• Fitting into clothes better is a common reason for weight gain.muscles image by Inhumane Productions from Fotolia.com
  
  According to Manuel Ortiz Braschi, author of "Gaining Weight 101," there are several reasons why a person might want to gain weight through exercise. Examples include athletic competition weight classes, aesthetic appeal or simply fitting into clothes in a more desirable fashion. Different types of exercises that build muscle mass can be used to successfully gain weight for any of the above reasons, says Braschi. Always consult with a health care professional before beginning any new exercise program.
  
  

Bodyweight Exercises

• Bodyweight exercises can be used to gain weight and build muscle mass, according to Brad Johnson and Randall J. Strossen, authors of "Bodyweight Exercises for Extraordinary Strength." A body weight exercise is any type of exercise that uses only the weight of the body as resistance to build muscle mass. In order to gain weight from body weight exercises, exercising four to six days a week is required. Perform three to five sets of each separate exercises in sets of 12 to 20 repetitions. Examples of weight-building body weight exercises include push-ups, pull-ups, sit-ups, crunches, squats, calf raises and back extensions.
  
  

Free Weights

• According to Michael Mejia and John Berardi, authors of "Scrawny to Brawny," weight training using free weights will build body mass and increase weight gain. Weight training with free weights is effective because, in addition to lifting the barbell, surrounding muscles must work to keep the weight steady and keep proper form. The weight of the barbell should be lifted enough that you can comfortably perform five repetitions with the weight before you begin to feel your muscles truly struggle. Each exercise should be performed in three to five sets of 10 to 12 repetitions with one minute rests in between, according to Mejia and Berardi. Examples of free-weight exercises include bicep curls, tricep extensions, weighted squats, chest presses and arm raises.
  
  

Weight Training Machines

• According to James L. Benson, author of "Gaining Weight for Skinny People," weight training machines help to build muscle mass and put on weight. A variety of weight training machines are typically available at local gyms to create your own comprehensive workout routine. According to the American Council on Exercise, each machine's weight should be altered to your personal fitness requirements. After you've performed six to eight repetitions, you should begin to feel your muscles strain to complete the set when the machine is set to the correct weight. Two to four sets of 10 to 12 repetitions on each machine incorporated in the routine is typically sufficient to build body weight.