Simulated malingering in the testing of cervical muscle isometric strength.

We sought to determine if simulated malingering trials of isometric cervical muscular strength in flexion, extension and right/left bending are substantially different from maximum effort trials in young, healthy subjects. A convenience sample of healthy, young adult subjects was used (M=9, F=9) who were free of neck pain. A uniaxial load cell was used to measure forces (N) produced by three trials of isometric flexion, extension and bilateral bending contractions of the head/neck muscles in two modes: comfortable maximum (MAX) and simulated (insincere) malingering (INSIN). An ANOVA model was created and tested post-hoc for paired differences within and between modes and genders. A separate ANOVA was conducted to test for differences in the ratio between flexion and extension (F/E ratio). In MAX mode, males were stronger in all ranges vs females; the expected F/E and bilateral ratios were demonstrated and good consistency of effort within and between trials was demonstrated by low CV's and high ICC's, respectively. In INSIN mode, all mean peak values were significantly lower in both genders; however, the difference between genders disappeared. Within-trial consistency was much poorer with significantly higher CV's while between-trial variability was good as demonstrated by high ICC's. The flexion/extension ratio was increased in INSIN vs MAX, with no difference between genders. It appears that simulated malingering trials produced consistent patterns of deviation from maximal effort trials: reduced peak values, increased flexion/extension ratio and increased variability of within-trial effort. These findings may provide a basis for valid indicators of insincere effort in neck pain patients.