The easiest way to increase the difficulty of an exercise is to increase the volume by adding more repetitions of a movement or more sets. It's possible to increase strength this way using just bodyweight movements, but that requires a moderate level of fitness to sustain the exercises with good form.To really feel the burn, add partial reps to a movement or slow it down, according to Noam Tamir, founder and CEO of TS Fitness.A 1 3/4 squat, for instance, involves lowering down into a squat, then rising 75% of the way to standing, then back to a low squat before standing up and repeating. Another technique, a tempo exercise, involves counting to five as you slowly lower down into a squat, push-up, or similar movement, holding at the bottom and moving up slowly."The muscle is under tension for longer so it's under stress," Tamir said.