It's OK to admit it: You don't do enough strength and conditioning work. Understandably so, since we runners will almost always prioritize the running over other forms of work. But, on the other hand, runners who include more strength training tend to get faster quicker and get injured less often. Even if you find yourself pressed for time and/or you don't have access to a gym, you can still add quality strength training to your weekly routine. Here are 5 strength moves that every runner should work on mastering. You don't need to be able to do these perfectly today, but you should spend some time working on these moves each and every week. The best part is, only one of them requires any weight other than your body.
Push-up: Simple and effective, the push-up will strengthen everything from your shoulders down to your hips and glutes. Proper form is key with all strength moves, and the key to a successful push-up is to keep the entire body from ankles to shoulders in a straight line. Clench your butt and core to lock in this form. Keep your elbows close to your body when your chest is near the floor, and press up through your chest. If you can't do a good-form push-up, you're not abnormal or a weakling; start with wall push-ups, modified (knees on the floor) push-ups, or push-ups on a bench (incline variety).
Standard Squat: These will strengthen your hips, glutes, and quads most of all; integrating squats with your routine will help manage and prevent IT Band Syndrome, knee pain, hip issues, and will make you a more powerful runner up hills and in late-race sprints. Good squats involve an upright upper body posture (no hunching or arching the back), and a squat form that is like sitting in a chair. The most important concept is to keep your weight centered over your heels, and not allow your knees to move in front of your ankles. Always push back up from the squat position through your heels.
Walking Lunges: Good lateral stability can be a major deficiency among runners, but is really important for anyone who spends time running and racing on uneven surfaces. At the same time, lunges can help strengthen the lower legs to prevent or treat issues such as Achilles tendinitis, calf pain, shin splints, etc. We tend to do a couple of things poorly when it comes to lunges: Going too fast, and allowing form breakdown. Lunges should be slow and deliberate, with all of the weight traveling in a straight line. Keep your plant leg aligned so that your knee doesn't go to the side of your ankle (or in front of it). Like with squats, push back up through the heel. You should also work on being able to complete walking lunges forward and backward.
Deadlift: You know what else helps runners kick ass, especially as the race gets longer? Strong lower back muscles. Deadlifts, if you do them right, will give you a strong back that will help maintain good running posture when you get tired. Good posture = efficient running = running faster for longer. Deadlifts are generally not done, which is a shame, because they really do help. Here's a great post on Nerd Fitness with form information and a video tutorial. You don't have to do these with a barbell; you can start doing deadlifts at home with free weights or jugs of milk.
Russian Twist: This is my favorite and one of the most versatile core moves. The Russian Twist works your abs, obliques, lower back, and hamstrings. Also, unlike some other core moves like sit-ups or crunches, the Russian Twist doesn't encourage you to strain your neck. Another added benefit of this move: The rotating motion is a good analog to the natural rotation of your body while running. Russian Twists are a big enough deal to have their own Wikipedia entry, which has a good description of the move and a couple of variations with a weight.
If you take these 5 moves, and complete a 15-20 minute session with a few sets of each a few times a week, you'll see some improvement in your running. Now that your arguments for skipping the strength work are invalid, get out there and get it done!