In 1992, Vladimir Zatsiorsky, who immigrated to the US from the former Soviet Union, was invited to speak before the International Symposium on biomechanics and sport. In this talk he introduced a unique perspective about the specificity of resistance training to an athlete's sport specific strength and power. His ideas became the foundation of the Science and Practice of Strength Training. The following discussion draws from Zatsiorky's ideas. Sport relevant strengths and power is accomplished by using two strategies. The first is to identify the main movements of the sport, and simply add resistance while the athlete is performing these movements, and the second is to identify the muscles used to perform the sport's skill, and use a variety of weight enhanced exercises that target these muscles. These weight enhanced exercises are referred to as assistance exercises. Now, adding resistance while the athlete is performing the main sport movements, depends on the coach's creativity. Examples include adding additional weight by using weight vest, belts, handcuffs, ankle cuffs, etc. However, this approach can lose its specificity. If it alters the posture and the way force travels between muscles while the athlete performs the movement. A second method is to use the force of gravity by asking the athlete to run, walk, or ski up a hill. And this approach can also lose specificity if the athlete's posture varies from the sport specific posture. So encourage the athlete to maintain correct posture if you are using this particular resistance training approach. The third method is to retard the athlete's progression by using a towing sled. This type of equipment is hard to transport, and can also lose specificity by changing the athlete's posture. So again, it has its disadvantages. But once again, just encourage the athlete to maintain correct posture. And fourth, you can use aerodynamic resistance, and speed skaters and runners really like this particular strategy. A small parachute attached to the athlete inflates and creates a resistance force, and the faster the athlete's speed, the higher The resistance force will be. The assistance exercise category is the most challenging strength training program to prescribe. It can be challenging to select the exercises that have a large of training effect to the main sports movement. Knowing what muscles need to be trained, and how these muscles move the various parts of the body will help you identify relevant assistance exercises. We're going to focus the remainder of this lesson on factors to consider when selecting a assistance exercises.