Endurance Performance Limiters: An Introduction
Training over the winter to improve your performance on a turbo trainer has been a cycling tradition and with the likes of Zwift, Trainerroad, BKool, etc emerging into mainstream over the last few years and thanks to the ever lowering price point of smart turbos equipped with power meters its now easier than ever to find some extra motivation to jump into your cycling kit in the winter months and get ready to smash out some sessions. Usually the point of training is to improve FTP or VO2 max and most platforms will offer an integrated ramp test to quantify your current performance level. At a deeper level, when it comes to Endurance performance VO2 max test results have been a valid quantification of performance potential and a lot of training plans aim to improve your VO2 max or FTP, with the premise being that the higher the score the higher the potential for a good result in any given endurance event. In practice a high VO2 max figure although nice to have on hand often doesn’t highlight the exact training an athlete may want to do to improve in order to further raise their VO2 max, or FTP for that matter, for that sort of information we look to descriptive testing such as 5-1-5 testing with a NIRS (near infra res spectroscopy) device. We use descriptive testing to identify performance limiters and thereby determine the mechanism by which the athlete failed to deliver a higher performance score.
A 5-1-5 test showing the haemodynamic response to cycling at every increasing power outputs. SmO2 on the L/R legs shown in the purple lines is descending as the power increases throughout the test suggesting that the ability to use oxygen at the muscle isn’t a problem this athlete has, this test suggests the athlete should focus more on training methods that work on the delivery of oxygen to the working muscle. Such as Zone1/2 work or some progressive interval training.
In a physiological context performance limiters refer to by what physical process in an athletes fitness held the athlete back from a better performance and hence if that limiter was to be trained and improved the performance would have been better, in endurance performance we can brake the limiters down to 3 main areas.
Respiratory limitations
Delivery limitations
Utilisation limitations
To dive into these a little deeper…
RESPIRATORY LIMITORS - An athlete who is respiratory limited struggles is one who fails to use their lungs to their fullest potential and is limited by the supply of Oxygen they can take from the air and put into the blood or by the amount of Carbon Dioxide they can blow off into the atmosphere. This can play out in a number of ways but a common factor is an athlete who is limited by the volume of air they can move per breath they take because they potentially lack the coordination required to fully use their diaphragm or are maybe restricted in their ribcage and their thoracic spine making the diaphragm and intercostal muscles hard to recruit around a poor skeletal posture during exercise. The corresponding lacking of enough volume per breath relative to the corresponding demand for oxygen drives up breathing frequency and an athlete breathing too fast and shallow struggles to keep air in the lung for long enough for efficient oxygen transfer to take place, this causes the percentage of (totally usable) exhaled oxygen to start rising per breath taken and the percentage of blood PH altering CO2 the potential for this issuer is measurable in a spirometry test by the amount of air blown out in 1 second (FEV1) and also by the total volume of exhaled air in a spirometry test (FVC6).
Graph showing % of CO2 on the outbreath dropping after 1600 seconds showing that the athlete is getting worse as the test goes on at exhaling CO2
The implication is the knock on effects of the resulting hyper or hypoventilation drive compensations in other areas - the subject of a future blog post! The upshot of course is if a respiratory limitation is identified it can be trained by either functionally improving an athletes ability to move more volume of air per breath or improving an athletes coordination of breathing to be able to match their breathing frequency with breathing depth to match their level of oxygen utilisation.
DELIVARY LIMITORS - Also known as cardiac limitations basically the heart cant pump strong enough or fast enough to supply the working muscle with oxygenated blood. In this case the rate of oxygen utilisation in the muscle is exceeding the rate of delivery. For delivery limited athletes, one of the main limitations is that their cardiac output is insufficient to deliver oxygenated blood to the working muscles. It’s not uncommon for these individuals to have very good mitochondrial and capillary density, and as a result oxygen extraction, but because they are limited by the maximal pumping capacity of their heart blood flow to the working muscles is restricted. As a result, oxygen utilization supersedes oxygen supply during maximal effort tests of work capacity and these athletes fail when muscle oxygen saturation reaches a point where the athlete cant push past any further. Another way this can play out is when a powerful athlete relies on generating too much muscular tension to create a certain amount of energy. working muscle creates tension which compresses the veins that pump blood back to the heart this phenomenon is actually a great work of design that assists in getting blood back to the heart, but as the amount of muscle required to match an energy output increases this compression can begin to get obstructive and keep blood backed up in the muscle. Since the cardiovascular system is a closed loop (as in nothing can enter or exit) and the heart is the central master pump, if blood is stuck in the muscle it reduces the amount of blood the heart can pump out per beat, compounding the issue.
UTILISATION LIMITORS - Utilization limitations differ from both respiratory and delivery limitations in that these athletes have sufficient oxygen supply to the working muscles. However, it’s difficult to create a standard picture of a utilisation limited athlete because the causes of utilisation limitations are so broad. For example, an athlete can be limited by their rate of oxygen utilization, or the magnitude of utilization. Additionally, these factors can be influenced by mitochondrial and capillary density, muscle damage, muscle coordination and recruitment, as well as shifts in blood chemistry changing a and causing a left shift in the hemoglobin dissociation curve from hypocapnic breathing (Google the Bhor effect). As a result, there is not a clear cut set compensations associated with utilization limited athletes that we can draw conclusions from or always a clear cookie cutter protocol to follow to improve an athletes Oxygen utilisation.
Assuming a utilization limited athlete is not over trained or injured, the primary adaptations they’ll want to target in their training are increased mitochondrial density, increased enzyme concentrations, improved coordination and recruitment, and increased metabolic oxygen utilization. Often a big picture view of an athlete will help the most here as it will inform and refine the style of training required in order to improve performance.
At the beginning of training the chances are you can follow a once size fits all training program and based on your current performance level it would be effective as there would be enough runway in each of your limiters that you would be able to improve. However if you are well trained already or if your training program has consisted of the same style of intervals for several years and the returns you used to get aren’t coming your way anymore, you may not be training in a way that allows your limiter to be physically challenged enough to elicit a training response.
If you are interested in finding out your limiter then book in a 5-1-5 test with us and find out how best to train this winter to stop them limiting your performance for the cross season or for next spring when you jump back off your turbo.