by Bret Contreras August 27, 2015
Hi Fitness Friends! This is part III of a 5-part series on squats versus hip thrusts. The data from this series comes from my doctoral thesis, which should hopefully be posted online for anyone to read next year (assuming I pass my defense in December…wouldn’t it be hilarious if I hyped this up and then failed my defense and PhD?). Parts I and III look at mechanistic data, namely what happens when you perform the two exercises while wearing electrodes or while on top of a force plate. Parts II and IV will look at what actually happens following a 6-week training protocol. Part V will summarize the findings and point out limitations and directions for future research. I posted part I three weeks ago and part II two weeks ago, and I’ll post parts IV andV over week or so.
This study portrays an awesome aspect of learning as a researcher as I ended up being wrong and changing my stance. My PhD supervisor John Cronin wanted me to carry out force plate research on the squat versus the hip thrust as part of my thesis (I didn’t want to at the time we planned it). Several years ago, I wrote an article about how silly I think forcetime data is with regards to optimal exercise selection (see HERE). Since then, my stance has softened, primarily due to the process involved in the present study I’m discussing – one can indeed glean valuable and practical information from performing exercises on a force plate and analyzing the data. However, longitudinal training studies are needed to test and validate any hypotheses that are generated from the mechanistic forcetime data.
Prior to the study, I was talking on the phone to my colleague Andrew Vigotsky. Here’s what I said to him. “Andrew, this study is so stupid. People are stronger in the hip thrust compared to the squat. The hip thrust is also the more explosive lift. Since force equals mass times acceleration (f = ma), the hip thrust will generate greater force. And since force output lays the foundation for work since work equals force times distance (w = fd), impulse since impulse equals force times time (i = ft), and power since power equals force times velocity (p = fv), the hip thrust is going to kick the shit out of the squat in every category. This study is merely a formality to show the obvious.”
Turns out I was quite wrong. Had we just looked at concentric data, I might indeed have been right (well, definitely for force and probably for power, but maybe still not right for work and impulse). However, what I failed to consider ahead of time was the eccentric phase and how this impacted total outputs that combined the concentric and eccentric phases. This isn’t the first time I’ve been wrong as a scientist and it sure won’t be the last time. What’s important is that I update my knowledge-base, inform my followers about the truth, and learn from the experience (which I’m doing). Now let’s talk specifics.
We had ten fairly strong dudes with an average of around 7 years of resistance training experience and a 10RM of around 216 lbs in the squat and 252 lbs in the hip thrust perform the two lifts on a force plate. Luckily, I spoke to badass UK biomechanics researcher Jason Lake prior to collecting my data – he was adamant about having the subjects hover silently on the force plate for a moment before starting their sets and performing their reps. This allows for the system load to be cancelled out when analyzing the data so that only the effects of muscular effort can be examined (we want to know what the muscles do, not what gravity + muscles do in concert with the body + barbell system).
Here are the results:
When I got the data, my initial instinct was like, “This is all off, there’s no way this is correct, something screwy occurred with the software.” At this point, I hadn’t looked at barbell displacement, time under tension, or concentric force, so the data didn’t make sense to me. I pondered what I knew about biomechanics and what factors could have impacted the data to come out the way they did. I decided to have my assistant check out barbell displacement, and I was shocked to find out how much greater ROM was used in the squat compared to the hip thrust.
I recall back when I invented my Skorcher, I tested barbell ROM in the hip thrust and it wasn’t much different compared to a parallel back squat or sumo deadlift. But the Skorcher involves more ROM than the traditional hip thrust because the feet are also elevated and the dorsiflexion that occurs throughout the concentric ROM translates into greater vertical bar displacement (not the case in the standard hip thrust off of a bench). In addition, we examined the full squat in this study, not the parallel squat. Hip ROM isn’t drastically different in a squat compared to a hip thrust depending on how the two lifts are performed and depending on the height and anatomy of the lifter, but since there’s not much knee ROM in a hip thrust, the total ROM in a squat is much higher. So this makes sense indeed.
Nevertheless, I went out to my garage and performed a set of barbell hip thrusts with a meter stick lined up with the barbell – turns out the forceplate/motion capture data was legit and my assumptions were off-based. I also had my assistant check out time under tension, and it wasn’t surprising to see that the squat took more time due to slower lowering speeds and more ROM.
Next, I asked my assistant to split up the concentric and eccentric force phases, and this is when I discovered how glaringly different the force outputs are during the lowering phases of the two lifts.
Between the differences in displacement, time under tension, and eccentric force, all of the data make perfect sense. Now, one could astutely point out that lifters can indeed lower the barbell slowly during a hip thrust if instructed to do so. What’s great about this study is that we examined what people naturally do during the two lifts. Future research can examine how the effects of hip thrusts with controlled eccentric phases impact forcetime data, or how higher box heights (this study used a box that was around 16″ high) impact forcetime data, or how anthropometry impacts squat versus hip thrust forcetime data, etc.
You’ll note that we didn’t separate all variables into concentric and eccentric phases. This is because my thesis deadline came to an end and we ran out of time. Had we had more time, I surmise that the hip thrust has greater concentric power outputs than the squat, but I’m not sure about concentric work and impulse. Everybody in S&C loves to talk about eccentrics, but it’s important to note that acceleration sprinting is mostly concentric in nature. This could impact training adaptations.
To wrap things up so far, Part I demonstrated a clear advantage of the hip thrust over the squat in terms of EMG activity. Part III (this article) demonstrated a clear advantage of the squat over the hip thrust in forcetime data (force, work, impulse, power) and displacement. Part II provided some clues as to how the two lifts differ in terms of actual training adaptations. In part IV, we’ll look at the effects of an actual training study in performance. These are vital in S&C as they show what DOES happen, not what SHOULD happen based on humans’ often limited and biased opinions pertaining to acute mechanisms, sensations, and transfer of training theories. In part V, I’ll wrap it all up and summarize my findings.
The post Squats Versus Hip Thrusts Part III: Forcetime Data appeared first on Bret Contreras.
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