Update on new workout

So how is the 15 to 20 minute workout going for me?

Just great!

In a short time I have put on a few pounds ...4 to be exact...and all muscle. I can tell because my waist size is the same 31 as when I started this routine.
My strength has increased, for example the crunch machine: I used 40 to 50 pounds for a set prior to this, now using 70 and ready to go up to 80. My abs are more defined, and for sure stronger in my mid section. This at age 66 is hard to accomplish for sure.

My only issue is some tweaking in my left elbow, from using cables for curls, and elevating them to above horizontal for the most effect.

To reiterate the workout:
Start with 4 HIIT exercises ... 30 seconds all or effort (after a brief warmup)... Followed by 30 seconds of recovery, then rinse and repeat. All together 4 times each for a total of 4 minutes.
Sounds easy huh? It isn't.

I use the stationary bike for this.
Then choose your weights...machines or free weights are fine.
A warmup on each activity for enough light reps to get the blood going. Then a low rep set of maximum weight. I do 4 to 5 reps with as much weight as I can handle. The last rep is a failed on, where I am unable to complete it. That is the secret to challenging the muscles.
So there it is a total of around 20 minutes.

I do this two days on, splitting back,legs,biceps one day...chest, shoulders, triceps the next.
If I feel,overworked or need extra rest, I take another day or two between workouts. Simply stretching on those days, or walking.It works!