Strength training and running: how to do both after 40

The question arrives in two versions, and they come from different places.

One comes from the gym: is my running eating the muscle I am trying to build? The other comes from the running path: are my gym sessions taking the legs out of my running and making me heavy?

Behind both sits the same thing, a phenomenon called the interference effect. It has been in the literature since 1980, and somewhere along the way it grew into a reputation considerably larger than what the studies actually say. For a body over forty, with limited time and a genuine need for both, the precise version is far more useful than the reputation.

The interference effect: what the research actually shows

The most cited summary is a 2012 meta-analysis covering 21 studies and 422 effect sizes. The question it asked was which components of endurance training undermine the results of strength training.

The answer was that strength training on its own produced larger average improvements than combined training across all three outcomes: muscular strength, muscle size and muscular power. But only for power was the difference between the groups statistically significant. The clear decrements in strength and muscle size turned up only when the analysis was split by the kind of endurance training involved. That is where it gets interesting.

It is the running that interferes, not the lifting

The analysis broke endurance training down by modality. Strength training combined with running produced measurable decrements in both muscle growth and strength. Strength training combined with cycling did not.

That distinction matters, because it moves the explanation. If this were purely about the body receiving two contradictory signals at once, cycling ought to interfere just as much. That the effect shows up with running but not with cycling points towards part of it being plain mechanical load: running involves thousands of footstrikes in which the muscle brakes the body, and that kind of work takes time to recover from.

The analysis also found negative relationships between the frequency and duration of endurance training and all three outcomes. The more often, and the longer the sessions, the clearer the effect. Interference is not an on-off switch. It is a dose.

Why researchers still disagree

Four years later, two researchers published a piece under a title that argued the opposite. Their point was that thirty years had turned it into an article of faith that endurance work blunts muscle growth, while a close reading of the literature shows the evidence is weaker than assumed.

The gap between the two camps largely comes down to what gets measured. Immediately after a combined session you can see certain molecular signals for muscle building being dampened. But in studies that follow people over weeks and months, that impairment does not show up nearly as consistently. Under certain conditions, chiefly when the sessions are separated and total volume is kept in check, the combination appears to cost nothing at all.

In the other direction there is no conflict at all

Almost the entire debate is about what running does to strength. The reverse question has a much clearer answer, and it surprises most runners.

A systematic review of strength training in middle- and long-distance runners concluded that two to three strength sessions a week are likely to benefit running performance. The mechanism is not a higher aerobic capacity. It is running economy, meaning how much oxygen you burn to hold a given pace. Stronger muscles and stiffer tendons return more of the energy stored at each footstrike, which makes the same pace cheaper.

Then there is the injury side, which outweighs everything else past forty. A large systematic review with more than 26,000 participants found that strength training cut sports injuries to less than a third. Running injuries are overwhelmingly overuse injuries: the Achilles, the front of the kneecap, the shin, the hip.

That asymmetry is the whole point of this page. Running can cost you some of your strength development. Strength training costs you nothing in your running, and pays you back in two currencies. The session itself and how to progress it are in the guide on strength training at home.

After 40 the priority is not evenly split

If you read one section on this page, read this one.

Fitness is forgiving. Miss three weeks of running and you lose some of it, then rebuild it over a few weeks. Muscle is not forgiving in the same way. Muscle mass and strength decline with age even in people doing nothing wrong, and the process speeds up the older you get. What you lose there takes months to rebuild, not weeks.

That does not make running worth less. It means the two things run on different clocks, so a compressed week should not be cut symmetrically. When something has to go, the run is almost always the right answer, however backwards that feels to someone who thinks of themselves as a runner.

The order when both fall in one session

Here the evidence is surprisingly specific. A systematic review with meta-analysis examined whether the order within a single session matters.

The result: a resistance-then-endurance order produced better lower-body dynamic strength than the reverse, with a weighted mean difference of 6.91 per cent. For everything else measured there was no effect of order at all: not on lower-body muscle growth, not on lower-body static strength, not on maximal aerobic capacity or body fat.

Translated to a Tuesday evening, it comes out simple:

• If getting stronger is the priority: lift first.
• If the run is the most important session of the week, an interval session or a long run for instance: run first and accept that the strength work will be slightly worse that day.
• If the run is easy and short: the order matters less than doing both.

One exception is worth naming. If you are running hard, arriving at the interval session on tired legs is a poor idea, because the entire point of a hard session is being able to hold the pace all the way through it. How to judge that is covered in the guide on interval training.

The gap between sessions

This is the least well-evidenced part of the field, so treat it as a rule of thumb rather than a prescription. The studies comparing different amounts of rest between an endurance session and a strength session point the same way: more separation beats less, and back to back is the worst of the options.

There is no agreed figure for exactly how many hours. The practical conclusion therefore needs no number at all: if you can put the sessions in different parts of the day, or on different days, do it. If you cannot, run them back to back anyway. A double session almost always beats a session you skipped. The exceptions are the obvious ones: illness, an injury that hurts, or a night that barely produced any sleep.

Three weeks that work

All three are built on 20-minute strength sessions and easy running. The easy pace is what makes the combination possible, because that is where the recovery cost is low. If every session lands in the middle, the week gets expensive and returns little, which is the same trap described in the guide on zone 2.

Model 1 and model 2 contain exactly the same training: the same three runs, the same two strength sessions, the same 150 minutes. The difference is how the week is packed: model 1 puts more space between the sessions, model 2 needs fewer days. That is worth pausing on, because plenty of people assume they have to drop the strength work when they do not have five free days. They only need to put it next to a run instead.

Model 3 is honest about what it is. It cuts running volume but keeps both strength sessions, which is exactly the priority the rest of this page argues for. Two training days are therefore enough for the muscle-strengthening half of general activity guidance, twice a week. What seventy minutes does not cover is the aerobic half, and that is precisely the part you rebuild fastest once the weeks settle down. More ways to fit training into a life that is already full are in the guide on training when you have no time.

Five mistakes that cost the most

• Putting the strength session the day before the long run. Your legs have not recovered, so the long run, which ought to be the calmest session of the week, becomes a fight. Do the lifting the day after instead.
• Turning the strength session into a cardio session. Forty minutes of circuits with your heart rate up is a third endurance session that you are calling strength work. Take the set close to failure, rest properly between sets, let your heart rate come down.
• Letting every session land in the middle. The easy runs turn moderately hard and the strength sessions turn half-hearted. The week costs everything and returns little.
• Cutting the strength work first when time runs short. See the section on priority. This is the most expensive mistake on the list and the most common.
• Eating as though only the running counted. Training is the signal; the building material comes from food, and protein needs rise with age. The numbers are in the guide on protein after 40.

Who should be careful, and when to seek care

Combining two forms of training is not risky in itself, but it raises your total load, and the total load is what decides it.

• Call emergency services for chest pain or pressure that does not ease within a few minutes of rest, particularly alongside breathlessness, cold sweat, nausea or feeling faint.
• Contact a doctor if exertion brings on pressure or pain in the chest that eases when you rest, even if it only lasts a minute. New symptoms on exertion should always be assessed.
• Contact a doctor for joint pain that is still there the day after a session, for pain that makes you limp or change how you move, or for Achilles pain that is worst on your first steps in the morning.
• Check with a doctor first if you have known heart disease, blood pressure that is not under control, or a current injury that has not been assessed.

This is general health information, not a diagnosis or personal medical advice. If you are unsure, contact your local health service.

Frequently asked questions

Can you lift weights and run on the same day?

Yes. If you can put a few hours between the two sessions, that is better than running them back to back, but a double session still beats cutting one of them. If they do end up back to back and your priority is getting stronger, lift first. If the run is the most important session of your week, run first and accept that the strength work will be slightly worse that day.

Does running ruin muscle growth?

At the dose a recreational runner actually runs, the effect is small. A meta-analysis of 21 studies found that combined training produced smaller gains in strength and muscle size than strength training alone, and that the association grew clearer the more frequent and the longer the endurance sessions were. The same analysis found the effect with running but not with cycling. Three runs a week alongside two strength sessions sit well below the dose where this becomes a real problem.

Should I lift before or after running?

If both fall in the same session, the research leans slightly towards lifting first. A systematic review with meta-analysis found that a resistance-then-endurance order produced better lower-body dynamic strength, with a weighted mean difference of 6.91 per cent, while the order made no difference to lower-body muscle growth, lower-body static strength, maximal aerobic capacity or body fat. For everything except dynamic leg strength, in other words, it makes no measurable difference.

How many strength sessions does a runner need?

Two a week is enough for most recreational runners, and that is also what general activity guidance sets out as muscle-strengthening work. Research on middle- and long-distance runners points towards two to three sessions a week benefiting running performance, mainly through better running economy rather than a higher aerobic capacity.

What should I drop first when the week falls apart?

Drop a run before you drop a strength session. Fitness comes back within weeks. Muscle mass and strength decline with age even when you do nothing wrong, and they take months to rebuild. If you are down to two days in the week, put a short strength session in front of each run rather than giving up the strength work entirely.

Will strength training make me slower or heavier?

No, not in the form a runner needs. Two sessions a week using bodyweight or moderate loads will not build the kind of muscle mass that would cost you in running, and the effect on running performance in the research runs the other way. Strength training is also the single best-evidenced measure against overuse injuries, which are the most common reason runners are forced to stop.