I could run a half marathon every week, but I couldn't lift 5.5kg on a single leg.

Many runners and cyclists assume that completing long runs or riding high mileage means they are physically strong. However, aerobic fitness and muscular strength are different qualities. Endurance training improves cardiovascular fitness, but it does not always develop the muscle strength and tissue capacity needed to tolerate repetitive loading. This article explains how one endurance athlete could run a half marathon every week yet struggle to lift 5.5kg on a single-leg exercise, and why targeted strength training became the missing piece for long-term performance and injury resilience.

Strength training for runners and cyclists over 30 is a game-changer for performance, resilience, and long-term health.

If you want the full breakdown, check out my Strength Training Over 30 Guides:

Strength training for runners over 30

Strength training for cyclists over 30

TRAINING BREAKDOWN

"You can be aerobically fit and structurally weak at the same time."

By Emma O'Toole

Hello!

17 years ago, my weekly long run was a half marathon. I was fit, consistent, and I genuinely thought that I was strong. I mean, if your body can cover half marathon distance week after week, it must be strong enough, right?

Around the same time I was also training on the velodrome with a Team Sky junior development programme. Madisons, flying laps, track starts, team pursuits. I was on the track with some seriously talented young cyclists and I was holding my own. On the bike I felt capable, powerful, and physically robust.

And then I was dabbling with some strength training after hearing coaches talk about it, so I sat on a seated leg extension machine and did a single leg extension.

5.5kg.

That was all I could manage, on both my left and right legs, which was circa 1/12th of my bodyweight. Not a fluke, I went back a few days later and tried again… same 5.5kg result and that was me giving it beans. Me, the runner whose long run was a half marathon every Wednesday. Me, the cyclist training on the velodrome with a Team Sky junior development squad could only do 5.5kg on a single leg extension.

I remember it clear as day because I was genuinely quite surprised, I guess I didn’t really fully understand what it meant until things started to go wrong slowly and then suddenly all at once.

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The VMO is the teardrop-shaped part of your quads on the inside of your thigh, just above the kneecap. It contributes to helping control the position of the kneecap during movement, working alongside the rest of the quads and surrounding muscles. At the time, my physio felt that weakness through my VMO was one of the key contributors to my knee pain.

First came the pain around the kneecap, a dull ache that was manageable at first and less manageable as the weeks went on. Then the swelling. Then the instability, that unsettling feeling that the knee was not quite doing what it was supposed to do, particularly on downhills and after longer efforts.

So I did what most runners do... I ignored it for a while. Then I bought knee tape and ran through it. Then I went to a physio… then I tried acupuncture... then I taped the knee differently and stubbornly tried to run a half marathon again.

This went on for 2-3 years. 2-3 years of niggles, appointments, money spent on physio and acupuncture, and sessions missed. That was the physical (and financial side) of it, the mental side was another kettle of fish. I was frustrated to say the least. I grappled with who I was - how could I call myself a runner or cyclist when I never knew if I could get through a session? I felt anxious wondering if things would ever get better, or if this was just it now. And I felt sad looking at the missed opportunities, races entered and then withdrawn from, training sessions with friends that I never got to do, moments that you simply cannot get back in life.

Caught in the rigmarole of injury

And all of this comes back to that 5.5KG on the single leg extension and ties into something I find really interesting about the way most runners and cyclists think about strength.

We measure our fitness by what we can do on the road, the trails, or the track. If you can run 13 miles, you must be strong enough. If you can hold 4w/kg for an hour then your legs must be powerful enough. In an aerobic sense, sure! Your cardiovascular system is working very well. However, what’s important to remember is that you can be aerobically fit and structurally weak (aka lacking muscular strength and tissue capacity) at the same time. I was living proof of that for two to three years and have worked with hundreds of runners and cyclists experiencing the same phenomenon. Your aerobic fitness won’t tell you whether the muscles around your knees, hips, and ankles are strong enough to tolerate and control the forces passing through those joints over thousands of repetitions that you put them through week after week, year upon year.

Running places repeated demands on the quadriceps, but it doesn't progressively overload the VMO or the rest of the quads in the same way that targeted strength training can. Cycling certainly uses the glutes, but it doesn't typically develop maximal glute strength in the way that heavy single-leg strength training can, especially as an endurance rider. You can spend years building your aerobic engine while the muscles that help to control those joints remain under-trained.

And they're much more likely to become a limiting factor as your training load accumulates; you can’t outrun or outride a lack of strength I’m afraid.

For me, whether it was specifically my VMO or more generally a lack of quadriceps strength and lower-limb capacity, one thing became very clear: I simply wasn't strong enough to tolerate the amount of training I was asking my body to do. The knee tape was not addressing that, the physio helped manage my symptoms and guide my rehab, the acupuncture helped with the pain, but the underlying strength deficit was still there.

I’d love to say that as soon as I started strength training that was it, I was cured! But that simply wasn’t the case, things, however, did change fairly quickly. The swelling began to settle, the knee became far more stable and for the first time in years I could run again without that “noise” of my knee, it’s like a humming which is there and you’re constantly monitoring because you don’t trust your body anymore.

I also got significantly stronger on that single leg extension (as well as many other exercises!) and as I did, niggles and full blown injuries got fewer and far between.

17 years ago, my weekly long run was a half marathon, but I couldn’t lift 5.5kg on a single leg. I know which one mattered more for my long term health as a runner and a cyclist and to that end it’s why I created 2x free quizzes:

• Are you strong enough to run?

• Are you strong enough to ride?

Both of these quizzes test key strength areas that most runners and cyclists don't realise they're missing and are often pretty eye opening.

Chris, a runner in our free coaching community summed it up perfectly after taking the quiz up when she said: "I can run a 45 minute 10k but I can't do 15 bodyweight single leg calf raises in my right leg!"

You don’t need any equipment and it’s completely free. Please click the link below to access each quiz:

• Are you strong enough to run?

• Are you strong enough to ride?

Happy running and riding!

Emma x

I can certainly lift more than 5.5KG on the leg extension nowadays!

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