Armless archer, brain and feet: Nakagawa 2020 study

The study concerns a single archer: a 35-year-old Paralympic athlete born without arms, who shoots holding the bow with his right foot and holds the record for the longest accurate shot, at 310 yards. The authors compared his motor cortex with that of people without disabilities and with no special skill with their feet. In a dexterity test, placing pegs into a board with the foot, the archer placed all 25 pegs inside a minute, at 2.2 seconds per peg against an average of 15.3 in the controls.

On functional MRI, while he contracted the muscles of his toes, ankle, knee and hip, activation in the primary motor cortex was wider than in the controls for the toes and knee; in the area that normally controls the hand the signal was stronger in all four tasks, with more active points in three. For the toes and knee the centre of activity was also shifted laterally, towards the trunk and arm areas, but not for the ankle and hip. With transcranial magnetic stimulation, the areas producing responses in the leg muscles were larger in all five muscles recorded and shifted laterally in four of the five. A check on shoulder movements showed no difference. The authors infer that the leg representation has spread until it overlaps those of the trunk and of the absent arms.

The control group was made up of 19 right-handed volunteers with a mean age of about 27, almost all men, spread across three experiments of 12, 12 and 13 people; four took part in all three. The archer had taken up the sport at 16 and has competed at two Paralympic Games. In the scanner (3 tesla) each participant lay down and contracted the muscles of the right leg at about 20% of maximum, in time with a visual cue, in 20-second blocks alternating with rest.

For the magnetic stimulation, guided by a navigation system, the coil was moved over a grid of points 1 centimetre apart, with five pulses per point at 120% of motor threshold, while surface EMG recorded responses from five muscles of the right leg: tibialis anterior, soleus, the short toe flexor and extensor, and rectus femoris. The maps were transferred to a standard brain so that their size and position could be compared. The archer was compared with the controls using a test designed for a single case against a small group (Crawford and Howell), with Bonferroni correction.

It is a single case, and the authors themselves list the missing comparisons: there are no able-bodied archers and no people born without arms who do not compete, so it is impossible to say how much of the reorganisation comes from archery, how much from a lifetime of using the feet for everything (the archer also uses them to eat and to drive) and how much from being born this way. Nor can it be ruled out that the hand area was missing from birth, which would change the interpretation. Muscle activity was not recorded during scanning, so there is no guarantee that the archer and the controls contracted in the same way, and the controls had no experience of fine movements with the foot.

The study measures nothing about shooting: the tasks are isolated contractions, lying down and seated. The idea that this brain organisation underpins the archer's performance is a hypothesis consistent with the data, not a finding. The magnetic stimulation mapping follows the traditional method, and the authors note that more reliable ones exist.

For archers who shoot with their arms the study changes nothing in practice: it is not about technique, training or score. What it does show is how different the motor organisation can be in an archer who shoots, and lives, using his feet in place of his hands, which matters to anyone working with archers with disabilities. One case, though, cannot show how that organisation comes about or whether specific training could reproduce it in others: the champion's skill goes together with a brain organised differently from the controls', and the study stops there.