6 Things I Learned About Cross-Training After a Stress Fracture

After running a marathon PR in May, I made a slew of bad decisions that led to a stress fracture.

Devastated but determined, I leaned fully into cross-training — adapting my running plan to the bike, elliptical, and pool.

Here are six things I learned.

#1: Why cycling HR zones are lower than running HR zones

Before being injured, I didn’t know why my heart rate shot up more in some sports, and stayed low in others.

Why is it easy to hit max heart rate while running or cross-country skiing, while much harder when cycling or weight-lifting?

Simply put, your heart rate is set by how many muscles are being used:

• When muscles are used, they need more oxygen.

• Oxygen is provided by blood, which the heart pumps around the body.

• The more muscles you use, the more blood the heart needs to move around.

• The heart moves more blood around by pumping faster.

Running and cross-country skiing simply use more muscles than cycling or weight-lifting, and so your heart has to supply oxygen to more muscles, which means more blood flows, which means your heart beats faster (in other words, your heart rate gets higher).

So for any given workout, your heart rate will almost always be lower on the bike than when running because you use fewer muscles on the bike.

That means, in turn, that the heart rate zones are also different between cycling and running.

On the bike, HR zones are usually 5-10 BPM lower (though it depends on various factors — if you’re a triathlete, for instance, you may have comparable HR zones).

#2: Stop chasing speed — cycle easy when it’s meant to be easy

At the start of cross-training, I was often super tired throughout the day, despite doing comparably less intense exercise than I was while running.

At that point, I focused on speed and distance during cycles. I wanted to cover as many miles as possible to “get a good workout in.”

But the reality is that these particular metrics aren’t helpful.

Just like with running, every session should have a purpose.

If the goal of the session is hitting VO2 max, then I should aim for zone 5; if the goal is recovery, I should be in zone 1 or 2.

In either of these scenarios (and everything in between), speed and distance are irrelevant.

Heart rate and cadence (more on that below) are all I should pay attention to.

But by focusing instead on speed and distance, I was always sitting in HR zone 3 or 4. That meant that every session was pretty exhausting, and that fed into my day.

So I stopped paying attention to speed and distance, and switched my Garmin data screens to just show me HR, HR zone and cadence — the stuff that ultimately matters.

#3: Cadence: the most underrated metric on the bike

In running, a high cadence (180+ steps per minute) is generally recommended.

So it is with cycling.

Running cadence is measured in steps per minute. In cycling, it’s the number of times you turn the pedal per minute — Rotations Per Minute (RPM).

RPM is measured on a single pedal, so a cycling cadence of 90 would be the same as a running cadence of 180.

To emulate the biomechanics of running, it makes sense to aim for a similar cadence (i.e. 90+) on the bike.

But the benefits go beyond that.

Lance Armstrong, one of the greatest cyclists of all time, cycled at a high cadence (110+) with the belief that it would stress the cardio system more (as opposed to stressing muscles, which are worked more in lower cadences).

So, a high cadence not only more closely emulates running, but also provides a better cardiovascular workout — which is the “aerobic engine” (the bedrock of endurance sport) that everyone keeps banging on about.

I’ve taken a leaf out of Armstrong’s book and been aiming for 95-110 RPM across all rides.

#4: You’re (probably) using the elliptical wrong — especially if you’re a runner

The elliptical trainer (or “cross-trainer”) is an odd beast.

Nobody seems to know how to use it, or why it even exists. It’s just kinda there.

I’d thought it was designed as a direct alternative to running. But it turns out, that’s not true.

The inventor, Larry Miller, didn’t even like running. He invented the machine to give him an alternative way to exercise.

“I jogged for a while, but I didn’t really enjoy it because it was pretty rough on the body. I kind of gave that up, which was part of the motivation for this I guess.” — Larry Miller, 1997

So the elliptical isn’t a direct replacement for running, and it doesn’t directly emulate running either. In fact, it more closely emulates cross-country skiing.

Then how do you actually use it if you’re a runner?

For runners, the trick is to emulate the bio-mechanics of running as closely as possible.

While the elliptical manages that in part (it’s weight-bearing, upright, and the lower body moves similarly), it doesn’t emulate all parts of running (those dumb arm cranks, for instance).

To get a more run-like workout, I realised that if you drive through your heels (instead of your forefoot), you’ll activate your hamstrings and glutes (essential running muscles), and you’re able to stand upright.

Once you’re upright, ditch the machine’s arms — and then you can pump your arms exactly as you would if you were running.

That’ll give you, it seems to me, the closest run-like workout you can get without actually running.

#5: Less of a lesson, and more a harsh reminder, but: swimming is hard

I’ve always dreamed of doing a triathlon.

While I’ve learnt so much about how to ride the bike effectively, I’m still figuring out how to get from one side of the pool to the other without drowning.

I haven’t made much progress here.

While I’m seeing some progress, I’m absolutely battered after every lap of the pool.

The experience has reminded me that no matter how fit you are at one sport, it doesn’t necessarily translate.

Some sports rely on technique and skill, not just raw aerobic power.

So alas, the triathlon remains a pipe dream.

#5.5 (BONUS): EVERYONE hates cyclists (but I get it now)

I’ve run in a lot of places, and I’ve rarely faced abuse from anyone.

While cycling, I’ve had a very different experience. Never in my life have I received so much hate.

At first, I cycled on the pavement. But I kept getting lambasted by pedestrians.

So I moved to the road. That didn’t help much. I get beeped at and flipped off on a daily basis.

What can I do?

I opt for cycle lanes whenever I can. But the cycling infrastructure in my area is lacking. Even when I do use it, so do pedestrians. You can’t win.

All I can say from this experience is that I have a lot more empathy for the “plight” of the cyclist.

#6: Cross-training always has a place

Abuse aside, the biggest takeaway from the whole experience is that cross-training will always have a place in my future training plans.

In the past, I’ve been a bit of a purist. When it comes to training to increase running fitness, nothing provides a better stimulus than simply running.

It’s the “principle of specificity” — if you want to be a better runner, running is the more efficient way to do so.

But running is also intense.

It’s brutal on the body — every mile (even the easy ones) hammer you with 2.5–3x your bodyweight every step.

I put my injury down to a bunch of factors, such as diet and a lack of rest after training. But running volume likely played a role, too.

During my last training block, I ran up to 102 miles a week. Before I got injured in this block, I was running 80+.

That’s a lot of impact.

This stress fracture has reminded me that I’m human, and I can only deal with so much.

But I don’t have any intention of reducing general training volume. I love training — but I also love being able to run.

So I’ll be swapping out some of my easy miles for spins on the bike, yards in the pool, and even a few sessions on the cross-trainer.

Perhaps that’s the key to sustainable running — these alternatives might not give as “good” a workout as direct running, but they’ll give me a way to maintain my aerobic engine without the impact of running.