The effects of Boxing on causing microfractures

Previously, running was analyzed in it's ability to induce bone adaptation or cause microfractures.  Now an equally high impact exercise known as boxing will be analyzed.

Boxer's fracture

"Boxer's fracture is a common name for a fracture of the distal fifth metacarpal and received its name from one of its most common causes, punching an object with a closed fist. It can occur from a fistfight or from punching a hard object."

 

Repeated fractures and healing of the metacarpals would result in an increased hand size.  Does anyone know of any instances observed of this?

[Modification of bone quality by extreme physical stress. Bone density measurements in high-performance athletes using dual-energy x-ray absorptiometry]

"Little is known on the influence of high performance sports on the bone density especially in athletes with high demands on weight bearing of the spine. In (n = 40) internationally top ranked high performance athletes of different disciplines (n = 28 weight-lifters, n = 6 sports-boxers and n = 6 bicycle-racers) bone density measurements of the lumbar spine and the left hip were performed. The measurements were carried out by dual-photonabsorptiometry (DEXA; QDR 2000, Siemens) and evaluated by an interactive software-programme (Hologic Inc.). The results were compared to the measurements of 21 age-matched male control individuals. In the high performance weight lifters there was an increase of bone density compared to the control individuals of 23% in the Ward's triangle (p < 0.01). The sports-boxers had an increase up to 17% (lumbar spine), 9% (hip) and 7% (Wards' triangle). In the third athletes group (Tour de France-bikers) BMD was decreased 10% in the lumbar spine, 14% in the hip and 17% in the Wards' triangle."

Remember DEXA does not measure volumetric BMD but aereal BMD; and aereal BMD incorporates size of the bone. The ward's triangle is in the neck part of the femur bone. Elite boxers do a variety of training so you can't really determine what causes what(confounding variables). Weight lifters could have naturally larger bones so this study can't really be used to detect microfractural causes. .Boxing causes a lot of spiral forces on the spine due to the twisting motion that occurs during a well executed punch. It's interesting that tour de France-bikers had a reduced bone density versus controls. This could indicate that lower bone density is beneficial for cycling as a sport. We don't know exactly what caused the increase in aereal bone density but it could be something that increases height like something involving the periosteum or new cortical bone deposition.

Hand injuries in boxing.

"Investigations of 100 consecutive hand injuries in boxing have shown that 39% occurred in the area of the thumb, including the radial carpals, metacarpals and phalanges and their joints. These injuries were mostly caused by forced abduction of the thumb. Thirty-five percent of the injuries occurred at the base of Metacarpals 2 to 5, including the wrist joint, and arose from forced flexion of the wrist. Twenty-six percent occurred in the phalanges and the rest of the metacarpals, excluding the bases."

If you're trying to cause tensile strain microfractures for instance.  Forced flexion may be a way to induce them.  Maybe stretching is a plausible way to induce forced flexion on the bone thus causing tensile strain microfractures.

There's not nearly as much research on boxing fractures as their is on running fractures.  In any sport there are always confounding variables because most athletes incorporate a variety of training methods.  However, bag punching remains a possible viable way to create microfractures in the hand and wrist.  Punching seems superior to kicking as you can generate more impact relative to the strength of the bone in punching versus kicking. 

The metacarpals are short bones so maybe only increasing periosteal width is needed(would have to see the histology to be sure as there could be periosteal patches) and it would be logical to assume that heavy bag punching would cause shearing forces on those bones.  As for the fingers, they can be increased in size via lateral synovial joint loading.  You can get a lot of leverage on your fingers so all you have to is pinch at the synovial joints of your fingers to result in an increase in bone length.

Boxing did beat weight lifting in increasing bone density in the spine.  Boxing causes a lot of shearing forces like by punch rotation.  So boxing should have very similar benefits to that achieved by interstitial fluid flow.  However, the effects of boxing can be mimicked via weight lifting exercise i.e. you can increase hand size by pushing your body off the floor with your hands and then landing on those hands(this would be an example of lateral tensile strain microfractures) and you can perform body rotations with weights mimicking the spiral forces that occur when a trained boxer throws a punch.