A Male Triathlete In A Full Tuck On The Bike During A Race

How To Understand Human Efficiency and Its Impact on Triathlon Achievement

BY Tom Epton

By breaking gross efficiency down into its constituent parts, we can make performance gains easier to find and quantify, making areas where an athlete has room for improvement easier to spot.

Triathlon coaches worldwide have been enamored with the approach taken by the coaches of the Norwegian Triathlon Federation. One of these is their seemingly mad scientist Olaf Aleksander Bu, who has yet to receive formal education in triathlon coaching. Bu’s background is one of engineering and physics, which has led him to great success as he recognizes his quest for peak human performance can be pursued through understanding, measuring and improving the gross efficiency of his athletes. The idea of efficiency is an exciting concept that most coaches already know — improve your athlete’s output through the same level of mechanical input. Athletes can find efficiency gains from improving swim technique, bike aerodynamics, running mechanics and many more aspects of body and machine mechanics.

Understanding what efficiency is

To understand efficiency within sport, we must consider some physics. Now, the laws of physics tell us that total energy will remain constant in an isolated system. We can show how a system uses energy with a Sankey diagram.

Efficiency Sankey Diagram
Epton Efficiency Sankey Diagram Copy

The width of the bar is proportional to the amount of energy it represents, meaning that we have a clean visualization of where our system can make improvements.

Efficiency is easiest to illustrate by imagining a car with a full petrol tank. This tank is our energy budget. The speed at a given time can measure the output of this car, and it can travel some distance at each speed. How can we make the car more efficient? A vehicle burns petrol in the engine, which drives the wheels to turn, but the amount of gas we have is fixed. Let’s say we want to go 100 miles and get there as fast as possible.

If we drive at 100 miles per hour, our car will run out of petrol after 98 miles. We will need to push the car the final 2 miles — the equivalent of the vehicle bonking. Instead, we drive at 98 miles per hour and get there in just over an hour with a perfectly empty tank. To improve and get under the hour, we must determine what energy the car is losing to inefficiency.

When a car drives, it must fight against two main adversaries: the resistance from the air and the resistance from the road. Of course, there are other factors to consider, but let’s stick to these for simplicity’s sake. If we remove the body of our car and replace it with a more aerodynamic one and our tires have the ideal inflation, we suddenly find ourselves able to drive at 105 mph for the same amount of fuel as 98 mph! We can also find improvements by cleaning the engine, replacing leaky valves and pipes and so on — many efficiency improvements could be made.

The human body differs significantly from a car, but we can highlight some analogies. We have a specific energy budget for getting from point A to B with whatever tools we have at our disposal, and efficiently utilizing this energy budget can allow us to get there faster than others with a larger budget. We can agree that in endurance sports, efficiency is king. It’s not just about increasing the amount of energy (or power) we can put into a system but reducing the amount of input energy our body wastes.

How can we measure efficiency?

Measuring the efficiency of a human is somewhat complicated. We need to understand the journey of energy input to generate movement. Most coaches are familiar with a power meter on a bicycle, these measure the amount of power an athlete puts out, but for our purposes, we will think of them as energy meters. Power is the time derivative of energy. That is to say that it’s the amount of energy we use per second. If we add up every power number at every tiny moment — a mathematical trick called ‘integration’ — we get the energy measured over that duration.

a screenshot of a TrainingPeaks Power Graph from the app

Here is an example shown in this graph from a 10-minute interval. It shows power (in purple) and heart rate (in red). The area under the purple line is calculated by TrainingPeaks and is labeled as “work,” measured in kJ. Power is an instantaneous measure of energy — 1W = 1J/s. Energy and power are the same. And efficiency savings allow us to use the same power for more speed, meaning less energy is used overall.

Measuring Mechanical Efficiency

Mechanical efficiency is the amount of energy that is output by our body (in cycling, our power meter tells us this) that is lost to the environment. On a bike, this would be the amount of energy lost to gravity (hills) or wind (aerodynamics) — so being lighter and more aerodynamic would make a rider more mechanically efficient.

The relationship of power to speed is studied quite intensively. An example field of study devoted to it is aerodynamics. These values are highly measurable, too. We can see how much power and speed we generate, then make some changes and see if we go faster using the same power. If so, then we can declare ourselves more efficient.

There is an arms race in many aspects of the cycling industry to find better aerodynamics to provide better mechanical efficiency. It’s also one reason you will see updated bike equipment, helmets, skin suits and so on.

What if we want to take it further? How can we measure the energy our body generates through our legs? Yes, we can, but it’s less accessible as we can’t just install a power meter in our bodies. We could describe this as biochemical efficiency, as in how efficiently the processes in the body contribute to producing mechanical power on the bike.

Measuring Biochemical Efficiency

The ability to measure biochemical efficiency is in its infancy and is an example of where theory is ahead of practice. Wasted energy from the body tends to come in the form of heat. If we can measure core body temperature changes and useful power at the legs, we can plausibly measure the biochemical efficiency of an athlete.

Hypothetically, an athlete could test at a given power, heart rate and core temperature to establish a baseline. The athlete would then do a heat tolerance block to train the body to adapt and generate more watts for the same heart rate and core temperature. This would be a result of improved biochemical efficiency.

Measuring this exactly isn’t a simple task yet. Calculating efficiency as a function of core body temperature will likely develop over the next several years and become more accessible to amateurs thanks to devices like CORE. We could be on the cusp of the next leap in human performance through various biochemical efficiency improvements measured by new technologies.

Adding it Up to Gross Efficiency

Improvements in the body and equipment ought to lead to overall improvements in efficiency. Again, this means we can go faster with the finite energy we have available. Indeed, training can increase the amount of power available, but it can also make the body incrementally more efficient so that we can convert more of that power into speed! The challenge for a coach is to identify areas of inefficiency, then implement a training intervention to address this.

If we put these ideas into a formula, it would simply be:
Gross efficiency = Biochemical efficiency + Mechanical efficiency

From Calories to Speed

Maybe you’ve read or heard this statement: “There’s no speed without power and no power without calories.” The relationship between the amount of energy available and the amount of food an athlete eats cannot be forgotten!

There are also efficiencies to be found in the fuel and hydration our athletes use. Nutrition has many variables to consider based on each athlete’s needs, so for now, we’ll stick to understanding these gross efficiencies.

Conclusions and Key Takeaways

  • The human body is not a simple machine but can be studied like one to find performance gains.
  • Mechanical efficiency measures the proportion of energy we lose to the environment through factors like air resistance and rolling resistance in cycling. Other sports also have other resisting forces to factor.
  • Biochemical efficiency measures the proportion of energy our body wastes moving our limbs in the desired pattern, like pedaling a bike or running.
  • Gross efficiency measures how much energy we waste and is the sum of mechanical and biochemical efficiency.
  • By breaking gross efficiency down into its constituent parts, we can make performance gains easier to find and quantify, making areas where an athlete has room for improvement easier to spot.


Triathlon coaches can improve their athletes’ efficiency by understanding the core concepts of efficiency and quantifying opportunities for free speed.

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About Tom Epton

Tom Epton is a writer and data scientist based in the South East of England. He is a founding member and principal data scientist at PyTri Ltd, a consultancy specializing in applying data science techniques to performance sports and healthcare. Tom has a first-class BSc in Physics and has worked at several well-known brands on big data and machine learning projects. Away from work, he is an elite triathlete racing a mixture of draft-legal short courses on the British Super Series to middle-distance non-drafting triathlons. Tom also offers coaching, physiological testing and endurance sport consultancy services. Email him for more information.

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