The ability to hold that classic pushup position is directly correlated to how long you can hold a plank and is an indicator of overall core strength.
A weak core can lead to a “sag” in the lower back that changes the angle of the shoulder joints and how the muscles are being worked.
That is why many workout routines offer upper body exercises on Monday-Wednesday-Friday and lower body exercises Tuesday-Thursday.
Some workouts even give up to 72 hours of rest before repeating the same exercises.
Push-ups work your arms (triceps and forearms), your chest, lower back, abs, quads and calves.