The one or two valve levers on today's trombones do not leave much of the left hand for the job of actually holding the trombone. The result can be strain and pain in the left hand and arm. The holding strap transfers much of the load to the back of the player's hand or wrist, depending on how the strap is worn, and a different set of muscles come into play in holding the horn. Fastened by a fully adjustable Velcro strap.