5x5 stands for 5 sets of 5 repitiions. A 5x5 workout is one that uses these low rep hight weight sets and focuses on compound exercise; squats, bench press, deadlift, power cleans and barbell rows and repeated 3 times a week. This method was popularised in the 1970s by Bill Starr in the 1970 in his book "The Strongest Shall Survive" to train footballers.
The 5x5 workout is progressive and all of the weights you should be lifting are planned well in advance, based on your one repetition maximum for each exercise. Once you know your 1RM for each exercise, you simply use the percentages detailed in the 5x5 workout. Each week, the loads are increased slightly to ensure a linear progression in both weight lifted and strength gained. This means that, regardless of your current level of strength, the program can be adapted to suit your individual requirements.
The 5x5 workout is a training system devised by football strength coach Bill Starr in the 1970s. Built around a small number of effective compound exercises that were performed three times a week, the 5x5 workout gained popularity because of its simplicity and effectiveness -- 5x5 is also shorthand for five sets of five repetitions. This is both a feature of Starr's workout and also a set/rep scheme commonly associated with exercise programs designed to build size and strength.
The Original Starr program was published in his book, "The Strongest Shall Survive" and designed for bulking up football players. Each workout consists of three primary exercises: squats, power cleans and bench presses. These three exercises ensure that each major muscle in the body is challenged. When performing the 5x5 workout, additional exercises are not necessary although some users of the program add supplementary exercises such as biceps curls or core work to great effect. Each exercise is rotated so that one of the three is performed with maximal loads once per week while the other exercises are performed using sub maximal intensity. Essentially, this means there is a heavy day, a medium day and a light day for each exercise during training the week. The program is normally followed for six weeks before taking a break and then starting the program from the beginning again with heavier weights.
The Classic Starr program is built around squats, power cleans and bench press. Squats target your legs and hips, the power clean develops total-body explosive power, especially your hips and back while bench presses focus on your chest, shoulders and arms. Each of these muscle groups is very large and provides essential force in football and almost every other high intensity sport including basketball, martial arts and rugby. By focusing on these big muscle groups, smaller muscles such as your abs, calves, biceps and shoulders receive an indirect workout. The 5x5 routine is not a bodybuilding routine in the true sense of the word. Bodybuilders target muscles individually to ensure the development of an aesthetically pleasing physique. The 5x5 program is more about developing functional muscle mass rather than a balanced, attractive physique.
The 5x5 workout is very simple and focuses on a small handful of exercises. This reduced variety of exercise can lead to boredom and increases the risk of developing overuse injuries. To get the most from a five repetition set, you must lift weights that are heavy enough to be challenging. This means that you will be placing your body under a potentially injurious load. This is fine and, is in fact, necessary for intermediate or advanced lifters but is not such a good idea for beginners. Beginners are often still learning how to perform exercises with good technique -- lifting heavy weights with poor technique can lead to short term and long term injuries.