A few years ago I practiced Muay Thai at a gym. I was there on and off for about 2.5 years. Due to a move and busy schedule *cough*lack of motivation*cough* I haven't practiced in about 2 years.

Yesterday I went to a new place that is near my home and the instructor there taught me a few things which are contrary to what I was taught before and I think may be a little dangerous.

I should say that both instructors, old and new, are accomplished fighters but I can tell that the old instructor is more traditional in his approach to Muay Thai as an art and the new instructor (on my first impression) approaches it more as a competitive sport.

  1. In the past I was taught to NOT straighten my arm when shadow boxing. I believe this is because it teaches me to control my arm better overall and will prevent injury when I don't land a punch by preventing me from hyper-extending my elbow accidentally. Last night the instructor specifically told me to straighten my elbow when shadow boxing.

  2. Similarly, I was previously taught to NOT straighten my supporting leg at all. Not at any time during any kicks or when guarding. I believe this was for greater balance and injury prevention when taking a strike to the leg. Last night I was instructed to do the opposite for the same reasons: better balance and injury prevention.

Who's right?? To be honest I feel like my original instructor is correct (overall) because the reasoning seems more sound to me. Obviously the instructor I worked with last night knows what he's talking about because, as I said, he is an accomplished fighter.

What should I do? Do I try to erase the habits of the past and conform to the new instruction or something else?

update: I voiced my concern via email (gym owner emailed me to ask about my first impression) and I got a reply that I feel is satisfactory. He explained they teach that way to reach maximum power and that I am free to let my coach know that I will be doing my own thing on these points during practice and that he hopes to see me back.

7 Answers 7


Obviously the instructor I worked with last night knows what he's talking about because, as I said, he is an accomplished fighter.

This doesn't make him an accomplished teacher at all.
During your travels you will encounter different instructors with differing quality. You need to recognise when they are either not the best instructor for you, or when they are lacking competence or run a sloppy studio/dojo.

Both what I was taught and what I've experienced have shown me that you do not straighten the arm fully when punching. I also mention this specifically to students, however I know that they'll eventually find out for themselves why it is important. An example of the injury that occur from this practice can be found here: British Kendo Association: Common Injuries 4: Elbow Hyperextension. To quote:

An elbow hyperextension injury occurs when the elbow is forcefully extended beyond it normally physiological range of movement. There is a little bit more movement available but the ligaments function is to prevent the joint moving to the anatomical range of movement. Movement beyond this will result in a fracture.

The increase in power you may get from the extra bit of travel has a high chance of resulting in an injury that can take months to heal properly.

You also shouldn't straighten the support leg while kicking - in fact I find it impossible to do so. Keeping the leg slightly bent keeps the muscles under load and more able to withstand a strike should your opponent kick it. Biomechanically it can also help at the moment of impact if you still have some extension available in the support leg. Even while in a traditional stance such as Zenkutsu Dachi, the back leg is still slightly bent while punching, and definitely (noticeably) bent while kicking.

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    Recently I was shown a couple of karate punches by friends at leisure time (lead and back hand at face). When I tried them without target, or when I missed the target, straightening my elbow in the process HURT. The joint clicked. Does this have anything in common with the current discussion?
    – Vorac
    Commented Sep 27, 2013 at 14:20
  • @Vorac, that is exactly what the question is about. I've added a link to my answer which is worth a read and explains it well.
    – slugster
    Commented Sep 27, 2013 at 23:25
  • I've run across almost the same issue with people "teaching" motocross on youtube. Some say stand with legs slightly bent, some say stand with legs straight. And then - someone said "Legs straight but not locked". And this is the key. it's ok to punch with a straight arm, but it's not ok for the arm to stop by hitting the joints' mechanical limits. Standing on a straight leg is fine, on a locked leg is not. Commented Apr 3, 2018 at 15:18

Your logical fallacy is: Appeal to Authority!

This is actually really common in martial arts; we assume that because our instructor has experience in a competition, but all this means is that the instructor was better in that match (and often we're simply taking their word on that experience).

Nearly every art teaches to not fully extend limbs – the extra ~2% of power that you'd get isn't worth the joint damage, and potential for breakage in an actual fight.

Balance has nothing to do with a straight leg, either. Your leg can be locked out, but your shoulders not counteracting the tilt of your hips still keeps you off balance. A locked out leg would potentially result in a nice, clean break, though, so it'll be less trouble for the doctors to set.

So, now, how do you determine who is more correct? Statistical probability. In an answer to a question What characteristics should I look for in a sensei? I posited that your observations of your potential new instructor should be compared to others, specifically those that are acknowledged widely to know what they're doing. As we're discussing Muay Thai in this instance, both instructors can and should be compared to any number of professionals collectively, and their combined average knowledge used to determine what is correct.

Any good instructor will encourage you to explore other available instructors, whether or not they would recommend them. Use that opportunity to explore and find the truth between the bits of misinformation, and grow as a martial artist.

EDIT: In Response to the Update

It is a copout for the instructor to teach something potentially injurious for the purpose of "increased power", especially since the increase is negligible so far as good technique is concerned.

Consider that full extension might gain you an additional 2 inches of reach, you're only adding a negligible amount of velocity with no additional mass. That extra distance is a minute factor in the equation of your power, but a major detraction from your capable years of functioning life on this planet. Those extra 2 inches will likely be countered by the increased contact time with the opponent, meanwhile the counter-force will be absorbed by your bones and joints rather than your muscles.

If you want to increase power, increase power. Don't do potential damage to your body for minimal gain.


The best thing to do is to consult a physiotherapist or biokineticist. If you're cheap like I am, you could also practice both techniques, one each week and write down how your joints feel after cooling down post-workout. The one that gives less discomfort is the better one.


The three most important factors in choosing a martial art are 1) Teacher 2) Teacher 3) Teacher

It doesn't matter who is correct. If you have concerns about safety after one visit to this teacher, then you should probably find a new teacher.

As others have said, an accomplished fighter may not know how to teach, and even if he knows how to teach may not know how to teach safely. Responsible teachers are willing to sacrifice a bit of authenticity in exchange for a lot of safety. There are too many martial artists who have experienced career ending injuries.


Your first teacher is correct. You should NEVER LOCK your joints or hyperextend anything as over time, you will start to have joint problems and eventual arthritis.

In Gung-fu, the warning against hyperextention is particularly warned against because we learn, in various styles and in general fighting, to block and grapple strikes, pull to push the person off balance, turn, step, apply joint locks to cause pain or break the joint if needed, all in one fluid motion in less than half a second or faster, so any hyper-extension only helps your opponent in breaking your arms or other joints.

You don't need to hyper extend anything to gain power because power is a component of muscle and tendon strength, relaxation, your overall chi strength, the mind and other factors that almost no martial arts today understand at all. So doing something dangerous like hyper-extending your punches and kicks is not going to add that much power, but it will increase the risk of joint injury.


Hyperextension of the elbow? I would be more concerned about a kick on your head or knee, or maybe an elbow. Muay Thai is a sport with certain risks and dangers. Some instructors teach with a bent arm, some with a straight. Don't worry so much. Learn what the new one is teaching you or move on. Most instructors do not want to see you do your own thing so if you can't adapt then you have to go to a money making gym where the instructor will take your money and not care what you do. I have been punching since 1990 with an arm fully extended when I jab and throw a right. Never had a problem with this. I went to another instructor and he teaches with a bent arm for power purposes. I learned that too. When in rome...

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    and an accomplised fighter is going to be one of the better teachers they have been there done that, you know walked your walk. Even if they were not a great fighter they have the experience of fighting against another skilled oppenent.
    – user1589
    Commented Jan 4, 2014 at 12:58

GRASS HOPPER listen up and start to remember then explore what you have been shown. there are man paths to victory in the ring.

bent leg or supper straight is a question and there is goodness in both . situations dictate which will be used , therefore having both methods in your arsenal, ready to use.

i beleave it the lack of english speaking ability to explain in detail all the subtleties and nuances that has created this story.

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    I suggest you focus your answer on explaining "there is goodness in both" and "situations dictate which will be used". As it stands, there is no useful information in this answer.
    – mattm
    Commented Aug 1, 2016 at 4:39

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