Divya Srinivasan

Interventions to reduce sedentary behavior and increase physical activity during productive work: a systematic review

OBJECTIVE This review addresses the effectiveness of workplace interventions that are implemented during productive work and are intended to change workers` SB and/or PA. METHODS We searched Scopus for articles published from 1992 until 12 March 2015. Relevant studies were evaluated using the Quality Assessment Tool for Quantitative Studies and summarized in a best-evidence synthesis. Primary outcomes were SB and PA, both at work and overall (ie, during the whole day); work performance and health-related parameters were secondary outcomes. RESULTS The review included 40 studies describing 41 interventions organized into three categories: alternative workstations (20), interventions promoting stair use (11), and personalized behavioral interventions (10). Alternative workstations were found to decrease overall SB (strong evidence; even for treadmills separately); interventions promoting stair use were found to increase PA at work while personalized behavioral interventions increased overall PA (both with moderate evidence). There was moderate evidence to show alternative workstations influenced neither hemodynamics nor cardiorespiratory fitness and personalized behavioral interventions did not influence anthropometric measures. Evidence was either insufficient or conflicting for intervention effects on work performance and lipid and metabolic profiles. CONCLUSIONS Current evidence suggests that some of the reviewed workplace interventions that are compatible with productive work indeed have positive effects on SB or PA at work. In addition, some of the interventions were found to influence overall SB or PA positively. Putative long-term effects remain to be established.

Between- and within-subject variance of motor variability metrics in females performing repetitive upper-extremity precision work

Kinematic motor variability is extensively studied in occupational, clinical and sports biomechanics, but the consistency of most motor variability metrics have never been reported. In this study, fourteen subjects performed a repetitive pipetting task on three separate days. Movements of hand, arm and pipette tip were recorded in 3D and used to compute shoulder elevation, elbow flexion and shoulder-arm coordination angles, as well as pipette-tip endpoint precision. Cycle-to-cycle motor variability was quantified using linear dispersion measures of standard kinematics properties such as peak velocity, range of motion, and inter-segmental relative phase. Between- and within-subject consistencies of these variability metrics were quantified by variance components estimated using a nested random effects model. For most metrics, the variance between subjects was larger than that between days and cycles. Entering the variance components in statistical power equations showed that for most metrics, a total of 80-100 subjects will be required to detect a 20% difference between two groups with sufficient power, while this difference can typically be detected in repeated-measures (paired) designs using 25 subjects. The reported between and within-subject variance components can be used as a data base to facilitate efficient designs of future studies of kinematic motor variability.

The size and structure of arm movement variability decreased with work pace in a standardised repetitive precision task

Increased movement variability has been suggested to reduce the risk of developing musculoskeletal disorders caused by repetitive work. This study investigated the effects of work pace on arm movement variability in a standardised repetitive pipetting task performed by 35 healthy women. During pipetting at slow and fast paces differing by 15%, movements of arm, hand and pipette were tracked in 3D, and used to derive shoulder and elbow joint angles. The size of cycle-to-cycle motor variability was quantified using standard deviations of several kinematics properties, while the structure of variability was quantified using indices of sample entropy and recurrence quantification analysis. When pace increased, both the size and structure of motor variability in the shoulder and elbow decreased. These results suggest that motor variability drops when repetitive movements are performed at increased paces, which may in the long run lead to undesirable outcomes such as muscle fatigue or overuse. Practitioner Summary: The size and structure of motor variability are associated with important outcomes in repetitive work, such as fatigue, pain and the risk of developing musculoskeletal disorders. Motor variability decreased when the pace of repetitive work was increased, indicating higher risks of developing undesirable outcomes such as muscle fatigue or overuse.

Nonlinear metrics assessing motor variability in a standardized pipetting task: Between- and within-subject variance components

The aim of this study was to estimate the between days test-retest reliability of nonlinear metrics used to quantify motor variability in a repetitive pipetting task. On three separate days, 14 healthy subjects performed pipetting as a general model of repetitive tasks. The task consisted of transferring liquid 20 times with a cycle time of 2.8s from a pickup tube to eight target tubes placed on a table in front of the subjects. The motion of hand, arm and the pipette tip was tracked in 3D and the shoulder elevation and elbow flexion angle were obtained. Motor variability was assessed using nonlinear metrics based on information theory and recurrence quantification analysis. Between- and within- (between-days) subject variance components were computed using a one-way random effect model, and intra-class correlation coefficients (ICC) were calculated from the variance components as standardized measures of reliability. Most of the metrics displayed a considerable between-days variance component and therefore the ICC showed a slight to moderate reliability. The reported data on between- and within-subject variability can be used to design future studies using nonlinear motor variability metrics on kinematics data.

The ability of non-computer tasks to increase biomechanical exposure variability in computer-intensive office work

Postures and muscle activity in the upper body were recorded from 50 academics office workers during 2 hours of normal work, categorised by observation into computer work (CW) and three non-computer (NC) tasks (NC seated work, NC standing/walking work and breaks). NC tasks differed significantly in exposures from CW, with standing/walking NC tasks representing the largest contrasts for most of the exposure variables. For the majority of workers, exposure variability was larger in their present job than in CW alone, as measured by the job variance ratio (JVR), i.e. the ratio between min–min variabilities in the job and in CW. Calculations of JVRs for simulated jobs containing different proportions of CW showed that variability could, indeed, be increased by redistributing available tasks, but that substantial increases could only be achieved by introducing more vigorous tasks in the job, in casu illustrated by cleaning. Practitioner Summary: Too little exposure variation is a general concern in computer-intensive office work. This study shows, using a novel metric, that available NC tasks can, indeed, increase variation compared to doing only CW, but also that a substantial increase in variation requires introducing more vigorous tasks such as cleaning.

Differences in motor variability among individuals performing a standardized short-cycle manual task

Motor variability (MV) has been suggested to be a determinant of the risk for developing musculoskeletal disorders in repetitive work. In this study we examined whether individuals consistently differed in the extent of motor variability when performing a standardized short-cycle manual task. On three separate days, arm kinematics was recorded in 14 healthy subjects performing a pipetting task, transferring liquid from a pick-up tube to eight target tubes with a cycle time of 2.8s. Cycle-to-cycle standard deviations (SD) of a large selection of shoulder and elbow kinematic variables, were processed using principal component analysis (PCA). Thereafter, between-subjects and between-days (within-subject) variance components were calculated using a random effects model for each of four extracted principal components. The results showed that MV differed consistently between subjects (95% confidence intervals of the between-subjects variances did not include zero) and that subjects differed consistently in MV between days. Thus, our results support the notion that MV may be a consistent personal trait, even though further research is needed to verify whether individuals rank consistently in MV even across tasks. If so, MV may be a candidate determinant of the risk of developing fatigue and musculoskeletal disorders in repetitive occupational work.

Effects of concurrent physical and cognitive demands on arm movement kinematics in a repetitive upper-extremity precision task

The effect of concurrent physical and cognitive demands on arm motor control is poorly understood. This exploratory study compared movement kinematics in a repetitive high-precision pipetting task with and without additional concurrent cognitive demands in the form of instructions necessary to locate the correct target tube. Thirty-five healthy female subjects performed a standardized pipetting task, transferring liquid repeatedly from one pick-up tube to different target tubes. In the reference condition, lights indicated the target tube in each movement cycle, while the target tube had to be deciphered from a row and column number on a computer screen in the condition with additional cognitive demands. Kinematics of the dominant arm was assessed using the central tendency and variability of the pipette-tip end-point trajectory and joint kinematics properties of the shoulder and elbow. Movements slowed down (lower velocities and higher area under the movement curves) and trajectory variability increased in the condition with additional cognitive demands, but there were no changes in the kinematics properties such as joint range of motion, times of acceleration and deceleration (as indicated by the time to peak velocity), average angles, or phase relationships between angle and angular velocity of shoulder or elbow movements between the two conditions. Further, there were also no differences in the size or structure of variability of the shoulder and elbow joint angles, suggesting that subjects could maintain the motor repertoire unaltered in the presence of these specific additional cognitive demands. Further studies should address motor control at other levels of concurrent cognitive demands, and with motor tasks that are less automated than the pipetting task used in the present study, so as to gain an increased understanding of the effect of concurrent cognitive demands for other activities of relevance to daily life.

Sit–Stand Tables With Semi-Automated Position Changes: A New Interactive Approach for Reducing Sitting in Office Work

OCCUPATIONAL APPLICATIONS Sit–stand tables with semi-automated position changes were developed in order to remind users to switch regularly between sitting and standing postures during office work. Tests of the system showed good user compliance: Desk usage patterns were sustained during the entire 2 months following intervention. Users reported the new system did not interfere with their work, that it impacted their perception of health and well-being positively, and that they would have liked to continue using the system beyond the intervention period. This could thus be a promising intervention to ensure adequate use of sit–stand desks and sustain their use over time. TECHNICAL ABSTRACT Background: Introducing sit–stand tables has been proposed as an initiative to decrease sedentary behavior among office workers and thus reduce risks of negative cardiometabolic health effects. However, ensuring proper and sustainable use of such tables has remained a challenge for successful implementation. Purpose: Assess a new system developed to promote and sustain the use of sit–stand tables. Methods: The system was programmed to change the position of the table between “sit” and “stand” positions per a regular preset pattern if the user agreed to the system-generated prompts prior to each change. The user could respond to the system-generated prompts by agreeing, refusing, or postponing the changes by 2 minutes. We obtained user compliance data when this system was programmed to a schedule of 10 minutes of standing after every 50 minutes of sitting. Compliance was investigated among nine office workers who were offered the semi-automated sit–stand table for 2 months. Results: The system issued 12 to 14 alerts per day throughout the period. Mean acceptance rates ranged from 75.0% to 82.4%, and refusal rate ranged from 11.8% to 10.1% between the first and eighth weeks of intervention (difference not statistically significant). During the first week after introduction, the table was in a standing position for a mean of 75.2 minutes—increasing slightly to 77.5 minutes in the eighth week. Conclusions: Since the workers were essentially sitting down before the table was introduced, these results suggest that the system was well accepted, and led to an effective reduction of sitting during working hours. Users also reported that the system contributed positively to their health and well-being, without interrupting their regular work, and that they would like to continue using the sit–stand table even beyond the 2-month period as part of their regular work. Compliance beyond 2 months of use, however, needs to be verified.

Comparison of Sedentary Behaviors in Office Workers Using Sit-Stand Tables With and Without Semiautomated Position Changes:

Objective: We compared usage patterns of two different electronically controlled sit-stand tables during a 2-month intervention period among office workers. Background: Office workers spend most of their working time sitting, which is likely detrimental to health. Although the introduction of sit-stand tables has been suggested as an effective intervention to decrease sitting time, limited evidence is available on usage patterns of sit-stand tables and whether patterns are influenced by table configuration. Method: Twelve workers were provided with standard sit-stand tables (nonautomated table group) and 12 with semiautomated sit-stand tables programmed to change table position according to a preset pattern, if the user agreed to the system-generated prompt (semiautomated table group). Table position was monitored continuously for 2 months after introducing the tables, as a proxy for sit-stand behavior. Results: On average, the table was in a “sit” position for 85% of the workday in both groups; this percentage did not change significantly during the 2-month period. Switches in table position from sit to stand were, however, more frequent in the semiautomated table group than in the nonautomated table group (0.65 vs. 0.29 hr-1; p = .001). Conclusion: Introducing a semiautomated sit-stand table appeared to be an attractive alternative to a standard sit-stand table, because it led to more posture variation. Application: A semiautomated sit-stand table may effectively contribute to making postures more variable among office workers and thus aid in alleviating negative health effects of extensive sitting.

Influence of Work Pace on Upper Extremity Kinematics and Muscle Activity in a Short-Cycle Repetitive Pick-and-Place Task

Objectives This study investigated the extent to which controlled changes in work pace in a cyclic pick-and-place task influence upper extremity kinematics and muscle activity, and whether an effect depends on working height. Methods Thirteen participants performed the task for 4 min at each of five work paces ranging from 8 to 12 cycles·min-1 in each of two experimental conditions where the hand was moved horizontally with an average upper arm elevation of 30° and 50°, respectively. For each work cycle, we calculated the average and standard deviation of the upper arm elevation angle and the activity of the trapezius and deltoid muscles, as well as the angular peak velocity. We summarized these seven variables by calculating averages across cycles and cycle-to-cycle variabilities. Results At 30° arm elevation, pace significantly influenced within-cycle angle variation, cycle-to-cycle variability of the average angle, angular peak velocity, and cycle-to-cycle variability of peak velocity. However, only angular peak velocity increased monotonically across all paces from 8 to 12 cycles·min-1). Average activity in the trapezius and the deltoid were the only muscle activity variables to increase consistently with pace. These effects of work pace did not change with working height. Conclusion The present study did not find any consistent work pace effect on upper extremity kinematics and muscle activity, in spite of a comprehensive empirical basis compared to previous literature. While our results suggest that work pace may not be of critical concern in an occupational health context, we encourage further studies verifying or disproving this notion.