Most people would love to more upper body strength. And for most people, the humble push up is one of the best exercise to build your upper body muscle and develop functional pushing power. Do it well, and you will develop your upper body from triceps, chest, all the way to your core. Do it incorrectly and you could develop shoulder and elbow pain among other things. Read the book and make sure that you will progressively develop your strength in a pain free way.