Unless you've spent a lot of time learning about how a car engine works, you'll be totally clueless about where to even begin fixing any problem that might arise. And don't even think about improving the engine's performance. If you don't know how the engine is designed to work under normal conditions, you can do simple things such as mixing some sort of additive in with the gasoline based on advice you read on the Internet. However, you won't know for sure if this additive works, nor will you be able to assess if it will damage your engine over the long term. And the same is true when you're training athletes. When you train athletes for high sports performance, you are forcing their bodies to deviate from normal functioning into a souped up version, more suited for sports-specific performance. You can't design the right engine for a sports-specific phenotype if you don't understand what body parts are involved, and how they normally function. Knowing the body's structural arrangement, or the anatomy, and how it works, or the physiology, will put you in a really good position to effectively design any sports-specific phenotype. From the outside, athletes are clearly very different in the way they look. Peel away their skin, however, and you'll see the same 37 trillion cells consisting of four different functional types. There are cells specialized for constructing and communicating. There are cells specialized for moving. There are cells specialized for sport supporting and protecting. And there is cells specialized for connecting the parts of the body together. So let's go through each of these cell types in some detail. Nerve cells are highly specialized cells designed to transmit information rapidly to various parts of the body and back again. Muscles cells are complex biological motors capable of producing movement. And there are muscle cells designed to keep the heart pumping, there are other muscle cells lining the blood vessels so they can dilate and constrict, ad there are skeletal muscles cells that move the skeleton itself. All these types of muscle cells cause movement of some sort. Skin cells and cells lining the stomach, and other hollow organs protect the body from wear and tear. And finally, there are cells forming the tough ligaments and tendons that link bones together to form joints. The red blood cells seem a little out of place in this category, but they serve an important connection function by delivering oxygen, and fuel, and other supplies throughout the body, so all the cells are able to do their designated job. These four cell types join together to form tissues, and from these tissues the organs are built. And then the organs join together to form an organ system. And these organ systems are capable of performing specific functions essential to the body's ability to survive. For example, a heart and the blood vessels are the key organs forming the cardiovascular system. And the organ systems combine to form the body of the performing athlete. There are 11 organ systems comprising the human body. And while all play a role in an athlete's sport phenotype, five of them are particularly important. And they include the skeletal system, the muscular system, the nervous system, the cardiovascular system, and the respiratory system. In this module, we're going to briefly review the structure of each of these five organ systems and examine how they function. So let's get started.