Concurrent Training Interference Effect Explained

You want to squat heavy and run well in the same training year. The worry that stops many lifters is the interference effect: the idea that cardio eats your strength gains. The good news is that the modern research is far kinder than the gym myth. With a few placement rules, you can build muscle and maximal strength while your engine improves.

What the interference effect is

Concurrent training means you train strength and endurance in the same program. The interference effect is the observation that strength, size or power can grow a little less than they would with lifting alone. Robert Hickson first described it in 1980, and it has been studied in dozens of trials since.

The effect is real, but it is narrow. It mostly touches explosive strength and, in experienced lifters, lower-body maximal strength. It depends on how you dose and place the endurance work, which is good news, because dose and placement are things you control.

What the research says now

The early reviews were cautious. A 2012 meta-analysis by Wilson and colleagues in the Journal of Strength and Conditioning Research pooled 21 studies and found that interference scaled with the frequency and duration of endurance work. Running, but not cycling, produced significant decrements in hypertrophy and strength in that dataset.

A larger update changed the headline. Schumann and colleagues (Sports Medicine, 2022) pooled 43 studies and compared concurrent training with identical lifting alone. Their 95% confidence intervals for maximal strength and muscle size both crossed zero, so they found no reliable loss in either.

"Concurrent aerobic and strength training does not compromise muscle hypertrophy and maximal strength development. However, explosive strength gains may be attenuated, especially when aerobic and strength training are performed in the same session."

Schumann M, et al. Compatibility of Concurrent Aerobic and Strength Training for Skeletal Muscle Size and Function. Sports Medicine, 2022.

Training status matters too. A 2021 meta-analysis by Petré and colleagues covered 27 studies of lower-body 1RM. Trained lifters lost some squat and leg press progress, but only when both modes shared one session. Untrained and moderately trained people saw no meaningful difference.

Who should care, and how much

Most readers can relax. If you are new to lifting, or you have trained for a year or two, the data say concurrent training costs you very little. Your strength and size will climb on a sensible plan.

You should plan more carefully in three cases:

• You are an experienced lifter chasing a squat or deadlift PR. Petré's subgroup showed the loss sat almost entirely in same-session training.
• You need power, such as jumps, sprints or Olympic-style lifts. Explosive strength is the quality Schumann found most sensitive.
• Your endurance volume is high, such as marathon blocks or long cycling weeks. Wilson linked longer and more frequent endurance work to bigger losses.

How to minimize interference

Use these rules in order. Each one costs you almost nothing and protects the lifting side of your week.

1. Separate the sessions

Lift and do your hard conditioning on different days, or at least 3 hours apart. Schumann found the explosive strength loss was significant within one session but not when sessions were separated by at least 3 hours.

2. Lift first when you must combine

If one session holds both, put the barbell first. An Eddens, van Someren and Howatson meta-analysis found a 6.91% greater gain in lower-body dynamic strength when resistance work came before endurance work, with no cost to aerobic capacity.

3. Keep heavy work heavy

Hold your main lifts in the strength zone. The ACSM progression models position stand recommends heavy loading of 1-6 RM with 3 to 5 minutes of rest for intermediate and advanced lifters, and load increases of 2-10% once you beat your rep target.

4. Manage the leg-heavy conditioning

Running loads the same muscles as your squat, with more impact and eccentric stress. Keep most easy aerobic work low intensity, and place the hardest intervals away from heavy leg days. If your legs feel flat, swap one run for cycling or rowing.

5. Ramp endurance volume slowly

Add one session or a few extra minutes per week, not a whole new block at once. Interference grows with frequency and duration, so build them gradually and watch your top sets.

A practical lifting template for concurrent training

This template fits 3 lifting days and 3 to 4 endurance sessions. Use RPE to auto-regulate, since conditioning fatigue varies week to week.

Day 1, lower strength (AM or rest day from running)

• Back squat: 4 x 4 at 80-85% of 1RM (RPE 7-8)
• Romanian deadlift: 3 x 6 at RPE 7
• Split squat: 3 x 8 per leg
• Hanging leg raise: 3 x 10

Day 3, upper strength

• Bench press: 4 x 5 at 78-83% of 1RM
• Weighted pull-up: 4 x 5
• Overhead press: 3 x 6 to 8
• Chest-supported row: 3 x 10

Day 5, full body power and strength

• Trap bar deadlift: 3 x 3 at 80-85% of 1RM, moving fast
• Box jump: 4 x 3, full rest
• Incline dumbbell press: 3 x 8 to 10
• Single-leg RDL: 3 x 8 per leg

Put easy runs or rides on days 2, 4 and 6, and your hardest interval session on day 2 or day 6. That keeps at least one easy day between the interval session and your heavy lower day.

How to progress

Add load when every set of a lift lands at RPE 7 or lower. Hold the load when your conditioning block spikes. Every 4 to 6 weeks, take a lighter week: drop one or two sets per lift and keep runs easy.

Build it in the free builder

You can turn this template into your own plan in a few minutes. Open the free program builder and enter your lifting days, your current 1RM for squat, bench and deadlift, and the days you run or ride. Mark your hardest conditioning day, and the builder keeps heavy leg work away from it.

Want a head start? Browse the starter programs and pick a concurrent block that matches your weekly schedule. Then edit the sets, percentages and RPE targets to fit your goal.