Being an athlete isn't just about making sure you are in peak physical condition. Sure, you can't really play soccer, baseball, basketball, football, or whatever your sport is, without being in top physical shape. Strength training and conditioning your body everyday is important but there is much more to becoming one of the top athletes in your sport than athletic ability. No matter the profession you're in, whether you're a soccer player or work in finance, you have to be mentally able to handle it.
Being an athlete means being in top physical and mental form. You need to make sure that your brain can teach your body when it's pushing itself to the limits and needs to slow down. To get in shape you have to train your muscles through repetition. An athlete only gets better through practice, a painter only improves their skill set by brush stroking repeatedly, and a goalie only improves their game by taking on penalty kick after penalty kick during practice.
When training or going to the gym your body will get use to doing the same thing over and over again. A set of weight lifting will only become easier on you the more you do it. Muscle memory and training go hand in hand as you see. Your body eventually gets used to routine. Whether that's leaving your house and jogging the same route every day, using the same elliptical machine at the gym every time you do cardio exercises, or working out with the same workout partner. Any personal trainer, coach or chiropractor (see here) will tell you that and be on you to keep training your brain as you train your body.
The more you workout, the better physical condition you'll be in and that will help you on the field. Having your brain and body working together you won't let anything take your focus off of the field. Whether that's being roughly tackled or being given a questionable yellow card. All you should be worried about is playing as hard as you can and giving your all. If your mind has properly trained your body you'll be conditioned to not feel tired or dehydrated if your game goes longer than expected.
If you workout at home you might want to record your sessions and then go over the footage with your trainer to show you how your body is responding and what you can do to improve your workout. Always remember that the most important organ in your body is your brain and you should use it to help you keep the rest of your organs and muscles in peak condition.