Zone 2 or HIIT? Or Neither?

My 58 year old patient walked in yesterday to the treatment room and the first question she asked was if she should start HIIT training. Woah! Hang on, I said to her do you really know what HIIT is? (*See end of article for what HIIT is please).

She said her friends, children and all the fitness influencers she sees extols the benefits of HIIT. Then without batting an eyelid, she said, "What about Zone 2 training?"

That is basically what is happening online. One group says train at Zone 2 while the other says go hard or go home, HIIT is the way to go.  

What do the best in the world actually do? A new study by Sandbakk et al (published in April 2025) investigated elite endurance coaches and their training were not what you expected. These coaches had athletes winning more than 380 international medals in long distance running, biathlon, rowing, cross country skiing, road cycling, swimming, triathlon and speed skating.

All the coaches stick to a traditional periodization model, including a gradual shift towards overall lower training volume and more competition-specific (race pace) training as the competitive period approaches.

Another common emerging feature was an emphasis on high volume low intensity training. Look at the picture above, MOST (80-90 percent) of the weekly training was easy. Here is the key insight, majority of the easy work was not in Zone 2. It was in Zone 1. Slower than what the internet experts are obsessed with. Slower means more sustainable and more adaptation over time. That's how you get stronger. 

True aerobic development is only possible from accumulating volume. It also allows one to recover and handle key sessions. 

This Zone 1 low intensity sessions along with combined with 2-3 weekly "key workout" days consisting of 3-5 intensive training sessions. The sessions are purposeful and focused, with recovery all planned. 

Finally, coaches across all sports focused on getting high training quality by optimizing training sessions by controlling the load-recovery balance to ensure optimal preparations for major competitions.

The athletes go through all the zones (see the above picture), not just high intensity (Zone 5), but also in between. Short, fast intervals and controlled thresholds. The exact proportion is dependent on their competition demands. There were not a lot of really hard anaerobic sessions. 

Why the big difference between these elite coaches and what we see online with all the fitness influencers? Firstly the fitness influencers usually do not compete in races or competitions. They won't be posting so many videos if they do. Train easy, adapt, get stronger does not sell as well as "unlocking this magic Zone of HIIT". High performance is not about shortcuts. It's about accumulating consistency over time. Not as attention catching, but it definitely works.

To sum up, it's mostly sessions of low intensity, with occasionally high sessions adjusted to the individual. Balance stress and recovery and consistency over all else. Now you know.

* Many gyms, fitness influencers and trainers get patients to do what is traditionally circuit training but call it HIIT. Circuit training is like 30 seconds doing push ups, rest a minute, go to another station and perform 30 seconds of high knee lifts, rest a min, 30 seconds of lifting dumbbells etc

HIIT stands for high intensity interval training. Or interval training for short.  Example, you run 15 intervals or repetitions of 400m with a one minute rest in between or the coach will say run 6 x 1km going every 5 minutes (meaning if you run your kilometer in 3:50 min, you get 1:10 min rest before starting again). You can also cycle intervals outdoors or on a trainer with your bicycle attached.

Circuit training does not sound sexy, but HIIT certainly does!

Reference

Sandbakk O, Tonnessen E, Sandbakk SB et al (2025). Best-practice Training Characteristics Within Olympic Endurance SpoRts As Described By Norwegian World-Class Coaches. Sports Med 11:45. DOI: 10.1186/s40978-025000848-3

Are Treadmill Calorie Counters Accurate?

My patient said he ran 20 km on a treadmill recently. He also told me stats like his average pace and treadmill incline of the run and calories burned. Since he mentioned about the calories he burned, I told him that they were not very accurate.

Different treadmill manufacturers will have their own formulas that they use for their treadmills, elliptical, X-trainer, stepper etc. Speed, treadmill incline, and distance are typically used to calculate how many calories you burned.

However, for a more accurate reading, your gender, height, weight, muscle, fat mass, heart rate and fitness levels are typically needed as well. Note that a higher heart rate may be associated with greater energy expenditure, hence a lower heart rate running at a certain pace means you are fitter and will burn less calories.

Heart rate is affected by temperature (of the gym), medication, food you ate, what muscles are being used and whether your run is continuous or in spurts/ bursts.

You may also notice that your run becomes much easier when you hold onto the hand rails while running. By taking some weight off by holding on to the rails, actual effort is reduced but the calorie counter does not account for that and will overestimate calories expended.

Treadmills and elliptical machines need to be calibrated regularly (especially in busy commercial gyms) otherwise the speed you may be running at may not be accurate. That discrepancy alone can influence the accuracy of the calorie count.

I could not find much research specifically on how accurate the calorie counts on treadmills. There was a 2018 study by Glave et al (referenced below) involving elliptical machines. Their study found that the calories burned were significantly overestimated. More than 100 calories were added for a 30 minute workout.

So take your exercise machine calorie counts with many grains of salt since they are definitely not accurate and may be way off in some cases.

You can certainly use a smart watch to track your calorie estimates too but even these tend to overestimate energy expenditure. My previous post covered that, but do note that fitness and smart watch technology is consistently improving so they may be more accurate now.

One can also use an online calorie counter to provide an estimate of how many calories you've used. Again it's just an estimate.

Remember not to totally rely on treadmill calorie counts or your smart watch to rule your workout. Sticking to your exercise plan consistently is what really counts, not just the numbers you see on the treadmill or elliptical machine.

Reference

Glave P, Didier JJ, Oden GL et al (2018). Caloric Expenditure Estimation Differences Between An Elliptical Machine And Indirect Calorimetry. Ex Med. 2:8. DOI: 10.26644/em.2018.008

Past Versus Present

Adizero PR (top) versus Adizero X Parley

I've always preferrred running in racing flats so I ordered the OG Adizero PR a few weeks ago when I saw them online. I'd worn quite a few pairs of those in the early 2000's when they were really popular. Actually, Adidas made a custom pair for me when I represented Singapore at the SEA Games triathlon event in 2005 (pictured below).

I did my first run in them on Friday 2 days ago. It was a terrible run! Compared to my previous Adidas racing flats, the Adizero X Parley (which I bought in 2023), I felt the hard ground with every single step.

Adizero PR

My calfs were sore and tired after less than a kilometer of running. Later, I went back to the Adidas website and realized that the Adizero PR's foam was EVA foam compared to the Parley's more advanced Lightstrike foam (pictured below).

Adizero X Parley

Meanwhile, have a look at the humble, really minimalist 1970 Onitsuka Tiger (now known as Asics) compared to the 2025 Asics carbon plated supershoe pictured below. One used for marathons back in the 1970's and the one used currently. The latest version is packed with space age technology. 

Those who raced marathons back in the 1970's used shoes with almost no cushioning, no support and definitely no energy return. The classic Onitsuka Tiger model has an almost zero drop profile and super thin outsole (to save weight). Runners back then needed super efficient running form/ technique, lots of grit and mental toughness since there was no technology back then. There will not be many runners who heel strike with these shoes. They will feel it straight away. Heel strikers back then were definitely 'handicapped'.

And guess what, these shoes are now still making the rounds as a casual sneaker and making Onitsuka Tiger / Asics lots of money.

Now in 2025, we have super highly stacked midsoles, super responsive PEBA foam, uppers that are  optimized biomechanically and carbon plates of course. These can offer runners with energy return on every stride, propulsion and fit designed to minimize fatigue over the whole marathon distance. Just like wearing a springboard when you run.

Today's footwear gives an undeniable edge to help you train and race and definitely run faster. Especially for weaker runners who cannot rely on their muscles as much and efficient running form to run injury free. Good to be able to run and not feel 'damaged' post run. 

I still prefer to be lower to the ground and more stable compared to feeling more 'wobbly' when the midsole is stacked higher. Definitely does not help when you have to turn around on a run or avoid a child on the pavement. I've treated many runners who have sprained their ankles as a result.

I probably will not run in super shoes yet. Call me old school (or OG- original gangster), but I still prefer to be lower to the ground. I prefer the newer versions of the racing flats using PEBA instead of EVA foam. But no highly stacked midsoles and no carbon plates. Not yet anyway.