ASSOS X WHOOP: Butt-measured HR on Whoop-branded, ASSOSS UMA GT C2 cycling bib shorts

ASSOS X WHOOP UMA GT C2 cycling bib shortsASSOS x WHOOP Mille GT Bib Shorts

These are perhaps the world’s first smart cycling bib shorts, or maybe the second or third if you include discontinued products like Incus Nova. Despite the excitement of relatively new technology, I was more interested in measuring HR on my butt :-). Someone had to. I stepped forward and took one for the team.

WARNING: There will be pictures of my lycra-clad butt. You might want to click away while you can. There’s a helpline number at the end for any of you who are traumatised. Sorry, I’m nice really.

This article reviews the shorts and looks at the accuracy of the Whoop device in the unique wear position offered by the bib shorts.

Must Read: Is WHOOP Accurate? Detailed WHOOP 4 Review

FYI: Free gift, unpaid

ASSOS x WHOOP – Background

First up the ASSOS brand is an excellent one. They are my preferred brand of cycling shorts, ASSOS is excellent quality and my other 3 pairs of ASSOS shorts are very comfortable even for rides over 100 miles, as are this pair.

WHOOP apparel includes lifestyle and functional clothing with a special pocket to slip your WHOOP into and still record HR – be that on your biceps, calf or…BUTT. The apparel is on the pricey side but is of excellent quality. The biceps sleeve is the best way to ensure you will get accuracy during land-based sports with your WHOOP.

In May 2024, WHOOP announced a partnership with ASSOS for cycling gear. I got a free pair and here is my write-up.


Whoop does not specify the pad type or thickness. However, the corresponding model on the ASSOS site has the thicker 11mm pads as shown below and this seems to be the same. More expensive ASSOS bibs have a thinner pad.

ASSOS X WHOOP UMA GT C2 cycling bib shorts pad detail

The shorts and pad are comfortable on 100+ mile rides for me. Well, it was on the one I used it for, plus it was equally as comfortable on shorter 1- to 4-hour rides.

The pads on cycling shorts always get damp but this and all similarly priced competitive models will nicely wick sweat away.


The X-Frame straps are 3-4cm wide, well made and attached to the main body of material. Of course, they are comfortable.

I’m assuming a snug fit is important here for Whoop as the straps will help keep the waist material in a consistent position thus maximising the quality of the HR signal.

Zero Pressure Waist

The waist area is only mildly elasticated. this helps comfort and helps for toilet breaks, at least for guys.

This is the same degree of ‘grip’ as on my other ASSOS shorts. It works great. Although as said in the previous section, for Whoop in particular the butt material needs to be static. Whoop doesn’t noticeably move in position if the straps aren’t used but I will always use the non-detachable staps regardless.

Thigh Fabric – 429

The 429 fabric used throughout the short’s construction is compressive, thin, strong and wicking. For me, the correct size is comfortably tight.

You might want something thicker for winter use and non-Whoop options from ASSOS include protective padding for off-road and higher UV protection.

ASSOS X WHOOP UMA GT C2 cycling bib shorts leg grippers
Leg Grippers

Ultra-Light Leg Grippers

This is a 6cm grippier section at the end of the shorts on the thigh. It stops the shorts from rolling up when cycling. It works.


Sizing ranges from XS to XXL in both men’s and women’s fits, also with an XXXL in men’s. It’s only available in black.



I am a medium size and the sizing for me was identical to normal ASSOS kit. Here are sizing guides in CM/INCHES if you are unsure. It is important to get the right size.



Product Details


  • 80% Polyamide, 20% Elastane
  • RX EVO lightweight insulation and high breathability
  • Three-layer perforated foam increases breathability and eliminates excess weight
  • Washing a garment means putting stress on fabric and seams. Therefore, wash cycling garments separately from other clothes/accessories to prevent friction.
  • Before washing, turn the garments inside out (seams on the outside).
  • Machine wash is possible but always use a wash bag, a delicate cycle and lukewarm water (max. 30 ° C).
  • Do not use bleach or softeners. Use a mild liquid detergent only. Do not soak, wring or rub. Do not spin after washing. To remove excess water from your garment, gently squeeze by hand.
  • Dry garments flat or hanging, but do not tumble dry.

Note: To stop your sports clothes from smelling you should either immediately wash them once finished cycling or, if that’s impractical, dry them immediately. This stops the bacteria from doing their stinky stuff.

Other Notes

The Whoop pouch comes with a piece of plastic inside it. On the piece of plastic, it clearly says “REMOVE ME”. You know what to do. I know I have my A-Team reading today.

The top of the pouch as a small velcro flap that securely keeps Whoop inside. That seems to work perfectly, however, on the occasions I put Whoop into the pouch when wearing the bibs, it often popped out during the insertion process. Much better to put it in beforehand.

The documentation says to remove the straps and metal bits from Whoop before putting it in the pouch. I’ve found it is OK to leave the metal clasp (the bit which attaches to the pod with the two pins)

A new version of Whoop (Whoop 5.0) is rumoured to be later this year. Owners of Whoop apparently will hope that the size of Whoop is unchanged so that it fits into the existing pouches in the apparel. FWIW I think it highly unlikely that any new iteration of Whoop will be too large to fit in the apparel pouches.

HR Cycling Tests

Whoop broadcasts HR as a Bluetooth sensor, which can be picked up by most cycling computers or your phone’s cycling app when on your handlebars.

I did a 4.5-hour indoor ride comparing Whoop to Polar SENSE, Apple Watch and Garmin HRM-PRO+. Whoop was recorded by my handlebar-mounted Garmin Edge 540 , position is relevant as the signal has the obstacle of my body to pass through to get from the Whoop on my butt to the Edge.

I stopped to get some food in the middle of the workout and Whoop lost the signal to the bike computer when I wandered off. So I’ve cut out the before-lunch and after-lunch sections. As you can see here it’s as close to perfect as it needs to be, I was expecting much worse than this and have double-checked the sensor pairings…it’s correct data.



Outside it’s not good, as shown below. I assume the signal cannot reflect off any walls as there aren’t any, so the signal has to pass through my body but can’t. there is also FAR more vibration and body movement when riding outside. Hence the incorrect readings.


This ride had a decent first half albeit with a significant error but the post-coffee bit was pants. Literally and figuratively.



Now, I have had various compliments over the years linked to my pert butt. I don’t want to go into too much detail here but suffice it to say it doesn’t wobble too much and that should be good for HR accuracy. If you have a butt of the more wobbly variety then maybe the extra fat will make the accuracy better or worse…IDK. It does seem that skinnier WRISTs, like mine, get worse optical HR results than chubbier ones. Maybe the same applies to butts. IDK. I’m not an expert in that particular area of optical HR accuracy and don’t want to be.


Take Out: My Detailed Whoop Review has LOTS of test results and my earlier conclusion was that it is accurate when worn correctly. Correct to me means on the biceps. You risk inaccuracy with any optical device, including Whoop, if you wear it anywhere else, including on your butt!


Take Out

Excellent bib shorts. You can easily buy other designs of bib shorts from ASSOS for twice the price or a bit less but they won’t have the Whoop pouch. I can’t see any need to pay twice the price. Even though the ASSOS-Whoop collaboration is not cheap the price is not too bad compared to the competition. I was planning to use the word ‘reasonably priced’ but didn’t.

The same degree of excellence can’t be applied to measuring HR on your butt. I’ve done similar tests on Whoop’s speed shorts and the scientific community has not coalesced around the butt as a place to accurately measure HR for a reason. It’s not a great place. It’s kinda perhaps vaguely an OK place if you really don’t want to wear something on your wrist or chest. In any case, maybe you’ll get better results than me optical HR varies between individuals and how they use it.

I *DO* plan to use these bib shorts with Whoop a lot. I just don’t want yet another device (Whoop) on my wrist and the strain/load that Whoop subsequently calculates probably won’t be a million miles off. That said, for accurate pacing by heart rate I’ll have to use a chest strap.

Talking Point: we tend to cycle in groups and we tend to cycle a lot behind other people. The Whoop pouch will definitely draw your friendly neighbourhood drafter’s eyes to your butt. whether that’s a good thing or not I’ll leave it up to you to decide. Either way, it will definitely be a talking point and definitely a great move for Whoop to get its branding squarely in front of your buddies’ field of vision.

TL;DR – Good quality apparel, dubious HRbutt accuracy

Get Yours Here



ASSOS X WHOOP UMA GT C2 cycling bib shorts full product overview

Wow! Coros DURA cycling Computer pictures leak


[Photo Leak] Coros Dura – Bike Computer – Coming june 2024

Reader-Powered Content

This content is not sponsored. It’s mostly me behind the labour of love which is this site and I appreciate everyone who follows, subscribes or Buys Me A Coffee ❤️ Alternatively please buy the reviewed product from my partners. Thank you! FTC: Affiliate Disclosure: Links pay commission. As an Amazon Associate, I earn from qualifying purchases.

3 thoughts on “ASSOS X WHOOP: Butt-measured HR on Whoop-branded, ASSOSS UMA GT C2 cycling bib shorts

  1. This makes me wonder how effective it might be to use a Polar OH1 (or Coospo or Scosche) optical sensor in much the same way. Just jam it down on the back of the hip or on the butt cheek and let the bike shorts compress it in place. I still wear chest straps on the bike because my optical sensor on my preferred location of the forearm “jiggles” too much while riding and recorded HR suffers as a result.

  2. OH1 is pretty small so you’re probably right. Btw I personally moved from a longtime Scosche user to a Coospo HW9 based on one of your reviews and I have been very pleased. So much so in fact when I lost my original a few weeks ago I immediately bought a replacement. The coospo would probably work pretty well in this application. I sometimes get chest strap blowups due to static electricity or being overloaded with sweat or SOMEthing, so I’ll have to test it out.

Leave a Reply

Your email address will not be published. Required fields are marked *