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The Defined Letter · Issue 01 · October 2026

The Defined Letter

7 min read · Make a coffee.

Welcome to the very first Defined Letter: the good stuff, the overhyped stuff and one thing to try.

This week we’ve got a treadmill study so big it needed its own postcode, a peptide that’s far more famous than it is tested, and three running shoes that reviewers can’t stop arguing about. Settle in.

The big one: your engine might be the most underrated thing about you

Solid evidence

The story

Picture a treadmill test. You start at an easy walk. Every few minutes the belt gets faster and steeper, until you tap out. It’s one of the most honest fitness measures there is: how much work your heart, lungs and muscles can do before they say “that’s enough, thank you”.

So a group of researchers in the US went through the records of more than half a million adults who’d done exactly that test in Veterans Affairs clinics. Then they followed them for around a decade to see what happened to them.

What they found

Fitness was measured in METs (multiples of the energy you use sitting still). The pattern was strikingly consistent: the fitter people were on the treadmill, the lower their risk of dying during the follow-up.

The really interesting part: doctors usually estimate risk from a familiar checklist: age, sex, blood pressure, diabetes, cholesterol and smoking. When the researchers added fitness to that checklist, the predictions got noticeably sharper. Fitness told them something the usual numbers didn’t.

The authors’ conclusion is refreshingly direct: “Incorporation of CRF into routine clinical risk assessment frameworks should be considered.” (CRF is cardiorespiratory fitness, or your “engine”.)

Strength builds the chassis. Conditioning builds the engine. You want both.

The small print (we always read it)

This is an observational study. It shows a link between fitness and outcomes, not proof that getting fitter changes any one person’s odds. Fitter people may differ in other ways too.

It’s also worth knowing who was studied. These were US military veterans referred for clinical exercise tests, and the programme it comes from is overwhelmingly made up of men. So this isn’t a study of women, and we’d love to see it repeated in women.

What it does do is add serious weight to something coaches have long built programmes around: fitness is worth measuring, and worth training.

What it means in real life

Fitness isn’t a personality trait you’re born with or without. It’s a capacity, and capacities respond to training at every stage of life.

It isn’t about being slim or doing endless burpees. It’s how much work your body can sustain: carrying shopping up three flights of stairs, keeping up on a hike, finishing a session with something left in the tank.

You don’t need to love running. You need a regular reason to breathe a bit harder.

What we’d actually do

Here’s how our coaches would turn this into a week. None of it is medical advice; it’s training.

  • Keep your strength sessions. Two or three a week remains our backbone. Muscle is what lets you do the conditioning well.
  • Add one or two conditioning sessions. Make most of it “chatty” (a pace where you can still talk in full sentences): incline walking, cycling, rowing, swimming.
  • Once you’re consistent, make one session a little spicier. A few short hill efforts or harder intervals, with easy recovery between. Build up gradually rather than heroically.
  • Pick a benchmark you can repeat. Time a familiar route, or note how far you get in 20 minutes at chatty pace. Check it again in a month.
  • Respect the heat. In Dubai, early mornings, evenings or air-conditioned options all count.

If you have a medical condition, are pregnant or postpartum, or notice new symptoms, check with your doctor before ramping up.

Source: Medicine & Science in Sports & Exercise, via PubMed · Related ETHOS paper on the VA cohort

Hype or helpful? BPC-157, the internet’s favourite “healing peptide”

Mostly hype

Why everyone’s suddenly talking about it

If your feed has started serving you tiny vials, tidy syringes and confident people talking about “healing stacks”, welcome to the world of biohacking peptides.

Reviews published this year describe unapproved injectable peptides being pushed by digital marketing and social media, and sold through grey-market websites. They’re promoted for everything from recovery and fat loss to skin and longevity. BPC-157 is one of the headliners, usually sold as a way to fix sore tendons and stubborn injuries faster.

Where the idea came from

BPC-157 is a lab-made peptide (a short chain of amino acids), originally isolated from gastric juice. Yes, stomach juice. In animal studies it has shown regenerative effects across a range of tissues, including tendons. That’s why researchers find it genuinely interesting.

But a rat with a repaired tendon is not a person with a sore Achilles. Plenty of things that look brilliant in animals don’t work, or aren’t safe, in humans.

What’s actually known in people

A new systematic review went looking for every human study of BPC-157 ever done. It found three, with 30 people in total. None was well controlled, and the reviewers rated their certainty in the findings as very low. Their verdict: it shouldn’t be used outside proper, regulated clinical trials.

The agency lacks sufficient information to know whether the drug would cause harm when administered to humans. US FDA, on BPC-157

The rules, in plain words

  • In the US: it isn’t an approved medicine. The FDA has flagged possible immune reactions and impurity concerns, and has proposed keeping it off the list of ingredients pharmacies are allowed to mix.
  • In sport: it’s on the World Anti-Doping Agency’s list of substances banned at all times.

Our verdict

Very loud online, very quiet in human research. If recovery is the goal, the boring trio of sleep, sensible training load and enough protein has vastly more evidence behind it.

This is reporting, not a recommendation, and BPC-157 is banned in tested sport.

Source: Systematic review, via PubMed · Background review · Biohacking review · FDA · WADA list · Our longer explainer

Kit we’re eyeing: three daily running shoes, three very different personalities

Shoe reviews are like restaurant reviews: useful, entertaining and occasionally contradictory. Here’s what Outside’s testers and RunRepeat’s lab (they literally cut shoes in half) say about three of autumn’s big names.

ASICS Superblast 3

The one everyone wants to be friends with

Who it suits
One-shoe people (long runs, easy days, the odd faster session) happy to pay a premium price.
What reviewers loved
Outside named it the best overall daily trainer, calling it “soft and energetic” and versatile across paces. RunRepeat rated it “Superb”, highlighting exceptional shock absorption and the “best traction we’ve seen to date”.
What they didn’t
Outside flagged “noticeably loud footstrikes” and a ride that may feel too soft for fans of the previous version. RunRepeat flagged the price bump and limited breathability around the toes.

Mizuno Wave Rider 30

The reliable friend who’s had a makeover

Who it suits
Easy and moderate-pace runners who like a stable, cushioned ride without paying top-tier prices.
What reviewers loved
Outside picked it as its best-value shoe, describing it as “stable without feeling corrective”, with a smooth heel-to-toe roll. RunRepeat liked the softer foam, the stable ride and the improved grip.
What they didn’t
Here’s where it gets spicy. Outside found the thick upper “reduces breathability” (noted, Dubai) and said it’s not ideal for faster paces. RunRepeat was blunter about the bounce: “The energy return of the Mizuno Wave Rider 30 is simply disappointing, and there’s no way to sugarcoat it.” It also felt durability fell short.

ASICS Novablast 6

The fun, light all-rounder

Who it suits
According to RunRepeat, runners who land on the midfoot or forefoot, and newer runners who want one dependable shoe for most sessions.
What reviewers loved
It tops RunRepeat’s daily-trainer guide as “best overall”. Its review praises the lighter build, “great breathability for warm runs” and excellent durability.
What they didn’t
RunRepeat found it less stable than the previous version, suggests heel strikers may prefer other options, and notes the tapered toe box won’t suit everyone.

Our take: reviews make a brilliant shortlist. Your feet still get the final vote.

Source: Outside, Fall 2026 guide · RunRepeat reviews: Superblast 3 · Wave Rider 30 · Novablast 6 · Daily-trainer guide · No affiliate links, ever.

Try this week: the 20-minute “chatty cardio” benchmark

Pick something repeatable: incline walk, bike, rower or swim. Go for 20 minutes at a pace where you could still gossip in full sentences, and note how far you got.

That’s it. That’s your baseline. Repeat it in four weeks, at the same pace, and see whether the number has moved. If you’re new to this, start shorter and build up. In this heat, early mornings and air-conditioned gyms count just the same.

In other news

Promising

Morning person or night owl?

In a 12-week trial, people who trained at their personal best time of day gained about the same strength as those training at their worst. The best time to train is the one you’ll keep.

Source

Early days

Why women take creatine

A survey found women were more likely than men to take it for healthy ageing and less likely to take it for performance. They also felt less confident at the same level of knowledge. It’s about habits, not results, and some authors work for the supplement platform behind it.

Source

Early days

On a GLP-1 medicine?

A new review points out that the “lean mass” lost on the scale isn’t all muscle, and names protein and strength training as sensible allies. Medication questions go to your prescriber.

Source

Solid evidence

Where are all the women?

A review of 570 muscle-building studies found only about one in nine recruited women alone, and most of the studies that did include women didn’t mention the menstrual cycle. It’s improving. Slowly.

Source

From The DB Method

See you next Thursday,
The DB Method team

Friendly reminder: this is for education and a bit of fun, not medical advice. For anything about your own health, talk to your doctor. You’re getting this because you signed up at dbmethodcoaching.com.

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