Physiological changes during prolonged standing and walking considering age, gender and standing work experience.

Occupational standing is associated with musculoskeletal and venous disorders. The aim was to investigate whether lower leg oedema and muscle fatigue development differ between standing and walking and whether age, gender and standing work habituation are factors to consider. Sixty participants (15 young females, 15 young males, 15 older males, and 15 young males habituated to standing work) were included and required to stand/walk for 4.5 hours in three periods with two seated breaks. Waterplethysmography/bioelectrical impedance, muscle twitch force and surface electromyography were used to assess lower leg swelling (LLS) and muscle fatigue as well as gastrocnemius muscle activity, respectively. While standing led to LLS and muscle fatigue, walking did not. Low-level medial gastrocnemius activity was not continuous during standing. No significant influence of age, gender and standing habituation was observed. Walking can be an effective prevention measure to counteract the detrimental effects of quasi-static standing.Practitioner summary: Prolonged standing leads to lower leg oedema and muscle fatigue while walking does not. The primary cause of fatigue may be in other muscles than the medial gastrocnemius. Walking may be an effective prevention measure for health risks of occupational standing when included intermittently.Abbreviation: BI: bioelectrical impedance; LLS: lower leg swelling; SEMG: surface electromyography; MTF: muscle twitch force; WP: waterplethysmography; Bsl: Baseline; L: Lunch; E: Evening; MTM: method times measurement; EA: electrical activity; IQR: interquartile range; p: percentile; M: mean; SE: standard error; Adj: adjusted.

Long-Lasting Changes in Muscle Twitch Force During Simulated Work While Standing or Walking.

OBJECTIVE: The aim of this study was to evaluate the long-lasting effects of prolonged standing work on a hard floor or floor mat and slow-pace walking on muscle twitch force (MTF) elicited by electrical stimulation. BACKGROUND: Prolonged standing work may alter lower-leg muscle function, which can be quantified by changes in the MTF amplitude and duration related to muscle fatigue. Ergonomic interventions have been proposed to mitigate fatigue and discomfort; however, their influences remain controversial. METHOD: Ten men and eight women simulated standing work in 320-min experiments with three conditions: standing on a hard floor or an antifatigue mat and walking on a treadmill, each including three seated rest breaks. MTF in the gastrocnemius-soleus muscles was evaluated through changes in signal amplitude and duration. RESULTS: The significant decrease of MTF amplitude and an increase of duration after standing work on a hard floor and on a mat persisted beyond 1 hr postwork. During walking, significant MTF metrics changes appeared 30 min postwork. MTF amplitude decrease was not significant after the first 110 min in any of the conditions; however, MTF duration was significantly higher than baseline in the standing conditions. CONCLUSION: Similar long-lasting weakening of MTF was induced by standing on a hard floor and on an antifatigue mat. However, walking partially attenuated this phenomenon. APPLICATION: Mostly static standing is likely to contribute to alterations of MTF in lower-leg muscles and potentially to musculoskeletal disorders regardless of the flooring characteristics. Occupational activities including slow-pace walking may reduce such deterioration in muscle function.

Assessing the efficiency of exoskeletons in physical strain reduction by biomechanical simulation with AnyBody Modeling System.

Introduction: Recently, many industrial exoskeletons for supporting workers in heavy physical tasks have been developed. However, the efficiency of exoskeletons with regard to physical strain reduction has not been fully proved, yet. Several laboratory and field studies have been conducted, but still more data, that cannot be obtained solely by behavioral experiments, are needed to investigate effects on the human body. Methods: This paper presents an approach to extend laboratory and field research with biomechanical simulations using the AnyBody Modeling System. Based on a dataset recorded in a laboratory experiment with 12 participants using the exoskeleton Paexo Shoulder in an overhead task, the same situation was reproduced in a virtual environment and analyzed with biomechanical simulation. Results: Simulation results indicate that the exoskeleton substantially reduces muscle activity and joint reaction forces in relevant body areas. Deltoid muscle activity and glenohumeral joint forces in the shoulder were decreased between 54 and 87%. Simultanously, no increases of muscle activity and forces in other body areas were observed. Discussion: This study demonstrates how a simulation framework could be used to evaluate changes in internal body loads as a result of wearing exoskeletons. Biomechanical simulation results widely agree with experimental measurements in the previous laboratory experiment and supplement such by providing an insight into effects on the human musculoskeletal system. They confirm that Paexo Shoulder is an effective device to reduce physical strain in overhead tasks. The framework can be extended with further parameters, allowing investigations for product design and evaluation.

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 Ω, respectively, for R1 and 3.4 and 9.4 Ω, respectively, for R2 with an ICC of 0.24 (p = 0.001). The differences between M1 and M2 (R1 = 3.9 Ω, p = 0.0001; R2 = 2.4 Ω, p = 0.049) and between M2 and M3 (R1 = 2.3 Ω, p = 0.012; R2 = 2.0 Ω, 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.

Local Muscle Fatigue and 3D Kinematics of the Cervical Spine in Healthy Subjects.

The authors aimed to further explore the effects of local muscle fatigue on cervical 3D kinematics and the interrelationship between these kinematic characteristics and local muscle endurance capacity in the unimpaired cervical spine. Twenty healthy subjects (38 ± 10 years; 5 women) performed 2 × 10 maximal cervical flexion-extension movements. Isometric muscle endurance tests (prone/supine lying) were applied between sets to induce local muscle fatigue quantified by Borg scale rates of perceived exertion (RPE) and slope in mean power frequency (MPF; surface electromyography; m. sternocleidomastoideus, m. splenius capitis). Cervical motion characteristics (maximal range of motion [ROM], coefficient of variation of the 10 repetitive movements, mean angular velocity, conjunct movements in transversal and frontal plane) were calculated from raw 3D ultrasonic movement data. Average isometric strength testing duration for flexion and extension correlated to the cervical ROM (r = .49/r = .48; p < .05). However, Student's t test demonstrated no significant alterations in any kinematic parameter following local muscle fatigue (p > .05). Although subjects' cervical muscle endurance capacity and motor output seems to be conjugated, no impact of local cervical muscle fatigue on motor function was shown. These findings underline the importance of complementary measures to address muscular performance and kinematic characteristics in outcome assessment and functional rehabilitation of the cervical spine.