Pushups work several muscle groups in the upper body and don’t require any extra equipment.

Bent Knee Push-up
Step 1
Starting Position: Come to a hands and knees position (quadruped) on the mat with your hands directly under your shoulders; fingers facing forward and knees under your hips. Engage the abdominals and pull the shoulder blades down your back.
Step 2
Reposition your knees as needed to create a straight line in your body from the knees, through the torso and out through the head. There should be no bend at the hips. Keep the abdominals braced.
Step 3
Downward Phase: Keeping the torso rigid and head aligned with your spine, slowly bend your elbows and lower your body toward the floor. Do not allow your low back to sag or your hips to hike upward. Continue to lower yourself until your chest or chin touch the mat or floor. Your elbows should remain close to the sides of your body or flare outwards slightly.

Source: AceFitting