What is VO2max ?
VO2max is the maximum rate at which a person's body
can process oxygen. It is measured in L/min but is
typically given as a ratio to bodyweight, in
ml/min/kg. So if a person has a 5.00 L/min VO2max,
if they weigh 70 kg, their VO2max can also be given
as 71.4 ml/min/kg.
Aerobic power production is roughly proportional to
oxygen consumption. A rule of thumb is that a cyclist
can produce 80W for each L/min of oxygen they consume.
So our rider with a 5.00 L/min VO2max can produce up
to 400W aerobically. How efficiently a person can
convert oxygen to power is fairly fixed, since it is
determined by muscle fiber type. Riders with more slow
twitch fibers are slightly more efficient.
Typically a trained rider can maintain their maximum
aerobic power for only 5-10 minutes.
What is threshold (LT, AT, VT, OBLA) ?
These terms (lactate threshold, anaerobic threshold,
ventilatory threshold, onset of blood lactate accumulation)
are defined differently by scientists, but they are
roughly measuring the same concept, thus coaches seem
to use them interchangably or simply refer to 'threshold'.
In each case it is trying to define a level above which
percieved exertion and lactate levels increase appreciably,
and roughly defines the percentage of VO2max an athlete can
sustain for long periods.
We'll use the term LT. For typically trained riders LT varies
between 65% and 95% of VO2max. VO2max doesn't change much
in athletes over the course of a season, but LT can change
considerably. For most riders, their greatest potential lies
in trying to raise their power output at LT, by raising the
percentage of VO2max that is their LT.
from Andy Coggan: What ultimately limits the power you
can generate for 5-60 min is your VO2max. Lactate threshold can
and will vary from as low as perhaps 55% of VO2max to perhaps as
high as 95% of VO2max (with 65-85% being a more typical range),
but if your VO2max isn't sufficiently high then you'll never be
able to generate 350 W for any significant duration no matter
what your lactate threshold is (since lactate threshold cannot
exceed 100% of VO2max). VO2max, in turn, is determined by both
genetic and environmental (i.e., training) factors, with each
contributing about equally to the final value.
With training, VO2max may increase by more than 50%, but a
15-25% increase might be more typical. For somebody who is
already training, even a 10% increase would be quite significant,
although performance of course can vary more than this, due to
changes in lactate threshold.
What is the main indicator of performance ?
The best indicator of road cycling performance is power at
LT. VO2max is a good indicator for shorter events (like
pusuit) but not as good an indicator in longer events like
road races and time trials.
In hilly races obviously power to weight ratio plays a greater
role, in flatter races power or power to aerodynamic drag ratio
is more important.
A typical rider might be able maintain 115% of their LT power for
about 1 hr. Actual power at LT is tricky to estimate, but it is
somewhere below the power most coaches think of as being 'threshold', the
power a rider typically maintains for longer TT-type efforts.
This is one of the reasons Andy Coggan builds his power training schema
around 40 km TT power.
How does (or should) HR respond to training ?
from Andy Coggan: The term "cardiovascular fitness"
has been used synonymously with VO2max, because the latter
is generally held to be limited by the heart's ability to pump
O2-carrying blood out to the exercising muscles. As such,
training-induced changes in submaximal heart rate (a cardiovascular
response) tend to track changes in VO2max, and indeed it is possible
to predict VO2max to withiin about 10% or so just based on
measurement of submaximal heart rates at known power outputs
(the famous Astrand-Rhyming test).
Although VO2max (a.k.a. cardiovascular fitness, a.k.a. aerobic power)
sets the upper limit to sustainable exercise intensity, the fraction of
your VO2max that you can utilize for anything more than a few minutes is
determined by your lactate threshold. There are probably numerous
factors that determine where one's LT lies in relation to their VO2max,
but one extremely important determinant is the mitochondrial respiratory
capacity of the muscles involved in the exercise.
A highly trained distance runner, for example, will have a high VO2max,
i.e., great cardiovascular fitness, even when tested on a cycle ergometer,
but because their muscles aren't specifically trained for the activity, will
tend to have a relatively low LT, or as I like to put it, poor metabolic
fitness. It isn't a term used by anyone else (to my knowledge), but I've
found that expressing things this way helps students grasp the
distinction.
Because heart rate is a cardiovascular variable and tracks with
cardiovascular fitness, it will be insensitive to changes in metabolic
fitness, or LT. (Indeed, there is no known mechanism by which LT could
influence heart rate, and except for Conconi, no one has ever proposed
that they are linked in any fashion.) In my own case, I find that my
heart rate at a given power hardly changes at all in and out of season,
although obviously my exercise capacity does. Only if I really slack off
in my training (as I have done the last few months) does my submaximal
heart rate change (rise). On the other hand, since VO2max increases
rapidly during the first few months of training in previously untrained
persons, individuals with a more limited training background may observe
changes in heart rate at a given power, in proportion to the change in their
VO2max.
So one expects to see higher sustainable heart rates associated with increases
in LT and lower heart rates at a given workload if there are increases in
VO2max.
What is the best way to improve power at LT ?
The concensus is that: to raise LT it is better to train by doing long (10-20 minute
intervals) at or slightly
below LT, mainly because that workload is easier to manage than a program which
has a lot of volume above LT. You might not even be able to do
multiple repeats at supra-LT power. Check out more information in the other
training articles.