WOW! What a fantastic workout. This really takes training at maximum aerobic heart rate (MAHR) as calculated by Maffeton’s 180-age formula to a new level. If you are unfamiliar with what aerobic training and development is, then refer to previous article in link https://regeneratehealthfitness.co.za/2019/07/30/aerobic-benefits/
When an athlete first starts out with aerobic training and conducting workouts below MAHR it usually is a very frustrating period for the athlete. This is due to having to slow down substantially, oftentimes walking as the athlete’s aerobic system is under-developed. Overtime the athlete starts to run further and faster at the same heart rate before having to walk. When the aerobic system is developed the athlete will often run a number of heart rate beats per minute (HRbpm) lower than their MAHR as their pace becomes ‘too difficult’ to sustain or enjoy for the duration of the workout or everyday.
What are aerobic intervals and what is the purpose of this training? This is mentioned in Dr Phil Maffetone’s Big Book of Endurance Training and Racing and consists of breaking a normal MAHR session into smaller sub-sections of training at your MAHR limit and the other sub-sections at a much lower HR. I decided to alternate 1min fast (at MAHR limit) and 1 min slow (15-20 HRbpm lower), all conducted below MAHR. In other words one runs for one minute as fast as you can whilst maintaining HR below MAHR and then the next minute is used as ‘recovery’ and to bring your HR well below MAHR. The purpose of this training session is to improve your aerobic speed.
How did I feel and what did I learn from doing this workout. Firstly, it was harder than I initially perceived it would be. When I train aerobically, I set my watch to only show HR and lap time as pace is not the focus of the session, heart rate is. This means that whilst on the training session I do not know what pace I am training at, nor do I care. Post my training session I then analyse this. This ended up being harder than previously expected simply because my 1min fast intervals were a lot faster than I imagined. I am very familiar what my MAF (Maximum Aerobic Function…see link https://philmaffetone.com/maf-gps-test for a detailed explanation of MAF) speed is and I expected to go a little faster than this but ended up going a lot faster…a good 30-40s/km faster.
This ability to run faster during this shorter one minute fast interval is due to what is termed heart rate inertia or the lag affect of your heart rate (graphically shown below). Essentially your heart rate needs to ‘catch-up’ with your pace so to speak. Hence this becomes a threshold type training session but without the added stress.
Other really useful observations to take note of, relates to how quickly your heart rate drops during the recovery section. If it begins to drop back quicker from one week to the next, then it is one indication of improved fitness. Another post training assessment that can be observed is your pace during both the fast and the recovery sections. If you pace during both the faster and recovery intervals improves, then this not only indicates improvements in your aerobic speed (best measured through regular MAF testing) but also improved fitness.
An observation that I made whilst on the run was as the session got longer it would take less than a minute, during the fast interval before I reached my MAHR and correspondingly would take longer to drop during the recovery interval. This is related to what is termed cardiac drift (ie: heart rate increases as exercise time increases at a steady intensity) and submax fatigue (refer to article link https://philmaffetone.com/fatigue-cardiac-drift by Dr Phil Maffetone for more detail on this). Hence this is something I will keep my eye on when conducting these sessions in future. If the onset of cardiac drift prolongs then it will indicate improved submax fatigue which is important for most endurance events.
I elected to do one minute intervals, however this can be adjusted as your training / desire requires. For example, you might consider 4mins fast and 2mins easy. Alternatively, simply employ a fartlek type session where you mix up the fast and easy sections on the fly with no prior prescription to time or distance.
If you are looking for some variety whilst training aerobically, then certainly incorporate the aerobic intervals &/or aerobic fartlek into your training program. Mix them up and have some fun with them.