In three or four weeks you can lay a good foundation. It's unlikely that, unless you have a very low percentage of body fat, you'll be able to see any muscular development in three weeks. Your poundages, however, should increase, which will demonstrate a strength gain. There's no trick to it. Train hard, plenty of rest and sleep, and eat properly.
Do the basic, multi-joint exercises, namely, squats, deadlifts, presses, rows, dips, and chins. Focus on overall growth. You can also use other multi-joint exercises such as farmer's walk or sled pulling, but generally avoid single-joint exercises. You must eat correctly. For example, you should be ingesting plenty of protein from natural sources and avoiding refined processed carbohydrates. Drink plenty of water. Avoid over-training and get plenty of rest. It's better to think of it as a lifestyle. For the free exercise and eating plans to get you started, see the page links, further down this page, listed under Related Questions.
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the best way to gain more muscle is resistance training which is weight lifting. When done consistently (about 30 minutes 4-5 days a week), one can see muscle tone very quickly. Also watching one's diet is just as important.
That's impossible to do in one week.
Is it possible that a fetus in utero can gain two and one half pounds in one week during your 38th week?
From research and personal experience, I have learned that it is not possible to gain 10 pounds in one week.
No.
If you want pounds fast, drink muscle milk and don't work out. It's got like 1,000 calories every cup.
You Dont...
Train With Progressive Resistance
5lbs
eat poo for a week
For 99% of you, these are a waste of money and will make you fat! Weight gain powders are protein and carbohydrate, usually sugar, and a bunch of vitamins and fancy sounding stuff that is supposed to magically build muscle - don't believe it. For most people the only weight you will gain is FAT. For the few people that have no appetite at all or are dangerously low in body mass, these products can be a life saver but for the rest of us they are not appropriate. Many people mis-label themselves as "hard-gainers" when in fact they are normal. When working out hard and having flawless nutrition, it is resonable to expect you will gain 5lbs of muscle in a year - maybe 10lbs/year if your are one of the genetically gifted few. Don't believe the ads claiming that mass gain powders help hard-gainers to add muscle, they don't, they just help add fat!
Unlike muscle, you can't gain fat on just one part of your body. If you gain, you gain all over. And the method is through increased calorie consumption; but do it moderately.