kyriakosel

Founder here

We worked on a publication for NPJ biological timing and sleep

A few things that are surprising from the research

- sleep duration decreases by 4.4 minutes for each additional hour of daylight

- The effect didnt get much stronger at higher altitudes (even though daylight swings are much larger)

Plain English summary here

https://tryterra.co/research/terra-research-nature-publicati...

great

that would be interesting to study - let me follow up on this

anecdotal -but- it took me 6 months after covid for my breathing rate to go back to normal, and to be able to do consistent max our efforts of >190BPM for >5 seconds like previously

indeed - fixed now, let me know if you can see it!

Cyprus summers are like 45C and its almost like a sauna :)

i was mostly refering to humidity/duration/temperature given that most devices do not report back these values

it works for me - what browser are you using?

Fair flag: 256 users, 59k days

we agree - but thats not that simple :)

Agreed - one is muscular/metabolic demand, the other (sauna) is thermoregulation.

Agreed on the long-term effect too: doing a study on long term health is a completely different story

Author here. Methodology upfront because I'd ask the same things:

Data: daily records from wearable users who logged sauna sessions via connected apps. Within-person design — each user is their own control, comparing their own sauna-day nights against their own non-sauna-day nights. No cross-user comparisons.

Stats: paired t-tests, FDR-corrected p < 0.05, Cohen's d > 0.2 threshold for "meaningful effect." Anything below d=0.2 we don't report as a finding.

What we measured: minimum nighttime HR, max and average HR, HRV, activity minutes and distance, menstrual cycle phase (for female subset).

What we found: - On sauna days, minimum nighttime HR drops ~3 bpm (~5%) vs. the same user's non-sauna days. - Effect survives controlling for activity level. It's not "sauna users just exercised more that day." - Strongest hypothesis: elevated parasympathetic tone from the post-sauna cooling phase carries into sleep. Consistent with heat-stress physiology literature. - Sex difference: for women, the nighttime HR effect only crosses the d > 0.2 threshold during the luteal phase. No meaningful effect during the follicular phase. We didn't expect this; worth replicating.

What we can't control for: - Sauna type (dry / infrared / steam), duration, temperature. Not captured. - Dose-response. We don't know session length per user. - Timing of sauna relative to sleep. - Reverse causation: people may sauna on days they already feel recovered. - Selection: wearable users who bother logging sauna are a health-conscious cohort.

What surprised us: the effect is larger than what we see for comparable-intensity exercise days. If you treat nighttime HR as a parasympathetic recovery signal, sauna beats a moderate workout on the same user. Not what I'd have predicted.

certainly - their ecosystem is a big reason why they are here

There are too many books that I would want to listen to and don't have audiobooks. i'd definitely give it a try with that in mind

TERRA (YC W21) | LONDON | Full-Time/On-Site |

Terra is an API for apps to connect to wearables and sensors. We are Backed by YC, General Catalyst, and many more

Positions: | AI Engineer | Software Engineer | Growth Engineer | Product Engineer

I'm shocked by how realistic it sounds. Can we embed it in our website/blog ?

Nice one guys! Congrats on the launch!

On the other hand, Tsitsipas probably not, unfortunately

TERRA API | Multiple Roles | Full-time (London) |https://tryterra.co/

Terra (YC W21) is an API that makes it easy for apps to connect to wearables

Some of the best health apps in the world are using our multiple products, such as the:

[1]: API https://tryterra.co/products/api

[2]: SDK https://tryterra.co/products/sdk

[3]: DOCS https://docs.tryterra.co/

We are hiring from multiple positions, from Full Stack, Front End, Back End, Growth and more!

Find more here:

https://www.ycombinator.com/companies/terra

TERRA | Full Stack Engineer, Growth Engineer, Integration Engineer, Product Designer, Operations | ONSITE | London,UK

TERRA (https://tryterra.co) is an API that makes it easy for apps to connect to wearables

You can find all the roles here: https://www.ycombinator.com/companies/terra/jobs

You can use Terra (tryterra.co) to access your garmin data !

are you connecting to wearables? if so check Terra! https://tryterra.co

How does the API work ? is it webhooks ?

Looking forward to testing this

Seems like a fantastic solution - congrats

thank you!

That's awesome, i reached out :)

Right, we saw many things with the accuracy of whoop, but hopefully their new one is better than before.

We will speak to their team for a partnership

Thats awesome !

Technically the onboarding takes 5 minutes - since we work with webhooks, and we just need a callback url from you ! You receive a PUSH whenever an activity is generated.

we are a widget + api that can be embedded inside your app.