Review 9 - How to Better Decipher Research

What’s up everybody. This is Dan with this month’s rant about how to better decipher research.

Today, we will look at this cross-sectional within-subject study looking at biomechanical differences between the BSS and BS. Or, in more general terms, single-leg vs. double-leg exercises. There is a lot of discussion amongst coaches around the pros and cons of unilateral and bilateral exercises and why some might be better than others. The cool thing about this study is that they look at joint-kinetics and not just the resultant ground reaction force. This gives us more insight into what the different exercises actually do and what joints they load. While this type of research has already been done in squatting, I’m not aware of any studies investigating single-leg exercises via inverse dynamics. If you have any, send them in, please.

So, what was done? Twenty trained participants, with an average 1RM of 150kg, which translates to roughly 1.75x their body weight, come to the lab and do a BS at 70% and a BSS at 35% of their 1RM. We know from previous research that just halving the external load going from bilateral to unilateral exercises doesn’t translate into half the imposed loading. So, just because the external load is 50% in the BSS, the imposed demands are likely higher. Anyway. They standardized the BSS box height and stance distance. BSS and BS depth were set to 90-degree knee flexion – so above parallel for the BS. Well, can’t have it all. The interesting part is how they quantified kinematics and kinetics. Kinematics, so joint angles, were tracked, which looks like a suit. IDK. Is this even validated? But then again, it’s just sagittal plane movement. How hard can it be? The concerning part is that they did not mention any force plate equipment or how it captures kinetics. Well, let’s assume they did a correct job here. But that’s a lot of assumptions already here, oh well. The dependent variable was: impulse, work, moment, and displacement.

So, what was found? Impulse, so the summed moments over the whole repetition. The most striking result is that the knee is doing nothing in BSS, not just on average but look at the SD. When we look at joint work, so moment times angular displacement, similar message. BSS is mainly a hip exercise. Knee nothing. And with the BS, we see high variability between knee and hip, which makes sense. Some are more hip or knee dominant than others when squatting, and we see that all the time. And that’s the peak moment, a very similar trend. Joint displacement is nothing too interesting here, but in the BS, they got to about 105 degrees of flexion in the BS, so maybe they did a half squat after all and not just 90 degrees as they described.

So, what does it mean? Well, if we want to understand exercises better, just relying on outcome measures such as the resultant GRF is a great start, but by for not everything. Let’s go back to joint work. BSS is not just halving the demands of the BS, it’s an accessory exercise for the hip extensors. It just can’t be the main lift and the BS can’t be replaced. It would have been cool to see how different loads or heavier loads affect this hip to knee ratio… what do you think?