The
principle of interval training is to work at alternating intervals of
higher and
lower intensity. The
objective is to use the body’s recovery during the intervals at lower
intensity
to make it possible to increase the total
amount of activity at higher intensity in the workout (adding
up all the
intervals at higher intensity), compared to if you were to work continuously at the same intensity.
A
classic series of experiments with running showed that an
individual who could sustain a total of 4 minutes
covering
0.8 miles at a certain fast continuous pace before exhaustion, could
sustain a total of 20
minutes
at that same pace (covering 4 miles) when the running was done
intermittently in intervals of 10 seconds of exercise and 5 seconds of
rest.¹"
The
body has three different energy transfer systems, that it uses
according to how
fast it needs energy and how long it needs to sustain it for. The fastest
energy
transfer system (Alactic) can
generate energy almost immediately, but it is exhausted within 30
seconds.
The intermediate energy transfer system
(Glycolysis) takes
about ten seconds to get going. After
after about 30 seconds of activity this will be the predominant energy
provider. This is very convenient because it can then
take over as the fast energy system is depleted and while the long term
energy system still is powering up its engines. It takes about ten
minutes for energy to be transfered in
(aerobic),
however it can keep going for a long time if you stay
at an intensity that doesn’t demand a sudden increase in energy.
You can vary the intensity and duration
of the intervals and in this
way effectively train the capacity of a specific energy transfer
system.
In
sports specific training
these principles are used to
prepare the body for work in specific energy transfer systems
relevant to the particular sport.If
for example you work 1 minute of moderate intensity followed by 1
minute low
intensity, you will mainly be training the aerobic energy system. If
in stead, you increase
the intensity from
moderate to high and you decrease the length of the interval to 20
seconds at
this intensity, and keep the one-minute recovery interval, your body
will have
time to recover between the intervals at high intensity and you will
mainly be
working the anaerobic systems.
You
can
also play with the number of repetitions
of the interval. The
intensity and
duration of the intervals will decide how many repetitions you should
go for,
together with your fitness level and your goal.
1) Data from CHRISTENSEN
EH et al:
Intermittent and Continous Running. Acta Physiol.Scand.1960;50:269
referred to in McArdle et al:Exercise Physiology 5th ed.2001p.171