With no access to a weight rack and workout bench, you turn to push-ups to build up your chest. Although push-ups are a killer overall exercise, lots of people consider them no match for the weight you can heft with a bar and iron plates.
It's true, a push-up just can't replace a bench press if you're looking for massive gains and already benching a lot more pounds than your body weight. But if you haven't built up to big weights, a push-up is a satisfactory substitute. Elite lifters can't replace the bench press with the push-up and see gains, however.
The bench press and the push-up target essentially the same muscles: the chest, the triceps at the back of the upper arm and the fronts of the shoulders. The action of the two moves is almost identical, too -- you push resistance away by bending and extending your elbows.
When a push-up is made to resist as much weight as a bench press, it does lead to the same muscle gains, showed a study published in a 2015 issue of the Journal of Strength and Conditioning Research. Researchers divided 30 experienced strength trainers into three groups: those who trained with the bench press, those who trained with a push-up resisted using elastic resistance and a control group. By measuring muscle activation using electromyography, it was determined that when the resistance in either the bench press of the resisted push-up was set at a participant's six-repetition max, similar gains in muscle were made over five weeks as compared to the control group.
The Key is Resistance
A push-up using just your body weight is not going to build muscle in the same way a bench press loaded with hundreds of pounds will, however. In 2012, the American Council on Exercise sponsored a study comparing nine of the most common chest exercises. Researchers from the University of Wisconsin–La Crosse found the bench press activated the pectoralis major, the primary chest muscle, the most. It was closely rivaled by the pec deck machine and bent-forward cable crossovers.
In this study, three variations of the push-up — standard, stability ball and suspended — came in dead last when it came to effective recruitment of the chest muscle. This doesn't mean these moves are useless; it simply means that they don't compare to the bench press in terms of chest development.
How Muscles Grow
It makes sense that adding resistance to a push-up makes it equal to a bench press when it comes to chest muscle development. Muscles grow in response to stress — according to the 2015 study, from a weight or elastic challenge. The stress of resistance breaks down the muscle fibers, and when you rest between lifting sessions, the muscle grows back stronger, thicker and more voluminous. This is why most protocols recommend at least 48 hours between strength training specific muscle groups. It's during rest that the major muscle change happens.
Your muscles adapt to stress, which means you need to keep upping your resistance to see gains. The bench press makes it easy to do so — you just pile on a few more plates. In the push-up, unless you have multiple levels of resistance bands, you're pressing against your body weight, which shouldn't markedly change by 50 or 100 pounds. Elite lifters who press 350 pounds or more will be unlikely to ever be able to load up a push-up to match this level of bench pressing.