Cardiorespiratory endurance is a key element of health and fitness. In sports, it is reflected in the ability to sustain exercise over an extended period of time. How well the body can take up oxygen, clear lactate, and move efficiently, determines your level of cardiorespiratory endurance, and these factors are largely influenced by age, physical training and genetics.

There are several methods to measure cardiorespiratory endurance. Amongst them - and probably the most important one - is the maximal rate of oxygen uptake by the body (VO₂max). A high VO₂max has been shown to be an important factor for success in intermediate and long distance endurance sports^{1 2 3}, which primarily depend on ‘burning’ carbohydrates and fats using oxygen.

VO₂max is a frequently used measure in sports and science to determine the effect of training, to study the influence of genetic factors on endurance capacity. And, when combined with heart rate and performance tests it can be extremely useful in customizing training plans.

VO2 Max and the rate for success

VO₂max is the maximal amount of oxygen (in millilitres) absorbed per minute per kilogram of body weight. The average VO₂max of untrained young men is around 40-45 mL/kg/min and for untrained young women it’s 30-35 mL/kg/min ⁴. The VO₂max of elite athletes in some sports can be double these amounts; values of 80 mL/kg/min in male and 70 ml/kg/min in female elite runners are not uncommon.

Although for many sports having a high VO₂max is a prerequisite to perform at a top level, having a high VO₂max is not a guarantee for success. The reason for this is that VO₂max only reflects the body’s oxygen uptake (depending on oxygen’s uptake by the lungs, transport by the cardiovascular system, and consumption in the muscle fibre), but it doesn’t say how efficiently the body uses oxygen for movement. And that’s what counts when performing at the elite level.

VO2 Max and genetics

A large proportion of your ability to improve VO₂max in response to training is influenced by your DNA. In fact, genetics can account for as much as 47% of the inter-individual variance in training responses¹⁰. FitnessGenes test for several genes that influence the trainability of your VO₂max - the ACE, PGC1A, CKM, AMPD1, AKT1, HIF1A, VEGF and ADRB2 genes.

These genes impact cardiorespiratory endurance either via regulation and adaptation of the cardiovascular system, lactate clearance, mitochondrial function and many other biological processes. The FitnessGenes reports explains these processes in further detail, and identifies how your genetic variation relates to your VO₂max and overall aerobic potential.

VO2 Max and training

Your capacity to improve your VO₂max depends on your current level of fitness. For untrained individuals it is relatively easy to improve VO₂max, mainly because there is a limit to VO₂max, whereas trained individuals are already closer to that limit. Although doing moderate and low intensity endurance training does improve VO₂max, high intensity aerobic endurance makes a more significant impact ^5,6. Note that it is a frequent misconception that simply increasing the volume (amount of hours) of low intensity endurance training will have a greater effect as doing specific interval training to improve VO₂max⁷.

Studies have shown little difference between the improvements in VO₂max arising from short or longer intervals in high intensity training. One study, for example, compared two 8-week programs (3 days/week, matched for total work) comprising short intervals of 15 secs work at 90-95% of maximal heart rate + 15 secs active rest, and long intervals of 4 min at 90-95% max HR + 3 min active rest. Both protocols affected VO₂max significantly, with an improvement of 5.5 and 7.2% respectively, thus fairly comparable.

If you are untrained, we would recommend starting with low intensity endurance training before incorporating interval training ⁸. This will improve blood flow, enhance the muscles’ capacity to use oxygen for the generation of energy, while slowly allowing the body to adapt to training, thereby limiting the risk of injuries.

If you are accustomed to cardio based training, we recommend adding interval training at high intensities to your regular cardio program. Improving your cardiorespiratory endurance results in an up- and rightwards shift of your VO2max in exercise tests as displayed in figure 1. Advanced endurance athletes ultimately reach their optimal VO2max, and will primarily focus on shifting their lactate and anaerobic thresholds closer towards their VO₂max(see next section). Ultimately improving these thresholds help to increase the speed at which you can sustain performance ^{8 6 5}. Going faster for longer: that’s what endurance sports are all about.

Physiological thresholds

Important parameters that are closely related to the VO₂max but give slightly more functional information for performance are:

1) Aerobic threshold – This occurs at an effort of around 60% of your aerobic capacity or around 80% of your lactate threshold, thus at a relatively low level of intensity that you can maintain for hours. It is measured by the point where lactate just begins to accumulate above the resting level.

2) Anaerobic threshold - This is the point where the amount of carbon dioxide exhaled becomes unaligned with the amount of oxygen consumed, indicating your body is starting to depend more on production of energy by the anaerobic system (glycolysis) than on the aerobic fat burning system (oxidative phosphorylation in the mitochondria). Well trained athletes can maintain performance at this level for approximately 1 hour.

3) Lactate threshold – This is often confused with the anaerobic threshold, but this is the point where the body can no longer clear lactate and thus lactate levels rapidly accumulate. Exercising at the lactate threshold can be maintained for a maximum of 1 hour.

References

1 - Brooks GA, Fahey TD, White TP. Exercise Physiology: Human Bioenergetics and Its Applications. Mountain View (CA):Mayfield Publishing Company; 2000.

2 - Astrand P-O, Rodahl K. Textbook of Work Physiology. In: New York, NY: McGraw-Hill Book Company; 1986.

3 - L. Véronique Billat, J. Pierre Koralsztein. Significance of the velocity at V̇O2max and time to exhaustion at this velocity. Sport Med. 1996;22(2):90-108.

4 - Bouchard C, Daw EW, Rice T, et al. Familial resemblance for VO2max in the sedentary state: the HERITAGE family study. Med Sci Sport Exerc. 1998;30(2):252-258.

5 - Gormley SE, Swain DP, High R, et al. Effect of Intensity of Aerobic Training on VO2max. Med Sci Sport Exerc. 2008:1336-1344. doi:10.1249/MSS.0b013e316c4839.

6 - Helgerud J, Hoydal K, Wang E, et al. Aerobic high-intensity intervals improve VO2max more than moderate training. Med Sci Sports Exerc. 2007;39(4):665-671. doi:10.1249/mss.0b013e3180304570.

7 - Thomas TR, Adeniran SB, Etheridge GL. Effects of different running programs on VO2 max, percent fat, and plasma lipids. Can J Appl Sport Sci. 1984;2:55-62.

8 - Laursen PB, Jenkins DG. The scientific basis for high-intensity interval training: optimising training programmes and maximising performance in highly trained endurance athletes. Sports Med. 2002;32(1):53-73. doi:10.2165/00007256-200232010-00003.

9 - Wilmore D, Kenney W. Physiology of Sport and Exercise, 6th Edition.; 2006.

10 - Bouchard C, Rankinen T, Chagnon YC, et al. Genomic scan for maximal oxygen uptake and its response to training in the HERITAGE Family Study. J Appl Physiol. 2000;88(2):551-559. doi:10.1152/japplphysiol.01163.2003.