I have installed many apps and searched the web, however, I can't find reliable information about which muscles are hit during each exercise. Some apps claim that exercises like pullovers hit only muscles like the pectoralis major and serratus anterior and some websites claim that it also hits the pectoralis minor.
Is there any reliable way to know which muscles are hit with each exercise?
You're probably finding conflicting information because assessing whether an exercise works a specific muscle is not a binary question, as muscles can be involved to different degrees, and so it comes down to the author's choice and interpretation whether a muscle's involvement is significant enough to include it in the list of muscles involved in an exercise. For example, the calf muscles absolutely must be active during the squat, but squats will never stress them to anywhere near an amount that would be required to drive an adaptation in those muscles, so squats are generally not considered a calf exercise.
The most sensible way around this problem is to just stop worrying about it, and perform a variety of exercises without focussing on any individual muscle unless you have a need to drive hypertrophy in a specific muscle for bodybuilding competition purposes. But that doesn't seem to be the case here, as pec minor is not a superficial muscle and could not possibly even be seen by a bodybuilding judge. There are 640 skeletal muscles in the human body and it is absolutely futile to try to account for them. Just focus on movements.
Also, if your apps or other resources say that pullovers only hit the pec major and serratus anterior, and fail to mention the latissimus dorsi (the primary muscle involved in the pullover) then those resources are indeed unreliable and you should probably stop using them.
If you really desire to know which muscle is the most activated, you can do that by performing an EMG. But it's no easy matter and equipment is not cheap. Maybe you could participate to a study in a university or something.
