Are two legs twice as good as one? A comment on bilateral v unilateral lower body training
Take home message
It’s not about two legs versus one. it is what the athlete needs and what they can do. There are a lot of tools in the toolbox. Need to pick the right one for each job.
For Coaches
Train the adaptation, not the exercise.
For Athletes
Get strong, safely. It’s quite simple.
Recently, the Journal of Strength and Conditioning Research (@JSCRonline) tweeted a free article: “Unilateral and Bilateral Lower-body Resistance Training Does not Transfer Equally to Sprint and Change of Direction Performance”, the final article from my thesis. This lead to a couple of neat tweet threads with interested coaches around the globe (a wonderful benefit of technology is being able to connect our world). Interestingly, earlier this month there was a tweet and subsequent thread from Coach Brett Bartholomew (@Coach_BrettB) author of “Conscious Coaching” (which I am yet to read, apologies Brett) about the “debate'“ between bilateral or unilateral lower body training. Given Coach Bartholomew’s post, the recent thread response to JSCR article and my study, I feel somewhat obliged to throw in my two cents. Particularly as replying to the great questions on Twitter I find hard in 140 characters (or whatever it is now). This is a longer post than I would prefer, but I am trying to condense a couple of hundred pages down to one (my PhD thesis).
Way back in 2010/2011, I started exploring the use of the step-up with the professional rugby players I was working with, as it looked like it was appropriate for leg drive in the tackle contest (single leg, similar hip, knee and ankle posture, asymmetrical trunk involvement being on one leg, etc). That was a mistake and one of the “morales” of my PhD - it is not what the exercise looks like on the outside; it is what it is doing (or requiring from a neuromuscular perspective) on the inside that matters. (Side note: At an ASCA conference many years ago, Alex Wolf from the UKSCA presented and said something along the lines of “train the adaptation, not the exercise” in relation to the use of an exercise in his rowing programs. I hope I am crediting this correctly because it has stuck with me and been a programming principle of mine ever since. Thanks Alex). Back to the rugby scenario of 2010/11, there was not a lot of research in the area, so eventually I commenced a PhD with those questions in mind.
Fast forward a few years (ok, quite a few years) and we finished with the following main points:
1. in a 90 degree knee angle step-up, a high ground reaction force is generated, compared to the force per leg in a squat at the same relative intensity of 1RM in elite, well-trained rugby union players, suggesting that the step-up at high loads, may be capable of strength development. We needed to see in a training study.
2. in a training study with academy rugby union players, development and transfer of maximal strength can be achieved using either the step-up or back squat (both at 90 degrees).
3. adaptations arising from strength training using either the squat or step-up can transfer to sprint acceleration, such as a 20m sprint.
4. although strength was developed in these academy level players, using either the step-up or squat, and did transfer to speed, the magnitude of improvement in change of direction was different, with the squat group improving more.
Let’s expand on each point and place them in context (I find context is rather important when taking someone else’s research and applying it to your situation):
Point 1. Highly trained (professional and well trained academy) rugby union players performed a one repetition maximum (1RM) 90 degree squat test, had a 20 minute rest and then did the 1RM 90 degree step-up test (or they did the step-up first and then the squat. The order was randomized for scientific rigor). About a week later, they went into a lab and using force plates and 3D motion analysis, performed 2 sets of 2 reps of 70%, 80% and 90% of the 1RM of each exercise (in the same order they tested the week before). It was found that per leg, the step-up produced a higher ground reaction force than the squat. This makes sense as the system mass (bar plus body weight) of the step-up was more than half of the squat. So, it appeared that there may have been sufficient stimulus to get stronger using the step-up, even though the absolute load was lighter. (There are some impulse and barbell velocity differences too, but we will save that for another time, or you can find it here).
Point 2. In a training study that had a familiarization phase (a period where all participants practice all tests and training exercises to minimize improvement due to learning how to do something better in order to attribute any subsequent changes to physiological adaptation), a training phase and a maintenance phase, two groups trained with their only lower body exercise being step-ups or squats. They tested their 1RM in both the squat and step-up exercises at the start, middle and end. Each group did the same reps, sets and percentage of 1RM - the volume was matched as best as possible so that no-one group trained more than the other. As expected, if a player trained with squats, their squat improved. If a player trained with step-ups, their step-up improved. Every player was tested for both exercises, even though they only trained with one. Both groups improved in the other exercise as well. That is, the squat training group improved their step-up and the step-up group improved their squat. Strength could be expressed in the other exercise. This suggested an element of mechanical similarity between the two exercises such that enhanced neuromuscular development in one movement can be expressed in the other. In this context, it applies to the squat and step-up, not a universal rule applied between all bilateral and unilateral exercises.
Point 3. In the training study, both groups did the 20m sprint at the start, middle and end. Given that acceleration from a stationary start requires concentric knee extension and influenced by strength, it is not surprising that both groups improved acceleration ability - regardless of training squats or step-ups as both involve knee extension.
Point 4. Here’s where it differs and may lead to slight confusion. In my opinion, it is not a bilateral versus unilateral verdict, but a squat versus step-up one. My research question was about differences between the squat and step-up as examples of a bilateral and unilateral exercise. First, both training groups improved change of direction. But, the squat group improved more. My guess (and it’s a guess because we did not test it), is that both groups improved their capacity to exit the change better (they could start as indicated by the improved sprint capacity), but perhaps the squat group improved their ability to stop into the change better as they practiced stopping under load every rep of the squat.
How does this place me on the unilateral versus bilateral debate?
It doesn’t. Because I have no interest in the debate.
It is not a question of which is better - unilateral or bilateral. In my humble opinion, the question should be:
“What capacity does my athlete need to improve to be better at their sport? And in the gym, what can they do to improve now?”.
So, for example, what capacity do my athletes need to improve to be better at the moment? Many need to get stronger. What can they do to improve strength now? Well, after years of playing hockey (or rugby, or football, whatever your sport may be), many of them have some limitations and exercise preferences they use to get better. Our current exercise battery for lower strength is diverse. We have one player who switches between clean pulls or hang cleans for heavy or light days. Quite a few deadlift and go quite well. A lot squat. I have one on a leg press to look after his back, a couple who step-up due to hip issues, some on rear-foot elevated split squats (RESS - because we need a single leg exercise with good hip range and that unloads their toes in that extreme range you can experience in the back foot of a split squat), and some that split squat (because they need the hip range and do respond well to the calf demands on the back foot). In a rehab program at the moment we have used squats, deadlifts, RESS, leg press, step-ups, cross over step-ups and walking lunges. A mixture of bilateral and unilateral exercises because the stimulus from each differs depending on the load, speed or range the athlete could perform during their progressions - train the adaptation, not the exercise.
That’s my brief opinion on the “bilateral v unilateral” thing with a bit of research. There may be more you would like to know. If so, please leave a comment or email.