Planked.
I have a workout that I, very affectionately, call “Plank To Death” that my clients cringe when they hear it.  Why you ask? Because they have to plank, in many variations, for one full minute before each of the eight segments of the workout and the final plank is two minutes long and they can do any combination of variations, including dancing in plank, that they want. The plank is one of the best exercises you can do for your core because it builds strength in your abdominals and lower back.  When done properly they can also improve your posture.  All the different variations you can try can also engage your arms, shoulder, glutes, hamstrings, quads, calves and just about all of them. You can always start planking for 20 seconds then work your way up to the one minute mark.  You can do anything for 20 seconds now can’t you?!  Any you don’t need any equipment to have a strong, lean body, just motivation and a reason to do them.  Well, I would say a really good reason is so that you look great in your summer clothes!  What is your reason?  Please share. For lots of plank variations, check out Health.com