I spent most of 2017 and 2018 running with little structure or knowledge of pacing. When I first started, I kept trying to PB my 5km time literally every single run. A lot of my time was spent injured from ramping up too quickly, and running too quickly.
I bought a heart rate monitor within a couple of months of starting, but never really looked at the data. It was just a data collection device rather than a training tool. Looking back now, most of my runs were essentially threshold runs. This is clearly the wrong approach for good training.
Around the end of 2018, I started learning about low heart rate training. It seemed to work well, and I gained a bunch of base fitness. Unfortunately I took an unplanned 3 month break off soon after, but let’s not worry about that.
I restarted again when I came back to Chiang Mai in June and saw some amazing results. Combined with adequate rest and a consistent training schedule, my last few months has seen me PB in almost every distance, and I ran a 55km ultra quite comfortably. My resting heart rate has never been lower and my pace at the zone 2/3 border has never been faster. It’s come down from ~6min/km in June to ~4:55min/km today.
If you’re not actually familiar with the concept of Zone 2, then it’s about 60-70% of your maximum heart rate (or heart rate reserve if you want to be a little more accurate). Exercising at this level should be very easy and it’s a level of intensity where you should be able to hold a conversation. The key point is that it stresses the cardiovascular system enough to produce a training response, but doesn’t exhaust the muscles and tendons in the way a faster effort would. This allows you to put in consistent efforts day-in, day-out and become a better runner overall.
Zone 2 has also been called the “fat burning” zone. It’s the level of exertion where your body tends to burn more fat than carbohydrates. In long distance races, you’re very likely to run out of carbohydrates and so training your body to burn fat easier is very beneficial.
When I was training for the Rugby half marathon, I never got anywhere close to the pace I ended up running in that race. I think the fastest I had been was about 5min/km (my top-end zone 2 pace) but I ended up running 4:17min/km. I was very surprised to be honest, I thought I’d only be able to hold around 4:30min/km. Towards the start of the race, I should have put in some faster efforts to see what I was capable of, but I definitely wouldn’t have been at that standard without all that low intensity training.
At the minute, I’m doing nearly all of my training in Zone 2, unless my heart rate drifts over during a hot day. I’m base building for next year, and don’t want to get injured by doing the fast efforts I know my body struggles with. I’m slowly building distance, about 10% per week if I feel comfortable.