The Palmer-Toggle Recoil Adjustment

In the earliest days of chiropractic, adjustments were, well, a little on the rough side. They were generally done with the doctor's arms completely straight and locked out, on an unpadded bench, and with a slow, but forceful, body drop. The doctor wasn't relaxed, nor was the patient, and the end result got the job done, but it was hard on the doctor and patient alike. In some cases, doctor's would even put a bag full of lead shot or sand over their shoulders to give the adjustment even more OOMPH!

Anyone can see this was not a comfortable proposition for any parties involved! The year 1910 was a big year for chiropractic innovation, as it was the year BJ Palmer introduced x-ray technology to the profession, as well as a year of big changes in the way chiropractic technique was performed.
BJ and one of his collaborators, James Wishart, had developed the technique of "nerve tracing" by this time, as well as a new type of adjustment called the Palmer Toggle-Recoil Adjustment.
The Toggle-Recoil method is often synonymous with upper cervical specific adjusting techniques today, but  it was originally applied as a full-spine adjusting method until the early 1930's when the Palmer School converted to teaching only upper cervical technique.
This new method was a thrust, rather than a body drop, utilizing a fast contraction of the triceps and anconeus muscles, with the depth of the adjustment coming from the pectoralis muscles, and followed by a speedy recoil off of the contact point on the patient's body.
The Toggle-Recoil adjustment really employed the physics equation of F=MA or force being a product of mass times acceleration. In other words, by employing greater speed in the adjustment, the force would be the same, but use less mass, for perceived improvements in comfort from the patient. Furthermore, the doctor and patient need to be relaxed in order for this adjustment to be effective, so it was much more comfortable and easy on both parties from that perspective, too.
There is a wonderful video (I'm not sure about the commentary, but the video is great!) showing BJ adjusting around 1924 using this type of adjustment, in slow motion. Chiropractic has still come a long way since this tape was made, but it illustrates the adjustment better than you could possibly ask for!

BJ illustrated these concepts beautifully, in my opinion, in his 1911 textbook on chiropractic adjusting. In the following series of photos, we see BJ first showing the concept applied to cracking a walnut with a hammer, then to replacing a board in a stack of boards. Initially, he cannot crack the nut simply by pushing hard, but he can when he uses the principle of acceleration applied to the hammer. Similarly, by pushing the "misaligned" board in the stack of boards, to try to align it, one can see how poorly it works out, but when the hammer is accelerated, that board drops right in line!