Sustainable Percent VO2 max / Fractional Utilization

The Sustainable percent VO2 max refers to the percentage of VO2max that can be sustained during an endurance competition. It’s a an important factor, especially during endurance events lasting longer than 30minutes. And becomes of increasing importance as race duration increases.

While it’s influenced by genetic factors, it’s also highly trainable and can be improved through specific endurance workouts.

Percent VO2max and race distance

As race distance increases the percent VO2max that can be sustained decreases. As an example, highly trained athletes can run at very close to 100% VO2max during a 5km race (~98% VO2max). This decreases to around ~92% during a 10km, and drops to around ~78% during a marathon. However, in less well trained athletes, these percentages can be significantly lower.

Why is this important? In order to maximize performance, endurance athletes must be able to sustain a pace, or intensity, that is as close to VO2max as possible. Research suggests that this is particularly important when race duration is longer than 30 minutes. And becomes increasingly important as race duration increases (Ghosh, 2004; Lucia et al., 2001; Fallowfield and Wilkinson, 1999; Coetzer et al., 1993; Coyle et al., 1995; Costil et al., 1973).

Over shorter duration races (e.g. 1500m-5km) the sustainable percent VO2max appears to be less important. Research looking at the sustainable % VO2max during a 5km race, did not find any relationship between the %VO2max sustained and 5km race performance (Støa et al., 2010). This is not surprising, since highly trained athletes are able to race at very close to VO2max during races of <5km. As such, there is only a very limited scope for improving this percentage during these events.

As race duration increases, it becomes increasingly difficult to maintain intensities that are close to the maximal oxygen consumption. Therefore it’s not surprising, that the ability to sustain work rates at high percentages of VO2max become increasingly important. And, even small differences in %VO2max sustained (e.g. 1-2% improvement) will have a more significant effect.

So, what factors influence our ability to sustain high percentages of VO2 max?

Factors influencing the sustainable percent VO2max

The percent VO2max sustained seems to be dependent on a number of factors including: the aerobic capacity of the active muscles, the percentage of type I muscle fibers (Coyle et al., 1991 & 1995;) and muscle capillary density (Coyle et al., 1988). It’s also strongly linked to the lactate threshold (Coetzer et al., 1993) and the VO2 at the lactate threshold (Coyle et al., 1988).

Individual variation in percent VO2max sustained

The sustainable percent VO2max can vary widely between individuals. As such, it can help to explain differences in race performance over varying distances. For instance, if two runners have equal VO2 max and vVO2max then the runner with the highest sustainable % VO2max would be expected to win in races of greater than 30mins duration.

However, it’s important to remember that the sustainable percent VO2max decreases as race distance increases, and the actual rate of decrease varies between athletes. 

This can help to explain why some athletes are more competitive over certain race distances. For instance, marathon specialists are able to sustain much higher percentages than non-specialists over marathon distances. However, a 10km specialist may be able to sustain a higher percentage of VO2 max over shorter distances like the 10km than the marathon specialist.

Assessing the sustainable percent VO2max

The percent of VO2max sustained, can be evaluated under laboratory conditions, by measuring oxygen uptake at average race pace (running), or average power output (cycling, rowing etc), or, during a treadmill/cycle ergometer time trial. Here, the athlete would run at speeds used during races, or cycle at power outputs recorded during time trials etc.

The VO2 is recorded for each of those speeds, or power outputs. It’s  then converted to a percentage of VO2max from a recent VO2max test.

The percent VO2 max, can also be established by comparing average race pace/power outputs with laboratory recorded VO2 values from a recent incremental exercise.

Using heart rate to assess sustainable effort

If you don’t have access to a sports science lab to test oxygen uptake, an alternative is to assess the percentage of heart rate max.

Heart rate follows a very similar linear relationship to speed and power. Therefore, assessing the percentages of heart rate sustained over various race distances, or intensities, can provide some information about your ability to sustain high work rates during endurance exercise. Here you would compare the percentage of maximum heart rate that can be sustained across different speeds (running) or power outputs (cycling).

Training to improve sustainable percent VO2max

Since, the sustainable percent of VO2max appears to be strongly linked to the muscles aerobic capacity, muscle capillary density, and the VO2 at the lactate threshold, training should focus primarily on enhancing the muscles aerobic capacity.

As such it’s important that training volume is sufficient to maximize the muscles oxidative capacity. In addition athletes should include an adequate amount of lactate threshold training to enhance muscle aerobic capacity, lift the lactate threshold and ultimately increase the ability to sustain higher percentages of VO2max.

Another, key factor is the training intensity used during training. It’s important that a proportion of training time is completed at the specific intensities used when competing. In this way, a 10k runner needs to devote a significant amount of time to training at 10km intensity, a marathon runner needs to devote time to training at marathon pace, and a time trial cyclist should train at the power outputs used during time trials.

It is important to remember that during races of shorter duration (e.g. 5-10km), there is less scope for improvement in the sustainable %VO2max, compared with longer duration races like half or full marathons. So the amount of time devoted to improving the sustainable percent VO2max should vary depending on race duration – with more time devoted to longer duration events.

Summary of sustainable percent VO2max

  • The percent VO2max that can be sustained is an important factor in endurance events of greater than 30 minutes.
  • While less important in shorter events, it becomes increasingly important as race duration increases.
  • It’s influenced by a number of factors including the muscle capillary density, % type I muscle fibers, muscle capillary density, aerobic capacity of the muscle, the LT and the LTVO2.
  • The sustainable percent of VO2max can vary greatly between individuals, with some individuals better suited to longer duration races (e.g. half-marathon, marathons, long distance triathlons etc), and others suited to shorter duration races (e.g. 5km).
  • The ability to maintain higher percentages of VO2 max can be improved through specific training that maximizes the fatigue resistance and aerobic capacity of muscle fibers (e.g. adequate volume of moderate intensity training, tempo training).
  • The scope for increasing the sustainable percent of VO2max is much greater in longer duration events (marathon etc) than during shorter duration events (3k, 5k etc).

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