Joint Strength and Weights
Strength can in fact be created by applying pressure to a joint, not too much…be smart, starting with a low weight can increase muscular endurance and therefore help strengthen a joint. The bones themselves will follow. Exercising with weights help to keep bones strong because it causes the muscles and tendons to pull on the bones, which in turn stimulates bone cells to produce more bone.
Bones are generally strong, but as we age, our bones become porous and lose water content which can cause them to become brittle as we get older. This is why incorporating weights into your exercise regime is important. It helps maintain bone health so they will remain stronger for longer.
So what weights are best?
Start off light
You should choose a weight that you are comfortable with, but that will work the muscles i.e. you should be able to feel the muscle working, but not so heavy you have difficulty lifting it smoothly. General rule: use a weight that tires the muscle(s) out within 8-12 repetitions.
York produce free weights as well as multigyms, so you can use the equipment that best suits you. Free weights are generally renowned as better as it requires you to use proper posture and form thereby helping your form as well. Multigyms are preset, so your form should always be ok. Both are effective in strengthening both your muscles and in turn your joints.
What is a rep?
Imagine a bicep curl. When you get into the starting position, with the weight hanging down at arms length, then curl the weight up to the fully contracted position then lower it. This is one repetition. Several repetitions are known as a set. 
Do One Set – Slowly
You don’t have to do multiple sets of each exercise to get good results. Research shows that, for most people, optimum benefit from weight training can be gained with just one set of 8-12 repetitions of each exercise, done slowly, with correct form.