Thank you to:
@NSERC for funding this work
Our incredibly team at @usherbrooke.bsky.social and CRCHUS
The reviewers for their very helpful comments that did improve the manuscript.

and more importantly congratulations 🎉to
@lauralynedumont.bsky.social for leading this challenging study!

📕 One more closing note:

Those who continue to propogate the flawed idea that an 'individulized cooling protocol' is the best way to activate BAT.

Here, we built a skin clamping system to individualize heat loss. Heat produciton was MORE variable than using a fixed temperature for everyone...🙅

📕 In closing:

✔️Cold-stimulated 🔥 is driven by muscle, including shivering and possibly non-shivering mechanisms in the muscle (not measured here).

✔️ Adipose tissue require a minimal cold stress to activate lipolysis, but it is either on or off.

✔️BAT 🔥 is therefore = to its thermogenic capacity.

🙋Is this only limited to BAT though?

6️⃣ WAT lipolysis also did not respond in a graded fashion - it increased in the cold but the magnitude of the lipolytic response was not dependent on skin temperature.

7️⃣ This implies that another 🔥 mechanism, GL/FA cycling also ⬆️, but was not dose-dependent.

🙋What about BAT, what about BAT!

5️⃣Importantly, BAT perfusion and oxidative metabolism increased in the cold, but did not increase as a function of skin temperature.

In other words, with a minimal stress to activate BAT, 🔥 is either on or off - there is not a graded response!

🙋Yes, but how does this impact myocardial 💖 metabolism?

4️⃣The perfusion and oxidative metabolism of the myocardium, determined by 11C-acetate PET, only increased at the colder skin temperature and primarily in women.

This represents the first measurement of 💖 metabolism in cold-exposed humans.

🙋 What about shivering?

3️⃣ Shivering intensity ⬆️ as function of skin cooling, with women shivering to a greater extent than men for the same skin temperature.

Women appeared to recruit a greater #️⃣ of motor units than men, reflected by the ⬆️ in both intensity of continuous and burst shivering.

1️⃣ Heat production 🔥 increased as a function of mean skin temperature, in both men and women.

2️⃣ ♂️♀️ differences in 🔥 are driven by differences in body mass. The cold-induced increase in 🔥 did not differ between the sexes.

We were then interested in understanding how different organs respond to different cold stimulations, particularly adipose tissue (brown and white adipose tissue).

So we took advantage of our closed-loop temp control system to clamp the mean skin temp of our participants to either 30°C or 26°C.

This was a follow-up on a paper we published recently (pubmed.ncbi.nlm.nih.gov/35411809/) which investigated the variability in shivering response when clamping mean skin temp to 31°C, 29°C or 27°C.

As expected:
✔️ Heat production ⬆️ as function of skin temp
✔️ Shivering paralleled this increase in 🔥

Hi Monica, I would love to be added to this feed. I study thermal physiology and energy metabolism mainly in humans.

My Google Scholar profile is: scholar.google.ca/citations?us...

Thank you!

Anyone interested in BAT research is encouraged to read through this insightful perspective from some of the top BAT researchers in the world for valuable insight on some of the matters of debate and the experiments required to address them.

The latter has been the most problematic method used in human BAT research because:

1️⃣ It's not reproducible.

2️⃣ Self-perceived shivering is not 🟰 to actual shivering.

3️⃣ It fabricates variability

4️⃣ Creates false dichotomy of BAT+ vs BAT-, which really means adequately cooled vs. not cold.

1️⃣ Fixed temperature vs. Personalized cooling - your research question will determine which is most appropriate.

2️⃣ If personalizing the cold, personalize using a reproducible metric: either heat loss or heat production.

3️⃣ DO NOT base stimulus on cold perception or visual detection of shivering.