Exercise form – informed?

Locking it up

963 words – estimated reading time: 4mins, 50s.

One of the things (and there’s a lot) that really perplexes me with exercise is the range of rules and guidelines that surround exercise and exercise technique. What I’m talking about here are the things that exercise professionals seem to repeat and reinforce automatically – and I’m suggesting perhaps at times unthinkingly. I’ve witnessed this in gym settings, exercise classes and also in strength and conditioning settings. You’ve all heard it – ‘engage your core – knees over toes – be careful not to lock your knees out!’

We’ll look at the ridiculousness of the engaged core comment in another blog, but I’d like to explore that ‘locked knees’ comment a little further. This is something that I often hear when assessing students instructing exercises. My question is always – Why is that? They’d inevitably answer with a blank stare, or with ‘it’s to protect your joints’.OK! No wait!….what? Really? I shouldn’t be fully extending my joints to avoid injuring them? Somehow that just doesn’t seem right!

I’m immediately intrigued and I’m really going to need to understand the logic and rationale behind such advice. I’m probably also going to want to see some research evidence. Why are you accepting and repeating this instruction if you really have no idea why? So, I’m trying to think what the logical arguments might be. Obviously I don’t want to move my elbow or my knee (or any joint) into hyperextension. But unless I have a hypermobile joint there should be little risk of that, provided I complete the exercise under control – which presumably a competent exercise instructor would ensure I do.Maybe it has to do with loads then? But again, I should only be dealing with loads that I can control and manage. If I’m at home and helping to lift a fridge then I’m probably going to fully extend and lock my knees during the lift and my elbows will undoubtedly be fully extended and under load – functionally that’s what we have to do! I understand that ballistically loading a joint at its end range is not going to be healthy, but so maybe the instruction needs to be around the speed of contraction and control of the movement rather than focusing solely on the disputable end point or extension. At this point I’m also thinking about crossfit and other extreme style exercise classes, and I wonder about the safety of multiple repetitions performed at speed and under fatigue and maybe
accelerating into the joint end range.

Scouring the research databases, I was unable to find any research that investigated or implicated locking knees or elbows out during resistance training in injury. I wondered whether Olympic weight lifters or power lifters – athletes who are more likely to emphasise high velocity and/or highly loaded weight training movements – may have a greater exposure to injurious forces and I imagine lots of joint injuries. Training status aside, I’m not convinced that those are normal physiological loads for joints. Turns out those athletes are not injured anywhere as much as I’d thought, in fact less than most team sport athletes (e.g. Keogh & Winwood, 2017). But the instruction has to have come from somewhere! Searching the web I can find plenty of assertions that locking out is dangerous, but no evidence other than the suggestion that ‘all of the load is going on your joints’. There is also the fairly hazy claim that locking out is cheating in that it provides a brief respite from exercise and unloads the muscle. That seems a fairly spurious argument as the instructor really has the ability to specify and coach the length of any pause in transitions from extension to flexion. This advice has to have come from somewhere – but I couldn’t find where . Perhaps somebody hurt their knee on a leg press or popped a biceps tendon during a curl – however it started, it has since become an urban myth. If anyone has solid contrary evidence, please let me know.

So, as I understand it the rationale for avoid fully extending joints during weight training seems to be 1. there’s an increased risk of joint injury through excessive loading, and 2. it reduces or interrupts the time under tension (and thus overall work) for a muscle or muscle group – neither assertion offers any supporting evidence. I’m afraid that I can’t offer any more insight than that. Possibly because this is another one of those things that are just out there, and that can’t really be proved or disproved. Readers of this blog will already know how agitated I get with those sorts of impasses – because by default they usually continue to fly! On one hand I find this kind of amusing, but then I think – hang on this is my profession and these are exercise professionals perpetuating misinformation….

That said, all of this doesn’t really interfere with my intended message. The perception is that one of the most important determinants for becoming an excellent exercise professional is knowing stuff (theory – knowing that) and knowing how to do stuff (application – knowing how). While I’m sure that no one really believes that is all that is required, it often seems as though in our haste to apply ‘knowledge’, understanding the important connections between knowing that and knowing how get lost in the process. I’m borrowing from Quinn et al (1996) here to suggest that knowing why (and caring why) are just as important for professional competence. My advice is to always be a curious professional. Don’t just parrot – think and question. Think about what you do and why you do it. As with my locking out problem presented here, you may not always find satisfactory answers, but uncovering uncertainty might help you to be a bit more judicious with your subsequent advice. Perhaps you would only use this kind of cautionary instruction or advice for those that we think may be at greater risk – someone with a prior joint injury, a hypermobile joint or someone who is generally not otherwise compliant with meaningful instruction.




  1. Keogh, J.W.L., Winwood, P.W. (2017) The Epidemiology of Injuries Across the Weight-Training Sports. Sports Med 47; 479–501.
  2. Quinn, J., Anderson, P., & Finkelstein S, (1996). Managing the professional intellect: Making the most of the best. Harvard Business Review, March-April: 71–80.