Heavy legs before your long run? Make strength training fit your running week.

You do not have to choose between lifting and running.

Strength training can improve running economy—how much energy it takes to hold a pace—and performance. But adding a demanding gym session to an already demanding running week can leave you carrying more fatigue than you can recover from.

The goal is to build strength while keeping enough energy for the runs that matter. That means adjusting the dose as your running changes, rather than doing the same gym workout regardless of mileage.

1. Review the amount of strength work.

One mistake I see is doing too much lower-body work during demanding long-run weeks. Sets, repetitions, load, exercise choice and how close you train to failure all affect the demands of a workout.

For the same exercise, sets × reps × weight is one way to track volume. It does not tell the whole story: unfamiliar exercises or taking every set to failure can make recovery harder even when the numbers look modest.

• Start with fewer working sets. For example, if three sets of a familiar exercise regularly leave you sore for your long run, try two and assess the response.
• Leave a few good reps in reserve. You do not need to finish every set unable to do another repetition.
• Keep exercises familiar. A demanding running week is not the best time to add several new lower-body exercises.

A larger reduction may make sense during a particularly demanding week, but cutting volume by 40–50% is not a rule every runner needs to follow. Use your training history, soreness and run quality to guide the adjustment. Lighter weights are not automatically necessary if a familiar load remains manageable with fewer sets and good technique.

2. Give your legs time before the long run.

Think of a football team's walk-through before a game: preparation without adding unnecessary fatigue. Your long run is not an all-out game every week, but the principle of arriving ready still applies.

Try placing your more demanding lower-body session farther from the long run. For a Saturday long run, Tuesday may work better than Friday. Your recovery response and other hard runs matter more than a fixed day of the week.

Mobility may help you move comfortably, but it does not replace sleep, adequate food or a lighter training day when you need one.

3. Fuel strength and running throughout the week.

Protein supports muscle repair and adaptation. Carbohydrates help fuel training and replenish glycogen, the stored carbohydrate your body uses during exercise. You need both throughout the week—not protein early in the week followed by carbohydrates later.

Build regular meals that include a protein source and enough carbohydrate for your workload. Examples include eggs with toast, yogurt with oats and fruit, or chicken, tofu or beans with rice. Before longer runs, plan familiar carbohydrate-containing meals and your practiced during-run fueling.

Eating more protein alone will not solve heavy legs if you are short on overall food, carbohydrates or sleep. If you need an individualized nutrition plan, a registered sports dietitian can help.

A lesson from my own training.

During a recent training week, I had a 20-mile run scheduled for Saturday and was in the gym on Tuesday. I felt good and wanted to push harder, but I stayed disciplined and completed my reduced-volume workout.

When I finished the long run strong, holding back earlier in the week felt worth it. One run does not prove that workout timing was the only reason, but it reinforced why I look at the whole week rather than chase a hard session every time I feel good.

Make one adjustment, then review it.

Before your next long run, write down when you last trained legs, what you did, how sore you feel and how the run goes. Change the clearest problem first: the placement of the session, the number of hard sets or how close you work to failure.

If easy runs keep feeling unusually hard, read my guide to fatigue during half-marathon training. If the opening miles feel fine but you fade later, review why long runs fall apart and your Marathon Wall-Proof Checklist.

Heavy legs are not always caused by lifting. Persistent or worsening fatigue, pain or a change in your running stride deserves professional assessment rather than repeatedly pushing through.

In the Race Ready Run System, we plan running, strength, fueling and recovery together, then adjust using your feedback. If those pieces keep competing in your schedule, let's talk about what support would help.

Further reading

Strength training and running economy: a 2024 systematic review; ACSM guidance on sports nutrition and recovery. The scheduling examples above are practical coaching options, not universal rules established by these sources.