Heart rate zones help

Listen to Marc.....he's on the money.  I am 58 years old and I can run at 6 mph for 3-5 miles and my heart rate never gets above 125......you need some long, slow work. (long being relative to your fitness)  Running efficiency is about patience.  You'll get there if you practice getting there.

First up, I've had many of my athletes follow the Maffetone method (specifically MAF running) over the years and have had excellent results.  Using the Maffetone formula will all but guarantee you'll be exercising well below your aerobic threshold - which is how you most efficiently force adaptation and develop the aerobic energy pathway (train your body to burn fat for fuel).  Based on what you've said in this thread, I agree you can benefit from low intensity training such as you would get with MAF running (if you can tolerate the often painfully slow pace).

Next, and this may spur some debate.  I'm not a big fan of using lab metabolic testing to set training zones. Any test - a field lactate threshold test, a FTP test, metabolic testing - is a snapshot in time.  Your thresholds - aerobic, anaerobic, lactate, etc. - can differ from day to day, even hour to hour by a number of beats per minute.  When you undergo metabolic testing, you are likely in a controlled environment where they are using advanced medical grade technology.  I'm willing to bet that isn't the case when you train.  The biggest problem I have with metabolic testing is it's difficult and expensive to repeat regularly.

You can closely estimate your Maximal Lactate Steady State (MLSS) with a field test.  Heart rate at MLSS is the number we most commonly associate with lactate threshold.  Once you know that value, you can then set training zones.  As you your body adapts to the training, you can easily retest and reset your training zones so you are always training at the proper intensity.  Some would say a field test isn't as accurate as a lab test.  Yes and no.  We've already established the lab test is a snapshot of your thresholds at the time of the test (as is any test) and was done under controlled conditions.  If the day you go for a run it's 20-degrees warmer than it was in the lab when you did your test, your threshold values and thus your training zones, are likely off by a few beats per minute.  The reality is, a field test will get you close enough to set valid training zones and is easily repeatable on-demand.

Here's how to perform the field test and set your training zones.