I was in London this week for meetings, and the journey home turned into a bit of a nightmare. My train got cancelled, I ended up on a late replacement to the wrong station, and my car was parked at a completely different station, around 15 miles away. By the time I actually got home, it was gone midnight.

The next morning I was up early, tired, and staring down a 12 mile run at marathon pace.

I train with a Garmin, and I’ve learned to at least glance at what it tells me before I lace up. My HRV on a normal day sits in the high 50s. That morning it read 38. Resting heart rate was up, sleep score was wrecked.

Now, I don’t think this data is hugely accurate. Garmin, and most wearables like it, are a good baseline, not gospel. If the numbers look bad but I actually feel fine, I’ll often ignore them and just get on with the session as planned. But when how I feel lines up with what the data is telling me, that’s when I really start to trust it and use it to make the decision. That morning, both things agreed. I felt rough, and the numbers backed it up. That combination is what made the call an easy one.

I knew straight away the session I had planned was going to be a bad one. Marathon pace for 12 miles needs a body that’s recovered enough to hold that effort steadily for over an hour. Forcing it that morning would have meant grinding through at the wrong heart rate, probably slower than target pace anyway, and banking fatigue I hadn’t earned with a good session in return.

So I bailed on the plan.

But I didn’t do nothing.

Instead I went out for a 5 mile recovery run, easy pace, no pressure. And it felt great. Legs moving, blood flowing, session logged, just not the session I’d written down in the plan.

That’s really the whole lesson. Sometimes you need to know when to rest, and when you just need a bit of discipline to get out the door anyway.

Two very different kinds of I don’t want to run

Most days when motivation dips, it’s just noise. You’re comfortable on the sofa, it’s raining, you had a long day at work, none of that is your body telling you anything meaningful. That’s a discipline day. You get dressed, you get out, and nine times out of ten you feel better for it within the first mile.

Then there are days like the one after my London trip. That’s not a motivation problem, it’s a recovery problem. The tiredness isn’t I can’t be bothered, it’s my nervous system hasn’t caught up yet. Those are genuinely different situations, and treating them the same way, always pushing through, or always backing off, will eventually catch up with you one way or another.

How I actually tell the difference

A few things I look at, roughly in this order.

Is there a clear cause. A late night, travel, poor sleep, or a hard session the day before all explain elevated fatigue. Random tiredness with no obvious trigger is worth paying more attention to, not less.

What does the data say. As I said, I don’t take Garmin as gospel. It’s a good baseline, useful for spotting trends over time rather than making a big decision off one bad night on its own. But when a big swing from my normal baseline, like that 38 against a high 50s norm, lines up with how I actually feel, that’s when I’ll use it to make the call. Data without feeling is just numbers. Feeling without data is just guessing. Together they’re a decent signal.

What does the session actually demand. An easy run has a lot of room for a bad day. A marathon pace session, a threshold workout, or anything with real intensity has much less room. You either hold the effort or you don’t, and forcing it rarely ends well.

Can I adjust instead of cancel. This is the bit people miss. The choice isn’t just do the session or do nothing. Swapping a hard session for something easy still gets you out the door, still logs useful training stress, and keeps the habit intact without digging a deeper hole.

Why training through it doesn’t always get you what you think

This is the part that took me years to properly understand. Yes, discipline matters. Yes, consistency is what actually builds fitness over months and years, not any single session. But there’s a real difference between discipline and stubbornness.

Training in a stressed state, physically wrecked from a bad night, mentally fried from travel, often means you don’t actually get the training stimulus you were chasing from that session in the first place. A marathon pace run is meant to teach your body to hold a certain effort efficiently. Do it on 38 HRV and a few hours of sleep, and you’re not practising marathon pace, you’re practising surviving. The heart rate drifts, the form breaks down, and the session teaches your body the wrong lesson entirely. You can tick the box that says you did it, but you haven’t banked the fitness you were actually after.

That’s why the recovery run mattered more than forcing the original session would have. It kept the habit and the consistency intact, without pretending my body was somewhere it wasn’t.

The actual discipline

It would have been easy to either force the marathon pace run and tell myself I was being tough, or skip running entirely and call it a rest day. Neither was the right call. The discipline wasn’t in gritting my teeth through 12 miles at a pace my body wasn’t ready for. It was in being honest about what the data and the day were telling me, adjusting the plan, and still doing the work I was capable of.

Rest days matter. Discipline matters. Consistency matters more than either on its own. The skill is knowing which one a given morning is actually asking for, and having a plan B ready when it’s not the one you wrote in your training log.