I was substituting in a different campus yesterday. I knew I wasn't like to have enough help because the most of the other senior instructors were off in Spain. (I couldn't get the time off work to go). So I had to do something that I could do with multiranks easily.
We don't generally incorporate strengthening/conditioning into our classes. We do a brief warm up in the typical format. Kids classes are 45 min. and adult is 1 hour. Our dojos are not connected to full service gyms.
I did a lot of strengthening exercises that I have learned over the years and I had great classes. After the first, done with 10 year olds, the Jr BB helping me loved it and told me we HAD to do it for the older and adults so we did.
You have people pair up by height. Strength and rank don't matter. One in each pair takes off his belt. One partner holds it and resists for the other partner who will do bicep curls, turn around and do tricep military press. Sit on floor and work the foot in the same way for dorsiflexion of the foot.
From the position of being "on all fours", work side kicks leading with the heel. Make sure the kicks are as forward as possible and high. You can make little circles at the end of the kick to add to the exercise. Make sure legs go and stay to full extension.
Work the back kicks from the same position. Keep the leg straight after the kick and tighten the butt. Little circles help too.
For core work, get on floor with body straight and lift up on just forearms and toes. For an easier exercise, the students should kee their bodies straight and OFF the floor and just "walk" forward, back, side to side, using just forearms and toes. At a harder level, they "hop" from this position, propelling themselves with just the forearms and toes and land on forearms and toes.
For legs, start with deep horsestance. Hop across the dojo. In our case, we did a few different punches from the horse stance then hopped once, repeated the arm strikes then hopped twice, etc. until they got to the end. Gives a good burn.
Add all the appropriate motivational slogans beathing, etc. and the kids got a good workout and some exercises for a full body workout that they can do with no equipment.
The older I get, the better I was!