Sunday, March 25, 2012

Bilateral Movement vs. Unilateral Movement- Phenomenon of Bilateral deficit

Our everyday weight training involves movement that requires both the extremities (Arms & legs) performing an action. Action in the gym requires the activation of muscles and it will be the executing muscles generating force to perform a movement.  For example to Squat 200lbs our leg has to generate more force than 200lbs to move that weight and control the weight. Any exercises performed when both the limbs are working in tandem will be termed as a bilateral movement. Even movements like getting up the chair will be termed as a bilateral movement.  Similarly, movement involving a single limb will be termed as an unilateral movement. Exercises like a single leg press, single DB curls, one arm overhead press and a single leg deadlift will be termed as a unilateral movement. In our day to day activities we perform movements that are unilateral movement; a beautiful example of this will be walking and running (3).

Bilateral Phenomenon
“Bilateral deficit is a slight decrease on the neural activation in the recruitment of motor units in the development of bilateral works, when compared to the sum of unilateral works" (1) .  For example, an unilateral (single) leg press movement (both left & right) added will be more than the force production of a bilateral movement on the leg press. We are able to generate more force production unilaterally as compared to bilateral. Incorporating single limb exercises quantifies the effort and the effectiveness of that particular exercise. In a single leg movement, the hip musculature will be more activated which will result in proper muscle activation. Depending on the intensity of an individual, he or she has to incorporate individual limb movement. 

Do we need to exclude bilateral movement?
 No, we do not exclude bilateral movement from our training program but we incorporate unilateral movement in our training program to enhance the rate of force development (2).

The advantages of unilateral movement in a leg workout would be the reduction of spinal compression and the recruitment of muscle contraction. Additionally, to achieve this contraction an individual wouldn’t require maximum poundage.  Hence, it would make sense to include single limb movement to improve the effectiveness of our lifts.

  1. Aagaard, P; Simonsen, E.B; Andersen, J.L; Magnusson, P & Dyhre-Poulsen; P. (2002). Increased rate of force development and neural drive of human skeletal muscle following resistance training.  Journal of Applied Physiology, 93, 1318-1326.

  1. 2.      Janzen, C.L., Chilibeck, P.D., & Davison, K.S. (2006).  The effect of unilateral and bilateral strength training on the bilateral deficit and lean tissue mass in post-menopausal women. European Journal of Applied Physiology, 97, 253-260.

  1. Seynnes, O.R., Boer & Narici, M.V. (2007). Early skeletal muscle hypertrophy and architectural changes in response to high-intensity resistance training. Journal of Applied Physiology, 102, 368-373.  

Frank Mapranny, 
Fitness Head, 

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