Brief Answer:
Focus on proper exercise and diet plan.

Detailed Answer:
Hello,

As you are medically fit, so I think you are asking about muscle volume. Kindly follow up with detailed history if you want something else specifically.

To increase muscle volume, take protein rich diet like eggs, soy, beef, chicken, fish, beans, milk or you can take protein supplement like Protein X powder or whey protein.

Kindly take oatmeal or whole grains, brown rice, peanut butter, cottage cheese, dry fruits in diet and eat more fruits and vegetables. Avoid processed and fast foods.

Along with that take training under expert trainer at the gym and focus on calorie intake. So you should not feel fatigues during exercise. For that always carry energy drinks during the training period. Take a proper six to seven hours of sleep. Avoid smoking and alcohol, if at all do.

Hope I have answered your query. Let me know if I can assist you further.

Regards,
Dr. Shyam Kale
Family and general physician.

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