Researchers from Imperial College London and University College London found that the make-up of the brain is the key to determining how much force is generated when somebody punches at close range, the Telegraph reported.
The study compared karate black belts trained to punch with physically fit members of the public and found the brain's white matter - which acts as the connections between brain regions - correlated directly with punching ability.
They concluded the power of a punch is not down to the strength of muscles but the timing, with synchronised movement between the wrist and shoulders essential.
While it is not yet certain whether differences in white matter were the cause or effect of successful punching, scientists suspect the brains of those who can punch changed and developed as a result of training.
The study used 12 karate black belts with an average of 13.8 years experience, who were fitted with infrared markers on their arms and torso.
Their results were then compared with the efforts of 12 control subjects of similar age, who exercised regularly but were not trained in martial arts.
Over a short range distance of 5 cm, those who had black belts in karate were found to punch harder.
Brain scans on each group revealed the white matter in cells, mainly made up of bundles of fibre that carry signals, were different in structure.
The scans used in this study, known as diffusion tensor imaging (DTI), detected structural differences in the white matter of the cerebellum and the primary motor cortex, known to be involved in controlling movement.
The difference correlated not only with the synchronicity between wrist and shoulder movements when punching, but also the age at which karate experts began training and their total experience of the discipline.
It suggested that the structural differences in the brain are related to the black belts' punching ability.
"The karate black belts were able to repeatedly coordinate their punching action with a level of coordination that novices can't produce," Dr Ed Roberts lead researcher said.
"We think that ability might be related to fine tuning of neural connections in the cerebellum, allowing them to synchronise their arm and trunk movements very accurately," Roberts said.
The study was published in the journal Cerebral Cortex.
