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METABOLIC & PHYSICAL FITNESS TESTING: UNDERSTANDING WHAT’S GOING ON UNDER THE HOOD

You do a workout or a competition and your performance is ‘X’ time, or ‘Y’ number of reps, or whatever the scoring is for that particular bundle of fitness fun you have undertaken.


WHY did you perform that way?


Psychology, fuelling and environmental conditions are fundamental to whether you can fulfil your performance potential on any given day. But it is your physiology and how well adapted (or not) it is to your sport that primarily determines your performance potential.


At the highest level, exercise physiology is summarised in the graphic below. Dependent on your sport, one or more elements (or sub-elements) will be of greater importance than others. For example, if you are a boxer, high repeat performance anaerobic capacity and explosive power (force generating capacity) relative to bodyweight supports performance across multiple bouts in a fight, and high aerobic capacity supports this and long training sessions. If you are an ultramarathon runner, a large aerobic capacity, the ability to sustain close to this for extended periods, muscular endurance (force generating capacity), and mechanical efficiency even when fatigued (neuromuscular coordination) is key. If you are a CrossFit athlete, you are trying to optimise it all! And so on …

Metabolic and physical fitness testing is the opportunity to understand your physiology, how well it is adapted to your sport, what might be holding you back, and why. Training and nutritional strategies can then be designed to address the weaknesses and support the strengths, with the goal of improving overall performance.


So what can be tested, and what insight might it give? Key tests are summarised below, and in blogs over the coming weeks we will dive into deeper detail on some of these, how we interpret the results, and more detail on how they can be used to inform nutrition strategies.


Energetic Capacity

There is a lot we can do to understand energetic capacity, at least with a little equipment!


First and foremost, we can understand what your energetic capacity is:


Aerobic capacity

By monitoring your breath during exercise of increasing intensity we can determine what the maximum oxygen you can use during exercise is and what intensity of exercise this can maintain


Anaerobic capacity

There are several aspects of anaerobic capacity that we can assay.


The anaerobic system is dominant over exercise bouts at high intensity lasting around 10 seconds to 10 minutes. To estimate how big your anaerobic ‘engine’ is, a common test performed is to exercise at the maximum possible intensity you can, i.e. “all out”, for 30 seconds and measure how much power you produce. You should be crippled on the floor after this!! This is a Wingate test, or a variation thereof.


By monitoring your breath during exercise of increasing intensity (as for aerobic capacity) we can estimate anaerobic threshold, which is how intensely you can you exercise before you get towards that ‘burning’ feeling that will ultimately slow you down, and how this compares to your aerobic capacity. This is similar to the lactate threshold, which we can measure through a skin prick blood test during exercise of increasing intensity. The lactate threshold represent how intensely you can exercise before lactate (a by product of anaerobic energy production) begins to accumulate in the blood. In both cases, these thresholds represent the body’s anaerobic machinery working so hard that the by-products of the process can no longer by removed by the body as quickly as they are produced. Which ultimately results in fatigue, directly and indirectly, that causes us to reduce our exercise intensity or stop entirely! The higher the anaerobic or lactate threshold, the higher exercise intensity you can maintain for longer.


Fuel utilisation

Again, by monitoring your breath during exercise of increasing intensity and also after fuelling on different foods, we can determine how much fats and carbs you are burning at any one exercise intensity.


So that is how we can estimate your energetic capacity. Now WHY is your energetic capacity as it is?


There is so much we can look at here!


Respiratory capacity and capability

This is how deeply and rapidly you can potentially breathe, and then how well you actually do this during exercise!


Cardiovascular fitness

This is how effective your heart seems to be at delivering oxygen to your working muscles. It can be estimated by measuring heart rate and seeing if you can reach your theoretical maximum during exercise of increasing intensity, and measuring oxygen saturation in the blood and at the muscle and how that changes during exercise of increasing intensity and the recovery period after.


Muscle oxygen utilisation

This is whether, once at your muscle, oxygen is actually effectively used! As with cardiovascular fitness, we can estimate this by looking at the change in oxygen saturation in the muscle across exercise of increasing intensity.


By understanding what and why your energetic capacity is, we can adapt training to address the weaknesses for your sport. And, alongside, adapt your nutrition to support performance in training and the adaptations that training is trying to achieve. There will be a lot more on this in the next blog, but to give an example: if we find that your lactate threshold is low we may consider a supplement to reduce the accumulation of acid in the muscle. This will enable you to maintain a higher exercise intensity for longer, which may in turn drive the adaptations that will improve the body’s own capacity at this intensity.


Force Generating Capacity

The most notable elements of force generating capacity are:


1. Raw strength: how much absolute weight can you move

2. Power: how much weight can you move and how fast

3. Muscular endurance: how many times can you move this weight


As with many things in science, we can get very fancy and precise with the equipment we use to test each of these. But we can also get a pretty good idea from rough and ready approaches. Take a barbell lift like a back squat for example and:


1. Raw strength: what is your 1RM

2. Power: how fast can you back squat a certain % of your 1RM, and how does this change as the weight on the bar increases

3. Muscular endurance: how many times can you squat a certain % of your 1RM, and how does this change as the weight on the bar increases


Now WHY is your force generating capacity as it is?


Strength is determined by contractile strength, as well as (because nothing works in isolation) energetic capacity and neuromuscular coordination.


Appropriate training and nutrition support enhanced force generating capacity. The appropriate training programme will be very much determined by factors such as your training experience, the training load you can tolerate, the aspect of force generating capacity you are focussed on improving. Nutrition will also be influenced heavily by these factors, but there are principles that are broadly applicable: sufficient energy and protein intake to support training, muscle repair and adaptation, a consideration of protein timing, and intake of certain supplements such as creatine.


For more on strength, check out this blog.


Neuromuscular Coordination

Mechanical efficiency is a key component of this, i.e. for any one calorie used in exercise how much power do you produce in any given movement. For example: For a cyclist, what is the watt output on the bike? For an Olympic lifter, how much weight do they lift and how fast? For a runner, what is their speed relative to bodyweight?


Our aim is to be as efficient as possible as this we can move ourselves or weight faster and / or for longer. Aka enhance performance!


We can test mechanical efficiency using the breath analyser discussed within ‘Energetic Capacity’ above. By measuring the oxygen absorbed and carbon dioxide exhaled per breath, calorie expenditure can be estimated. This is then compared to the amount of power you are producing at that time in your movement, e.g. the watt output on the bike and other examples given above, and a mechanical efficiency score given.


Now WHY is your mechanical efficiency as it is?


It is determined by how effectively your muscles convert energy to movement, as well as how efficient your movement pattern is.


Movement pattern can be analysed visually and with tools that measure how you distribute weight and force during a movement. To bring this to life: if you are a runner and you wave your arms and legs all over the place, slam your feet down with a huge amount of force, and take tiny strides you do not have an efficient movement pattern and will be using a lot of energy to produce relatively little speed! Typically, movement pattern will be improved through technical training sessions focussed on this.


In the field it is very tricky to test how efficiently muscles convert energy to movement, however we can make inferences from how good our movement pattern is relative to our mechanical efficiency. And adapt our training to address any potential weaknesses: for example threshold training that forces the muscles to work at the extreme end of their capacity, triggering adaptation in the muscle that will make them more efficient so that working this hard is not so stressful next time around!


In summary: metabolic and physical fitness testing is the chance to look under the hood and work out why you perform the way you do. And knowledge us power! By understanding where your strengths are, and what is holding you back, you can adjust your nutrition and training to capitalise on those strengths and tackle those weaknesses … and be fitter, go faster, and for longer!!


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