New to optical heart rate monitors? You need to read this.

Time for an update

After nearly three years of wearing my Forerunner 230, I thought it was time to do an upgrade. For a while I had my eye on the Forerunner 235 but the price was never right. In the process, I had read multiple reviews and was pretty convinced it was the right watch for me... until I bought it.

After about a week of wearing it, I was utterly disappointed with the performance of the HR monitor and the battery life. And nothing I had read before warned me about it so I figured out it would make sense to write a piece in here so that other people may be aware before they take the plunge, especially now that the prices have dropped to under $170 as rumour has it that the 235 is on its way out.

Rather than writing a new review for an old watch, I'm going to concentrate on the HRM. First of all, yes, it is oh so convenient, especially if you've ever trained with a chest strap and you still have the the scars to prove it. But also, it's different technology and you need to understand it to make the most of it.

Chest strap vs Optical 

A chest strap measures your pulse via small electrical signals generated as your heart contracts. It then sends the information back to a connected device, usually, your smartphone. Optical monitors, on the other hand, use light (generally green) shone through the skin to detect blood flow through as bones, blood and skin reflect the light differently. The key takeout here is that both methods require a good connection (i.e. contact with the skin) to be effective.
That was my first disappointment. As a rule, I don't like wearing my watch too tight and my F230 was perfect in that sense. I could wear it whichever way I wanted. the F235 wouldn't take any reading accurately until I tightened it.

A tight watch is not enough

So I tightened the watch and still, my training session readings were all over the shop. Usually, it would record readings in Zone 5 as soon as I stepped out of the house. Enter disappointment number 2. No matter what pace I was doing, I was always overtraining as far as the Garmin was concerned. I had sessions where I wanted to scream and stamp on the bleeping watch! As it happens, it's not just a matter of wearing the watch tightly. You also need to ensure you're wearing it on a "flat" surface of your skin. For me, this meant wearing it about 2 fingers above where I normally wear any other watch. Other people claim it works best on the inside of the wrist. Some others say, it needs to be covered so the light bouncing from the skin doesn't get any external "noise".

The HR monitor will impact the battery life

So, Garmin tells us the battery life is about 11 hours of training or up to 9 days of normal wear... blah, blah, blah... the thing is, they phrase it in a way that you think, 9 days of normal wear? Yeah, that's what I'm used to with my current watch. Oh disappointment number 3... the optical HRM actually uses up battery like a demon if you combine 5 days of training and everyday heart rate tracking resulting in a measly 3/4 days' battery life.

In short

Once you get over all of this, the watch is actually fine. I'm learning to like it (not love it) and learning to train by heart rate zones.