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Before you begin training in cross-country, be sure to revisit the basics on staying flexible and well stretched. Don't forget to warm up before heading out, and to warm down. You might also like to include some minor weight training and some cross-training such as swimming, cycling, and walking, as these will work other parts of your body as well as giving you a break from running but still providing you with exercise and stress relief.  Additionally, if you're not already running, speak with your doctor about taking up this strenuous sport if you have any fitness concerns. If you're in bad shape, don't give up; just take it more slowly and be very kind to your body as you get used to the running and exercises. The beauty of running is that you will gradually improve your fitness and stamina.  Do push ups and sit ups every day. This will strengthen your upper body, which is also vital in a race. Start with fifteen push-ups and twenty-five sit-ups and work your way up. You may discover that your calves and hamstrings get a little sore if you're not already a seasoned runner. This is a good thing; it means that you're working the muscle in a way it's never been used before. This is similar to when you go to the gym after a long absence and do a complete weightlifting workout. Of course your muscles will be sore, but that isn't a bad thing! You might want to consider cutting back a little if they are especially sore. Your fitness as a cross-country runner also depends on what you're eating. Be sure to eat healthy foods and to provide your body with the high energy input that it needs for running. It's also helpful to eat smaller meals, but eat more frequently throughout the day (maybe 6 - 8 smaller meals every 2 to 3 hours).  Cut down or cut out the fast foods. They provide empty, non-nutritious calories that don't give long-term energy. Instead, fill up on the complex carbohydrates. Eat lots of veggies, fruits, whole grains, and drink water. Also, get plenty of high quality protein. Before a race, eat lightly. It is recommended that your meal be 2 to 3 hours before a race, and 1 hour before training. Eating any closer to a race can cause you to cramp up. Drink 230 to 460 ml (8 to 16 fl oz) of water or a sports drink an hour before running.  Read up on sports nutrition. It's a complex area with lots of ideas but only you know your own body's needs and can make the right choices for fueling it. Do some research and trialing to see what energizes you the best. Once you've trialed the terrain for a bit and become used to running on all sorts of different surfaces, focus on little goals and big goals to help build up your resilience and endurance.  Set a big goal. Now that you've started, it's time to focus on your first cross country race. Which one will it be? Choose one that is coming up and start working toward it. Start adding one long, hard run to at least one day a week. Do your best to keep running without stopping over a long period of time, such as an hour or two and build it up. Weekends are best for this, although you can also make good use of evenings during daylight savings in the warmer months of the year. Continue training by observing the easy day/hard day routine. No matter how experienced a runner you are, training should not consist of all hard days. Your motivation and your body will soon wear out! Instead, implement a system of training that allows for some days where the runs are easy and other days where you really push yourself. As a beginner, slowly build up to harder training days. Keep a training log. This will help you to keep track of your running progress and will enable you to note when it's time to switch up your training to its next level. Look online for training program ideas. There are different training programs suggested by different coaches and cross-country runners. Tailor these to suit your local environs and personal needs. The key is to increase your ability gradually and to ensure that you have covered all the bases including different terrain, inclines and declines, all-weather running, increased stamina and speed, and ability to push yourself just a little further every time.

Summary:
Remain flexible. Eat for best performance. Set goals. Do some research.