🏋️ Training · 4 min read

Combining endurance and strength: what there is to the interference effect

What was observed

The term describes the assumption that strength and endurance training reduce each other’s effect when pursued in parallel. The original observation dates from the 1980s: a group combining strength and endurance training developed less strength over several months than a group doing strength training alone. For endurance performance this disadvantage did not appear.

The relationship has been studied many times since. The synthesis shows: a disadvantage is most likely measurable in explosive strength — movements requiring rapid force development. For muscle gain and maximal strength it is smaller or not detectable in many studies.

The direction matters: the described disadvantage concerns strength training. Conversely, endurance performance suffers hardly at all from additional strength work — for running economy an improvement is even described.

Possible explanations

Two explanations are discussed, and they are not mutually exclusive.

The first is molecular: endurance and strength training trigger different signalling pathways in the muscle cell that partly inhibit each other. These mechanisms are described in cell experiments; how strongly they act in humans under everyday conditions is less clear.

The second is more mundane and probably more significant: fatigue. Doing a lot of endurance work means entering the strength session with fewer reserves, moving less weight and thereby setting a smaller stimulus. Energy expenditure comes on top — at high total volume with unchanged eating, a deficit easily arises that makes building harder.

For practice the second explanation is the more useful, because it can be steered.

What determines the magnitude

Several factors influence how strongly a disadvantage shows.

• Endurance volume. The more, the more likely it is measurable. At moderate volume the effect is small to undetectable in many studies.
• Type of endurance work. Running appears to interfere more than cycling — probably because of higher mechanical loading and braking components.
• Gap between sessions. Several hours apart or on different days reduces the overlap.
• Order within a session. Whatever comes first is done with more reserves.
• Energy intake. With sufficient intake the effect is smaller.

How to plan?

A simple order of decisions follows from these factors. First: which goal takes priority? Pursuing both equally will progress more slowly in both than having a clear emphasis — that is not a planning weakness but a consequence of limited recovery.

Then: if both happen in one session, the priority goal comes first. If they can be separated, several hours apart or a different day is more favourable.

And finally: energy intake has to match total volume. A common error is expanding endurance work without adjusting eating — the combination then becomes a deficit, and that explains part of the stagnation attributed to the interference effect.

The gap in time

If both belong in the same week, the question of arrangement arises. Studies on this usually compare three options: both in one session, both on the same day with a gap, or on different days.

The results point in an expected direction: the larger the gap, the smaller the mutual influence. Precise thresholds cannot be derived; the studies use different gaps and loadings.

In practice the gap is often a question of the calendar rather than of physiology. Anyone with time on only three days a week will have to combine them — and then the order within the session is the remaining lever.

For most people this is not an issue

One framing point belongs at the end, because for most readers it is the most important. Studies on the interference effect predominantly use high volumes — training plans as found in competitive sport, not in training after work. Doing strength training twice a week and two easy endurance sessions sits in a range where the effect is small to unmeasurable in most studies.

In practice: the worry about spoiling muscle gain with some endurance work is unfounded at usual recreational volumes. The same applies in reverse for strength training alongside running.

The question becomes relevant at high volumes in both areas simultaneously — and then it is above all a question of recovery and energy intake, not of molecular signalling pathways.

Last reviewed: 14.08.2026

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