Answer Wiki. The system would be cued off the pilot's helmet, so it will definitely look where your head is pointing, not your eyes specifically (that would be a gaze-tracking system, which AFAIK hasn't yet been used for this kind of application).
Exercise to Gain Leg Weight. Although you can't make your body gain weight in your legs, you can perform exercises that encourage the growth of leg muscle. Squats, lunges and step-ups are examples of such moves that target the legs and recruit a lot of muscle fibers for growth.
There can be two facets of weight gain; one is that weight gain could mean an increase in body fat and the other being an increase in muscle mass. It is of course a wise thing to aim for the latter. One of the best known ways to gain weight is drinking protein shakes.