YOUR BODY IS BETWEEN AN
ECTOMORPH AND A MESOMORPH.
Ectomorph: You should concentrate on gaining weight in the form of good, lean muscle tissue. Weight training should be fairly heavy and done at a slower workout pace with longer rest periods between sets. Don't weight train too often or for too long per training session. Eat a diet high in quality foods, eat more than you're used to, and eat often. Keep aerobic activities to a minimum.
Mesomorph: You have a naturally fit body but, to maintain or improve it, you should adopt an exercise and diet regimen that compliments your build. You can strength train more often and for longer periods of time, but be careful not to overdo it. Train with moderate to heavy weighs and keep a moderate pace, making sure not to rest too long between sets. You'll find you gain muscle quite easily. Don't fear; you won't get "bulky." When you're happy with your muscle size, simply train to maintain. Stick to a good, healthy diet to stay lean and muscular, and watch for any slow-creeping fat gains. Engage in and enjoy aerobic activities, but be careful not to overdo it.