Interval training: Are you working hard enough?

It's an Olympic year everyone!  I was watching some of the qualifying matches for the U.S. team in both gymnastics and track and field yesterday (fantastic athletes), when, not for the first time, I asked myself why people are still breaking their backs trying to get in as much road time during the summer, or get in their "cardio for the day."  Looking at the two picture above can pretty much tell you the whole story, but let me break it down.

Muscles adapt to the stresses and types of stresses placed upon them.  Basketball and volleyball athletes train and "teach" their muscles to be able to jump very high, whereas Triathletes train their muscles to work at sub maximal levels for extended periods of time.  What happens is that a certain percentage of muscle fibers change from type 1 (slow twitch) to type 2 (fast twitch) or vice versa, given THE TRAINING STIMULUS.  Marathon runners (I'm going to pick on them for a moment) will see a reduction in their fast twitch fibers as they switch over to slow twitch to accommodate the need to run for lengthy periods of time.  This switch, by the way, is also the same on that happens as we age.  By coming in to get your "daily cardio" you are actually helping to exacerbate this condition, as noted by Robb Wolf in The Paleo Solution.  Haven't you noticed that heavy duty runners always look a bit sick?  Look at the man in the picture above.

My first experience with this was in college running NCAA Cross Country.  One day the captain of the team, towards the end of the running season, was playing lacrosse with some friends and noticed that his speed had decreased by a fair amount.  He couldn't keep up with the other players who hadn't participated in Cross Country.  Even the founder of Aerobics now recommends a combinations of strength and interval training.  Is this really the best way to train your cardiorespiratory systems?

Interval training has been shown time and time again to be the best method of training the cardiovascular and respiratory systems.  And I'm sure that all of you have, at some point, experienced interval training.  Think back to the last time you were moving.  You might have had to help carry a desk and then carry in the drawers to that desk.  How about splitting wood?  You had to split some, either with a splitter or by hand, and then stack it.  Gets your heart pumping right?  The reason that this training works so well is that LIFE HAPPENS IN INTERVALS.  We move for a bit then rest, followed by more movement.  This type of training fits in to what we are designed to do. 

So, working up to it properly and safely of course, do sprints instead of miles on the treadmill, mix in some circuits to get in your "cardio for the day".