Rethinking Bilateral Training
by Kevin Neeld
Bilateral training frequents athletic development programs everywhere. By bilateral I mean both legs or arms working simultaneously to produce force/motion in the same direction. Exercises such as front squats, deadlifts, standing shoulder press, and bent over row are just a few examples. While bilateral training and the associated exercises are deeply rooted in the history of strength training, it may be time to reconsider their use. Heresy you say?
I’m certainly not the first to make this suggestion. Michael Boyle has been making the case for single-leg training for years now. After reading one of his articles on the topic, I began thinking more about the lack of respect single-leg training receives. As the article mentions, people are probably reluctant to use single-leg training because they require less external load. This raises a few more questions. Is external load completely indicative of internal stress to the muscle? If so, is neglecting the movement pattern and maximizing the external load really the goal of training athletes? The article also mentions the “functional” inclusion of the medial and lateral musculature of the hips that is present in single-leg training and not bilateral training, functional being defined as “training the muscles that we’re using in the way that we use them.”
I want to preface the rest of this article by stating that I’m not yet calling for a complete abandonment of bilateral training. Instead I simply want to present some of the research supporting the empirical evidence that Coach Boyle presented in his T-nation article. In light of the available research on the nervous system, a working knowledge of functional anatomy, and injuries associated with heavy spinal loading, I think it is time to reconsider the efficacy of predominantly bilateral training programs.
A look into the literature on the nervous system’s role in force production revealed an interesting occurrence known as the bilateral deficit. For those of you that aren’t familiar, the bilateral deficit simply describes the fact that the sum of individual extremity force production is greater than bilateral force production (1-5). In other words, if you performed a one-legged knee extension with your left leg only, then your right leg only, and added these two forces together, they would be greater than if you performed a knee extension with both legs together. Bilateral Deficit: Leg A + Leg B > Both Legs
In fact, the bilateral deficit is said to be as large as 20% (6,7) during slow contractions and as high as 45% (7,8) during rapid contractions! Luckily, researchers were quick to monitor the changes in this relationship following a bilateral resistance training program and found that the deficit decreased. In some instances the relationship even reversed so that both legs produced more force than the sum of individual leg efforts (9,10). Phew! Disaster averted.
Neural scientists refer to the bilateral deficit as a phenomenon. I would question whether it is a phenomenal occurrence or a long-term adaptation to repeated movements. As many of you already know, performing a movement repeatedly strengthens the associated neural circuitry resulting in improved force production. In the words of my old neurobiology professor, “Neurons that fire together, wire together.” This is the primary explanation for why novice lifters can experience rapid gains in strength in the first eight weeks of training.
Is it possible that the bilateral deficit is simply a life-long adaptation to producing force on one-leg? I realize that no one grows up performing one-legged squats off their kitchen stools on a daily basis, but think about the movements we perform regularly, notably walking and running. While one leg is producing a triple-extension force, the other is usually producing a triple-flexion force. Let’s come back to the knee-extension example. In consideration of the “neurons that fire together, wire together” statement, it would make sense that as one leg is extending the neural circuitry is telling the other to flex. This pattern predominates in most human movements: walking, skipping, running, and even crawling!
The neural circuitry to explain this pattern is well-established. Some of you may have been introduced to it through the flexor crossed-extensor reflex. In this example, if someone steps on a sharp object or other painful stimulus, they will withdrawal that leg by flexing the hip and knee. At the same time, they will extend the hip and knee on the other leg. This is a stabilization mechanism. If both hips and knees flexed, you’d like end up sitting on the painful stimulus you’re trying to avoid. Basically, as the flexor group on one limb is excited, the contralateral flexor group is inhibited, and the contralateral extensor group is excited.
What does this have to do with athletes?
We are wired to effectively produce unilateral movements. Athletics involve unilateral movements. Most strength and conditioning programs revolve around bilateral movements. Why? I understand the benefits of including single-leg training is being increasingly recognized and that more unilateral training is being prescribed. However, it still seems that we’re adding some single-leg training to a double-leg program, instead of the other way around. What happens if we abandon double-leg training altogether? Compared to double-leg training, single-leg training:
1. Requires greater force production from more muscles. Picking up one leg immediately requires greater force production from the hip abductors and adductors (among others) to stabilize the pelvis. Some of the affected muscles would include: pectineus, adductor brevis, adductor longus, adductor magnus, gracilis, obturator internus, obturator externus, gluteus maximus, gluteus minimus, gluteus medius, psoas major, iliacus, sartorius, gemelli inferior, gemelli superior, piriformis, and tensor fascia latae.
2. Increases the proprioceptive and sensory demand. Decreasing stability by narrowing the base of support will absolutely necessitate greater proprioceptive and sensory feedback to maintain balance.
3. Decreases spinal loading. I’ve heard a saying a few times that goes something like “Live your life the wrong way, you’ll end up in a cardiologist office. Live your life the right way, you’ll end up in an orthopedic office.” This has come to be accepted as an inevitable truth. Research supports the idea that repetitive heavy spinal loading, as is common in long-term weightlifting, results in a myriad of spinal issues including an increased incidence of spondylosis (11), decrease in intervertebral disc height (12), lumbar spine degeneration (13). But does it need to be this way? If we can maintain or even improve the quality of the stimulus to the muscle and cut the external load in half, could some of these injuries be prevented?
4. Reinforces the neural circuitry common to most athletic movements. The majority of athletic movements occur from one-leg or a staggered stance. Could this more similar training approach help to decrease the incidence of injury? I’m thinking specifically of hamstring strains and ankle sprains. Hamstring strength absolutely plays a role in preventing hamstring strains. But how do we explain the athletes with monstrous hamstrings that suffer an injury? Bad running form? Maybe. Is it possible that these strains are occurring due to a neural mishap associated with hamstring momentarily attempting to contract concentrically bilaterally when one side should be lengthening? The causative factors associated with ankle sprains remain relatively allusive, but there does seem to be some evidence that decreased proprioception and increased peroneal stretch reflex latency may be related to ankle injury. As a global factor, fatigue seems to be related to injury, with more injuries occurring as fatigue increases. Of interest is that muscle fatigue is training-specific, meaning that if double-leg training predominates, the athletes will resist fatigue more efficiently in double-leg movements than single-leg movements.9 Naturally, the opposite is also true. Both of those factors are neural in nature, and may be positively affected by the increased demand on the sensory system provided by single-leg training. Prior history seems to be the greatest predictor of future injury. Therefore, if we can prevent an injury from ever happening, we significantly decrease the risk of future occurrences.
Admittedly, some of the proposed benefits of single-leg training on injury prevention are speculative. There is a clear list of benefits to single-leg training, however, that shouldn’t be overlooked. While I believe that largely moving away from double-leg training is premature (and somewhat scary), I think it is worth considering. Albert Einstein once said, “The significant problems we face cannot be solved at the same level of thinking we were at when we created them.” Weigh the pros and cons associated with eliminating double-leg training. Is it time for a change?
This article was originally published on www.StrengthCoach.com, an athletic development website where some of the world’s experts in strength and conditioning print their articles and discuss current issues.
Kevin Neeld, BSc, MS, CSCS is the Director of Athletic Development at Endeavor Fitness in Sewell, NJ and the author of Hockey Training University’s “Off-Ice Performance Training Course,” a must-have resource for every hockey program. Through the application of functional anatomy, biomechanics, and neural control, Kevin specializes in guiding hockey players to optimal health and performance. Kevin developed an incredible ice hockey training membership site packed full of training programs, exercise videos, and articles specific to hockey. For a FREE copy of “Strong Hockey Core Training”, one of the sessions from his course, go to his hockey training website.
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