Bilateral Deficit


At this time of year, for many track and field athletes in the southern hemisphere who are not at the elite level; they will have transitioned into the off-season; enjoying some much needed down time. Both athletes and coaches alike, will formally or informally begin to dissect their season identifying the good, the bad, strengths, weaknesses, and planning their attack on the upcoming season.

This past week I did some strength testing with one of my athletes (100/200/400), largely to map out their strength programme across the GPP, but also as a basic screening tool (something we did not address last season). Although we did perform field tests throughout the preparation phase (jumps/throws/bounds), we did not place as focus on weightroom numbers. Both the athlete and I discussed the various phases of their race(s) where we could look for improvements, and with a mature training age, finding as little as 0.5% matters!

So getting back to the title, using the deadlift as an example (as per the graph), Bilateral Deficit refers to the sum of the individual legs performing single leg deadlifts e.g. 115kg on the RL, 100kg on the LL (total 215kg), being greater than the sum of their double leg back DL of 200kg; a 15kg deficit. Now this is just an example, and would be numbers expected of a semi-elite/elite sprinter. However, my athlete did not show any deficit. The sum of the two limbs individually equalled the 3RM bilateral sum, 120kg. Now, the actual overall number suggests room for improvement, but I guess more concerning for me was why was the strength in one limb 50% as strong as the other?


Without getting into the argument of why perform unilateral lifts… Read here


Watching him get into position and perform the lift on his RL looked messy. The base of support compared with the bilateral lift is heavily reduced to the size of his right foot; his coordination in the set-up appeared awkward; and it took him a few efforts to balance the counter-movement of the free leg. When performing unilateral tasks for the first time(s), often disccordination will appear for a range of reasons including neural activity (inter/intramuscular), synergist strength and actitity and general movement dysfunction. Without having access to velocity based performance metrics, e.g. PUSH Strength, to measure bar speed or power, the athlete is demonstrating their ability or inability to put force into the ground to perform the lift; and in this case there is a 50% discrepancy between the limbs.

In a sprint setting, especially in the blocks from the zero step (which happens to be the limb with the least level of strength) when we are looking to pre-load the rear foot and maximise the stretch-shortening cycle and impulse, especially throughout the acceleration phase (~30m), having one limb which applies half as much force than the other, both worries me and excites me. Now, it is not like I have a longtiudinal study of athletes to determine whether this discrepancy is rare or common; even though I would expect some assymmetry, I would not expect 50% difference. It worries me as I am thinking why is this the case, and it excites me because I am thinking if we can look to address this, then how will this affect the outcome.

I can only make a hypothesis that once the strength level in the weak limb catches up to the strong limb, there should be an increase in various performance metrics (e.g. testing). Who knows, maybe it will make ZERO difference to both the testing and event specific performance. BUT, I am of the opinion that by performing these tests during the post-season, monitoring the progress throughout the GPP and SPP, we should see significant improvements in a variety of areas.

So, although a bilateral deficit was not evident with this athlete, there was a large strength deficit between the limbs. I know some coaches are anti-testing, the race is the true test (correct), but to avoid monitoring something in the preparation of your athletes is stupid. Running is a unilateral activity; for elite level 100m athletes who on average will take 45 strides across the duration of the race, to be putting 50% less ground reaction force into the track every alternate stride is significant and something which once addressed could lead to rapid improvements. We will wait and see.

I would love to hear people’s thoughts on this, whether track and field or sport specific, so feel free to post a comment below.