Intra-and inter-rater reliability of lower leg waterplethysmography, bioelectrical impedance and muscle twitch force for the use in standing work evaluation

Objectives. Prolonged standing is associated with multiple risk factors for musculoskeletal and venous disorders. In Germany over 50% of the working population spend most of their working time in a standing position. Basic understanding of prolonged standing physiology is lacking. We therefore plan to investigate the influence of 5 h standing (including breaks) on lower limb oedema measured by waterplethysmography (WP) and bioelectrical impedance (BI) and fatigue in the triceps surae muscle using muscle twitch force (MTF). In order to interpret our results, test-retest and inter-rater reliability of these measurement methods was evaluated first. Approach. 20 subjects (9 female) were included to test each method three times (M1, M2, M3) in 30 min periods with two raters (R1, R2) on separate days. Intraclass correlation coefficient (ICC; 2,1), standard error of measurement (SEM) and smallest real difference (SRD) were calculated for both raters. Main results. The SEM and SRD calculated for WP were 27 and 75 ml, respectively, for R1 and 23 and 64 ml, respectively, for R2 with an ICC of 0.98 (p < 0.0001). Statistically significant mean differences between M1 and M2 (R1 = 23 ml, p = 0.004; R2 = 19 ml, p = 0.027) but not significant mean differences between M2 and M3 (R1 = -6 ml, p = 0.45; R2 = 4 ml, p = 0.27) were calculated for both raters. BI data revealed SEM and SRD values of 3.8 and 10.5 Omega, respectively, for R1 and 3.4 and 9.4 Omega, respectively, for R2 with an ICC of 0.24 (p = 0.001). The differences between M1 and M2 (R1 = 3.9 Omega, p = 0.0001; R2 = 2.4 Omega, p = 0.049) and between M2 and M3 (R1 = 2.3 Omega, p = 0.012; R2 = 2.0 Omega, p = 0.008) were found to be statistically significant for both raters. SEM and SRD for MTF were 0.19 and 0.53 N, respectively, for R1 and 0.23 and 0.64 N, respectively, for R2 with an ICC of 0.71 (p < 0.0001). Mean differences between M1 and M2 were statistically significant for rater 1 but not for rater 2 (R1 = 0.13 N, p = 0.022; R2 = 0.12 N, p = 0.082) and the same was found for the difference between M2 and M3 for both raters (R1 = 0.04 N, p = 0.37; R2 = 0.08 N, p = 0.12). Significance. All three measurement methods showed good reliability and should be suitable for detecting effects of standing work on oedema development and fatigue as seen in previous results of long term standing experiments. Inter-rater reliability is found to be satisfactory as well, demonstrated by the small differences in SEM values of R1 and R2. Statistically significant differences shown for all three measurement methods could be due to lacking standardisation of leg placement and thus an actual lower leg volume change between measurements, indicating possibilities for further improvement of SEM values.