORis the signal to build muscle triggered by heavy lifting.
• AMPKis the burn signal triggered by endurance exercise.

Older research² suggested that AMPK directly inhibits mTOR, essentially cancelling out your workout. While performing cardio and strength training in the same session may have a small negative effect on muscle fibre growth (hypertrophy) compared with strength training alone, an updated meta-analysis³ shows that this inhibition is transient and localised. 

The data shows that, while doing cardio and lifting together might slightly limit the growth of individual muscle fibres, your overall muscle size usually looks the same as if you only lifted weights.

Interestingly, running seems to interfere with leg gains a bit more than cycling does, likely because the ‘pounding’ of running is harder for your muscles to recover from than the smooth motion of pedalling.

In reality, the interference people feel is usually just poorly managed fatigue (under-recovery), not a biological cancellation of the respective pathways.

How cardio helps you lift

On the flip side, aerobic fitness can make you a better lifter.

1. Increased work capacity:A stronger aerobic engine (your heart and lungs) allows you to recover faster between sets. 
2. Better nutrient delivery:Cardiovascular training increases capillary density. This means more ways for amino acids, glucose and oxygen to get to your muscles, which speeds up recovery and growth.
3. More efficient waste removal:Better circulation means your body is more efficient at clearing out the metabolic byproducts (like hydrogen ions) that cause the burn and late-session fatigue.

Hybrid programming

All you need to become a hybrid phenom that can squat 150kg and knock out a sub-20-minute 5k is some logical exercise programming.

• The 6-hour rule:If possible, separate your running and lifting sessions by at least 6 hours. This allows the acute signalling from one session to settle before you trigger the other.
• Prioritise training modes:Perform your most important session of the day first. If you’re focusing on strength, lift in the morning. If you’re prepping for a race, run first.
• Manage volume:The interference most people experience is simply doing too much too soon. If you add 20km of running a week, you might need to drop two sets from your leg day to stay in the recovery lane.
• Fuel your efforts:Most people lose muscle when they start running simply because they don’t eat enough to cover their higher daily calorie expenditure. If you run for 45 minutes, eat an extra 400–500 calories that day.

Building durable athletes

While concurrent training can impact your muscles negatively, the interference effect has largely been sensationalised.

By training both systems, you aren’t subtracting from your gains; you’re becoming a more resilient, efficient athlete. 

Follow the right approach, and you’ll become a more durable and versatile athlete – the hallmarks of the ultimate hybrid warrior.

References:

1. Coffey VG, Hawley JA. Concurrent exercise training: do opposites distract? J Physiol. 2017 May 1;595(9):2883-2896. doi: 10.1113/JP272270. Epub 2016 Oct 9. PMID: 27506998; PMCID: PMC5407958.
2. Garza-Lombó C, Schroder A, Reyes-Reyes EM, Franco R. mTOR/AMPK signaling in the brain: Cell metabolism, proteostasis and survival. Curr Opin Toxicol. 2018 Apr;8:102-110. doi: 10.1016/j.cotox.2018.05.002. Epub 2018 May 17. PMID: 30417160; PMCID: PMC6223325.
3. Lundberg TR, Feuerbacher JF, Sünkeler M, Schumann M. The Effects of Concurrent Aerobic and Strength Training on Muscle Fiber Hypertrophy: A Systematic Review and Meta-Analysis. Sports Med. 2022 Oct;52(10):2391-2403. doi: 10.1007/s40279-022-01688-x. Epub 2022 Apr 27. PMID: 35476184; PMCID: PMC9474354.