With HYROX, marathons and run clubs everywhere at the moment, plenty of people are setting themselves a goal to "get fitter", myself included.
Getting fitter can mean different things to different people, but it's largely about going faster, going for longer and recovering better. The tricky part is chasing these outcomes without understanding what's actually driving them, so training ends up scattered rather than targeted.
I wouldn’t say I can run very fast or very far, so both of those sit within my goals. But focus on both at once, or try to increase by distances and then speed it up, or the other way around. And what about my strength goals - where do they fit?
Let's look at what getting fitter actually means physiologically, so that we can understand what approach to take if this is your goal. And luckily, Matt is on hand with a straightforward approach on how to plan your week around a goal that pushes your fitness up and up.
Get Familiar with the Numbers
If you want to get fitter, there are two numbers to pay attention to: your resting heart rate and your VO2 Max. You can track them with a smart watch or band, or get them professionally measured.
Resting Heart Rate
Your resting heart rate is how many times your heart beats per minute when you're doing nothing. Think lounging on the couch, watching TV.
It’s one of the simplest signs your fitness is improving. As your heart gets fitter, the muscle itself gets stronger and pumps more blood with each beat, a measure called stroke volume. A stronger heart can move more blood around the body, meaning it doesn't need to beat as often, so your resting heart rate drops as your fitness improves.
It's essentially your heart idling at a lower rate because it doesn't have to work as hard to do the basic job of keeping you alive.
VO2 Max
VO2 max is the maximum amount of oxygen your body can use during intense exercise.
It depends on how much blood your heart can pump, how well your blood carries oxygen, and how efficiently your muscles can extract and use that oxygen once it arrives.
The higher your VO2 max, the bigger your aerobic ceiling, meaning more capacity before you hit your limit. It's also one of the strongest predictors we have of long-term health, more closely linked to longevity than almost any other fitness marker.
Given that a VO2 Max test has you on a treadmill or bike until you reach total exhaustion, an estimate from a smart watch will suffice. The main thing you're looking for here is the trend over time rather than the exact number.
Knowing your numbers is one thing, training them is another. That's where heart rate zones come in.
Heart Rate Zones
Your resting heart rate and VO2 max shift based on how you train. Heart rate zones are how you can target that training on purpose, rather than hoping for the best.
Zones 1-2
Roughly 60-70% of your max heart rate. This is where you can hold a full conversation without gasping for breath between words. At this intensity, your body works aerobically, using oxygen to produce energy, and relies mostly on fat for fuel. This is where significant adaptations happen: more capillaries deliver blood to your muscles, and more mitochondria are available to use the oxygen once it gets there.
Zone 3
70-80% of your max heart rate. Welcome to the awkward middle, where exertion starts to increase and holding a conversation becomes a challenge. This is where your brain is going to try to talk you out of the activity. You start to shift from mostly aerobic work to a mix of aerobic and anaerobic, meaning your body is now also producing some energy without oxygen. Here, you're not spending enough time at either end to get the best adaptation from either.
Zones 4-5
80+% of your max heart rate. Short, hard, can't-finish-a-sentence effort. Here, your body leans heavily on anaerobic metabolism, producing energy without oxygen, and lactate builds up fast. Training at this intensity improves how efficiently your aerobic system clears that lactate, which is what lets you sustain higher efforts for longer before you have to back off.
How to Program for Fitness
Now for the fun part. We have the science, let’s put it into practice and look at how much time to spend in each zone every week.
If your goal is general fitness, with a focus on your resting heart rate, recovery and longevity, spending most of your training time in zone 2 will get you there.
If you're chasing bigger aerobic capacity gains, you'll need to do two things: build the aerobic base and teach your body to handle higher intensity.
Think of your VO2 max like your engine; important to perform well, but a big engine doesn’t guarantee you’ll win the race if you can’t rev it up too.
Matt, our Head of Coaching, has a simple recommendation for three sessions per week, focused around getting you fitter.
1. Build the Engine
In order to improve your VO2 max and give you a bigger base to work with, aim to hit at least 90 minutes of steady-state work across the week in zones 1-3, with zone 2 being the sweet spot.
Break this up however best suits your schedule, but a good way to approach it is two sessions per week of 40 minutes each, gradually increasing by 5 minutes per week, up to 60 minutes.
2. Rev it Up
Your third session of the week is where you want to push into zones 4 and 5.
Matt’s a big fan of the 4x4 protocol, four rounds of four minutes in zone 4, with three minutes of recovery in between.
Matt also happens to be my coach, and this protocol just landed in my own program. It's tough, but it's already making a difference. Simple but brutal.
3. Add Strength
From there, layer in your strength. You want to make sure you don’t overdo it, though, so if you also want to prioritise strength at the same time, 2 sessions per week is a pretty solid start.
We did a deep dive on how to do concurrent training - prioritising multiple goals at once - in another article. Check that out here.
How to Stay in Zone 2
You’d think it would be easier to stay in the lower heart rate zones, but I can tell you from experience that it isn’t!
If running sends your heart rate through the roof five minutes in, that's not a sign you're totally unfit, but your aerobic base isn't there yet, and trying to push intensity before it is just leaves you gasping on the side of the road wondering why running feels impossible.
Change modality instead. Get on a bike or in the pool, somewhere you can actually control the effort and stay in the zone you're meant to be training. Focus on building your base there and bring running back once you've got the foundation to support it.
Overload Over Time
As always, keep making it harder over time. Progressive overload isn't reserved for strength training. As you get fitter, keep nudging yourself further. That might mean more speed, more distance, more time, or a mix of all three. Small, steady steps, week after week.
TL;DR
(Too long, didn’t read)
- Getting fitter comes down to a few key numbers and knowing how to train them.
- Resting heart rate drops as your heart gets stronger and pumps more blood per beat
- VO2 max is your aerobic ceiling, and one of the strongest predictors of long-term health
- Zone 2 builds the aerobic base, zone 4-5 teaches your body to handle and clear intensity
- Aim for around 90 minutes of steady-state work weekly, plus one higher-intensity session
- The 4 by 4 protocol, four rounds of four minutes hard, three minutes easy, is a solid place to start
- If a modality spikes your heart rate too fast, swap it while you build the base
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