Developing skilled performance of lumbar spine manipulation

We are grateful for the time and energy taken by Ms Coloma and Mr Faubion in reviewing and, more importantly, thinking about our work. We agree that this is but a beginning of investigations that may lead to improved methods of training in chiropractic procedures, as well as enhancement in overall skill development. We disagree, however, with the characterization of our speculation that aids may help to optimize procedure training programs as being “presumptuous.” There is substantial science behind the use of knowledge of results (KR) to enhance performance, a sample of which is available in the references listed in our original manuscript. First, however, it is required that some determination be made as to what changes in performance are considered beneficial. Then, it is clear that KR can be used to reach that goal.

The letter authors posit that it is the additional rehearsal alone (eg, 750 repetitions estimated) that is responsible for the gains we observed. Such an assumption would require 2 circumstances that are highly unlikely. First, rehearsal requires that the person performing the procedure have a subject on whom to work. It is unlikely that a student would be able to locate a subject or number of subjects within the student body to permit 750 procedures to be performed by 39 separate students over a 15-week interval (750 × 39 = 2925 procedures). Without a live subject, it is necessary for there to be a surrogate of some type that can permit procedure application. In this case, the Dynadjust device operated as that surrogate, empowering repetitions that would not previously have been likely or feasible under normal academic conditions. Second, the authors assume that each repetition actually represents a desirable performance. This also is unlikely. KR literature supports the assertion that practice, without knowledge of outcome, is essentially undirected and has little value in reinforcing desirable effects. The Dynadjust, with its ability to report adequate depth of motion, speed of load application, and control of line of action, provided important feedback on desirability of performance.

Finally, in the letter, authors raise concerns with respect to the homogeneity of the study groups. The concern, however, begs the question as to homogeneity with respect to what? More importantly, the question being asked by this study and the research design makes these issues irrelevant. The students were paired expressly to create a pretest/posttest experimental design for both the control (CS) and experimental (DI) groups. In so doing, all anthropometric features (age, height, weight, and gender) are canceled out. Each subject performed procedures only on her/his partner. Presumably, and in fact, none of these variables changed over the 15-week course of the follow-up interval.

The assertion that, “It is well known that a person’s age and sex determine their body type, and this may play into the biomechanics of adjusting” represents an extreme oversimplification on both counts. First, age and sex do not determine body type. They are related to body type. Other parameters involved include height, weight, muscular fitness, and body fat content. The former 2 are genetically controlled, while the others are environmentally controlled. Second, the factors in the biomechanics of adjusting include both patient- and operator-based factors far more detailed than operator anthropometrics. An insight into these can be obtained in Herzog’s book on the biomechanics of spinal manipulation.1 These have been detailed further in a text currently in submission by Haldeman.2 They include postural configuration of the procedure for both patient and operator; effects of gravity acting through the operator’s body mass; muscular effort of the operator, as well as the patient’s intrinsic spinal muscles; and the inertial load of the spine caused by motions induced. Finally, it is noted that since the groups were paired for all procedures on a random basis, there were no significant differences “at baseline.” Moreover, statistical comparison of demographic information by group assignment is given in Table 1 and shows that there are no differences. Group SC had 1 more male subject than group DI, and conversely, DI had 1 more female subject than SC (χ2 = 0.1279, P = .721). Consequently, homogeneity of sample population is, conclusively, not an issue.

Table 1. Anthropometric data

		Height (in)	Weight (lb)	Age (y)
	Group SC	69.4	186.4	27.7
	Group DI	69.2	183.8	25.8
	P value	.895	.880	.290

SC, Control group; DI, experimental group.