Is “Efficient” Movement Unsafe?

Which is more “efficient?”

I have made the claim several times on this blog that quality of movement is primarily determined by its efficiency. In fact, I have stated that “efficiency is the “essence of coordination” and that the best movement is always the most efficient movement.

I defined efficiency as “the ratio of useful work performed to the energy expended to do the work.” The logic of this idea is discussed here, but to briefly summarize, great movers such as athletes and dancers appear to move in an effortless fashion. For example, an elite marathon runner seems to float over the ground, and in fact their gaits are more energy efficient than less accomplished runners. Further, our bodies must have evolved to move in a way that is both energetically efficient and mechanically unstressful, so it would be surprising if one quality came at the expense of the other.

Well I recently read a post from Bret Contreras, a blogger I respect, and he basically took the exact opposite position! In this post (which in fairness is really addressing a separate issue) he discusses his idea that most “crappy” movement patterns such as valgus knees actually result from being too energy efficient, and that our natural inclination to efficiency is kind of like a pathological laziness that causes bad form and will compromise joint safety in the long run! I am not convinced this is true, but he does have an interesting point that I want to address.

Are Rag Dolls Efficient?

The problem with defining optimal movement purely in terms of energy efficiency is illustrated by a simple example. The most energy efficient way to land a jump is to just collapse on the floor in a heap like a rag doll. That would minimize energy expenditure, but I think we can all agree this is not the optimal way to land a jump.

That is because even though the “collapsing in a heap” method imposes a very small cost in terms of energy, it imposes a large cost in terms of mechanical stress on the body. So, in the context of jump landing, there is a conflict between energy expenditure and joint safety – you can either minimize the damage to the joints or the energy expended, but not both at the same time.

Is this just a weird exception to my general rule that good movement patterns are energy efficient? Or are there other examples of a conflict between energy efficiency and joint stress?

Bret’s post refers to many of the movement flaws he sees as a trainer, such as overpronation, valgus knees, excessive low back flexion, or other forms of postural collapse. These “floppy” movements reduce energy demands on local muscles because they transfer the work of stabilization to ligaments and other connective tissues. This saves energy but creates mechanical stress because body weight is just “hanging” passively off the ligaments and connective tissues.

I agree that hanging off your ligaments can reduce the work of local stabilizing muscles. But I think it is probably the case that in most contexts, any local gains in energy efficiency from “floppy joints” are more than offset by a general loss of energy efficiency that comes from poor alignment of the bones and inadequate stabilization of the joints.

In other words, valgus knees, rounded backs, and overpronated feet are not actually energy efficient at all, because they sacrifice the stabilization and proper bony alignment which is the key to efficient movement and posture. In fact, they create energy leaks that destroy any ability to efficiently transfer force to its intended target.

The bones transfer compressive forces through the body at no energetic cost, and this benefit is lost if the bones are not well aligned. For example, a valgus knee or flat foot might save some muscular work in the lower leg or glutes, but it will compromise the stability and bony alignment that is necessary to efficiently transfer ground forces to the rest of the body. If you want to create effortless power in a throw, jump or punch, you need good bony alignment. This will make the movement safer by reducing shearing forces, and more powerful by accurately channeling energy to a target.

Thus, the floppy joint strategy usually fails in terms of energy efficiency, just as it does in terms of joint safety. That is why the most efficient athletes don’t look floppy. They are great examples of alignment that would please any trainer concerned with minimizing mechanical stress. So if we think in these terms, there is not so much of a tradeoff between energy efficiency and joint safety.

But the jump example shows that there is at least some tradeoff, and a study I came across recently (via Alex) also provides some interesting food for thought on this issue.

Running from Paris to Beijing

In this study, researchers gathered data on an experienced ultra marathoner three weeks before, three weeks after, and five months after running from Paris to Beijing. Yes, he ran from Paris to Beijing.

Three weeks after the race, his gait had changed in several ways – his stride was shorter, less forceful, involved less aerial time, and was less energy efficient than his stride before the race and 5 months after.

The researchers concluded that as the joint stress of running increased, he changed his movement strategy in a way that imposed less cost on the joints and more cost on energetic demand to move. In other words, it appears that maximum energy efficiency was not consistent with maximum joint protection, at least for this (completely insane) runner.

So here is evidence that we sometimes need to choose between movements that are safe and those that are energy efficient.

But as I said before, I think this is the exception to the rule. If you watch the athletes who have the highest level of skill in being energetically efficient, you will generally see movements and postural alignment that also maximizes joint safety for the particular job being done. So for the most part, energy efficiency and joint safety travel together. (But maybe not all the away from Paris to Beijing.)

What do you think? Let me know in the comments.

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16 Responses to Is “Efficient” Movement Unsafe?

  1. Hi Todd,
    Great post. Both of you are probably right in different cases! I wonder if it’s that beginners simply move poorly because of lack of experience – and whatever they practice, they’ll become ‘efficient’ at that specific pattern (high mechanical stress or not). But mechanically stable form both lessens joint stress, and likely allows for optimal force production – which is why you see elite performers using ‘perfect’ form, and being so highly practiced, they are also efficient.
    This is probably super complex… But it’s also super interesting!

    • Hi Tony,

      Thanks for stopping by. Yeah beginners probably get more and more efficient at inefficient patterns. Its like they start down the wrong road and progress down it, but its kind of a dead end and they need to backtrack a little to find a better one.

  2. Hi Todd: I don’t think, in most cases, “crappy” movement is efficient regarding energy conservation. Even if we assume “crappy” movement is efficient, any efficiency gained by hanging on the passive structures (ligaments etc.) would probably be offset by the increased metabolic demand of global stabilizers/global mobilizers that will compensate for the local stabilizers, as described in Panjabi’s model of joint stability and Gray Cook’s” high threshold strategy”. While I don’t agree “crappy” movement is efficient, I don’t think Brett necessarily took the exact opposite position since Brett states “While this is indeed “efficient” from an energy-conservation standpoint, it is incredibly “in-efficient” from a long-term joint health standpoint.

    • Hi Anthony,

      I totally agree that crappy movement is energy inefficient. Locally efficient perhaps, but globally inefficient.

  3. “Efficiency” is a response to proper training. In the meantime, crappy form can be more efficient until the body masters good form. Rounded backs are initially more efficient for some folks on their deadlifts because they haven’t trained to proper muscles to fire yet (for example). BUT you can train efficiency into correct movement patterns. Like the dancer analogy… dancers don’t start with such flow, they train very hard for it. Proper mechanics might not be initially efficient due to weakness in the systems, but guess what training does? If the CNS can only fire the quads for a squat with no ass or hammie activation, the buckled knees will be more efficient, i.e. the only option. So yes, let’s train to make proper mechanics the most efficient technique… which it usually isn’t in the beginning.

    • Hi Chip,

      Thanks for the comment. Maybe my road analogy described in my reply to Tony has some relevance here.

  4. Hi, I think all all posts have an element of truth, and laws of physics and physiology explain perfectly all of this.
    When the body detects that a certain muscle is not required to contract to control or direct movement it will atrophy as we all know. But it will also change composition becoming more fibrosed in order to reduce the metabolic demand of that tissue so that the body can remain as energy efficient as possible. This is of course part of the process in poor movement and postures. Therefor it could be argued that a sedentary individual can become much more energy efficient at being sedentary whilst the athlete with lots of metabolic muscle mass would still have a large energy demand. Of course as soon as the sedentary person steps out of the safe sedentary zone there energy requirement will soar and as stated in previous posts damage will ensue. I think that the biomechanics of this process needs a little more thought to make this model easier to understand. In simple terms stress is caused to ligaments joints etc due to an inability of muscles to withstand forces. Just a quick response to the point of the most efficient use of energy on landing a jump, to roll out of the jump. .. I agree this is a great way to dissapate and transfer the force to the floor and not damage tissues but a more efficient use of the energy would be to recycle it back into the tendons for the next movment using the stretch shortening cycle, that’s if we are taling efficient and not just safe as the roll method just loses the energy.

    • Hi Ski,

      Good point about the next movement after landing the jump. I wrote a paragroah and then cut it from the post which basically stated that the rag doll method is energetically inefficient if you want to do anything functional after landing the jump – say jumping again or immediately moving in one direction or another.

  5. Todd, I agree with your post! Efficiency is more than muscle energy expenditure. Although it could be that our organism is not a good long term predictor and that indeed sometimes prefers hanging in the ligaments. I think a full unloaded squat (like the one in the video you posted about the hadza) is an example.

    Another thing to consider, althoug not brain centered ;-), is the muscle length-tension curve. This is something Shirley Sahrmann talks about a lot. Muscles are more efficient somewhere mid range (in muscle length, not necesserily joint mid range). Too long or short muscles alter this, and can influence efficiency big time. See this illustration

    Let’s take your example of knee in landing. A normally long glut med has optimal length-tension in the correct knee alignement. A long glut med will work most efficient with the knee ‘in’. To keep the knee aligned well, it has to work relatively hard. That is, relatively to a normal lenght.

    Hope this makes sense? Cheers

    • Darn, I meant a full unloaded squat is a good example of hanging, that could be good. A sway back posture is an example of hanging where the long term benefits are probably negative. But our organism may not be a good long term predictor, so does not care.

      Then of course, the question is: Why is our organism not a good long term predictor? But that’s another topic…

    • Hi Peter,

      I think you are saying that different structures will have different optimally efficient movement patterns right? So what is efficient for one person is not necessarily efficient for another. That is why Feldenkrais never told anyone how to do something, he let them discover what was best for their particular structure.

  6. Hey Todd

    Another great, thought-provoking post.

    I’ve got no data to back me here, but I think that “poor form” will always be more inefficient, when the whole system is taken into account.

    Lifting a weight, moving a body (ours or another object) will always take a certain amount of force as determined by fundamental laws of nature/physics.

    What can change is how we use our body to achieve this outcome – (again no data) but it would seem to me that those who perform effortlessly at any task are those who are using the minimal amount of resources to achieve an outcome.

    Often I think poor form is adopted as it allows the recruitment of additional resources – additional muscles to either achieve the movement or stabilise.

    In this sense it makes the outcome easier – ie it can be achieved, but perhaps at the cost of additional energy from the total system.

    From memory (its been a while since I studied paediatrics)when babies learn to walk, they will often abduct their arms, allowing lats to perform a stabilising role through reverse origin-insertion behaviour.

    I would think that this results in a net increase in energy demand, ie less efficiency. As they get better and stronger at walking, less resources are required and the lats no longer used.

    However, have you ever watched someone trying to descend stairs and noticed their “wings” flapping out – watch elderly people descending stairs with no hand rail, or others with poor strength.

    In adults, valgus knees or flexed spines during squats or any other functional activity would need to be assessed for efficiency in regards to the TOTAL system- as you point out in relation to energy leaks and demand on other structures – I would be certain that additional energy is required somewhere in the system to compensate.

    Individuals with physical disabilities will often adopt tricks or strategies to achieve movement that might otherwise not be possible, but at the cost of increase energy demand, so that the overall system is less efficient.

    Back to the original post/idea – if one was to look purely at one, small ‘arc’ of a bigger ‘circle/loop’, then valgus knees would appear to be more efficient perhaps, but looking at the whole system – the ‘loop’- the price has to be paid somewhere.

    • Tim,

      Exactly and well put. Interesting about the babies I have always wondered why they walk with their shoulder pinched up and back like that.

  7. Great article Todd, and responses … always enjoy a good debate.

    The brain is incredibly efficient (concussion lesions or complications aside) in finding a comfortable and “efficient” movement pattern among dynamic movements. It’s always important to take a holistic approach to any situation as mentioned through the article and the posts…..even though locally it may be more efficient (valgus knees or other movement compensations), in the grand scheme there really is no such thing as a “local” anything during a dynamic movement as simple as walking, let alone sprinting or other athletic movements.

    • Thanks Adam. Yep. Valgus might be efficient for the muscles that take a break to let it happen, but for the others that have to take up the slack its not efficient at all.

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