I’m sorry that you’re having trouble.
To find your AeT HR:
1. As you mentioned: if all else fails, use the MAF method (180-age). That will be remarkably helpful for a lot of individuals, although there will be some outliers.
2. It looks like your equipment was set up correctly and sending good data on Saturday. If you can keep it working like that, you can do your AeT Test with an uphill hike. You’re lucky because: a) you don’t have much tree cover in your area, and b) a Garmin tends to have some of the best GPS accuracy. It’s important to select the right trail – to keep your effort consistent, you’ll want to find a continuous uphill trail. Don’t use a trail that completely flattens out in sections or has wildly changing grades throughout. Again, you’re lucky in that many trails in your area will meet that criteria. I think that there are a lot of options if you drive east over to Topanga or Palisades. Definitely good options if you head all the way to Wilson observatory or Verdugo Hills. If you get a continuous 60min uphill at what you think is your AeT pace, you can look at that segment in TrainingPeaks and check the Pa:HR. If it’s between 3-5%, you’ve found your AeT HR (it’s the HR in the first few minutes of the test).
3. If you CAN’T find AeT with heart rate monitoring, it’s still reasonable to train using perceived exertion. Athletes have done this forever with great results. Make sure that your easy sessions are EASY and your hard sessions are HARD. That’s what we are trying to do using heart rate monitoring. The HRM obviously has much more unbiased feedback and precision which gives us the ability to monitor for small changes over time. The other reason HRM is helpful is because most athletes can get in their own way with training – it’s easy to push harder on an easy outing when it feels easy, and without HRM, the athlete might be more inclined to push harder. Once the athlete is outside of the desired training range, they are no longer following the training plan.
AeT HR is very helpful because it’s the best option mountaineers have to measure the intensity of their workouts. We can’t measure our training load with the same precision that cyclists with power meters can. Your heart rate is the best metric for objectively looking at your training load. AeT HR and AeT Pace are the most practical ways for mountaineers to assess the efficacy of their training programs and other contributors to fitness.
We have the program set up so that you can run or hike. There is no need to run with this program. We give the option to run because it is an easier way to exercise at a target intensity for athletes that are in vertically-challenged locations. Stair machines and treadmills are given as other options for those who have zero access to hills. If you have trails, those will be great, especially since you get to descend. The stair machines and most treadmills have no opportunity to practice descent.
There are a lot of great hiking opportunities in the Santa Monica Mountains, especially for the workouts through this initial 12 week program. It sounds like Don has had his boots on the ground in your area. There are some simple websites that give good trail descriptions, like Hiking Project and AllTrails.