4iiii Viiiiva V100 Bridging Dual-Band Heart Rate Monitor Review

4iiii Viiiva V100 Heart Rate Monitor Bridge
4iiii Viiiva V100 Heart Rate Monitor Bridge

Readers of this blog will recognise my unhealthy interest in heart rate monitors, noting my rising excitement over the last year or so with the MIO Link, Suunto’s SMART Band and the Wahoo TICKR-X. All great products but serving differing needs.

Well, things have just got better/different with the 4iiii V100 AND there is more exciting stuff to come down the line.

Scenario: You’ve just discovered a problem with your Garmin. Maybe you lose all ANT+ sensors at certain times in triathlon mode. (A known bug in earlier firmware releases of the 920). But. The BIG BUT is that you have to return the device and you have a longstanding ride with some mates this weekend. You’re a bit of a sports data geek and would love to have the power/hr and cadence info for the record. Maybe, like me, you use power or HR to track your overall training load so a long ride will be an important chunk of HR/power data to ensure you have recorded properly.

Of course you can use your smartphone to record ‘the trip’ but that will be just GPS/speed data.

Fear not. 4iiii is here.

4iiii Viiiva V100 Heart Rate Monitor Bridge
4iiii Viiiva V100 Heart Rate Monitor Bridge on a Garmin Strap

4iiii’s V100 can take all those ANT+ sensors and rebroadcast their signals as Bluetooth Low Energy (BLE/BTLE/Bluetooth SMART) for Strava and other apps.

The V100 doesn’t convert the Garmin heart rate monitor’s signal as the V100 is a heart rate monitor itself. The V100 can also broadcast BLE/ANT+ HEART RATE simultaneously.

It’s pretty much as simple as that.

OK, it’s a slightly contrived example. Another example could be that you simply prefer the large screen navigational interface offered by the STRAVA/smartphone combination you already have. Strava also has lots of great in-exercise functionality that you want to use on your ride. Yet you are perfectly happy to stay with your Garmin for the turbo work. Sure, you could change all your sensors JUST for STRAVA but changing the power meter in particular would be expensive for most people.

So where’s the catch?

There’s no real catch!

I’d just be aware, as the following diagram shows, that the 4iiii bridging device only works for re-broadcasting your ANT+ sensor data TO SMARTPHONE APPs. The data may NOT be able to be received by some POLAR or SUUNTO sports watches because of those vendors’ restricted implementation of the BLE protocol. As Per says below, the Polar V800 works and the Polar M450 bike computer works fine for me for cadence and power.

4iiii Viiiva V100 Heart Rate Monitor Bridge
4iiii Viiiva V100 Heart Rate Monitor Bridge

So if you are looking for a solution that enables you to use BOTH ANT+ AND BLE SPORTS WATCHES then the only way forwards is to choose accessories that broadcast both frequencies ie both ANT+/BLE. Those that fulfil that criterion are the 4iiii PRECISION power meter, the WAHOO BLUE SC Speed & Cadence sensor and others such as by Powertap or adidas.

Creating a Bridged Device

This is the meat of why you are probably reading this review. Having earlier completed a similar process with the MIO Velo I can say that the 4iiii V100’s bridging process pretty much worked first time and was very straightforward.

Have a quick glance at this slideshow:

So: wear the belt; open the iOS/Android app; activate your ANT+ sensors (spin the pedals/wheel); and then pair the devices that are found. Simple. You can then calibrate wheel circumference to calculate speed from wheel revolutions (mostly indoor usage).

The first step was to pair an ANT+ power meter such as the 4iiii PRECISION power meter (or any other ANT+ power meter, actually the PRECISION is dual band). However I paired an unusual ANT+ power meter alongside the new Garmin speed-only sensor.

Then I tried the Garmin Cadence-only sensor. I had an issue with the new Garmin cadence-only sensor. Whilst the cadence-only sensor did work, the power signal would drop out when cadence data started to be produced (I tested on two bikes).

I didn’t get to the bottom of why this happened. Perhaps it was the ‘unusual power meter’ or perhaps it was the relatively new cadence sensor (not the GSC-10 sensor that most people have). [Edit: it may be the presence of 2x cadence devices which seems to cause several other devices problems too].

FYI: The unusual power meter was, in fact, a rather neat device. I have the SportTracks LIVERECORDING plugin on a PC. It takes speed data from the Garmin speed-only sensor (or GSC-10) and then converts it into proxy power using a speed:power curve specific to the turbo trainer you are using. It then re-broadcasts that power signal out from the PC via a USB ANT+ dongle. My Garmin 920XT and the 4iiii Viiiiva V100 both picked up this rather convolutedly-derived power signal…a good sign that the V100 will pick up a more normal one that you probably have. Please note that not all vendors strictly adhere to the BLE/BTLE and ANT+ specifications and if those specifications are not adhered to then there is a chance your sensor may be incompatible.

Using the Data In Apps

There are lots of compatible apps such as STRAVA, ENDOMONDO , RUNKEEPER, RUNTASTIC, the 4iiii APP and others.

First up I did a quick test in the 4iiii app.

4iiii APP
4iiii APP

Cadence is not displayed for the reason stated earlier. But here’s proof that it does work.

4iiii App Cadence
4iiii App Cadence

I managed to get things working in the WAHOO app but there was a VERY significant delay in the app recognising the sensors. It took two and a half minutes! In defence of the WAHOO app I did have over 12 HRMs paired and that may have been a contributory factor. (Edit: This same delay also happened with the Wahoo RFLKT+ and so may be app-related)

Moving swiftly to STRAVA I encountered an immediate error. This is an iOS setting error and once enabled STRAVA works fine. You may well encounter this error in indoor mode if GPS is disabled on the ipad/iphone and that is why I have left a reference here.

STRAVA - Background App Refresh Disabled
STRAVA – Background App Refresh Disabled

So here we go, STRAVA recognises the new ‘Bluetooth’ Power Meter that I have just created. Super cool.

Running Apps

I will update this review when I use a running footpod in earnest. The following quick test, however, showed that a Garmin footpod can send running cadence data (spm)through to the 4iiii app. Quite equally any other vendor ANT+ footpod would have worked, such as 4iiii’s STRIDE footpod.

4iiii Viiiiva V100 Running Cadence
4iiii Viiiiva V100 Running Cadence

The 4iiii App

Another great feature of the 4iiii app is that it can export .FIT formatted data. This will have ALL the proper bits in it. For example GPX files do not have laps and TCX files do not have HRV data. So FIT is the way to go.

Indeed if the 4iiii Viiiiva V100 could cache data then swim-based HRV data could be produced and exported to FINALLY complete the missing link in Garmin’s HRV-data-for-triathlon ecosystem.

Currently it is convolutedly possible to get swim data into the Garmin ecosystem using Suunto’s SMART belt or WAHOO’s TICKR-X but both only support TCX export of data and so HRV data is missing.

In theory the 4iiii app can now be uninstalled as the pairing/bridging information is stored in the V100’s pod. I didn’t test that.

HR Accuracy


  1. 30 minute steady-state: Garmin 920XT+4iiii V100 vs Polar M400 + Polar H7 ie ANT+ vs BTLE/BLE two tests running simultaneously
  2. 1 minute HRV snapshot reading using Elite HRV iOS app: 2 consecutive tests both  using BTLE/BLE. 4iiii V100 vs. Wahoo TICKR-X vs. Polar H7 vs. Suunto SMART Belt. This test had all the pods using the same Garmin Belt/strap (it’s prettier).


1. Tests against a Polar H7 for accuracy of HR showed no discernible difference between the two devices, which was as I expected.

4iiii Viiiva V100 Heart Rate Monitor, Polar H7, Wahoo TICKR-X, Suunto SMART Belt, Garmin HRM-RUN
4iiii Viiiva V100 Heart Rate Monitor, Polar H7, Wahoo TICKR-X, Suunto SMART Belt, Garmin HRM-RUN

2. The 1 minute snapshot is a good, non-scientific test as the HRV app gives a single figure ‘answer’, aiding comparison. On the downside I could only do one test at a time. In my experience HRV readings start to go awry as the device’s battery deteriorates over time, so be aware of this if you do similar tests yourself.

Here are the results. My caffeine-induced, resting HR in each was about 50bpm.

TICKR-X: 70, 72, 71

Polar H7: 72, 71, 72

4iiii V100: 72, 70, 71

Suunto SMART Belt: 69, 71, 71

They look pretty similar to me.


Just in case you don’t know what HRV is: HRV looks at the variability of your heart rate from one beat to the next. You could have 60bpm every minute throughout the day but your HRV for each of those minutes could be quite different. I’m confusing you, sorry! If you train more than 6 hours a week you should learn a bit more about HRV. Mr Google can help as can this site and many others.

The reason I used HRV in this test was that it is measuring something that requires more accuracy than just the average number of beats in a minute.

Back of the PODS

And just for completeness here is an image of the back of the HR pods…riveting stuff 🙂 Arranged in the same order as the previous image. There’s a bit of rust on the Garmin which I’ve just noticed. It’s quite new as well. Hmmmm.


Strap Compatibility

In general the pods all seem to fit each other’s straps and the previous image suggests just that. The Suunto will clearly not fit the others and Polar’s strap sometimes has issues with non-Polar pods.

4iiii's V100 on the new Garmin HRM-RUN's strap
4iiii’s V100 on the new Garmin HRM-RUN’s strap

As I said above, I used the Garmin strap. If you really think that Polar’s strap (minus pod) is the best on the market, as seems to be the prevailing view circulating the various forums, then feel free to use that. I prefer the Garmin one as it looks nicer and it has 4x sensing pads on the strap which might help accuracy or longevity. The ‘more is better’ rule must surely apply here to sensing pads as would it equally apply to French fries.

I’m joking. Although there may be an element of truth in that.

The 4iiii strap that is shipped with the 4iiii pod is more like the Garmin strap from a couple of years back. Nothing noteworthy.

Performance Over Time

On a slightly more serious note, many people experience deterioration of the HRM’s performance over time. I’m not sure that anyone really knows why but we all agree that the deterioration IS annoying. Lessening charge in batteries is, for sure, a contributory factor but degradation of the physical structure of the strap and/or the pod’s shell could also be an issue; as could many factors pertaining to the usage environment (static, moisture levels, temperature, wind chill).

My tests took place over one day so I can’t guarantee the longevity of 4iiii’s device compared to the others. But bear in mind with 4iiii or any other strap manufacturer that it may not be a faulty pod that causes your problem. It could equally be the strap’s deterioration or other factors.


Overall I was pretty impressed. From a personal perspective I want the tantalising promise of HRV data from swimming to be fulfilled and I hope that 4iiii will be the first to do that by enabling the FIT export of cached HR swim data.

I’m in the minority on the swimming, I imagine. Very many of you will be interested in converting power and cadence ANT+ data into BTLE/BLE for your smartphone and probably for the STRAVA app on your smartphone. Despite Garmin’s recent Strava partnership, I suspect that Strava will be the leader in ride-based functionality for some time to come.

For the runners out there the need to get running cadence and speed from ANT+ to BTLE/BLE is more limited I imagine. Yes it would be nice to do; even necessary to do if you live in a cold country for most of the year. But in reality you could just buy an extra BTLE/BLE footpod to give you the desired data. At least the V100 gives you an alternative.

Triathletes? If you are thinking of migrating your sensor usage when going from Garmin to Suunto/Polar watches then the V100 may not help you out, I’m afraid. Not all BTLE/BLE watches fully support the BTLE protocol and so may not receive the data. So, at present, only compatible smartphone apps on iOS/Android are sure to work. As Per says below, the Polar V800 works.

Black Friday 2015AmazonUKAmazonUSA
4iiii Viiiiva V100 HRM£79.99Link$77.64Link
4iiii Viva MiniTBC
SMS Bio Sport Ear Bud£40.97Link$69.99Link
Garmin Heart Rate Monitor (Hard)£31.00Link$39.09Link
Garmin HRM-RUN (Soft)£51.36Link$99.99Link
Garmin Premium (Soft)£31.89Link$39.99Link
Garmin HRM-Swim£76.00Link$98.99Link
Garmin HRM-Tri£96.52Link$129.99Link
Jabra Sport Pulse£99.00Link$123.10Link
LifeBeam Smart Helmetn/aLink$185.49Link
MIO Fuse£94.95Link$129.95Link
MIO Link£58.95Link$61.51Link
MIO Velo£84.35Link$111.19Link
Polar H6£54.50Link$42.99Link
Polar H7£37.49Link$51.45Link
PowerTap PowerCal ANT+£104.49Link$95.99Link
PowerTap PowerCal Bluetooth£87.53Link$95.99Link
Scosche Rhythm+£70.00Link$79.95Link
Suunto Smart Belt£43.68Link$54.91Link
Under Armour Armour39$62.99Link
Wahoo RFLKT£71.99Link$89.99Link
Wahoo RFLKT+£79.99Link$128.57Link
Wahoo TICKR£44.14Link$59.85Link
Wahoo TICKR-RUN£64.99Link$71.92Link
Wahoo TICKR-X£79.90Link$99.90Link

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6 thoughts on “4iiii Viiiiva V100 Bridging Dual-Band Heart Rate Monitor Review

  1. The viiiiva bridges the Ant+ signal from my SRM power meter perfectly to my Polar V800 as well as cadance and speed.

    1. Anyone had any experience of the Viiiiva with a Suunto Ambit3 e.g. bridging Ant+ signal from a power meter to the A3 using Bluetooth?

  2. Can one use an ant+ footpod through the viiiiva heart rate to do treadmill runs?

    I can see the cadence and heart rate directly in the strava app. But strava does not have a calibration capability…. will it calculate the distance?

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