Try training in the sand for a month.
Moving to a soft surface for body weight exercise and cardio works in a number of ways to improve your fitness response. It requires better balance and also limits the elastic energy return from your muscles, making them work harder. Both of these things require a larger fitness response, at least until you get used to it. After a month, switching back to hard surface training will again allow you to utilize the elastic energy. In addition, your increased fitness and force output will encourage your body to improve the elasticity of your connective tissue. So in the long run, you will have better balance, be fitter, be stronger, and have a lower risk of a connective tissue injury.
Sand training also increases the strength of the muscles within your feet and all supporting muscles. This will strengthen your arches and also improve knee pain.