Does Strength Training Make You Slower?

Ask a club runner why they avoid the weights room and you'll usually hear some version of the same thing: "I don't want to get bulky." It's an understandable worry — bodybuilding imagery is what most people picture when they hear the word "strength training," and nobody wants to carry extra mass up a hill.

The trouble is, this idea is built on a misunderstanding of how muscle actually adapts to load. Building significant muscle mass (hypertrophy) requires a specific combination of training variables — moderate-to-high volume, a calorie surplus, and months of dedicated focus. It does not happen by accident, and it certainly doesn't happen from two structured strength sessions a week layered on top of running mileage.

The strength training that benefits runners looks nothing like a bodybuilding programme. It's built around heavy compound lifts performed for low reps (typically 3–6), with full recovery between sets. This style of training targets the nervous system far more than it targets muscle size.

• Improved running economy — the amount of oxygen you burn to hold a given pace
• Greater tendon and ligament stiffness, meaning less energy leaks out of your stride
• Increased motor unit recruitment, so your muscles fire more force per contraction
• Better fatigue resistance late in a race, when form usually falls apart

Multiple lines of sports science research (published in journals such as the Journal of Strength and Conditioning Research and Medicine & Science in Sports & Exercise) point the same direction: heavy strength work paired with endurance training improves running economy without a meaningful change in body mass or a drop in aerobic capacity. This is sometimes called the "concurrent training effect," and for the vast majority of amateur and club-level runners, the benefits far outweigh any theoretical interference.

In our experience coaching runners across Eltham, Greenwich and Blackheath, the runners who slow down or plateau usually have one of these problems, not a "bulky" physique:

• Chronic low-grade injuries (ITB pain, runner's knee, Achilles issues) that quietly cap their training volume
• A stride that leaks force through weak hips, glutes or ankles
• No structured strength work at all, so speed is entirely dependent on running volume — which has a ceiling before injury risk climbs

Strength training addresses all three. It's protective, it's performance-enhancing, and it lets you absorb more running mileage without breaking down.

If you're still cautious, the fix is simple: train for strength, not size. That means:

• Low reps (3–6) on your main lifts, heavy load, full recovery between sets
• Two sessions a week is plenty for almost every runner — this is not a bodybuilding split
• Prioritise compound movements (squat, deadlift, hip hinge variations, single-leg work) over isolation exercises
• Keep total weekly volume modest — this is supplementary to your running, not a competing discipline

Done this way, strength training adds resilience and power without adding noticeable mass. If you want a structured place to start, our guide to the four lifts every runner should do is a good next stop, or you can read about how we build strength blocks around a marathon build.