Weight Training 2x Weekly Cuts Marathon Running Efficiency Loss by More Than Half in New Study

A marathon rarely falls apart because the first 15 minutes feel hard. It falls apart because the same pace becomes more expensive as fatigue builds.

That is what makes a new study from Zanini et al., published in Medicine & Science in Sports & Exercise in 2025, interesting for distance runners. In well-trained male runners, adding weight training twice per week did not appear to make them more efficient when fresh. The change showed up later, during a long run at marathon effort.

After the strength-training block, the drop in running efficiency during a 90-minute marathon-effort run was cut by more than half, from 4.7% to 2.1%. The running-only group did not improve in the same way.

That is a practical result. Marathon performance is not only about peak fitness. It is also about how well a runner holds form, stiffness, rhythm, and economy when the legs are no longer fresh.

The study focused on what happens after fatigue begins to build, not just how running feels at the start.

What the study looked at

The study involved 28 well-trained male runners. The key comparison was between runners who kept running only and runners who added two weight-training sessions per week.

The test that matters here was not a short treadmill check when everyone felt fresh. The researchers looked at a 90-minute run at marathon effort and compared how running efficiency changed across that run before and after the training period.

The headline finding came from measuring the change from the 15-minute mark onwards. In other words, the researchers were not only asking, “Are these runners economical at the start?” They were asking, “How much does that economy decay as marathon-effort running continues?”

Study detail	What was reported
Study	Zanini et al., Medicine & Science in Sports & Exercise, 2025
Participants	28 well-trained male runners
Main comparison	Running only versus running plus weight training
Strength frequency	2 sessions per week
Running test	90 minutes at marathon effort
Key measurement window	From the 15-minute mark of the run
Main result	Efficiency loss fell from 4.7% to 2.1% in the weight-training group
Fresh running efficiency	No meaningful change reported
Running-only group	Efficiency drop stayed similar to before

This distinction matters. A runner can look smooth and efficient early in a race, then lose the same pace later because every stride costs more energy. The study suggests that strength training may help reduce that late-run cost.

In this study, the benefit of lifting was not that runners became clearly more economical when fresh. The benefit was that they lost less efficiency during prolonged marathon-effort running.

The key numbers from the marathon-effort test

The central finding is simple enough to understand without overcomplicating it.

Before adding weight training, the strength-training group’s running efficiency dropped by 4.7% during the marathon-effort run, measured from the 15-minute mark. After training, the drop was 2.1%.

That is less than half the previous decline.

Group or condition	Before	After	What changed
Weight-training group efficiency drop during 90-minute marathon-effort run	4.7%	2.1%	Drop reduced by more than half
Running-only group efficiency drop	Similar to before	Similar to before	No comparable reduction reported
Fresh running efficiency	No meaningful change	No meaningful change	Benefit appeared under fatigue

The “fresh” result is just as important as the fatigue result. If the runners were tested when rested, nothing major changed. That can seem disappointing at first, but it makes the finding more specific.

The lifting did not simply make the runners look better in a clean lab test at the start. It seemed to help them preserve efficiency deeper into sustained work.

For marathon runners, that is often where the race is decided.

Why a smaller efficiency drop matters in marathon running

Running efficiency is the cost of moving at a given speed. If two runners hold the same pace, the more efficient runner uses less energy to do it.

During a marathon, the problem is not only fuel. Muscles become tired. Tendons and joints may lose some spring. Ground contact can change. Stride mechanics can drift. The nervous system has to keep coordinating thousands of repeated steps while fatigue accumulates.

A 90-minute run at marathon effort is not a full marathon, but it is long enough to reveal some of that decay.

A smaller efficiency loss could mean:

• Less oxygen cost at the same pace later in a hard run

• More stable mechanics as fatigue rises

• Better ability to hold marathon rhythm

• Lower relative effort late in long sessions

• Less need to slow down to keep effort under control

  
  

This does not mean lifting twice per week suddenly makes marathon pace easy. It also does not prove every runner will get the same result. The sample was small and included only well-trained male runners.

But the result fits a pattern many coaches already use in practice. Strength work may not always show up as a faster easy-run pace. It may show up as less slowing, less form collapse, and better durability when the workout gets long.

Running economy is often about small changes repeated thousands of times.

Why weight training might help without changing fresh economy

At first glance, the “fresh, nothing changed” result can feel odd. If lifting helps, why did fresh running efficiency not clearly improve?

One likely answer is that well-trained runners already move efficiently at the start of a run. There may be less room to improve when they are rested. The bigger gap appears when fatigue starts to expose weaknesses.

Strength training may help in several ways.

Stronger muscles may resist fatigue for longer

Marathon effort is not maximal force, but each step still requires repeated force production. Stronger legs may handle each stride at a lower percentage of their maximum capacity.

That can reduce the strain of each step. Over 90 minutes, that may matter.

Tendons and muscles may store and return energy better

Good distance running is not just muscle strength. It also relies on leg stiffness and elastic return. The calf, Achilles tendon, hips, and surrounding tissues all contribute to how much energy is lost or recycled with each stride.

Strength training, especially when well designed, can improve the body’s ability to tolerate and produce force. That may help runners keep a more efficient spring late in a run.

Better force capacity may protect form

When runners fatigue, they often lose posture, increase ground contact time, change cadence, or overwork smaller muscles. These changes can raise the cost of pace.

If lifting helps preserve mechanics under fatigue, the benefit would appear exactly where this study found it, later in a sustained effort rather than at the start.

The nervous system may keep recruitment cleaner

Heavy and controlled resistance training can improve how the nervous system recruits muscle. For a runner, that does not mean turning into a sprinter. It may mean using the right muscles at the right time with less wasted effort.

Again, that kind of benefit may be hard to see when fresh but more visible after fatigue accumulates.

What this means for marathon training

The practical message is not that runners should swap mileage for bodybuilding. The study points to a more modest and useful idea: two well-planned strength sessions per week can support marathon durability.

For many runners, that is enough. It fits alongside running without turning the week into a gym programme.

A simple marathon-focused strength plan usually needs to cover:

• Squat or split-squat pattern

• Hip hinge, such as Romanian deadlifts

• Calf and soleus work

• Step-ups or lunges

• Core and trunk control

• Hamstring and glute strength

  
  

The goal is not to leave the gym sore for three days. The goal is to build force capacity while still protecting key runs.

A sensible week might place strength on the same day as a harder run, later in the day if possible, or after an easier run. That keeps easy days easier and reduces the chance of constant low-grade fatigue.

For example:

Day	Running focus	Strength option
Monday	Easy or rest	Strength session 1
Tuesday	Quality session	No lifting
Wednesday	Easy run	Mobility or light accessory work
Thursday	Marathon-pace or tempo work	No lifting, or short session if well adapted
Friday	Easy run	Strength session 2
Saturday	Easy or rest	No lifting
Sunday	Long run	No lifting

This is only an example. The best placement depends on the runner’s history, training load, and how quickly they recover.

Strength work for marathoners should support running, not wreck the next session.

How to apply the finding without overdoing it

The most useful part of the study is the frequency. Twice weekly is realistic for many runners. It is also enough to create a training signal without taking over the whole plan.

The mistake is jumping from no lifting to hard, high-volume sessions during peak marathon training. That can make legs heavy, disrupt workouts, or raise injury risk.

A better approach is gradual.

Start before the hardest marathon block

Strength work is easiest to introduce before mileage and long runs reach their peak. The body needs time to adapt to lifting, especially eccentric loading from exercises like lunges, deadlifts, and calf raises.

Starting 8 to 12 weeks before the heaviest race-specific work gives more room to learn movements and manage soreness.

Keep the work heavy enough to matter

Very light circuits may help general conditioning, but they may not create the same strength benefit. Marathon runners do not need maximal lifting every week, but the exercises should become challenging over time.

That might mean sets of 3 to 8 controlled reps for main lifts, with accessory work in slightly higher ranges. Technique comes first.

Avoid turning strength into another endurance session

A common runner habit is making every gym session feel like a workout class. Lots of reps, little rest, and constant sweating can create fatigue without much strength gain.

For marathon durability, the aim is quality force production. Rest between hard sets is useful. Smooth movement is useful. Leaving one or two reps in reserve is often smarter than grinding.

Reduce lifting load close to race day

Strength training can stay in the plan during marathon preparation, but the dose should drop near race day. Heavy new work in the final fortnight rarely helps. Maintenance is enough.

That could mean fewer sets, slightly lighter loads, and no exercises that create unusual soreness.

What the study does not prove

The result is promising, but it should not be stretched too far.

The study included 28 well-trained male runners, so the findings may not apply equally to newer runners, elite marathoners, older runners, or female runners. The test was a 90-minute marathon-effort run, not a full 42.2 km race. The reported result focused on running efficiency, not direct marathon finishing times.

That does not make the finding weak. It just keeps the claim honest.

The study suggests that adding strength training twice per week can reduce the decline in running efficiency during prolonged marathon-effort running. It does not prove that every runner will run a personal best because they lift twice a week.

Training still has to be balanced. Mileage, long runs, threshold work, fuelling, sleep, and injury history all matter.

This is informational only and not personal medical or coaching advice. Runners with injuries, health conditions, or no lifting experience should get qualified guidance before adding heavy resistance training.

Why this study is useful for real-world runners

Many strength-training studies focus on short tests, fresh running economy, or lab markers that do not always feel relevant during a marathon build. This one is useful because it looks at a problem runners recognise.

Early in a marathon-pace run, the pace feels controlled. Later, the same pace starts to bite. The watch says nothing has changed, but the body knows otherwise.

The Zanini et al. result gives a possible explanation for why strength work can be worth the time even when it does not make easy pace suddenly faster.

It may help protect the cost of running when the cost usually rises.

That is a different kind of fitness. It is durability.

The most useful strength programme is the one that fits around consistent running.

The takeaway

The new study from Zanini et al. adds a clear point to the marathon training conversation: lifting weights twice per week did not seem to change fresh running efficiency, but it cut the efficiency loss during a 90-minute marathon-effort run from 4.7% to 2.1%.

That is the kind of improvement that matters when fatigue builds.

For marathon runners, the case for strength training is often framed around injury prevention or power. This study adds another reason: preserving efficiency late in sustained running.

The practical lesson is simple. Keep the running as the main course, but treat strength as a serious support tool. Two focused sessions per week, built gradually and placed wisely, may help the legs hold their economy when marathon effort starts to get expensive.

Reference

Zanini et al. (2025). Study published in Medicine & Science in Sports & Exercise.