Speedflex machines employ only concentrically based forces The Speedflex machine has a free motion bar which, unlike traditional resistance exercise machines, requires members to apply force through the entirety of the exercise, as opposed to increased force in one direction, followed by a controlled movement back to the starting position The Speedflex Training System was first developed in 2009 in the USA by the 13yr Major League Baseball Player and World Series Champion Darren Holmes, Orthopaedic Surgeon and Sports Medicine Specialist Dr. Jim Silliman and Athlete and Mechanical Engineer Joe Worley