This was a prospective, observational study of human volunteers participating in an Axon CEW training course.
The institutional review board at the University of Minnesota approved the study.
The research took place at an Axon facility located in Scottsdale, Arizona. The participants were selected from a convenience sample, primarily consisting of individuals from law enforcement, military, and security backgrounds, but also including civilian volunteers. In exchange for their participation, the subjects received compensation in the form of an Axon CEW device. To ensure their eligibility and safety, participants completed a medical screening questionnaire, which was then reviewed by a study physician. An HCMC representative was specifically brought in to oversee the informed consent process. Participants were given the opportunity to address any questions they had with the study physician.
The sole exclusion criterion for participation was pregnancy, which was verified through questioning of prospective study subjects. Those who met the inclusion criteria were enrolled on a first-come, first-enrolled basis and were assigned to different groups based on probe configuration.
A commercial body composition monitor and scale (Omron Full Body Sensor, Model HBF-516B, Omron Healthcare, Inc., Hoffman Estates, Illinois) was used to determine participant weight that was combined with stated height to determine body mass index (BMI).
Thirty-four subjects were assigned to eight study groups (figure 1). Twenty subjects in five groups received one exposure from a TASER 10. Five subjects in one group received two exposures, one from a TASER 10 and a TASER 7. Nine subjects in two groups received two exposures from a TASER 10, with an additional dart added for the second exposure. A total of 48 exposures were recorded, 43 from a TASER 10 and 5 from a TASER 7.
An “Off-the shelf” Axon TASER 7 was used. The TASER 10 was not yet available in its handle form-factor so the final printed circuit board and wires/probes were used. Probes were attached by hand-placing the probes at a 90° angle to the skin to full dart depth (11.5 mm) after an isopropyl alcohol preparation of the site. Axon engineers confirmed the CEW to be operating according to manufacturer specifications with each exposure.
The probe position was one dart on each thigh – group 1, one dart on the mid abdominal wall and one on the thigh – group 2, one dart on the upper back and one on the frontal thigh – group 3, one dart on the upper and lower back (first exposure) and on the opposite side (second exposure) – group 4, two darts on the upper back and two darts on the lower back – group 5, three darts in the lower abdominal region (first exposure) and one additional dart on the opposite thigh (second exposure) – group 6, three darts in the lower abdominal region (first exposure) and one additional dart on the same side thigh (second exposure) – group 7, one dart on the upper arm and one dart on the same side thigh – group 8. There were four volunteers in groups 1, 2, 3, 5, 7, 8 and five participants in groups 4 and 6. A total of 48 exposures were performed, of which 14 participants received two shots (figure 1).
The starting position of each participant was a balanced and stable “fighting stance” with one foot slightly forward and weight balanced on a padded training mat. For security reasons, spotters were standing on each side and behind the volunteers (figure 2). The task at hand was to reach and touch a suspended martial arts dummy 12 ft (3.65 m) from the starting position. The 12 ft distance was established to prevent a simple fall forward from allowing the subject to reach the target and to prevent leaping. For motivational purposes, the subjects were told that the CEW would discharge until contact was made with any part of the dummy or until 20 seconds of exposure had elapsed. However, the test was stopped when the study investigator with policing experience decided that the subject was incapable of progressing. Subjects were verbally encouraged to reach the dummy during the exposures to avoid subjects just giving up. All subject exposures and their attempts to disable the dummy were video recorded using two high-speed cameras (Sony FDR-AX700 4K, 1080p HD at 50 frames per second) for follow-up analysis.
The video analysis and evaluation of each participant was done by a quasi-blinded expert panel with significant volunteer exposure observational experience (thousands of human volunteer exposures). Similar to our previous studies [4, 5], each exposure was rated for level of goal achievement and limb muscular capture (table. 1). The “goal score” (primary outcome) was ranged from 0 (for “no significant advancement towards the goal”) up to 2 (for “successful completion of the goal” of reaching the dummy). The “limb score” (secondary outcome) implied 0 indicated “no evident capture” and 3 “complete and full capture” (i.e., “tetanic contraction”). For every participant, the expert panel decided on one number resembling the degree of incapacitation and mobility (table 1 and 2).
A low goal score and a high capture score corresponded to high incapacitation effectiveness. During the review process, the video recordings were randomized and the weapon model, probe spread, and probe location (except as obvious on video) were blinded to the raters. While the expert author raters conducted the original experiments, so were quasi-blinded, the video recording ratings were done four months after the experiment to decrease recall bias.
Median and interquartile range values were calculated for the incapacitation scores. Paired analysis with Wilcoxan sign rank test was used for the TASER 10 to TASER 7 shot comparison and second shot with additional dart comparison given non normally distributed data.
