Concurrent Training
The interference effect is real, and it is a dose. The meta-analysis found running cost strength and size while cycling did not.
Last updated: 30 September 2026
Overview
Concurrent training is doing strength and endurance work in the same programme. The worry attached to it is the interference effect: the idea that endurance training blunts the strength and size you would otherwise gain.
It is real. It is also a dose-response relationship rather than a switch, and the details decide whether it applies to you at all.
Quick Answer
The interference effect is real but depends on the type, frequency and duration of endurance training. A meta-analysis of 21 studies found that running, but not cycling, caused significant decrements in strength and muscle growth, and that higher endurance frequency and longer sessions correlated with worse strength, size and power outcomes.
Key Points
- Interference depends on modality, frequency and duration.
- Running interfered. Cycling did not.
- Power is hit hardest, then size, then strength.
- Moderate cardio alongside lifting costs little or nothing.
- Separate the sessions where you can, and lift first when you cannot.
What the meta-analysis found
Twenty-one studies, 422 effect sizes, comparing strength training alone against strength plus endurance:
| Outcome | Strength only | Concurrent | Endurance only |
|---|---|---|---|
| Hypertrophy | 1.23 | 0.85 | 0.27 |
| Strength | 1.76 | 1.44 | 0.78 |
| Power | 0.91 | 0.55 | 0.11 |
Concurrent training is worse than lifting alone for all three, and far better than endurance alone. Power shows the largest relative gap, which is why sprinters and jumpers take this seriously and general lifters need not.
The moderator analysis is the useful part:
- -Modality. Resistance training concurrently with running produced significant decrements in both hypertrophy and strength. With cycling, it did not.
- -Frequency. Negatively correlated with hypertrophy, strength and power, between −0.26 and −0.35.
- -Duration. More strongly negative still, between −0.29 and −0.75.
So the things that cause interference are: running specifically, doing it often, and doing it for a long time. Not cardio as a category.
Why running is worse
Two plausible reasons, and it is probably both.
Mechanical. Running is a high-impact, eccentric-loaded activity for the same muscles you squat with. Cycling is concentric and low impact. The interference may be muscle damage and residual fatigue rather than anything molecular.
Overlap. Running loads the quadriceps, hamstrings and calves hard. A rower or a cyclist shares less with a squat than a hill runner does.
How to programme both
| Priority | Approach |
|---|---|
| Strength and size first | 2 to 3 short cardio sessions, cycling or incline walking |
| Genuinely both | Separate sessions by 6+ hours, or alternate days |
| Endurance first | Lift 2x a week, heavy and low volume, to maintain |
| Same session, forced | Lift first, cardio second |
Lifting first when you have no choice follows from [exercise order](/wiki/articles/exercise-order): whatever comes first gets your best effort, and a heavy squat is far more sensitive to pre-fatigue than a steady bike ride is.
The practical version
If you are a general lifter who also wants to be fit, the interference effect is mostly not your problem.
| Cardio dose | Realistic cost to lifting |
|---|---|
| 2 to 3 x 20 to 30 min, bike or walk | Essentially none |
| 3 to 4 x 45 min running | Noticeable on leg days |
| Marathon training | Substantial. Accept it |
| Daily long runs plus lifting | Something will give |
Cardio also buys you work capacity, better recovery between sets and a healthier heart, none of which show up in a hypertrophy effect size. [Cardio and muscle growth](/wiki/articles/cardio-and-muscle-growth) covers that trade in full.
If you want to do both properly
A [hybrid programme](/wiki/articles/hybrid-strength-endurance-routine) is a real thing and it works, with two honest conditions attached: you will progress more slowly at each than a specialist would, and you have to accept that rather than fight it.
The programming rules that make it survivable:
1. Hard days hard, easy days easy. No medium-intensity everything.
2. Put the hard runs and the heavy lower body days apart.
3. Eat enough. Underfuelling both is how this fails — see [not eating enough](/wiki/articles/not-eating-enough).
4. Cycle or row when you want volume without the interference cost.
5. [Deload](/wiki/articles/deload-weeks) both at once, not separately.
Common Mistakes
| Mistake | Why it causes problems | Better approach |
|---|---|---|
| Avoiding cardio entirely | Loses health and work capacity for a small gain | 2 to 3 sessions a week |
| Long runs the day before heavy legs | Compounding fatigue on the same muscles | Separate them |
| Cardio before lifting | The lift gets the tired version of you | Lift first |
| Running when cycling would do | Running is the modality that interfered | Bike or incline walk |
| Eating for one sport while doing two | Underfuelling stalls both | Raise intake |
Frequently Asked Questions
Does cardio kill gains?
Not at sensible doses. Interference depends on modality, frequency and duration; a meta-analysis found running interfered with strength and size while cycling did not.
How much cardio can I do while building muscle?
Two to three sessions of 20 to 30 minutes costs essentially nothing, particularly on a bike or as brisk incline walking.
Should I do cardio before or after lifting?
After, if they are in the same session. Better still, separate them by several hours or put them on different days.
Can I train for a marathon and build muscle?
Not well at the same time. Marathon training carries a real strength and size cost, and the honest plan is to maintain muscle while the running block runs.
Sources
Wilson et al. (2012), concurrent training: a meta-analysis examining interference of aerobic and resistance exercises - https://pubmed.ncbi.nlm.nih.gov/22002517/
National Strength and Conditioning Association - https://www.nsca.com/
American College of Sports Medicine - https://acsm.org/