In order to not get bored and stay motivated, you might consider
some fun alternatives to interval training on the treadmill or bike.
Really, it is only your imagination limiting your choice.
One of my favourite tools is the trampoline. As a former Olympic
moguls skier I used the trampoline a lot. I needed to do
intervals of 30 seconds at max intensity as in a mogul run and on the
trampoline I could assimilate the movements from skiing pretty well.
What was really great though, was that it is fun at the same time as
being
efficient. I love that!
You can
get
a free example of a trampoline interval workout here
or you can read more about
Trampo-Lean,
my fitness dvd with a 3-step interval training program on the
trampoline here