Insulin sensitivity is important to allow our bodies to store fuel in muscle cells- otherwise all fuel is shuttled to our fat cells to be stored as fat. Resistance training is a great way to improve insulin sensitivity because it drains the glycogen stores in our muscles and creates a demand on our bodies to refuel them, either from the food that we eat or from fat cells.
A simple, full body circuit training routine of large muscle groups, performed two to three times a week can be enough to create the energy turnover we need to maintain insulin sensitivity.