HIIT is AWESOME. 

You burn A LOT of calories during the workout itself... and the calories burned over the next 24 - 36 hours are astonishing as your metabolism is cranked up at a whole new level. 
 
However...
 
HIIT after 40 can be really hard on the knees, joints, and hips. 

It takes longer to recover (as in days VS 12-24 hours). 

And to get the max benefit of interval training, you would need to do it 3-4 times a week.
 
Sometimes, traditional HIIT is just not a good fit anymore.  
 
Another option is high intensity DVDs. The only problem with these is that many of them have a lot of jumping. Someone in their 20s would recover quickly from this. However, folks like you and I are another story. I don't like to sugarcoat it, but it's the truth :)
 
So what is the best "cardio" for those 40 and older? There's a formula to "Joint-Friendly HIIT". 

Here it is:

-- Keep it short (10 minutes or less)
-- Use movements VS just exercise (example: Hip Extensions or Step-ups VS a treadmill)
-- Use Total Body sequences - the more muscles that are used, the more calories you burn
-- Use strategic "active" recovery exercises within the sequence 
-- Use low to no-impact exercises to allow optimal recovery so your body burns fat easier after you're done
-- Use a variety of tempos to hit different muscle fibers
-- For even faster results, you can "plug in" this joint-friendly HIIT at the end of your favorite exercise routine. This digs deep into your fat stores and helps you overcome trouble spots, plateaus, and my favorite... allow more wiggle room in your diet. ;)

Check out 40 workouts designed around these principles at the link below:

=> new "joint-friendly" HIIT
 
Here's to harnessing the power of HIIT in a joint-friendly way! -

- Forest Vance
KettlebellBasic.net