While I'm not as familiar with how Crossfit classes are structured, I am familiar with using a heart rate monitor for barbell training. I used to use it to time when I should start the next set so that I could keep the training pretty dense, but be relatively assured that I would hit the required reps. I'm getting back to using it to time when to do the next round in my supersets. As a result, I do have some insights that apply here.
While I'm waiting for the 3-2-1 count down I'd rather not be messing about pressing buttons to start recording.
This can be solved relatively easily by using the "lap" feature on the heart rate monitor. Just start the heart rate monitor before class, but just before and after an exercise starts hit the "lap" button. The analysis software remembers these so you can easily see what's happening during a set and the rest period between. On my wristwatch, the same button that starts recording the heart rate doubles as the lap button. Just tapping it is enough. Most other HRM watches should behave similarly.
When looking at the charts afterwards, it's actually pretty easy to see the difference between work and rest, so I started only hitting the lap button when starting a new exercise. You should see a sustained spike in heart rate while you work, and then it return to a higher baseline while you rest.
When working with a bar (e.g. multiple cleans) I run the bar down very close to my chest which knocks the sensor of a regular HR monitor off.
This is a tougher challenge. It's essentially the choice between good technique and measuring the heart rate. Unfortunately none of the wrist-only heart rate monitors keep a stable enough contact during the dynamic movements required by weight training. Otherwise they would be ideal. Hopefully in a couple years that can get worked out since it is relatively new technology.
Your options boil down to:
- Try and find the lowest profile HRM puck you can for your chest. The smaller the target, the less likely it will get hit. You also would have the hope of growing the chest enough to have it protrude more than the HRM.
- Allow the bar to come up a little farther from the chest, and really focus on the shrug to pull yourself under the bar once it is level with the HRM. It's not as ideal as letting the bar stay skimming your chest as you focus on that shrug to get under the bar, but sometimes it's the only option.
Keep an eye on the wrist only HRM options over the next couple of years. Right now, they are good tools for runners, and the manufacturers are aware of the challenges with using them for other activities. The technology will catch up, it's just a question of how soon.