2+2=3: The bilateral strength deficit

What is it? How does it impact on training and how can this be beneficial for the motorsport athlete?

The bilateral strength deficit relates to an observable difference in the maximal force generated during bilateral movements (using two limbs) vs unilateral exercises (one limb).

“The whole is not always the sum of its parts”

When it comes to training, performance and the human body we would expect ‘global’ influence such as the impact of whole body movements to directly carry over to ‘local’ influence such as single limbs. To put this into an exercise perspective using the squat as an example. If an athlete has a back squat (bilateral movement) with a one rep max (1RM) of 100kg, it would be reasonable for us to assume that individually each leg would be contributing roughly half of the maximal force required to complete the movement. However what we will often see if that each individual limb when performing a single leg variation such as a split squat (unilateral exercise) will be able to produce a significantly greater force. The whole is not as great as the sum of its parts and 2+2=3.

Bilateral vs Unilateral force generation

While this doesn’t happen for everyone, and while there are a number of different theories as to what influences and causes this to occur, thats a conversation for another day. Instead here we are going to focus on what this can mean for performance in the car or on the bike and how we can use this to an advantage in training.

Sticking with the example of the back squat from above, utilising bilateral movements for training will allow us to lifts a higher weight per rep the relative load will be lower. So while they are crucial when it comes to establishing good movement patterns and have a strong place in a training program, utilising unilateral movements can allow us to lift a relatively heavier load. This therefore will increase the total volume although overall tonnage will only be fractionally higher. The inclusion of the unilateral variations will often lead to an increase in muscular activation in the surrounding muscles as well and a higher global hormonal response.

This therefore poses a strong argument for the inclusion of more unilateral work into a training program especially when in sports such as motorsport where there is a strong demand to generate force and power through single limbs while competing.

The added benefit of this is the ability to help address and counter any strength imbalances that could be present, reducing therefore the potential injury risk for athletes too.

So in summary there is strong evidence and research supporting the existence of the bilateral force deficit, while the research shows this isn’t found in everybody it does present a strong argument for the inclusion of unilateral work in the training programs of motorsport athletes for the development of strength, power and performance.