The researchers scrutinised the brain scans to see if they could find any patterns that tallied with the protein level results from the lumbar puncture tests.

BBC: Brain scan 'can sort dementia by type'

Because endorphin levels can only be measured directly through an invasive lumbar puncture unfeasible, even for notoriously pain-hungry oarsmen the researchers used a readily accepted proxy: they deduced pain tolerance, and hence endorphin levels, by gradually tightening a cuff around each rower's arm.

ECONOMIST: Exercise and company