Which Exercise is Best for Weight Loss?

A decades old debate that appears to have taught us nothing in the having. It's always seemed to me like asking which food is best for weight gain. The correct answer is that they'll all get you there if you're determined enough. Naturally, one chooses using a simple algorithm involving questions like: what is most pleasant/ least unpleasant and: what am I best at/ least rubbish at, and: what's most convenient/ least inconvenient. The answers to each of which depends on the individual.

On the small chance that you have been hoodwinked into believing there is substance behind the idea that there is a best choice of exercise for weight loss, your intuitions were correct from the start. It's a nonsensical question. Weight loss and maintenance isn't hard because you're doing the wrong type of exercise. It's hard because our bodies change and so do we (as people).

Here's an interesting and perhaps useful way of looking at the challenge. What would you expect if, rather than weight loss, your goal was to complete a big event or acquire a new, specialised set of exercise or sporting skills, e.g. to complete a cycle tour or to take up a new sport and do well. With these types of goals, we accept that we will need new skills, lots of practise and hardwork, and plenty of time. We get that the kind of change needed is profound in the same way any kind of learning is. We expect to have to change at the level of our personness. 

Why then do we expect less or different for weight loss? Why do we believe weight loss is just a matter of subtracting mass from our body’s? The evidence of the difficulty of the challenge would suggest that it is much more than that. Perhaps we can borrow from ourselves by comparing it to something else in our lives. Some other kind of challenge that we have undertaken that we accepted would change us as a person or require a more comprehensive, more patient kind of investment*.

*a small albeit important qualification at this point - positive psychology is far more effective than negative psychology for long-term change. Weight loss might be more achievable when it isn’t driven by self-loathing but by the excitement of a new experience or as a new chapter in our lives.

Fitness: What It Is, What It Does, and How to Correctly Train It

Fitness is the capacity of the body to do work. Time taken and work done are the two factors or variables. With these in mind, we could define fitness as either the time taken to complete a fixed amount of work, e.g. running a race, or the work completed in a fixed amount of time, e.g. playing a game of sport. 

If we look a little closer at how the body responds to work we can see that neither of our definitions captures the true meaning of fitness. In turn, they don't work well as rules or instructions for fitness. 

The human body has three work modes: low mode, high mode, and a blend or mix of the two. Low mode is aerobic. High mode is anaerobic. The capacity of the body's aerobic energy system is synonymous with cardiovascular capacity. 

We need to take a moment here to fully recognise the importance of the aerobic system: every organ, tissue, and cell uses aerobic metabolism to do its work. The aerobic system is the body's essential power plant. This system is designed for sustained work output. The corollary of sustained work output is a lower rate of work. Aerobic or low mode can only sustain work up to a certain intensity level.

Cue, anaerobic, high mode work output. Some tissues and cells, such as muscle fibres, have two additional power production mechanisms. Both of these are anaerobic - the high mode. Anaerobic metabolism involves a higher rate of work than aerobic metabolism. However, just as aerobic work is limited to lower work intensities, anaerobic, high mode work cannot be sustained. These are the trade offs.

What is the third work mode, how does it work, and why is it important for our story?

It matters at this stage to paint a picture of how aerobic and anaerobic metabolism are organised. Aerobic metabolism is always on. Anaerobic metabolism switches on, over and above, aerobic metabolism when intensity of cellular work reaches a critical threshold. Note: the aerobic system continues to chug away at the same time. We can measure the switch from aerobic to anaerobic metabolism as lactic acid production. This is essentially what is measured in a VO2max test: concentrations of lactic acid and oxygen consumption.

The switch to anaerobic metabolism occurs because the aerobic, low mode system cannot keep up with the demand rate of the work. The cardiovascular system meets the increase in the demand rate of work by raising heart rate - as a means of moving more oxygen into and carbon dioxide out of the body. This is a fixed relationship: higher work rates = a higher heart rate. It is true of all bodies and for all conditions. We, therefore, also know the heart rate zone in which the switch occurs. More about this in a moment.

Back to the work modes. As heart rate rises, anaerobic metabolism switches on and superimposes aerobic metabolism, and the two systems cooperate to meet demand. This is the third work mode: mixed aerobic and anaerobic. It is the sweet spot for athletes; performance mode. Competitive games, races, crossfit-styled workouts etc. all occur in mixed low+high work mode. Performance mode is a compromise between sustained low power output and unsustainable high power output.

How sustainable is performance mode?

Sustaining performance mode is the singular purpose of conditioning for sport. It is the holy grail of the hours and hours of weekly cycling, swimming, rowing, running etc. It is also where considerable debate and confusion takes place because the basic questions remains: what is fitness and how do I create more of it. Is it aerobic capacity, anaerobic capacity, or a mix of the two?

To answer this we have to go back to one specific idea: sustainability. What we are really asking with our question is what sustains work output? In turn, this will enable us to define fitness and give us a basic training directive. 

We can extrapolate the information we need from the heart rate response curve. Remember that this curve is essentially the same for every human performing work of increasing intensities regardless of the nature of the work. 

Anaerobic metabolism switches on between 60 and 75% of maximum heart rate. Higher for trained athletes and lower for untrained athletes. Mixed aerobic+anaerobic or performance mode comprises the next 5% of the curve as heart rate rises. Above this, the curve steepens quickly. 

The boundary between low and mixed mode is termed the first threshold or turn point, while the boundary between mixed and high mode is termed the second threshold or turn point. Exercise is essentially sustainable before and after the first turn point, but is not sustainable after the second. Though the mixed zone is the performance sweet spot, the first turn point - the heart rate value at which the body switches on anaerobic metabolism is the critical boundary. The higher the first turn point, the higher the sweet spot. A high sweet spot means a higher rate of internal or metabolic work. By extension, the higher the external work: tempo, power, load etc.

Let’s run back over that last statement one more time because we’ve arrived at the key idea that gives us a definition of fitness. The first turn point, which is the heart rate value above which the body switches on anaerobic metabolism (to support aerobic metabolism), determines the rate of work we can sustain. It is the capacity of the low mode system that ultimately determines how hard and for how long mixed aerobic+anaerobic can be sustained. 

Fitness = absolute aerobic or cardiovascular capacity.

The relationship between aerobic and anaerobic capacity is analogous to the relationship between cooks and serving staff in a restaurant. Serving staff can only serve meals as fast as the cooks can prepare them. However efficient and effective the serving staff may be, it is the kitchen that ultimately sets the serving rate for the whole restaurant. Aerobic capacity sits at the heart of the metabolic kitchen.

What does this tell us about how to train fitness?

Let’s return to the definition we have already: the performance of the aerobic system determines the sustainability of effort. The work we can sustain is the result of the capacity of the system. Work appears on both sides of the equation: as a stimulus or cause to the left of the equals sign and as the product on the right. However, as a stimulus it does not vary much around values on or slightly below 60-70% of maximum heart rate. What changes is the other stimulus or cause, which is time.

Time is the training variable we are supposed to program or change. Aerobic capacity increases with more and more sub-threshold training time. Remember that the aerobic system is designed for sustained work.

The most important idea that defines fitness and conditioning for fitness is found in one word: sustainability.

Before I sign off I should point out that there is a small piece of the fitness puzzle that matters, way up at the top of the heart rate curve: medium interval sets at 90% of max heart rate to increase VO2max. Another small piece involves tempo sets in the performance sweet spot. These are ‘small’ pieces of the overall puzzle both in training time or load and mileage. They also matter not one iota if they’re not complemented by an appropriately large aerobic system. “Low mode is high mode” should be every athlete's conditioning motto.

Summary of the key points:

• Fitness and fitness conditioning should be defined by how the body does work.

• The human body has three work modes: low mode aerobic metabolism, high mode anaerobic metabolism, and a mixed aerobic+anaerobic performance mode.

• Aerobic metabolism - low work mode - sustainably supports low intensity work, including all of our life support systems, thinking, and exercise. 

• Anaerobic metabolism - high mode - supports high intensity work but cannot be sustained. Mixed performance mode is sustainable but tenuous.

• Aerobic metabolism is always on, and anaerobic metabolism switches on to complement low mode when power or work rate values reach a heart rate threshold. The anaerobic switch or threshold is called the first turn point. 

• The first turn point occurs between 60 and 75% of maximum heart rate. Higher for trained athletes and lower for untrained athletes.

• Mixed aerobic+anaerobic mode is sustained for an extra ~10 beats per minute until a second heart rate threshold or turn point is reached. Above the second turn point, heart rate rises quickly and power cannot be sustained. 

• Sustaining performance mode - the zone between the first and second turn points - is the holy grail of conditioning.

• Larger aerobic or cardiovascular capacity is associated with a higher first turn point and higher work and power values in the performance zone.

• Fitness is, therefore, proportional to absolute aerobic or low mode capacity.

• The performance of the aerobic low mode system determines the sustainability of effort.

• Higher work or power values are the product of conditioning. The work we do to stimulate these adaptations is fixed on or slight below 60-70% of maximum heart rate.

• Time is the training variable we are supposed to program or change. Aerobic capacity is increased with greater sub-threshold training time.

• The most important idea that defines fitness and conditioning for fitness is found in one word: sustainability.