This picture was taken in May of 1963 while Liston was in training to face Floyd Patterson for the second time. Liston knocked out Patterson in the first round just like he did the first time they fought. With this victory Liston retained the WBA, The Ring, and lineal heavyweight titles and won the vacant inaugural WBC heavyweight title.
The great boxer Sonny Liston used to strengthen his neck by doing a headstand on a table and working his body back and forth then left and right, in order to hit all four “sides” of the neck. I can say from experience that this method is simple but very effective.