Metabolic vs. Mechanical Efficiency

Metabolic vs. Mechanical Efficiency

Efficiency is defined as the work done related to energy expended. Basically, when it comes to running, it’s a way to describe how much energy is required to run at a specific speed.

However, since running speed itself is not a direct measure of work or energy, exercise physiologists prefer to use the word “economy.” This is why you’ll see economy used predominantly in published research studies.

Running economy is defined as the energy demand for a given velocity of submaximal running. That is, how much oxygen your body needs to run at any given pace below your all-out racing stride.

Measuring this directly requires monitoring steady-state consumption of oxygen and the respiratory exchange ratio. Taking weight into consideration and assuming the same speed, runners with good economy naturally use less energy and oxygen than runners with poor economy.
In the end, this is an even stronger predictor of race performance than maximal oxygen uptake in elite runners with similar VO2max levels.7
Admittedly, this is a very complex matter to measure. That’s why economy is traditionally assessed by running on a treadmill in standard laboratory conditions. This is not the same as running outside or on a track, but it does provide a decent indication of how economical a runner is and how economy can change over time.8

We’re not in a lab right now, however. Nor are we on a treadmill. And chances are high that, if you’re reading this e-book right now, you’re not either. That means that, for practical purposes, we can use ef- ficiency and economy interchangeably – even though they do have different technical definitions. Also for practical purposes, we’ll only be referencing efficiency going forward.

So here it goes.

Before digging into specific methods for improving efficiency, it’s worth understanding that the term itself can be broken down into two main groups:9

  1. Metabolic Efficiency
  2. Mechanical Efficiency

METABOLIC EFFICIENCY

Metabolic efficiency is all about energy systems and training the body to use available oxygen and energy stores as effectively as possible. It’s no surprise then that endurance runners excel here. The many miles spent running at slower speeds is exactly what has the biggest impact on metabolic efficiency.

Energy optimization is a huge factor here: the ability to use the correct energy conversion system to supply the most energy possible.10 Our bodies blend multiple energy systems to power our muscles while running, and the better these energy systems work the better
we can make use of available oxygen and macronutrients. This is at the core of metabolic efficiency, and, as previously discussed, this is the factor best trained by running more.

Physiological, environmental and mental factors also play a role. For example, gender, age, temperature, fluid loss, fatigue and motivation impact your metabolic efficiency.

Some of these influences are out of our control, of course, but maintaining optimal hydration, body temperature and mindset are things we can influence.

MECHANICAL EFFICIENCY

Mechanical efficiency, meanwhile, is all about technique, coordination, running skill, body movement, the shoes we wear and the surfaces we run on. Mechanical efficiency dominates when running at high speeds, which is why sprinters tend to have outstanding mechanical efficiency.

To transfer high forces into fast running speeds, sprinters train to recover steps very quickly and have very short ground contact times. Naturally, this is something endurance runners need to practice too, just to a lesser extent.

Regardless, back to our previous point, biomechanics play a large role in determining mechanical efficiency. Body mass, body structure, movement dynamics, cadence and shoe selection are just a few examples of how we can leverage biomechanics to our benefit.

Neuromuscular facilitation also plays a role in influencing mechanical efficiency. Your coordination, skill and overall athleticism often come down to neuromuscular programming.

Ultimately, both mechanical and metabolic efficiency blend together to form the complete picture of one runner’s overall efficiency at a specific speed. Mechanical efficiency is most important as speed increases and metabolic efficiency dominates at lower speeds. The best runners excel in both!

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