A man that looks for his limits, will find them.
Progressive overloading ends usually in an injury. Pushing yourself to your limits by constantly adding weights is a surefire way to get stronger and to promote muscle growth. But it's also the main reason why most gym rats over 35 have knee, shoulder and elbow pain.
But you really don't need a lot of extra resistance when training. Since most people are overweight, we can assume that bodyweight should be more than sufficient. In this video, I'm demonstrating a simple leg workout done in a very small gym. It might seem like a warm-up, but it felt like a work-out. The main resistance used was my big fat butt.
Some of the unilateral exercises require a bit of balance. For someone sitting at a desk allday, the movements are not as basic and natural as they may seem.
The biggest benefit of using a box, is that it forces you to stretch, extend your reach and increase your range of motion. If you constantly use machines in a gym, there is a risk that you unintentionally avoid stretched out positions. Isolated exercises, such as hamstring curls and leg extension, are great for developing specific body parts. But a functional human body is more than the sum of the muscles.
Everything doesn't have to RX+. Skip the squats once in a while and try out some unilateral bodyweight exercises. Then add some of the more explosive movements, shown at the end of the video, to make it more fun.