Unilateral strength training for runners.

For this issue of the AMAAJ we are delighted to have a guest author for
the "Talking About Training" feature that I usually write. I was off
competing for Team USA in the Age-Group Triathlon World Championships in
Hamburg, Germany, so we invited Tom Holland to take my place--and what a
highly instructive article he has provided for us (dealing with an area
of athletic training upon which I am uniquely unqualified to expatiate,
strength training). I hope that you will find it as useful and
instructive as I have.--Steven Jonas

We were meant to move, and to move forward. Runners are constantly forced to defend the sport from non-runners who contend that "running is bad for you." Of course the research clearly indicates otherwise, including definitive longitudinal studies, but most people are not perusing the latest scientific literature on running. They simply remember all of the aches and pains they experienced after attempts to begin a running program. My personal contention is that running is one of the simplest yet most important physical tests at our disposal. It is not "bad" for us but rather illuminates individual weaknesses, allowing us to work on making our musculoskeletal system as strong as possible.

As the saying goes, "we are only as strong as our weakest link" and nowhere is this truism more evident than in the sport of running. A consistent running program will soon expose whatever an individual's weakest link is, presenting itself as minor discomfort or pain. Knee pain, hip discomfort, or lower back tightness can present at the onset of a running program. The primary focus should then be to determine the underlying causes, rather than immediately dismissing the exercise modality entirely.

There are many potential etiologies for the myriad of running-related pains including flexibility issues, muscular imbalances, and relative muscular weaknesses. The great news is that if any of the aforementioned causes are the sources of discomfort, they can often be remedied through an intelligent strength training program. This article will focus on unilateral strength training and its benefit to runners for injury prevention and rehabilitation, as well as its use in improving running performance.

Unilateral strength training simply means working out one limb at a time, such as performing one-legged exercises. There are two basic ways to perform unilateral exercises. You can simply use the lower-body machine exercises with one leg at a time or you can perform standing exercises relying on one leg instead of two. An example of the first type would be doing a seated leg curl machine for the hamstrings with the right and then left leg. The second type would be performing one-legged squats with a stability ball.

There are numerous potential benefits from performing this type of weight training including:

1. Balancing lower limb strength

2. Better strengthening of weak leg musculature

3. Improved balance and coordination

4. Improved core strength and stability

5. Better transfer of running-specific strength

6. Improved running economy

The first benefit, balancing lower limb strength, is made possible by forcing each limb to work independently of each other. Take the example of a leg press exercise. You sit in the leg press machine and push the weight away from your body with both feet. We all tend to have a dominant side which has the ability to exert more force than the weaker leg. By only performing bilateral exercises such as the two-legged leg press, the dominant leg will continue to do more work, consequently getting stronger and further exaggerating the strength imbalance between both legs. The same holds true with the leg extension exercise; if you always perform it with both legs working simultaneously, you risk creating or exaggerating an imbalanced state.

I believe that the standing unilateral exercises, whether performed with body-weight or additional resistance such as dumbbells or weighted vests, can significantly force the strengthening of the runner's "weakest links" which are often the lower leg muscles. A one-legged squat is by definition an extremely difficult exercise; part of the difficulty lies in the fact that it is almost impossible to cheat during the movement while maintaining proper form. I contend that this is one of the primary advantages of this type of training. Unilateral exercises such as the one-legged squat, one-legged box jumps, and one-legged step-ups require our bodies to optimally recruit all the major leg muscles, weaker ones included.

Standing unilateral exercises are difficult because they challenge the runner's musculoskeletal system perfectly and add in the elements of balance and coordination. You not only need to be strong enough to perform these exercises but also need to keep from falling over when doing so. This helps improve body-awareness and can help improve running economy.

The added element of instability that comes with standing unilateral exercises can also help improve overall core strength. As balance and coordination are challenged, you are forced to recruit muscles of the lower back and abdomen, muscles that are inactive in traditional machine-based exercises. When standing on one leg, you challenge your entire body to stabilize itself by relying heavily on core musculature to maintain proper alignment. These core muscles are extremely important to runners, especially in the later miles of endurance races when a weak core can lead to poor form and decreased performance.

The S.A.I.D. principle of strength training [Specific Adaptations to Imposed Demands] posits that when designing a sport-specific training program, the most effective exercises will be those that mimic the motor pattern of the sport as closely as possible. Unilateral exercises, especially those performed while standing, are very similar to the motor patterns of running and therefore provide a tremendous transfer of running-specific strength. Many of these exercises not only closely simulate the running mechanics used by the lower body, they also incorporate the arm swing motions to maximize the full-body running-specific exercise.

This leads to the final benefit of unilateral exercises to runners--the potential for improvement in running economy. Increasing running-specific lower-body strength, improving core strength, and refining balance and coordination can lead to better overall running mechanics and faster times. When you are stronger and more balanced, you waste less energy, especially in the final miles.

So what about bilateral training? Are traditional two-legged exercises, whether in the machines or done with bodyweight or free weights still worthwhile? Are they of any use to runners? Absolutely. You must walk before you run and this applies to the implementation of a unilateral strength training program, as well. Because many of these exercises are advanced and require a great deal of strength and stability to perform safely and correctly, you must first have a strong base of strength before adding them to your resistance training program.

To help many of my runners move from a traditional strength training program to a unilateral program, I often suggest this progression:

1. Two-legged machine exercises

2. Two-legged free-standing exercises

3. Unilateral machine exercises

4. Unilateral free-standing exercises

My favorite unilateral exercises are:

Machine-Based:

1. One-legged leg extension

2. One-legged leg press

3. One-legged leg curl

4. Plyometric one-legged leg press jumps: This must be performed in a leg press machine where the platform is fixed while the seat slides back. Using a light weight and one leg, press off forcefully enough so that your foot comes off the platform an inch or two. Catch yourself on the way down with your other leg, repeating the jump with that leg as well. Alternate back and forth.

Free-Standing:

1. Step-ups: Use a step just under knee height or lower.

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2. One-legged ball squats: Lean back against a stability ball for balance. The depth of the squat can be just an inch or two at the start; as your strength increases so can the depth of your squat, stopping just before 90 degrees of knee flexion.

3. One-legged box jumps: As these are much more difficult than two-legged box jumps, I recommend using a much lower step, one that is just several inches high. As you get stronger you can gradually raise the elevation.

4. One-legged deadlifts: This is also an advanced exercise so start slowly until you have perfected the form. Beginners should do these without weights, making sure to keep the supporting leg slightly bent and their back flat through the entire movement. Once your leg is lifted to hip height, slowly lower it as you lift your torso to upright position. I recommend you aim for 10-15 repetitions with one leg, then switch to the other. You can either try to balance on the supporting leg the entire time or tap your foot down after each rep. Using a mirror to watch your form can help tremendously.

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My philosophy with strength training is you must be proactive rather than reactive. You can either choose to do certain exercises before you become injured, or you can wait and pay for the privilege of doing them in physical therapy later. Adding unilateral exercises to your program will help immensely to prevent injuries from occurring by fixing the weak links that can inevitably lead to problems later.

If you or your patients are already experiencing running-related discomfort, unilateral exercises can help with recovery and if you incorporate this type of training into your overall fitness plan, it may just keep you running injury-free for many years to come.

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Exercise physiologist Tom Holland, MS, CSCS, is the president of TeamHolland, a fitness consulting company. Author of The Marathon Method and The 12-Week Triathlete, Tom is a sub-3 hour marathoner and 14-time Ironman triathlete. If you have questions for Tom, please send e-mail to [e-mail].

By Tom Holland, MS, CSCS