Far too many cross-country runners avoid weight training. But these endurance athletes will benefit by incorporating strength training into their programs. Increased upper body strength helps delay arm and posture fatigue during a race. Increased leg strength enhances running efficiency, force application and speed.
Another bonus of strength training is injury protection. As a distance runner, your legs absorb up to five times your body weight with each stride. The  cumulative effects can add up over the season. Muscle weakness and imbalances are two prime causes of overuse injuries. Incorporating strength training will go a long way to prepare the muscles, bones, tendons and ligaments for the high intensity loads placed on the body during the season.
A good cross-country strength-training program should focus on strengthening and balancing the quadriceps, hamstrings and hips. This will develop the powerful strides needed for end-of-race sprints to the finish. Getting stronger also helps to absorb the repetitive shock of each stride and contributes to a successful season.
The best days to include strength training into your workout are after hills, intervals, tempo or fartlek runs. Stay away from lifting weights on recovery days and long run days.

Lunges

Sets/Reps: 2×12-15
♦ Hold dumbbells in both hands with arms extended at sides of body
♦ Bend front knee to lower into lunge position until thigh is parallel to ground; keep front knee behind toes
♦ Push off  heel to extend hip and knee to drive up to start position
♦ Repeat with other leg

Calf Raises

Sets/Reps: 2×12-15
♦ Assume position on Calf Raise machine with slight bend at hips and knees
♦ Drive up on toes, fully extending hips and knees
♦ Descend slowly; repeat for specified reps

Push-Up-to-Row

Sets/Reps: 2×12-15
♦ With a dumbbell in each hand, assume push-up position with straight arms
♦ Perform a Push-Up
♦ At the top of the push-up, keeping your core stiff, row the dumbbell to the side of your chest, bending your arm as you pull it up
♦ Pause, then lower the dumbbell. Repeat with other arm.

Dumbbell Arm Swings

Sets/Duration: 3×10-20 seconds
♦ Assume staggered stance holding lightweight dumbbells at sides
♦ Keeping arms at 90 degrees, drive arms forward and back
♦ Repeat for specified reps; alternate lead leg each set

Bridge Circuit

Sets/Duration: 2 x 30-60 seconds each position
♦ Perform Front, Side and Glute Bridges (Plank) in a circuit
♦ Keep back flat with body in perfect Plank position
♦ Tighten core to prevent bad form
♦ Keep neck in neutral position