The Physiological Demands of Ultra-Distance
Whatever your discipline of choice, one of the key training principles is specificity. This entails that, when preparing for a particular event, one’s training should increasingly resemble the demands of that event the closer to the goal date. Traditional coaching advice is commonly tailored to the demands of ‘endurance’ events which naturally attract more attention from researchers and form the basis of many training plans. However, if the demands of ultra-distance events differ from those for other cycling disciplines, then a more nuanced approach should be taken to training and preparation.
Some people will have you believe that ultra-distance events are more a mental challenge than a physical one. However, you can be as mentally tough as you like, but without turning the pedals you aren’t going to get very far. Although psychological and logistical factors are hugely important in ultra-distance events, particularly when self-supported, if the physiological side isn’t up to the job, then accomplishing one’s goals will be beyond reach. Having faith in one’s physical capabilities can also have a huge positive knock-on effect to self-confidence and belief, hence feeding back to the psychological piece.
As Zaryski & Smith (2005) succinctly put it:
‘Successful ultra-endurance performance is characterized by the ability to sustain a higher absolute speed for a given distance than other competitors.’
An understanding of the fundamental physiological demands of ultra-distance cycling is thus the first step towards defining a successful outcome and deciding upon the areas that need to be improved upon through specific training and preparation.
Explaining Endurance Performance
In 2008, Joyner & Coyle, drawing on earlier pioneering studies such as A V Hill’s first description of VO2 max in 1923, proposed a conceptual model describing the key factors influencing ‘Performance Velocity or Power’, with the key elements for endurance being:
Performance VO2. This being a function of:
Maximum Oxygen Consumption (VO2 max) - the maximal capacity to take up, transport, and utilise oxygen.
Lactate Threshold - the ability to maintain high velocity without accumulating blood lactate.
Performance O2 deficit – the anaerobic contribution. However, this is (and should be) close to zero in an ultra-endurance event so will have almost no impact on overall performance.
Gross Mechanical Efficiency - often expressed as the oxygen utilised while producing a given constant power output.
The relative emphasis between these three factors clearly depends on the duration and intensity of the effort. Ultra-distance by definition falls at the extreme end of the scale, namely very long and at a (relatively) low intensity.
Having a high VO2 max is crucial for any endurance discipline as it effectively sets an upper limit to aerobic capabilities, but to really maximise performance one should aim for the highest sustainable percentage of VO2 max for the given duration of the event. This is termed Fractional Utilisation. For ultra-distance, this will be a lower percentage than, say, a 40km time trial.
The Lactate Threshold with greatest relevance for ultra-distance is the first turnpoint (also known as LT1 or the Aerobic Threshold) where the body shifts from primarily metabolising fat as a fuel source towards carbohydrates. This intensity is found roughly at the top end of Z2 and can theoretically be maintained forever, given adequate fuelling (until other factors intervene). There are also two precisions to be made here. Firstly, lactate is used as an indirect marker of fatigue and is not necessarily the cause itself of said fatigue. Secondly, the use of fat and carbohydrate as a fuel source is on a continuum where the relative emphasis shifts, rather than solely using one or the other.
Gross Mechanical Efficiency (GE) can be described as a measure of effective work, commonly expressed as the percentage of total energy expended, or oxygen cost, that produces external work (Moseley & Jeukendrup, 2001). Think of this as your body’s equivalent to miles per gallon.
The effect on performance in connection with the other two factors should be clear, as demonstrated by Horowitz et al. (1994) who found that cyclists with a high GE were able to generate a greater power output for the same VO2 than riders possessing a lower GE. Factors which have been shown to affect GE in cycling include cadence, body mass, cycling position, pedalling technique, prior exercise, muscle fibre type, and training status.
During cycling, the efficiency of the human body is in around of 10–25%, implying that 75–90% of all the energy produced is used to maintain homeostasis or wasted as heat. Small percentage increases in efficiency can therefore have a large impact on performance power and the longer the event, the more these differences will be pronounced. Gross Efficiency is therefore of huge importance for ultra-distance events.
The Fourth Dimension?
A further consideration is the extent to which these physiological variables can be maintained over the duration of an event, particularly for timescales associated with ultra-distances. This is a hot topic in endurance sport at the time of writing and a number of recent studies have taken interest in this ‘fourth dimension’. It is now widely accepted that the three variables in Joyner & Coyle’s model are not static but are prone to significant deterioration as fatiguing endurance exercise proceeds (Jones, 2023).
This measure of the deterioration of these factors over time is described as ‘fatigue resistance’ and ‘physiological resilience’ by Jones et al. (2021), but the term ‘durability’ seems to be prevailing. Maunder et al. (2021) define durability as:
‘the time of onset and magnitude of deterioration in physiological-profiling characteristics during prolonged exercise’.
As the length of the effort required extends, performance is therefore not solely a function of physiological status when fresh but related to the resistance to deterioration in the three main indices when in a fatigued state.
It is still relatively early stages in the research and understanding of this concept, and Jones (2023) identifies that further research is needed to better understand the physical mechanisms underpinning durability, the factors that determine one's resiliency and the interventions that could improve durability.
Application to Ultra-Distance
As signposted in the intro, reliable research on the physiological determinants of performance in ultra-distance sporting events is lacking in comparison with shorter, more frequented disciplines. Studies on triathlon have shown that VO2 max is a good predictor of performance for Olympic distances, but the relationship is not as strong during Ironman events (O’Toole et al, 1989; Laursen & Rhodes, 2001).
In a case-report studying the physiological impacts of a 460km ultra-endurance cycling event including 11,000m climbing, Neumayr et al. (2002) found that nearly the entire workload (99.6%) was done under aerobic conditions. Additionally, exercise intensity was below 70% VO2 max during 87% of the race and below 60% VO2 max during 73%, which would likely be below the athlete’s Aerobic Threshold.
As events become increasingly long, factors such as the Aerobic Threshold and Gross Efficiency become the dominant performance determinants. Although VO2 max and GE are important factors in all cycling disciplines, the longer the event the greater the influence GE exerts on success compared to outright VO2 max. On top of all this is the concept of durability and being able to resist the decline of the three other elements.
Perhaps for logistical challenges, as well as a lack of funding and widespread interest, detailed studies on the physiological demands of multi-day ultra-endurance events are lacking. Nonetheless, it is evident that the physiological requirements for ultra-distances differ to those termed simply ‘endurance’ events. It logically follows that training and preparation for these longer events needs to be tailored for these specificities. This is the approach that Acier takes, with specificity and individuality forming part of the foundations of any training plan. Contact us or email Samuel@acier.cc for a no-commitment conversation on how this approach can work for you and your ultra-endurance goals.
References
Zaryski, C & Smith, D. 2005. Training principles and issues for ultra-endurance athletes. Curr Sports Med Rep. https://pubmed.ncbi.nlm.nih.gov/15907270/
Joyner MJ, Coyle EF. 2008. Endurance exercise performance: the physiology of champions. J Physiol. Endurance exercise performance: the physiology of champions - PMC (nih.gov)
Moseley & Jeukendrup. 2001. The reliability of cycling efficiency. Med. Sci. Sports Exerc. https://journals.lww.com/acsm-msse/fulltext/2001/04000/the_reliability_of_cycling_efficiency.17.aspx)
Horowitz JF, Sidossis LS & Coyle EF. 1994. High efficiency of type I muscle fibers improves performance. Int J Sports Med. High efficiency of type I muscle fibers improves performance - PubMed (nih.gov)
Jones AM, Kirby BS, Clark IE, Rice HM, Fulkerson E, Wylie LJ, Wilkerson DP, Vanhatalo A & Wilkins BW. 2021. Physiological demands of running at 2-hour marathon race pace. J Appl Physiol. Physiological demands of running at 2-hour marathon race pace - PubMed (nih.gov)
Jones, A. 2023. The fourth dimension: physiological resilience as an independent determinant of endurance exercise performance. The Journal of Physiology. The fourth dimension: physiological resilience as an independent determinant of endurance exercise performance - Jones - The Journal of Physiology - Wiley Online Library
Maunder, E., Seiler, S., Mildenhall, M. J., Kilding, A. E. & Plews, D. J. 2021. The importance of ‘durability’ in the physiological profiling of endurance athletes. Sports Med. Durability is improved by both low and high intensity endurance training - PMC (nih.gov)
O'Toole ML, Douglas PS & Hiller WD. 1989. Lactate, oxygen uptake, and cycling performance in triathletes. Int J Sports Med. https://pubmed.ncbi.nlm.nih.gov/2628359/
Laursen, P & Rhodes, D. 2001. Factors affecting performance in an ultraendurance triathlon. Sports Med. Factors affecting performance in an ultraendurance triathlon - PubMed (nih.gov)
Neumayr G, Gänzer H, Sturm W, Pfister R, Mitterbauer G & Hörtnagl H. 2002. Physiological effects of an ultra-cycle ride in an amateur athlete - a case report. J Sports Sci Med. https://pubmed.ncbi.nlm.nih.gov/24672268/