• 27 DEC 13
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    The shape of things to come

    The shape of things to come

    VO2max testing has long been regarded as the ‘Gold Standard’ and ultimate physiological measurement in many types of endurance sport. Even though this performance parameter is seen as the holy grail in sports performance, the numbers are unreliable and have very little value for helping an athlete wishing to progress in training. This might sound controversial, but it has long been known by mainstream sports scientists. In fact, Lambert has published vast amounts of scientific evidence against the validity of capturing improvements in VO2max and their significance (check out the real nitty gritty of the science here). In one study, variability of VO2max between elite althletes was around 25%, and that the absolute value only changes by about 1% between pre- and in-competition, while the Typical Error in Measurement (TEM) was 2-3%. The numbers speak for themselves.

    Lambert actually suggests that Heart Rate Recovery (HRR) and Peak Power Outputs (PPOs) or even simple time measurements are much more robust indicators of performance. However, many applied physiologists and professional coaches now believe that lactate is the ideal standard to predict cycling ability and derive accurate zones for targeting physiological systems.

    I would like to take this opportunity to put the scientific principles and current understanding of cycling performance into perspective, which means examining what the VO2max (sometimes called peak VO2) parameter is about and how it relates to more important physiological systems critical to cycling performance…….

    The most important physiological factors (at sea level) that determine VO2 max in a given individual are:

    • the ability of the heart to pump blood
    • the oxygen-carrying capacity of the blood (hemoglobin content)
    • the ability of the working muscles to accept a large blood supply (amount of capillarisation within a muscle)
    • the ability of the muscle cells to extract oxygen from the capillary blood and use it to produce energy (number of mitochondria and aerobic enzymes)

     

    The measurement values of oxygen uptake from the lungs and delivery to the muscles are calculated in volumes of oxygen in (ml/min/kg) and it is the peak value which is regarded as the number that competitors aspire to and compare themselves with the competition. Why? If you are looking to become world champion, fair enough. A few performance cyclists who don’t have a peak VO2 value well above 65ml/min/kg will probably never make it to the national level or beyond…..but knowing this number doesn’t help you improve your overall performance!

    However, like many principles in science, this is not a hard and fast rule. It is known that the maximal aerobic power (at VO2max) is not as strongly associated with VO2max uptake and delivery as previously thought, and is more closely associated with cycling efficiency (the ability of your muscle mass to convert oxygen and fuel into energy, more formally defined as the ratio of work generated to the total metabolic energy cost) , more about cycling efficiency below.

    As anyone who has done a VO2max test knows, it is extremely uncomfortable, this is because it is an acute (brief) test designed to capture the upper ceiling of your body’s ability to absorb and deliver oxygen, in a similar way of capturing maximal heart rate.  Two main issues immediately spring to mind, firstly that the peak or maximum VO2 value is incredibly short lived (less than a minute) and hence is not practically relevant to a performance situation….More clearly, as soon as you reach your VO2max, the next thing to come is complete fatigue before recovering your energy systems for the next effort, hopefully much, much later. The only relevant practical scenario for this would be close to the end of a long climb when you are ‘all-out’ to reach the finish (it should be the finish of the race or event! Otherwise you might be in trouble trying to recover before the next climb). If you have gone into the red-zone like this, then you would expect to take a considerable amount of time to fully reconstitute your energy, which is usually done while descending or drafting and DEPENDS most importantly on your threshold level or critical power. This doesn’t mean training your VO2max is not invaluable, but it should be done with the right foundations in place and for the right durations.

    Thus, the best situation is not to reach maximal at all, but somewhere just below it and maximise your ability to maintain that intensity, then you can recover from the effort more quickly. The same applies to riding on the flat, some of the best training stimulus can come from pushing your aerobic capacity by increasing speed on the flat, not sprinting, but intervals of more intensity which ‘nudge’ the upper limits of your aerobic capacity. These are not ‘all-out’ but close enough, as this gives you time to recover and repeat the exercise to increase the volume and exposure at this intensity, ie training with intervals.

    EPOC_Graph

    Sprinting is slightly different, as even though it involves an intense aerobic stimulus, the short nature of it relies more heavily on anaerobic capacity which is demonstrated by the considerable Excess Post-exercise Oxygen Debt (EPOC, ie how much oxygen is consumed and the total theoretically required for the effort = Anerobic Work Capacity). ‘Attacks’ should also be of sub-maximal nature too, and based on predominantly anaerobic capacity before relying on a strong VO2 component just above your threshold to ‘stay-away’. All these systems have subtle yet crucial differences and are easily mastered once you have a feel for your zones.

    The second observation taken from VO2max testing, although obvious,….. it is a maximal test, requiring maximal cardiac output and hence maximal heart rate (as Cardiac Output = Stroke Volume (SV) x Heart Rate (HR)). This lies at the extreme end of your ability which may be subject to considerable day-to-day variation. If you measure your heart rate upon waking each morning, it will vary between occasions. This also applies to the maximum heart rate you can achieve on any given day. It has been reported that there can be up to an 8% variation in the VO2max value due to this natural daily variation. Further, for comparative testing you need two independent measures to capture any change in performance and so a combined variation in test values is likely to be affected by daily variation and other factors such as hydration, stress, illness, nutrition, and environmental temperature, rather than a true change in VO2max.

    Much of the information above is further highlighted by the fact that VO2max or peak is largely determined by your genetic make-up. This is true to an extent, although different sports dictate different VO2max values. Cross-country and biathlon skiers have some of the highest VO2max values due to the amount of muscle mass that is recruited during the activity. A runner may have a large stroke volume (amount of blood pumped by the heart per beat) but if you put them on a bike, their VO2 max measurement will come out lower than when they are tested on a treadmill. Similarly, a cyclist will not do as well on a treadmill. This is because of the difference between systemic adaptations to the training impulse and peripheral adaptations. Both runner and cyclist have large stroke volumes but the runner’s quadricep muscles cannot accept as large a volume of blood and extract oxygen as efficiently as the cyclist’s quads. Likewise, the hamstrings and especially the ankle extensors (gastrocnemius and soleus) of the runner are able to receive larger amounts of blood and extract oxygen more effectively than those of the cyclist.

    Studies on the effects of de-training have shown that VO2max values during the off-season decline as soon as racing or training stimulus is ceased. BUT, these levels only decline to approximately 85% of peak values within 2 or 3 weeks and can remain elevated for over 8/12 weeks. This allows seasonal competitors to take a break and allow their physiology to re-charge, usually by starting some cross-training (using a different activity to stimulate the body before Winter training commences). Hence training to keep your aerobic ‘ceiling’ as high as possible should be your main objective during periods of specific conditioning, without the need to actually know how high it is, as you will probably never know the true value.

    As mentioned above, cycling efficiency has an inverse relationship with VO2max and can explain why an athlete with a low VO2max number can still be competitive against higher ranking opponents. Cycling efficiencies can be considered as the oxygen cost needed to produce energy when glycogen or fat is metabolised (or lost as heat) and has been suggested to be a key determinant of endurance cycling performance along with the lactate threshold turning point. The more streamlined this process is in both the liver and muscles, and the optimal proportion and capacity the muscle units have, the better someones cycling efficiency will be. Whilst VO2max and lactate threshold, have been shown to explain some of the variance in cycling power output between individuals, gross efficiency accounts for a large component. This is where it starts to get a little confusing for everyone!

    Gross efficiency, anaerobic capacity and lactate.

    Blood lactate concentrations are a function of the interaction of anaerobic and aerobic capacity. This may explain lactates close link with gross efficiency and how oxygen utilisation affects lactate production. Lactate is produced at varying rates when at rest, when at maximal exertion and most importantly at any intensity between these limits, where daily variation is at its lowest. Resting blood lactate concentrations could vary by 5% between occasions (more significantly if an individual is ill or over-trained) but the multiple measurements provide a profile which can be compared between occasions with validity. The curve that is created when blood lactate is plotted against work done over time (power output) really can provide an excellent biophysical profile highlighted by the following aspects:

    • Baseline – resting lactate values show us the general condition of a cyclist, higher levels indicating if they have a larger anaerobic capacity, as muscle tone is maintained at rest lactate is produced in larger amounts. Increased levels due to illness are confirmed by an individuals health status, although testing should always be avoided if this is suspected.
    • Sub-threshold intensities- demonstrate important aerobic management of lactate as clearance and distribution of blood levels are observed.
    • Gradient of the curve- shallower curves often reflect athletes with a higher proportion of Type I A oxidative muscle and thus aerobic capacity. Usually athletes with a higher proportion of slow twitch fibers will have a flatter curve.
    • Threshold turning points- MLSS and OBLA determine the point before and after at which energy production turns predominantly anaerobic as clearance of lactate is overwhelmed by its production. This is the key sub-maximal reference point used to compare subsequent testing. Increased power or decreased heart rate at this point suggests an improvement if this occurs at the same concentration of blood lactate as previously measured. A new threshold point may be accomplished after a period training as even better conditioning allows the cyclist to maintain threshold power at a lower steady state depending on the discipline being trained for (time-trial vs sprinting for instance).
    • Maximal lactate production – this is a good indication of the total anaerobic capacity of an individual. Although peak lactate values do not allow for direct comparison between athletes, maximal lactate production may reflect how well that athlete may perform compared to the competition.
    • Clearance, this secondary parameter is equally important as the threshold turning points when it comes to demonstrating performance improvements. Simply put, the more efficient you are at clearing lactate, the better performance you can expect in your all-round cycling ability. An analogy would also be the duration it takes for your maximal heart rate to recover to resting values. The quicker that is, the fitter you are.

    VO2max and lactate threshold parameters are related, as training to increase your aerobic ceiling will push up your threshold turning point at the same time but will remain at the same proportion of your VO2max. In this instance, slow-twitch muscle recruitment is favoured to maximise this capacity.

    Briefly explained; as lactate is used as a fuel during anaerobic metabolism, lactate will dictate maximal aerobic power as the aerobic system relies on the anaerobic system to metabolise carbohydrate (glucose) via lactate and pyruvate which enter the mitochondria to produce energy in the presence of oxygen. It is only when sufficient oxygen isn’t available and the muscle relies predominantly on inefficient anaerobic metabolism and the recycling of lactate fails and starts to accumulate. However, limitations exist….if the anaerobic capacity is too high, the athlete will be slowed down by too much acidosis that accompanies lactate production. So for this athlete to participate well in endurance events it is necessary to reduce the anaerobic capacity if this is too strong, this forms the basis of the principle ‘Go slow to get fast’. The lower it is the more the aerobic system can be utilised before acidosis occurs. Although this shouldn’t be too low. If the anaerobic capacity is too low, less carbohydrate will be available for aerobic metabolism. This in turn will cause the athletes metabolism to rely too much on fats and slow down the metabolism. Therefore the ideal situation is to raise the point at which this occurs (termed the lactate threshold) so that fat is the predominant energy supply up to as high an intensity as possible before precious glycogen is needed.

    This is true until peak VO2 reaches its natural limit at which point training your threshold level to be as large a proportion of that capacity as possible is the only natural way of improving performance. Therefore, the performance model suggests that overall cycling performance is much more reliant on lactate threshold than it is on VO2max, and that gross efficiency is a determinant of how high that threshold can be sustained. In fact, to add even more to the confusion, lactate threshold and VO2max values can go in different directions, possibly in an over-training scenario where aerobic capacity has been the sole focus of a cyclist and the anaerobic capacity has dwindled away.

    Gross efficiency can therefore be influenced by high intensity work rates as seen by changes in muscle biochemistry which at the same time may help to keep a high aerobic ‘ceiling’ and resistance training, which may mimick the effects longer and slower endurance training or even accentuate the physiological enhancement of the muscles.

    Both will positively influence where your lactate threshold occurs, before working to improve that value alone by fine tuning the optimal proportion of aerobic to anaerobic capacity in your functioning muscles.

    VO2max may have created itself a reputation, but it isn’t set on the most robust of foundations. Ultimately understanding how your anaerobic and aerobic systems interact through lactate production is extremely valuable insight into any athletes physiology. The rich lactate data is enhanced by periodic testing, as all of the profile aspects highlighted above will suggest either performance improvements or a decline. So now we can see why this is an ideal tool for steering any training programme in the right direction!

    Dr. Jesper Medhus explains here how effective interval sessions can be used to improve aerobic capacity using sub-lactate threshold and supra-threshold efforts. Although a critical power calculation will provide you with the most time efficient and effective means of targeting the right energy systems for the correct duration for a minimal effective dose of training, keeping intensity high and volume low for specific conditioning and adaptation.

    Take home message:

    Individuals new to cycling are right to focus on improving their total aerobic capacity, pushing their VO2max levels to their natural limits, either done alone with intervals on short climbs or in chain-gangs where you are expected to ride at a level that makes you over-reach your abilities for the longest duration (ie avoiding getting dropped). So be sure to join a ride that is suitable to you and doesn’t stretch you too far that the elastic snaps!

    Adequate recovery is essential from any long threshold (or above) efforts. Over-time, you will begin to realise that your improvements plateau as you maximise your aerobic ceiling. This usually happens because the need to improve your anaerobic capacity is relative to this. Training to raise your VO2max may negate the available time and energy needed train other systems important for performance. Once you address this issue, you are able to pump enough lactate into your aerobic system to take it to the next level and your threshold rises. The idea is to maintain the right balance between aerobic and anaerobic (as assessed through periodic lactate threshold profiling), and improve both. More experienced riders (those who have larger total capacities) have trained to the limitations of their aerobic and anaerobic capacities, and have consistently pushed those to close to maximum, depending on the type of racing. They focus on maintaining that system but more importantly optimise their threshold (dictated by the fine tuning of anaerobic and aerobic systems) to be as close to their maximal aerobic power as this allows (ie the proportion of VO2max). So, they have as much power for the longest duration that their muscle and liver glycogen allows, then they can be competitive to the best of their abilities.

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