by Matt Weik, BS, CSCS, CPT, CSN
Have you ever wondered why sometimes it feels like one side of your body is stronger or more coordinated than the other? It’s not just your imagination at play. A fascinating phenomenon called the “bilateral deficit” can explain this imbalance.
In simple terms, it’s the idea that your body sometimes works less efficiently when using both sides simultaneously than when using each side independently. This concept may have implications for how we approach activities and exercises in our daily lives.
In this article, we will dive deeper and explore more about bilateral deficit as it relates to exercise and your results.
Disclaimer: This article is for informational purposes only and is not meant to treat or diagnose any condition. It is recommended that you speak with your doctor before starting any exercise program.
What is a Bilateral Deficit?
In recent years, the concept of the bilateral deficit has gained significant attention in the realm of training and fitness. Simply put, this phenomenon, primarily studied in the lower body, refers to a situation where the combined force generated by each leg individually is greater than the force generated when both legs work together.
There has been a growing misconception that any exercise performed with a single limb carrying more than 50% of the load of its two-limb equivalent falls under the bilateral deficit explanation.
It’s crucial to recognize that the bilateral deficit primarily relates to neural factors, though other factors like stability and muscle force production also play pivotal roles in exercise performance. Understanding these nuances can be key to optimizing your training regimen and overall physical development.
Possible Training Implications
According to several studies, there appears to be little disparity in tonnage between unilateral and bilateral exercise methods. This observation is intriguing, especially when considering that unilateral methods involve twice as many sets, which might suggest a higher total volume. However, the total tonnage tends to balance out when the loads employed in unilateral exercises are typically a fraction of those used in bilateral exercises.
Consequently, a heightened awareness of an athlete’s specific force production requirements becomes paramount when selecting the most suitable method. When the impact on work capacity remains relatively equal, the focus shifts towards determining the force application adaptation that offers the athlete the greatest benefit.
An established principle in exercise science is the inverse relationship between the resistance encountered and the velocity achieved. Recent research has uncovered a force-velocity profile that many athletes tend to exhibit, predisposing them to favor either force or velocity in power generation. Moreover, targeting the opposite quality of an athlete’s bias has the potential to enhance their overall power output.
For athletes favoring speed, emphasizing force production can boost overall power. Understanding how bilateral and unilateral exercises affect force and velocity guides program decisions. Athletes needing more speed engage in more bilateral exercises for greater velocity. Conversely, those requiring added force focus on unilateral exercises.
Stability Can Be a Limiting Factor
If you visualize a rectangular box drawn around your feet, it can provide valuable insights into the concept of stability during different squat variations.
In a traditional back squat, this box represents your base of support. A narrower stance or having smaller feet naturally narrows this base of support. However, during a traditional back squat, the challenge typically doesn’t lie in lateral stability — the side-to-side balance is usually well-maintained.
For some novice lifters, the struggle may revolve around anterior-posterior (front-back) stability since the rectangle is wider from side to side than from front to back.
In contrast, in a split squat (acknowledging that it’s a distinct squat pattern), the base of support represented by the rectangle around the feet might be similar in size to that in a traditional squat. However, now, the rectangle becomes elongated from front to back and narrower from side to side. In simpler terms, this implies that anterior-posterior stability is robust, but lateral stability becomes more susceptible and may become a limiting factor in the exercise.
Lastly, consider a 1-leg “pistol” squat, where the base of support is as large as an individual’s foot. In this case, both anterior-posterior and lateral stability are compromised. This significant reduction in the base of support inevitably restricts the amount of external load an athlete can handle during this exercise.
If someone can back squat 400 pounds but can only manage 50-100 pounds of external load in a 1-leg squat, the bilateral deficit may still play a role, but the limiting factor for further loading in this exercise does not stem from neural drive issues. Instead, it’s primarily attributed to compromised stability.
