The Best Heart Rate Strap : Comparing Scosche Rhythm+, Mio Link, 4iiiii Viiiiiva, Wahoo KickrX

The Best Heart Rate Strap : Comparing Scosche Rhythm+, Mio Link, 4iiiii Viiiiiva, Wahoo KickrX

I do a ton of sports tech testing. Some days it feels like I’m on a never-ending search to find the best heart rate strap. I’ve tested them all. However, straps are boring to video record so this will just be a text-based blog post. In short, here is what I’ve learned about HR data collection sensors in the past few years and thousands of hours of testing that I’ve done on myself and my athlete friends.

Screenshot 2015-01-13 21.07.08

Top to bottom: Garmin ANT+, Polar H7, Scosche Rhythm+, 4iiii Viiiiva, Wahoo KickrX


  • Viiiiva HR strap by 4iiii (EKG chest strap)
  • Mio Link Heart Rate wristband (optical/wrist)
  • Scosche Rhythm+ (optical/forearm or upper arm)
  • Polar H7 Bluetooth (EKG chest strap)
  • Garmin ANT+ HR strap (EKG chest strap)
  • Basis Peak (yes, it’s a watch – but it has built-in optical HR which it broadcasts on BTLE)


People have differing needs for their heart rate tracking devices. I mostly use mine to collect HR data when I’m under heavy training load so I can convert my workout data into a universal work score called hrTSS (HR training suffer score), which I do using an app called TrainingPeaks. So here are some things I look for in a strap to make it sustainable for me. Again, others may have different needs and use cases.

  • comfortable and easy to wear;
  • works in all training conditions (or as many as possible)
  • is multi-protocol (speaks both ANT+ and BTLE)
  • has a great battery life


4iiii Viiiiva HR strap: I love these straps. They have great battery life (months) on a single cell battery, have survived a ton of harsh training, and when one did fail, 4iiii immediately sent me a new one for free. This company was built by Kip Fyfe – one of the founding inventors behind ANT+. For a company with such terrible naming capabilities (4iiii? Viiiiva?), they make kick-ass stuff. Also, it’s dual-protocol ANT+/BLE which I think is mandatory these days.
Grade: A

Wahoo KickrX: I also like this strap. It’s comfortable (as far as chest straps go) and has the added bonus that it will record HR data even if the phone or watch is not around to record it. Then later, you can connect it to the Wahoo app and download the HR data for the workout. I suppose somebody might find that useful. I always have a data collection device on me like my Garmin 920XT or iPhone so I have not needed the memory feature. But it seems solid and the integration with Wahoo for post-event downloads is interesting. The issue is that you end up with HR data with no GPS data, which is sort of weird to me but I suppose somebody might have a use for that. Also, it’s dual-protocol ANT+/BLE which I think is mandatory these days.
Grade: A

Scosche Rhythm+: As far as optical HR straps go that strap onto the wrist, arm, leg, or where-ever, this is the best I’ve found. I’ve tested the Scosche on multiple athletes doing all sorts of crazy workouts including kettlebells, handstand pushups, pullups, sprints – you name it. And it is usually within 2-3% of the EKG type straps like the Viiiiva or Wahoo KickrX which in my books is damned good for an optical strap. I have three issues with the Scosche. First, the strap is the wrong material and the little bits of velcro fall off. Second, the thing is too thick. It needs to be much thinner. Third, like all optical devices, it burns battery fast. Since there is no battery life indicator on it, I can never know if it’s 10% charged or 95% charged or somewhere in between. I’ve had mine die mid-workout WAY too many times because I was not charging it after every workout. So I always feel like I’m playing Russian HR data roulette with this strap or I feel beholden to keep putting the damned thing back on the charger. This is just a byproduct of this technology approach. I think for many people who spend less time training in a given week, this is still a good option. And it works well for people who really don’t like chest straps (which is pretty much everybody). Also, it’s dual-protocol ANT+/BLE which I think is mandatory these days.
Grade: B

Polar H7: I have nothing against the Polar H7. As far as bluetooth straps go, it seems to solidly connect to almost if not all apps that need a BT HR strap. However, at this mid-point in the market when we’re still straddling ANT+ and Bluetooth LE and many users like me are streaming our HR to both an app on the phone (using a bluetooth HR profile) and also simultaneously streaming HR and maybe other sensors to our sport watches (mostly speaking ANT+), I don’t see the point in having a single-protocol strap. I think everything needs to be ANT+/BLE at this point to be competitive. If you already have this strap and/or only ever want to use your phone, then it’s a great strap.
Grade: C

Mio Link: I have tested this strap for months under many conditions and my overwhelming learning is that it’s unuseable except for mild exercise. In aggressive training, with highly variable workouts, (think Crossfit or other similar functional training with high interval work thrown in), it gives data that is anywhere in the range of +/- 40% of what the EKG strap will pick up on the same athlete at the same time, doing the same work. I have documented this in hundreds of photos of workouts we’ve done. My athletes also hated the strap design and found that it was too restrictive (if it was on tight enough to pick up data) or that it was just in the way. Overall, I would never recommend this for any active athletes.
Grade: D

Basis Peak: One of the more amazing and interesting things that the Basis Peak watch does, that very few people even realize, is that it acts like an optical HR monitoring strap and it broadcasts your heart rate on BTLE, using Bluetooth GATT, so that your iPhone or Android phone can pick up the BTLE HR signal and feed it into your other apps like Strava, Wahoo, MapMyRun or anything else that can listen for BTLE HR devices. But there’s a problem. I’m going to cover this in more detail in a future post but the data that is collected during exercise is still so bad, that all it’s doing is broadcasting either NO data or very inaccurate data. So, while it’s great that they put this feature in, bad data is still bad data and they’re making it available to your other applications. I’ve regularly seen my EKG-strap workouts show 90 min at an avg 120 or 130 bpm but the HR data coming from the Basis will say the workout (window) was in the 80-90 bpm range because there are so many drop-outs in the data. The more aggressive the exercise, the worse this is. Basis promised to fix this for years and even promotes the Peak as being “a heart rate tracker you can count on – even during exercise”, it’s not true. I’m pretty sure that the writers who wrote the glowing fan-boy posts at Forbes, Gizmodo, and PC World did not use their demo units for any aggressive workouts. If they did, they wouldn’t have called it “The best activity tracker yet!” or “the band to buy if you obsess over heart-rate and sleep tracking.”
Grade: F


I’m interested in seeing how some of the upcoming clothing based HR collection tools such as Athos or OmSignal work out, but honestly I’m much more interested in products like the  AmpStrip that will be able to attach to the body and collect continuous data streams for analysis in real-time and after the fact. Stay tuned for a slate of these to arrive in 2015/2016.


Edit 1: added paragraph/score for Polar H7.