What happens if you do MAF and Speedwork together (on separate days) that our body can sustain?

by SThomas
(Dallas, TX, USA)

I am 55 male. I have lived sedentary life for most of my adult life and even though I have not been a perfect couch potato for most of it, I rarely stretched myself consistently for months/years. I joined a running club last year and did a full marathon and 8-10 halves. I did full in just under 5 hours, halfs were about 130min :-(. Most of my full marathon run was in the Zone 4 and the lower end of Zone 5. Running became easier after full though.

We are in the offseason and I have been doing 20-30miles per week (4M,4Tu,4Th,8/10/13Sa,4Su).
Few weeks back I came across MAF, I thought I could give it a try... who does not want to run injury free after all. My MAF bpm is 125 :-( which is ridiculously low. Summers make it even more depressing/challenging. So, I am doing some of my MAF runs in the gym. Digging a little further, I started thinking that I am not looking for any specific formula such as MAF, 80/20 etc. I am looking to run faster.

So now, the two questions I am trying to answer are:
#1. What happens in my body if I do speedwork (say on Tuesday) and the rest of the days do MAF? Why is this discouraged particularly in the first 3-4 months of MAF-based training? What really happens biologically that causes problems

#2. If I run in zone 3 which my body never says no to, what can happen to the body's adaptability? Ideally, I want to adapt my body to learn to burn (more) fat (in zone 3 & 4)and expand mitochondria. In zone 3 my body keeps clearing the lactic acid without any problems. The question is: does my body start burning fat less and less as I run faster OR just that proportion of energy from fat start to drop which should be considered ok as long as the body is still trying hard to burn fat? Why its ability to adapt to burning fat is 'eliminated'(become zero) the moment I go above my MAF BPM?

Would love to be enlightened :-)

Thanks in advance.

Nicole's reply:
Hi, thanks for your question. Firstly, congratulations on your marathon and half marathon achievements. You sound like you have the running bug!

The thing to realize about MAF training is that it is not a quick fix to make you run faster. It is a slow process which takes time as all your body systems (primarily your aerobic) need to adapt, hence the 3-4 months base building. It’s also about keeping your body as healthy and stress free as possible in order to achieve its maximum potential.

Nearly everyone feels frustrated at first about how slow they must go but you need to remember that you are going slow because your aerobic system has room for improvement. Once your aerobic system adapts you will be able to run faster and at the same low heart rate.

#1. What happens in my body if I do speedwork…
If in the base building period you start mixing in anaerobic speed work with your aerobic MAF training, then you are placing extra stress on your body and you are targeting the wrong system for aerobic development. This will have the effect of slowing down your aerobic development which in turn means your MAF pace will not improve as quickly. Many runners wonder why their MAF pace is not improving and it’s often because they are doing speedwork on the side.

Here's a response from Phil Maffetone to Why do you often recommend running slow to get faster?

#2. Does my body start burning fat less and less as I run faster …..
There are 2 fuel systems that the body uses for energy. Fat and sugar. At higher intensity your body uses more sugar and at lower intensity it uses more fats. During MAF training it uses primarily fats as you are only using your aerobic system. When running faster and you start using your anaerobic system, there eventually comes a crossover point where you go from primarily fat burning to primarily sugar burning. This is known as your fatmax.

The aim with developing your aerobic system is to train it to use fat first for energy and to continue using fat even when exercising at higher rates. The more developed your aerobic system, the more you can continue to burn fat for energy and thus avoid the discomfort of when your body runs out of its sugar fuel source.

Have a look at these links as they may well help answer all your questions in more detail.
White Paper: MAF Exercise Heart Rate – How it can help improve health and sports performance
Five ways to run faster on fat

I hope that helps.