Low versus high heart rate conditioning for fitness. Which is best?

You want to improve your cardiovascular fitness.  What approach will you take?  Aerobics classes, such as spin and pump, are one option.  These classes combine low intensity movement with high heart rate.  Another option is cross conditioning, e.g. CrossFit or F45, which combines high intensity movement with high heart rate.  A final option might be to go for a run or to cycle.  Observe anyone running or cycling and you're very likely to also observe someone working hard; exercising with a high heart rate. 

There may be more than one way to get fit but the common denominator appears to be that improvements in fitness are associated with exercising with a high heart rate.  If I want to get fitter, I need to work hard.  The harder I work, the greater the outcome.  As one goes up, so does the other.  Is this correct?  No, it's not.

The human body has two energy systems for exercise or activity: an aerobic or low power system, and an anaerobic or high power system.  The aerobic system powers us more or less all of the time.  The high power system does not kick in until muscle work approaches a peak.  It's only good for a few seconds up to about one minute.  The body draws on the aerobic system for work below maximum and when muscles are working at peak.  The aerobic system is used to replace the fuel used during anaerobic and aerobic work.  We experience this as high breathing rates during and after exercise.  Where fitness is concerned, regardless of context, the aerobic or low power system is paramount.

Returning to our question: which training approach is best, the question we need to ask and answer is this: what is the strongest signal to expand the aerobic system?  The aerobic system works at every intensity level but are they all equal where outcomes are concerned?  The answer to this question is that there is a heart rate band or zone that produces the strongest signal for the aerobic system to expand and it may surprise to know that it's not very high: 60-70% of max heart rate.  In this heart rate zone, your breathing rate is often not elevated much above normal and it is possible to chat with someone.  That's why the advice given to endurance athletes is to work at levels that would allow you to talk.  

Low heart rate training is not the only level of work endurance athletes need to complete but it should be most of it - about 80% of total training load or volume.  Aerobic fitness is also not the only kind of capacity for work needed for exercise.  Strengthening muscles, for example, is also useful!  However, if fitness or endurance are your primary goals then you need to know how to effectively perform and distribute work to gain the best outcome.  The most common mistake in endurance training and exercise for fitness is believing that the harder I work, the greater the outcomes. 

Walking is a profound human activity

I wrote a post a few weeks back about walking in which I downplayed the transformational properties of walking.  I am ‘walking’ that back a little today.  Walking is a profound activity for humans; probably for all quadrupeds and bipeds.  Walking is human design at its most obvious.

I recently watched a Netflix documentary about a Mexican woman: Lorena Ramirez.  Ramirez is a native Raramuri Mexican.  She lives with her family in the high canyons of Chihuahua, many miles from their nearest neighbours.  The Raramuri or Tarahumara are famous for their capacity as long distance runners.  Running is how the Raramuri move between communities.  

Ramirez loves to run but running is not at the beginning of her story.  Like any individual who lives a subsistence life, Ramirez's life is made of walking.  For the Raramuri, like their more storied counterparts, the Africans of the Rift Valley, walking is a constant.  There is no data that I can find for this - it would make an illuminating research topic - but my educated guess is that subsistence farmers like the Raramuri would accumulate tens of thousands of steps in an average day.  Moreover, Raramuri children would rise to a daily step count far exceeding that of an adult in a modern Western nation very early in life.

Lorena Ramirez lives in a valley or canyon and her walking (and running) is consequently highly varied.  She is strong and balanced.  There is an obvious rhythm to her movement.  When she runs, it is an extension of her walking gait.  Ramirez is no slouch over half and full-marathon distances but she comes into her own for distances above 60 miles or 100 kilometers.  At these distances, running gait is not concerned with power but with rhythm and balance.  Every system in the body is in harmony and for Ramirez this comes naturally because she has a foundation of millions of walking steps with which metabolic and biomechanical balance was built.  

Herein lies the secret.  As we raise power - increase the rate of work - our bodies must 'know' how to locate balance or harmony to properly harness energy.  Without balance across and within systems, one or more of them will overwork and we experience that as fatigue and discomfort.  It was while watching Ramirez that I saw this.  She holds no expectation of herself when running.  She simply seeks harmony within the act and when it arrives, as it usually does, she is then able to accelerate if that is her wish or stay the course.
There are compelling lessons for all of us through the example of individuals like Lorena Ramirez:

• walking is a profound functional and health platform for the human body
• the more walking we do, the stronger and more adaptable our bodies become
• first seek balance or harmony - physiological and psychological - and then raise power
• moving back down in the gears, to re-establish harmony, is a sensible choice and solution.  Ramirez walks when it is sensible to do so
• harmony reduces wear on the body and 'spends' energy far more effectively and efficiently
• low intensity cardio is the most important training zone with which to build performance
• high volume supercedes and must precede speed and power for mid and long distance runners
• learn to listen to your bodies messages.  Walk-jogging is not weakness, in the moment it is exactly what your body is instructing you to do