I ran consistently for two years training for marathon after marathon (three in a 12 month period!) and I never got any faster, gained weight, and started to get a bit frustrated. I incorporated speed work into my weekly runs, eventually getting my 5k time down to 25:30 (which was awesome for me) but my long run paces wouldn't go below 10:15 at BEST. My first marathon pace was 10:54 and my subsequent marathons were slower (around 11:15.)
About that time I started seeing some bloggers mention low heart rate training, or Zone 2 training, and while it interested me I never wanted to fully commit to it. Until now.
What is Low HR training?
Basically, training at a lower intensity so your body burns fat instead of carbs.
During exercise, the body utilizes two primary sources of fuel, namely carbohydrates and fats. Unlike carbohydrates, which are limited and break down rather quickly, fat breaks down slower in the body and releases more energy. Plus, the amount of fat athletes can store is virtually limitless, even in the most slender of individuals. By teaching the body to burn more fat than carbohydrates, endurance athletes will be more efficient over longer distances. This translates to faster times and better performances. For many runners, it also means easy — but tedious — training. Source
Low HR training is good for people who enjoy long slow runs, have plateaued at current paces, have frequent injuries, and don't mind investing 6-12 months to see results.
So what HR should you train at? There are a few different ways to calculate it but here's a popular one:
Maximum Heart Rate = 220 - age
To train at Zone 2 levels you want to keep your HR between 75-85% of your Maximum HR.
Using myself as an example my maximum HR is 189 (220-31.) My Zone 2 heart rate is 142-161. I've been keeping my HR at an avg of 155 for all runs since the start of 2015.
In order to keep my HR that low I have to run really, really slow. When I was running previously it wasn't unusual for my average HR to be around 175-185. That's about 95% of my maximum HR! It felt like it too. I was always having problems breathing, and I could never talk and run when I ran with friends. I thought that was kind of the point in running and training, to be pushing yourself as hard as you can.
My average LR pace has gone from about an 11 at the end of last year to 14:30 when I started low HR training and now it's about 13:30. I've already taken a minute off my average pace time and that's with only running an average of 2x a week for 3 months. Plus my runs are SO MUCH EASIER now. It's weird adjusting to running in what feels like slow motion, but it feels great.
Low HR training doesn't just apply to running. If you are a triathlete interested in doing HR training you'd do all your runs and bike rides at your Zone 2 rate. Most plans allow for a small percentage of runs to be done at Zone 3 (races and speed work) so it's okay to include 1 day a week of higher training intensity. Plus, speed work/HIIT is another great way to burn fat off!
An endurance athlete should never stop training in zone 2. The ideal training plan should include 3-4 days a week of zone 2 training in the first 2-3 months of pre-season training, followed by 2-3 days a week as the season gets closer and 2 days of maintenance once the season is in full blown. Source
Obviously I have a ways to go with this type of training but I was getting so burned out with running and maximum effort and seeing minimal improvement that I'm happy with the change of pace. With the temperatures starting to rise here already it will become more of a challenge to stay in Zone 2 but I know my body will appreciate it, and I feel like I'm setting myself up to finally conquer my first ultra next year!
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This discussion forum has a lot of great personal experience with Low HR training
The Big Book of Endurance Training (kind of the bible for Low HR training)