I've been doing push ups on a daily basis, and I feel like I need to also train the opposite muscles, to make sure I'm training evenly. What would be a good counter-exercise for push ups?
The row is the exercise that best antagonizes the push-up.
It's an easy conclusion to make just by considering the force vector of the push-up. The direction of force is outward and perpendicular to the body. If you reverse that vector, you have a row.
To clarify further, imagine only the upper arm and the chest when doing a push-up (imagine you just have stub arms). What's happening is that your [stub] arms are adducting -- they're coming together. The pectorals are driving this movement. To be scientific, the primary movers in this adduction are:
Again to use the stub arm image, think of the same thing when doing a row. The stub arms are abducting -- they're moving apart. Your back is also retracting to pull the weight back even further, and providing isometric contraction so your arms don't get ripped out of their sockets. Now think about all the muscles that need to be involved for this to happen:
The reason we can't consider the pull-up a very complete antagonist exercise to the push-up is that it predominantly targets the lats. It's missing a couple of key components:
We could consider the pull-up to be a downward rotation rather than abduction. The pull-up could be considered the antagonist exercise to the overhead press (upward rotation). Read more about scapular and clavicular articulations here.
Pull ups (or chin ups), if you have a pull up bar available – or something else where you can do pull ups. They not just train the shoulders and the upper back but a lot of other muscles, too.
You should try to counter every push movement – one where you exert force away from your body – with a pull movement that works in the opposite way.