I was feeling good about my interval training on the elliptical machine.  I’d been doing 4 intervals of speed-up in 12 minutes and feeling energized when I got off the machine. 

Then, a week ago, I did 3 intervals and I felt tired.  My thoughts went into loops. Am I catching a cold? Am I getting weak? Is something seriously bad going on with my health?  After all, a few days before, I’d gotten a slipped disc in yoga.  Maybe my body was in a slump.  Waaaah!  

I’ve worked too hard, too long, in far too many ways, to let that happen.  But it was happening anyway.  I felt tired.  Me. After only three 30-second speed-ups.

Then I remembered something from the 70s.  Biorhythms.  Everybody has a cycle of bad days and good days.  Here’s a website with a free calculator:  http://www.facade.com/biorhythm/

Sure enough – I was at the bottom of my physical cycle.

Okay. I could expect my body to be stronger in a few days.  

And PostureDoc, a channel I subscribe to on YouTube, uploaded a video about interval training:http://www.youtube.com/watch?v=aKiVaJk4eYw

He made the point that I shouldn’t do a 2nd interval until my heart rate has returned to my normal range.   That isn’t necessarily 2 minutes, like I’d been doing.  The elliptical machines at my gym has a 50 second delay before displaying the heart rate.  So, during the speed up, my heart rate may look like it’s staying at about 116 bpm.  Then a minute later, it will jump up to 148 or higher.  So, it may take 3 minutes to get back to my normal range.  And even then, I may still have an oxygen debt.  

I noticed that after each subsequent interval, it takes a bit longer to return to my normal heart rate.  But if I wait for it, I can do 4 intervals even at the bottom of my biorhythm cycle.  It may take longer that 12 minutes, but what’s a few minutes when the goal is a lifetime of an active body?