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Power Models  :  HR-VO2-Power Relationship Model
HR-VO2 Empirical Relationship
Swain (%HRmax = 36.8 + .643 x %VO2max)
This is quite a simple model designed to illustrate, through a range of scenarios, the theoretical relationships between a cyclists VO2max, sustainable heart rate, and sustainable power output. In some way this model allows a rider who has taken a VO2max test to contemplate the effects of improving his aerobic capacity, or a rider with reliable time trial power data to estimate his VO2max. This model could also justify the importance of so-called “VO2max training/intervals”. In cycling the importance of aerobic fitness or capacity should not be underestimated.
20,700 joules of carbohydrate energy will be “burned" or "released” for every litre of oxygen consumed.
The riders mechanical efficiency (how much of every joule “burned” is actually converted into work at the pedals rather than wasted as other energy forms such as heat) is equivalent to the percentage specified. Note that cyclists have typically been reported as 20-25% mechanically efficient so a safe estimate such as 23% might be a good choice.
The relationships between a rider’s heart rate (% of maximum) and rate of oxygen consumption (% of VO2 max) is assumed to be linear and as sampled in the specified empirical research (see the relationship dropdown).
HR Max. Input the riders maximum heart rate or a sensible estimate if this is not conclusively tested.
Threshold HR%. Input the riders threshold or sustainable heart rate which will act as a reference level of oxygen consumption.
VO2max (ml). Input the riders VO2max as tested, in millilitres (e.g. 4 litres = 4000).
Efficiency. Select a mechanical efficiency in percent.
Show. Opt to display calculated outputs in watts or watts per kilo. In the latter case there will be an input box specify weight in kilos (e.g. 85).
HR-VO2 Empirical Relationship. This model relies on a simple relationship between %MaxHR and %MaxVO2. Various pieces of research have suggested different relationships and the paradigm used in this model will be as selected.
Estimated watts of power or watts per kilo achievable or sustainable by the cyclist at the specified VO2max and threshold heart rate, with scenarios illustrating the possible effects of variations in heart rate selection and improved (trained) VO2 max.