Further off topic still... you need to add some pulling exercises to balance your pushups, maybe some vertical pulling and pushing (pullups, overhead presses) as well, and swapping the squats for lunges or step-ups once in a while will give you better overall leg development (squats for quads, lunges and stepups will work glutes and hamstrings a bit more)

You're probably not going to run into issues with that low of an intensity (20 pushups is not nothing, but if you stop at 20 every time, it's not like you'll keep making the imbalance worse) but adding another few exercises will only add like 5 mins total to your workout, and will give better overall results

Great input! I believe a serious workout would involve some sort of lifting routine before hand. This exercise is really just intended to get some cardio/endorphins without being heavily aerobic.

Further off topic, you have essentially described the model that CrossFit uses! You could steal workouts from https://www.crossfit.com/ as the publish them for free. There is also a lot of good material tied to the crossfit name for high intensity interval training if you google around.

The body-weight push-ups and squat are only a very light strength building exercise. Sadly, you'll still be above average in fitness if you do this workout.

The trick with body weight exercise progression is to use leverage to increase the effective resistance. For example: http://stevenlow.org/the-fundamentals-of-bodyweight-strength...

Done correctly body weight alone can allow one to achieve great strength. In fact, it’s probably superior on account of gymnasts can easily do weight lifting exercises while weight training doesn’t really transfer to gymnastics.

If you keep some progression going, and don't over-eat, you'll end up with a pretty nice physique at least.

I think a big reason why so many have a hard time maintaining a life-long fitness habit is because their goals are merely cosmetic. The first thing an excercise routine needs to be is fun, and after that the rest is butter.

The entire discipline of calisthenics would disagree with you on this one... (oh, and me too)

The discipline of calisthenics does not consider plain push-ups, bodyweight squats and crunches as anything more than beginner-level exercises.