7 Aug 2013

The Biomechanics of Arm Wrestling

Arm-wrestling is a complex sports that involves most of the muscles acting on the arm, wrist and shoulder. Which one of these muscles that become the limiting factor for arm wrestling success is determined by the specific arm wrestling technique used by the athlete. This article aims to explore which muscles that are important for different arm wrestling techniques and also a look at arm wrestling from a physiological and neuromuscular perspective.

The Hook

There are many different ways to perform the hook and depending on the specific technique used by the athlete the muscle activation may vary slightly, but in general three important factors will be most important.

The ability of the arm wrestler to:
  1. To Flex the wrist
  2. To Flex (bend) the arm at the elbow
  3. To statically hold or medialy rotate the upper arm (Humerus)  basically keeping the arm from rotating outward down to the pad.
Muscles involved in wrist flexion
Flexor carpi radialis
Flexor digitorum superficialis (also closes the hand )
Palmaris longus ( also closes the hand)
Flexor carpi ulnaris

Note that if you apply full flexing force to the wrist your hand will close automatically since they are largely controlled by the same muscles.

Muscles involved in flexing arm at elbow ( bending the arm at the elbow)

Biceps brachii (also supinates the hand, turning it outward)
Brachioradialis ( actually located in your lower arm)

Note that if your hook technique is to turn the wrist down and inward (supinate and flex) your are to a large extent using your biceps which also locks your arm at the elbow.

Muscles involved in medial rotation ( turning the arm inward often referred to as side pressure)

Teres major ( also adducts the arm pulling it inward towards your body)
Latissimus dorsi (Lats) ( biggest muscle of the upper body)
Pectoralis major (your chest muscles)

To have a strong inward rotation of the arm or “side pressure” it is very important to activate the muscles in the right way.  The muscles involved in medial rotation are the biggest and strongest muscles that you have in your upper body but they have a limited range of motion where they can perform at their best, they are also at a huge biomechanical disadvantage. (Read more about this in the injury section).

To put your arm at its strongest biomechanical position place your shoulder slightly in front of your body and slightly raised upward toward your ears. Now squeeze the arm inward like you were trying to crush and apple in your armpit. This is to get your chest muscle, Subscapularis and Latissimus (your lat) in the optimal position. These muscles now work statically to keep your arm from rotating outward and away from you. Experienced arm wrestler keep their arm in this position at all times and  lean over with their entire body to pin their opponent. All muscles are stronger statically (locked in the same position) than dynamically (moving) So by keeping the arm and shoulder at it´s strongest biomechanical position and holding it statically you can exert the greatest force.

The Top Roll

When I think of a Top-roll I see Devon Laratt pulling straight towards his chin with his biceps, and as soon as he has unlooked his opponent’s fingers just a little bit he pronates and slightly flex his hand  and takes the wrist of his opponent. He then goes straight to the side taking his opponent with him to the pad, beautiful.

The muscles involved are to a large extent the same as for the hook but with two significant differences. The involvement of Extensor Carpi radialis which  raise your hand upward towards your thumb (radial   deviates) and Pronator Teres that turn your hand and lower arm inward (pronate)

A strong Extensor Carpi  prevents you from dropping your wrist (thumb down). For this muscle static strength is most important, It is often the limiting factor of how much bicep power you can utilize when Top-rolling especially if your opponent has a high grip on your hand.

Extensor Carpi also extends your wrist so you can train it by doing wrist extensions.  I see many arm wrestlers doing wrist curls but rarely wrist extensions which are equally important for the Top-roll technique. It is definitely not intuitive, you never want to extend your wrist in a match but those same muscles keep your hand from ulnar deviating (dropping your wrist in direction of little finger)

Pronator Teres turns your lower arm/hand inward like turning something anti-clockwise with your right hand. This is obviously very important in a Top-roll. If you can pronate your wrist, you will extend your opponent’s wrist which is more or less what top rolling is all about.

Muscle fibre composition

In competitive arm wrestling most matches are over in less than 2 seconds. Competitive arm wrestling therefore mainly involves fast twitch muscle fibers ( type-2a, type-2b and type-2x) that are fast and explosive.
  • During super explosive matches lasting for a second or less Type-2x will be most important. They are also very important for a quick start.
  • During a long tournament or an arm wrestling match lasting for more than a about 8 seconds  Type-2a muscle fibers will be most useful since they have more lactate resistance and are able to replenish ATP faster that type-2x. 
  • Type-2b are in between.

It is important to realize that you always have to compromise between these 3 types of fast muscle fibres. You can not be extremely explosive and have good endurance at the same time it will always be a compromise.

In arm wrestling endurance means the muscles ability to quickly replenish their ATP supply between and during matches. This will to a large extent be done by Creatine Phosphate.

Type-1 muscle fibres used for very low intensity long duration activities like walking or running a marathon does absolutely no good to an arm wrestler. On the contrary the presence of Type-1 muscle fibres in your muscles slows you down simply by being in the way.

For example, Say that you want to be able to flex your wrist as fast as possible. Your brain sends a powerful electrical signal to the muscles in your lower arm to contract. The fast twitch fibres react immediately and contract. The slower type-1 fibers takes almost 3 times longer to react to the signal so they will just come a long for the ride, while your fast twitch muscles contracts (shortens) the entire muscle head. I.e. the type-1 muscle fibres needs to be squeezed together by the type-2 fibres during a fast contraction of the muscle. The type-1 fibres therefore hinders the contraction mechanically.

I have a feeling that most arm wrestlers mainly train their type-2a muscle fibres. This is done by long training matches with short rest in between building up a large amount of lactic acid. This is like running 400m intervals to train for a 60m competition.  To be good at any sport you must build the proper muscle fibre composition for competing in that sport. Train like you compete.

I do think that long  training sessions at the table with a lot of static holds, trying different angels and slow negative movements ( loosing  a match slowly) is important for strengthening tendons ligaments and bones and also for technique development. But in this way you are not building an optimal muscle fibre composition for competitions. Include more competition like training with proper starts and try to keep matches relatively short and very powerful. Your gym training should be done with weights at about 85% of you 1 rep maximum, that corresponds to a weight you can do about 5 repetitions with. Remember to lift the weight with maximum force. I.e. as fast as you can in the positive phase of the movement. This will improve your nervous system and your ability to simultaneously contract as many muscle fibres as possible crating the maximum force.

Nervous system, Speed and explosiveness

Every muscle action starts with the brain sending an electrical impulse to your muscles. When the muscle fibres receive the signal they contract. Each individual muscle fibre can only be either relaxed or  contracted, nothing in between. Your brain therefore has to control the number of muscle fibres it activates to produce a certain amount of force.

The nervous system is limited:

Normal Person can activate about 30% of their muscle fibres at the same time.

Explosive athletes like Olympic weight lifters can activate over 70% at the same time.

This means that for the same amount of muscle fibres they can generate more than twice as much force in one bout as a normal person. This ability is easy to train and is the reason why people who start strength training see increases in strength long before muscle mass.

Explosiveness is the ability to contract a large number of fast twitch muscle fibres at the same time. It is influenced by your nervous system and your muscle fibre composition.

The nervous system also coordinate your movements, this is why you have to arm wrestle to become a good arm wrestler. When you arm wrestle your nervous system learns to perform the movement in the correct way making the 50 or so muscles work as one.

Arm Wrestling Injuries

Spiral fractures
During an arm wrestling match your lower arm works as a lever on your elbow join creating a huge twisting torque on your Humerus ( upper arm) This is also the cause of most arm wrestling injuries creating a spiral fracture of the Humerus.

We can calculate the torque exerted on the Humerus quite easily.
Torque = Force x length of lever (M=F*d)

Your opponent exerts a side pressure on your hand with 20kg of force which is about 200Newton (N). The length of your lower arm is apx 40cm. The Twisting Torque exerted on your Humerus is then 200*0.4 = 80Nm which is about half of what you get in a normal car. So there is a tremendous force. This force must be absorbed by your muscles and tendons because such amount of force would brake the Humerus if it were not supported by muscles, tendons and ligaments.

Medial Epicondylitis

Many arm wrestlers experience more or less constant pain or irritation on the inside of the lower arm near the elbow. This is also known as golfers elbow. The pain originates from the medial Epicondyle which is the origin of your wrist flexing and pronating muscles.

Medial Epicondylitis is caused by over use of the wrist and hand flexors resulting in small ruptures and micro trauma of the tendons attaching these muscles to the Epicondyle. Many arm wrestlers damage their Epicondyl during a competition or hard training session. It is very important that you rest and let the tendon heal before arm wrestling again, It usually only takes 3-4 weeks and it will be stronger than ever if you let it heal properly. In the mean time do exercises that are not painful. It is not an inflammation so do not try to treat it with anti-inflammatory drugs that my actually delay healing according to some studies (PMID: 21675467, PMC1320354). 

Arm wrestling strength takes many years to develop. Not only because it´s a complex and technical sport but also because tendons ligaments, bones and joints take far longer than muscle to strengthen and adapt to the extreme stress of arm wrestling, Your muscles will not exert a force strong enough to rupture the tendons or the bone, even if they could the nervous system prevent us from doing so. Therefore if you are a young arm wrestler, take your time. And remember that many of the world´s greatest arm wrestlers are well into their 40´s.

Author: Magnus Westberg 

Read all articles written by Magnus Westberg in section Arm Science by Magnus Westberg