This questions comes a lot in exercise groups: What is better, going by how I feel (percieved effort or PE) or wearing a heart rate monitor (HRM)?
Two answers come to mind when answering this question. If you like to see benefits immediately, then wear a HRM. If you have a hard time pacing yourself, wear a HRM. (If you have a problem just getting out the door, then used PE.)
Tracking your progress can be as simple as estimating the time it took to cover the distance. The problem is, you have no idea HOW you did in the workout other than: I feel great or I felt bad. Being able to gauge your effort with a simple tool like a HRM gives the workout credibility. For example: I feel great because: I ran at a faster pace with a lower heart rate. This is an immediate affect. You can clearly see that after that particular workout, there is an improvement. If you did poorly, ie. slower than usual, using the heart rate data will show if this is in fact true. Maybe you went to slow and didn’t work hard enough. Or maybe, that head wind in the last 5Kms really forced you to slow down. Using a HRM allows you to reflect on the workout with more intelligence.
Heart rate data can keep also keep you on track. Generally, at the beginning of a hard workout, it is much easier to go faster. A HRM keeps you in check so you can finish your intervals efficiently.
Having a lactate test done, is a further step in gauging your efforts. The test can accurately show where your recovery/endurance pace ends and where your intervals should be. This is the gold standard for training. Pairing the information from the test with a HRM is a recipe for success.
Once you have worn your HRM for along time, you begin to know how your body works. At this point, PE can be used for some workouts. A recommendation is still keep track of some of the key workouts like the long run/bike and intervals. This is to ensure you are working at the correct intensities to get maximize your training.