It is important when you write your fitness plan to involve opposite muscles. Around our body we have muscle groups at the front and back. Most people concentrate on the muscles on the front of our bodies as these are the ones we can see in the mirror. All the front muscles have opposite muscle groups which we need both for our bodies to activate normally and to produce movement.Just think if we only had the use of the muscles at the front of our bodies! For example, when awaking in the morning, we would need to contract our abdominal muscles to lift our bodies out of bed. In doing so, we would place our back into an L shape. It would be impossible to fix if we did not have the use of the latissimus dorsi, a muscle, which is located in the lower back. We would need this muscle to contract so that we can become straight again and carry on with our day. Remember a muscle can only shorten; it needs an opposite muscle to contract so it can bring us back to our original form of shape.