If you feel too shy or timid to take fitness/athleticism classes (get over that - timid and shy are bad habits for life), you are stuck with doing your calis and HIIT on your own 2 days/week if you follow the Maggie's balanced fitness ("Functional Fitness For Life") advice of 2 days powerlifts and other heavy weights, 2 days calis/cardio, 2 days mixed cardio).
Every few weeks, I will cut a day out for recovery if I feel I need it. That's an age factor, I think. However, consistency is key.
Two years of that program will get anybody of any age, gender, or condition into decent fitness - with the appropriate nutrition for weight-gain or loss. Physical renovation, literally. Lean, no bulging muscles but just solid strength, endurance, and athleticism. I am towards the northern region of middle age, so I can speak to this with some authority. Not to mention a deplorable history of intermittent tobacco abuse.
Re the calisthenics component, right now I take one cross-train class/week (basically no-rest cardio/calis, lots of burpees, rowing, mountain climbers, and jumping around), and a mixed calis/HIIT session I do on my own for 75 minutes/wk on Sat. morning.
Typically I do 3 circuits of each group of four exercises until my time runs out. I see many guys and gals doing similar sorts of circuits on their own at the gym, but classes push the cardio and sweat harder than many will do on their own.
Below the fold, the typical circuits I use after a 5-minute elliptical warm-up and calf stretch. It's not classic HIIT, but it works in the same way. I do classic HIIT weekly on the treadmill - 30-sec sprint, 2 min slow walk.
This is classic old-fashioned "exercise" (asterisks for the things I consider HIIT) --
Three rounds of each numbered item -
1.
Push-ups to failure
Jump rope (speed rope, 30-60 secs - I can't do double-unders yet)*
Box jumps*
Lunges - forward, sideways, and backwards
2.
Pull-ups or hangs (I need assisted to get to 10)
Kettlebell swings
Farmer walks, heaviest kettlebells I can manage
Roman chair leg lifts
3.
Ski Erg 45-60 sec. sprints*
Squats with heavy ball wall throw*
Mountain-climbers
High step-ups (18-20") - forward and sideways
4.
Kettlebell squats or body-weight squats
Combat rope slams, all variations
Row erg, 30-60 sec sprints*
Wall ball chest passes with heavy ball
5.
30-60 sec. fast jumping jacks or mixed jump rope routines*
Arm or elbow plank
30-60 sec. sprints on stair machine*
Low step up and press (hand weights)
I do not get through all 5 circuits, but I try to minimize rest time. The next time I do these, I start from the bottom of the list. I like to do a 10-min cool down on the stairmaster, slow, like level 3. A fine way to begin a day.