Fatigued legs and cramping calves are common among distance runners. Most of the time the fatigue or cramping is due to depleted glycogen stores and/or dehydration. But, has your upper body every fatigued? Do your arms ever go numb or cramp?
Many times all runners do is run and that's great cardiovascularly, but strength-wise that can cause problems down the road. I've mentioned this before in previous posts (Getting to the Core ) but the core is the power center for a runner. If your core is not strong eventually, you'll become too exhausted to maintain good running form and posture. When this happens your running becomes less efficient and you begin to tire and slow down.
Strengthening your core can help avoid this. [Click here] for a good core work out using a medicine ball. Strengthening the muscles in your arms and shoulder girdle can also help fight fatigue and cramping. Focus your exercises on your shoulders (mid- and rear-deltoids), the back of the neck (upper- and mid-trapezius), the upper arm (biceps and triceps). Free weights (dumbbells) or machines can be used, however using free weights will give you better range of motion allowing you to also help increase your stability because you'll be using a variety of muscles to help keep your balance while targeting the specific muscle you're working on.
Remember the point of these exercises is to build muscular endurance. You're not trying to become the next Arnold. So, think "lighter weight and higher repetitions." Choose a weight that you can lift 12 to 15 times before becoming tired. To start do one set of 12-15 repetitions of each exercise. Eventually work out to three sets (12-15 repetitions) of each exercise.
Check out the following workouts from carveyrunningtips.com for sample workouts.
Upper Trapezius (from AskTheTrainer.com)