An athlete will be able to gradually
improve this session over time by increasing
any of the variables (distance, either of the
paces, or the length of harder effort). There
is no reason why three different paces should
not be included.
This kind of session is often more fun than
a steady run and can help an athlete psychologically
break up a routine, if they feel they are stuck
in a rut. As well as being fun it is a relatively
easy session mentally since there are no strict
targets to worry about.