If you consume only the amount of calories you need to maintain your existing lean muscle mass, you may get stronger but there just won’t be enough spare resources to generate new muscle fibre. You can work out the amount of calories you need by first establishing your basal metabolic rate using the following formula: BMR = 66 + (13.8 x weight in kg) + (5 x height in cm) - (6.8 x age in years) To this base rate, you'll need to add the amount of calories you believe you expended during your workout, plus an extra 200-400 calories. .