Bodyweight exercises are great! I love them. I feel like after the past few months I have become a lot more experienced with them to the point where my standard programming for my athletes will include a lot more bodyweight variations. These workouts provide so much benefit from a movement competency, work capacity, and variation standpoint. You also may have found training from your home enjoyable. No traffic on the way to the gym, no coach yelling at you, and no loading a heavy bar and lifting it over and over (which is hard).
While training with bodyweight for a time can be excellent, once you get to certain training age, bodyweight training has a decrease in the return on investment. Someone who is used to squatting 300+ lbs will have a hard time getting the same benefits from doing sets of 20 bodyweight squats. Even if you have had access to some lightweight or dumbbells your parents had around the house, that 10lb DB won't replicate your body's demands that playing a hockey game or soccer match will.
What exactly are the physical demands of playing sports?
- Jumping and landing create forces up to 10 times your body weight on each landing. Volleyball players may have to jump over 200 times in a 5-set match.
- Running places forces 2-3 times your bodyweight upon each leg on each step. There are many steps in the 7,000 meters you may run in a 90-minute soccer game!
- Change of direction requires 7 newtons of force per kilogram of body weight to decelerate your body. Then an additional 6.5 newtons of force per kilogram to reaccelerate the other way. A basketball player does up to 500 changes of pace/direction in a game.
- Getting tackled in football or rugby causes an average of 22 G's of impact on your body. That is the equivalent of a car crash at 65 km/hr! That is a lot of impacts when you consider football and rugby athletes will amass double-digit tackle numbers!
Sports place HUGE demands on your body, so if you are unprepared for it, injury risk goes way up, and performance goes way down (the opposite of what we want!)
The heavier you are, the more forces are placed upon your body. As you grow (as a younger athlete), controlling your body as you grow is what can separate you from your peers. If you are not strong enough to handle your body or the loads placed upon it, they can break you down over time (which increases injury risk and decreases performance).
These forces go through your body, which includes your bones, muscles, tendons, and ligaments. Sometimes the best aspect of weightlifting (even with moderate weight) is to build bone mineral density (stronger bones) and tendon stiffness (ability to sprint & jump faster/higher) to handle these loads. While push-ups and bodyweight lunges are challenging, they don't place the same demands on all of your body's structures that need to be prepared for these forces. That is where the Overload principle comes into play. You can overload your legs by controlling tempo and base of support in your squats, but the adaptations probably won't be as significant as utilizing various loading parameters (Barbell, Dumbbell, Kettlebell, etc)
Instead of getting into the physics of the specifics of lifting weights and how that actually will help prepare you for the demands, I will simply ask my question again. Do you really think that squatting with that 10 lb dumbbell at home will get you ready for the chaos that is sports, help you manage and keep injuries at bay, and increase your performance? I didn't think so.