I can tell from experience that it sucks when hard work doesn’t pay off. It is even more frustrating when you train harder, but seem to get slower. As you might have guessed, training intensity has been too high far too often for me.
I felt fast during training, but when races came I was going much slower than what I was training for. That is if by that point I haven’t caught a cold.
Turned out, I may not have done everything right. I started to read about it and talk to specialists and found out that the problem was wrong training intensity. If you feel you may have the same problem, read on to see what I’ve learned.
Physiology of training intensity
Human body can produce energy in 2 ways – aerobically with oxygen and anaerobically without it.
When the intensity is low or moderate (aerobic) mitochondria in muscles use oxygen to produce energy. This process is slow, but cashes in lots of energy.
During high intensity work (anaerobic) body needs more energy and mitochondria can no longer produce it fast enough. Body then starts to use glycogen stored in muscles and liver. This is much faster, but the amount of energy created is also smaller.
Glycogen stores have only around 350 grams of carbohydrates or around 1,400 kcal of energy. It’s enough for roughly 2 hours of intense exercise at most. When an athlete runs out of it – he can hardly move (it is also called “hitting a wall”).
In both aerobic and anaerobic mode body first converts blood glucose to pyruvic acid. In aerobic mode it is then converted to acetyl coenzime A and taken to mitochondria to produce energy. In anaerobic mode, however, pyruvic acid is converted to energy and lactic acid right away. Lactic acid is then quickly split into lactate and positively charged hydrogen ions (H+). And these bad boys are the cause of all problems.
High density of H+ ions creates a burn in the muscles and causes muscle fatigue. As a result, performance, speed and sometimes even technique suffer after a while of hard effort.
It’s all handy dandy, of course, but how it all affects training?
That comes next.
High training intensity – a slippery path
Muscles need stress to develop strength and endurance.
It promotes hormone production (growth hormone, testosterone, etc.) and results in mitochondria and myofibril growth. And yes, it is true that high training intensity make you feel strong, young and lean.
Mitochondrial density is what creates endurance and myofibrils are the source of strength. The more of both the better.
When athlete trains in anaerobic mode, mitochondria utilize H+ ions created during energy production. As long as athletes doesn’t accumulate H+ ions he can perform indefinitely at high speed (if he consumes enough calories). When he starts to accumulate, on the other hand, muscles will reach fatigue.
Good news is you can increase the time until muscle fatigue with training. It is called muscular endurance and it can be confusing. I’ve got this wrong myself for too long. I trained until exhaustion thinking I’m growing endurance when actually I was just taxing all my reserves.
What exhaustion does is produce more H+ ions and more fatigue than mitochondria can handle, even leading to death of some. In human words it means over-training, illnesses and reduced endurance after hard sessions.
It is exactly everything I’ve experienced.
The key to muscular endurance is to create enough mitochondria to utilize H+ ions immediately.
Yes, it’s not through more and harder, but the other way around. For this to happen training intensity has to be high and duration short to activate hormones, but avoid accumulating fatigue.
3-5 second short sprints are best for building mitochondria, btw.
Low training intensity – the key to balanced program
So what do athletes do if they can’t work out at high training intensity all the time?
They train at low intensity to improve technique, flexibility, reaction, tactics and other skills. In fact, they spend most of their time doing that. Low training intensity is also used before the season to “stretch” the left chamber of the heart, which increases the amount of blood the heart can push in the system and bring more oxygen to the working muscles.
The purpose of low intensity work is not to build muscles or even drop fat. High training intensity is best for doing it.
High intensity training promotes hormone production and utilizes the whole muscle. Slow-paced efforts favor muscle economy and only a small share of the muscle works.
Low training intensity teaches the body to utilize lactate for fuel. Over prolonged period of time athletes’ bodies learn to utilize it very quickly as additional energy source. This results in faster recovery between intervals and between workouts.
This is why it’s always good to have an easy run or bike spin after an intense effort. It allows blood to circulate and it speeds up lactate utilization.
How to balance training intensity
Pure focus on high or low intensity work is not efficient.
If all workouts are done at high intensity, muscles don’t have enough time to recover and endurance will suffer. Focus only on low intensity work may improve the cardiovascular fitness, but it will not promote the hormone production and mitochondrial growth. As a result, peak form or even proper fat loss will not be possible.
Balancing intensity load is a form of art and every coach is an artist. It is really tricky to get training intensity just right and not over-train. In many cases it is trial and error to find the proper balance between high and low intensity.
In that sense my coach was like Monet – as crazy as him. Somehow for me it was always much easier to over-train than under-train.
There is one thing, however, I learned the hard way:
The worst possible thing you can do for endurance is to let your muscles accumulate fatigue.
Training until exhaustion will only lead to over-training, reduced endurance and, possibly, illness. Scroll up to remember how.
A good rule of thumb is to spend on average 80% of the time on low intensity work and leave 20% for high training intensity. Such proportion will allow the body to build speed and endurance and not over-train. Just remember to still avoid muscle fatigue in those 20%.
How to measure training intensity
The best and most precise way to understand how your body responds to training intensity is to take blood samples before, throughout and after the workout to determine the level of lactate. From what I learned, work under the lactate level of 2-3 mmol/L can be considered low intensity. These figures are also used in stress tests to find the aerobic threshold.
This is not something very convenient, right? It’s not like we all have a Dexter-style lab behind our bookshelf where we can test every now and then.
However, there are also tools like these that allow you to take your blood sample and check the level of lactate in the blood yourself.
These are quite handy to test how well rested you are after previous workouts or how intense was the workout that you just did.
A much easier way of measuring intensity of the exercise is by checking your heart rate. The higher the training intensity the faster the heart beats and moves the blood to muscles.
That’s about it. Let me know about your experience with training intensity in the comments below.
Until then, happy training!