Serious athletes will tell you that there is simply no way to substitute doing squats. Those who are regular squatters seem to be very passionate about this and will often insist over and over that no exercise can compare to the squat when it comes to lifting for your legs.
Yes, there are exercises you can swap out instead of squats however the average athlete that you will find in a gym do not like to do them. You could certainly get exactly the same benefit from doing leg curls, press or any sport that focuses on stabilizing your muscles. Squats are king but that doesn't mean they are the only exercise that can get the same job done.
The athletes who rave about the benefits of doing squats will tell you that it is the only movement which will increase your own testosterone production. Well this is simply not true because any increasing on your own testosterone production will not last more than a day or two at the most and we cannot squat every day.
So the truth about squats boosting your own testosterone production is something that comes from doing intense workouts because it is the hard training that boosts testosterone and not squats alone. You can effectively boost your testosterone that your body makes by doing leg press in an organized HIIT program.
One can easily assume that the hormone release corresponds with the amount of stress the body is under. What this means is that doing hand grip strengthening movements while you watch a movie will not be equal to the testosterone release you get while squatting.
So in theory the stress your body is under will equal the force applied over the distance. So the athlete on the leg press will release an equal amount of testosterone as the athlete doing squats.
The reason why this will happen is because if both the leg press athlete and the squat athlete are pushing 400 pounds of weight they are both moving the weight the same amount of distance. Therefore they should expect the same amount of testosterone release.