Walking instead of standing
Influence of movement on sensations of discomfort and the volume of the lower legs during standing loads
Abstract
Summary:Background: Leg discomfort is common in the general population. Volume increase and discomfort in the lower legs especially occur in occupations with long standing or sitting periods and less movement. Are both related to each other? Patients and methods: A time-controlled standing period of 15 min was performed in this nonrandomized controlled study to investigate the change and temporal relationship of volume increase and the occurrence of lower leg discomfort. Sensations of discomfort and the urge to move were queried using a numerical rating scale from 0 to 10 (NRS). Correlation analysis was conducted between the lower leg volume and the data regarding the discomfort and urge to move in each subject. Further, linear mixed effect models were performed to detect a causal relationship between the lower leg volume and the sensations of discomfort/urge to move in the standing period. Results: Lower leg volume increased by an average of 63 ml (p<0.001) during the standing period. The sensations of discomfort increased by a mean of 3.46 points on the NRS (p<0.001) during orthostasis. Participants’ urge to move increased by 3.47 points on the NRS (p<0.001) during the standing period. A significant correlation was shown between the increase of lower leg volume and the occurrence of discomfort sensation in 9 out of 15 subjects (p<0.05) and between the increase of lower leg volume and the urge to move in 11 out of 15 subjects (p<0.05). Association was shown between volume increase and symptoms in linear mixed effects models. Conclusions: Prolonged standing with lack of movement leads to an increase in the lower leg volume and a sensation of discomfort in venous healthy subjects. Causal relationships are indicated between these variables by linear mixed effects models.
Introduction
The issue of standing load and the associated complaints are highly relevant for the working population in Germany, where paresthesia in the legs is very common. More than half (56.4%) of the participants in the Bonn Vein Study 2003 had experienced discomfort in their legs in the last four weeks of the survey [1]. Working people suffer from complaints such as pain and swelling in the legs especially in occupations with a heavy standing load [2, 3]. Patients with such symptoms often have a high level of suffering in their daily work life, therefore, possibilities to improve their quality of life are an ongoing research focus. Occupations including a high level of standing stress are common in Germany. A survey by the German Federal Ministry of Labor and Social Affairs in 2018 found that 53.5% of the 19,979 employed people surveyed performed their work predominantly in a standing position [4]. Of these, 26.7% felt burdened by this requirement. This means, that about every seventh worker is affected by standing strain and feel burdened by this situation.
It has already been shown in several studies that prolonged standing without movement leads to an increase in discomfort and the volume of the lower leg [5, 6, 7].
Physical exercise reduces the swelling of the legs [8, 9, 10, 11]. The relationship between an increase in lower leg volume and the development of leg discomfort, as well as the effect of physical exercise on both, has not yet been clarified.
This study, therefore, investigates the increase in lower leg volume and the changes in sensations of discomfort and the urge to move during a time-limited controlled standing period. In a second step, the influence of exercise on the lower leg volume and the sensation of discomfort is investigated.
Patients and methods
Study design
The study was performed at the Clinic and Polyclinic for Skin Diseases of the University Medical Center Greifswald. It is a non-randomized, controlled study on 15 venous-healthy volunteers. The study included two visits. Firstly, each subject appeared for a screening visit. A standing exercise was performed at the day of the second visit.
Screening visit
The study participants were informed in detail about the study procedure and the data collected about them during the screening visit. Written informed consent was then obtained, and inclusion and exclusion criteria were checked (Table I). Medical history and physical examination were performed to assess venous or other preexisting diseases. The screening visit also included a dynamic venous function test with digital photoplethysmography, in which subjects were each tested to show a venous refill time of >25 s to demonstrate venous health.
Procedure of the experiment and measurements
All measurements took place at the same time of day, between 10 a.m. and 2 p.m. The standardized room temperature was in the range of 19–21 °C. Each experiment started with a lying time of 10 min for each participant. The legs were elevated 30° to the horizontal level. Afterwards, the subjects performed the standing period for 15 min. The volume of the lower legs was measured with the Bodytronic 600 (Bauerfeind AG, Zeulenroda, Germany) at the beginning and then at two-minute intervals. The subjects stood on the rotating platform of the Bodytronic 600 for the entire test procedure. All volume measurements were performed on the right leg only. The subjects were verbally asked about their general leg discomfort and current urge to move at the beginning of the experiment and then at two-minute intervals, using the numerical rating scale (NRS) from 0 to 10. In this context, “zero” implied the absence of sensation of discomfort/urge to move and “ten” implied the highest degree of sensation of discomfort/urge to move. The subjects performed a practiced movement immediately after the 15 min standing period to activate the leg muscles and, by so doing, improve venous return [12]. This movement involved lifting and simultaneously bending each leg to a 90° angle at the hip and knee joints. The foot was dorsiflexed in each case on the swinging leg. Subjects were also asked to perform plantar flexion on the standing leg. The movement was performed five times with each leg alternatively. This movement sequence lasted 15 s. Immediately after the subject’s movement, the lower leg volume, sensation of discomfort and urge to move were measured for the last time. The measurement sequence can be understood with the help of Figure 1.
Optical three-dimensional volume measurement system for determining the circumference and volume of the lower legs
The Bodytronic 600 was used to measure the volume of the lower legs. This device uses a light grid to create a three-dimensional (3D) model of the subject’s feet, lower legs and thighs. Accordingly, light beams from an LED light source (wavelength 460±20 nm) are projected onto the skin of the subject’s legs in the form of stripes and grids. These are read digitally and combined by the software to form a 3D image. The test subjects are positioned on a rotating plate during the measurement. The plate rotates 360° within about 50 s. Measurement errors are, thus, minimized [13, 14]. A handrail is attached to the rotating plate that moves simultaneously. Each subject was asked to hold onto it during the measurements and the standing load. The position of the feet on the platform is defined by markings. The resulting data were used to determine the volume of the legs during the standing load performed by each subject. Consequently, the measurement was performed every 2 min in order to be able to measure the change in the lower leg volume of the subjects steadily (Figure 1). Tischer et al. [14] investigated the effectiveness and precision of the circumference and volume measurement of the Bodytronic 600 in comparison to computed tomography and rated the measurement procedure as accurate and reliable (coefficients of variation for leg and foot circumference of 0.3–2.0% and leg volume of ≤2.5%). They recommend the method for measurements that require rapid and accurate recording of leg circumference and volume in both research and diagnostic applications [14].
Statistics
Statistical data were collected using a Microsoft Excel spreadsheet. Analysis functions of Microsoft Excel (Microsoft Corporation, Redmond, USA), the statistical software JMP (SAS Institute, Cary, North Carolina, USA), and R (R Core Team 2020. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria) were used for the analysis of these data. Furthermore, the three additional packages “Philipp Schauberger and Alexander Walker (2020). openxlsx: Read, Write and Edit xlsx Files. R package version 4.2.3.”, “Yihui Xie (2021). knitr: A General-Purpose Package for Dynamic Report Generation in R. R package version 1.33”, “Stefano Meschiari (2015). latex2exp: Use LaTeX Expressions in Plots. R package version 0.4.0.” were used. Paired one-tailed T-tests were performed to test for an increase of volume, the urge to move and the different sensations of discomfort over time within the 15 min standing period. In addition, the relationship between the lower leg volume, the sensation of discomfort and the urge to move of the study participants were investigated. Accordingly, Pearson’s correlation coefficients were calculated for every single subject between the increase in the volume of the lower leg and the occurrence of sensations of discomfort and between the increase in the volume of the lower leg and the urge to move in the standing period. Individual correlation coefficients were presented as boxplots. Furthermore, two linear mixed models were conducted to test whether the relationship between the above mentioned variables is causal. Linear mixed effects models include fixed effects and individual or cluster-specific random effects. The advantage is, that they can also be applied to repeated observations of individuals in longitudinal studies or to the analysis of cluster data [15]. The first model was performed to investigate the influence of lower leg volume increase on the occurrence of discomfort within the standing period. The dependent variable was ‘leg discomfort’. In the second model the influence of lower leg volume increase on the urge to move was tested with ‘urge to move’ as dependent variable. The fixed variable in both models was the ‘change in lower leg volume’. The subject ID was chosen as a random variable by normalizing the lower leg volume by the individual baseline value at minute 1 of each experiment.
Ethics committee
The study was ethically evaluated (Ethics Committee of the Medical Faculty of the University of Greifswald, BB 061/17). It was registered at the German Register of Clinical Studies (DRKS) with the ID: DRKS00013066.
Results
Study participants
Fifteen participants with an average age of 22.7 years (SD: 1.79) and an age range from 20 to 27 years were included in the study. There were 8 male and 7 female subjects. The mean body mass index of the subjects was 23.39 (SD: 1.57). The inclusion and exclusion criteria are shown in Table I. Each subject included was able to perform in all phases of the study. There were no exclusions. All measurements were taken on the right leg only.
Lower leg volume
The lower leg volume increased in the right leg by an average of 63 ml (p<0.001) during the standing load (Figure 2). The lower leg volume was reduced by 6 ml (not significant) during the movement following the standing load.
Sensations of discomfort
The sensations of discomfort during the standing period increased by a mean of 3.46 points on the NRS (p<0.001) (Figure 2). The sensations of discomfort after the movement were reduced by 1.67 points on the NRS (p<0.001).
Urge to move
Participants’ urge to move increased to 3.47 points on the NRS during the standing load (p<0.001) (Figure 2). The urge to move after the exercise was reduced by 2.40 points on the NRS (p<0.001).
Correlations between the individual parameters
Correlations of the lower leg volume with sensations of discomfort and the urge to move were performed for each individual subject to investigate the relationship between the individual parameters. It was found that the increase in lower leg volume was significantly correlated with the sensations of discomfort experienced in 9 out of 15 subjects (p<0.05) (Figure 3a). It was also discovered that the increase in the lower leg volume was significantly correlated with the perceived urge to move in 11 out of 15 subjects (p<0.05) (Figure 3b).
Linear mixed effects models
The linear mixed models did show an association between the changes in the volume of the lower leg and the changes in the sensations of discomfort/the urge to move in the standing period that implies a causal relationship in this controlled setting. The results are shown in Table II.
Discussion
Prolonged standing leads to an increase in the volume of the leg and the occurrence of sensations of discomfort [1, 2, 5, 6, 7, 16, 17]. This has already been shown by several authors. An increase in the lower leg volume and sensations of discomfort were achieved by a standing load of 10 min in two studies by Blättler et al. [5, 16]. Lin et al. demonstrated that a standing load of 4 h led to an increase in the volume and discomfort in the legs [18]. The increase in the lower leg volume and the occurrence of leg discomfort measured demonstrated in the study performed here fit well within this existing consensus.
In contrast to the experiments in previous studies, a measurement of the urge to move (Figure 2) was also performed in the present study. The increase in the urge to move detected showed the same dynamics as the change in the sensations of discomfort and confirmed the increase in discomfort measured.
It has not yet been fully clarified whether there is a relationship between the increase in the lower leg volume and the increase in discomfort in the context of the standing load. This issue has been investigated in several studies by Blättler et al. [5, 16]. The experimental design was similar to the study performed here. The mean age (34.4 years) of the participants in Blättler et al. was greater than in the present study (22.7 years) and the body mass index was also higher (25 in Blättler et al. and 23.4 here). In this context, Blättler et al. discovered that a correlation between the increase in the lower leg volume and the increase in sensations of discomfort with a standing load did not exist [5, 16]. They calculated the correlations between the mean values of the discomfort and the mean values of the leg volume of all subjects using the Spearman correlation coefficient. By contrast, a significant correlation between the increase in the lower leg volume and the occurrence of discomfort was demonstrated in 9 out of 15 subjects in the study performed here (Figure 3a). Unlike Blättler et al., Pearson’s correlation coefficients between the parameters mentioned previously were calculated for each individual subject. Thus, a mathematical correlation between the volume increase and the sensation of discomfort developing could be regarded in the majority of the subjects. In order to clarify a causal relationship between leg volume and changes in discomfort, statistical analysis on repeated measures (“mixed model”) was carried out. Based on the data presented here, a causal relationship is indicated. This is inconsistent with the results of Amsler and Blättler [5].
The occurrence of the sensation of discomfort or the urge to move during the standing load in individual participants in the study performed here was significantly milder than in other participants, or hardly even present. The reason for this is probably the different subjective perception of stimuli, such as the development of edema. Each subject has a different level of self- and body-awareness. The functions of nerve endings are different in each person, resulting in an unequal tolerance for sensations of discomfort and the urge to move [19]. Accordingly, the differences in correlation coefficients between subjects would also be explained.
Further research was done by Lin et al. [18]. They were able to demonstrate a correlation between the increase in the volume and discomfort in the lower legs during a standing period lasting 4 h. The mean values of all subjects were formed for the lower leg volume and the discomfort to calculate the Pearson’s correlation coefficient.
In the end, it can be argued that there is a correlation between the volume increase and the development of discomfort due to standing loads, although not in all people. However, further studies are needed to investigate whether the causality of this relationship can be demonstrated. Metabolic processes at the molecular biological level should also be included. Overall, it is difficult to correlate subjective expressions, such as pain and the urge to move, with objective measurement results, such as the increase in volume. One way of positively influencing leg complaints has been investigated in the targeted activation of the muscle pump by performing a fixed sequence of movements. Our study showed that the movements performed were able to reduce the occurrence of discomfort and the urge to move of the test subjects significantly (Figures 3a and 3b). These results are similar to those of the study by Lin et al. [18]. They also demonstrated that half-hourly movements resulted in a smaller increase in leg discomfort when subjects had been standing for 4 h. In their experiment, subjects pulled their toes (ankle movement) or lifted their legs at the hip joint (hip movement) for 2 min, then stood for 1 min before performing the movement (ankle or hip) again for another 2 min. By contrast, the movement in the study performed here was slightly more comprehensive in comparison because several joints were bent simultaneously.
A decrease in the lower leg volume of the subjects was also observed as an effect of the movement in the study performed here (Figure 2). However, this was not statistically significant. In this context, Stick et al. [8, 9] succeeded in two studies in significantly demonstrating a preventive effect of movement on edema formation in the legs. After performing standing period for 10 and 12 min, riding an ergometer for 20 min showed a reduction in the leg volume of −1.6 and −1.1%. Comparing our study with that of Stick et al., the different rate of decrease in the leg volume seems to be due to the unequal duration of exercise. During the standing test in the study performed here, the lack of activity of the muscle pump combined with the decreased venous return led to an increase in hydrostatic pressure in the capillary area. According to the Sterling equation, the balance in the capillaries shifts in favor of filtration across the vascular barrier, resulting in a decreased reabsorption of fluid. During standing without movement, the consequence is interstitial edema [20]. A movement sequence of 15 s at the end of the standing period, as performed in our study, has no relevant influence on the volume already filtered into the interstitium, and can only decrease the volume of the veins by using the muscle pump. Therefore, the volume decrease due to exercise measured in our study was only small. Steady exercise lasting 20 min, as in Stick et al. [8, 9], provides a longer-lasting reduction in hydrostatic pressure in the capillary area, thus, helping to reduce the interstitial edema and, consequently, affecting the leg volume in a relevant and more measurable way. The removal of the interstitial edema can be done through the lymphatic vessels as well and is also supported by the constant muscle activity of the ergometer.
An effect of movements on the leg volume could also be shown by Seo et al. [10, 11]. They found that subjects who stood still for 30 min during standing work developed greater swelling in the lower legs (6.9%) than those who were allowed to move during work (3.7%). Muscular activity was able to reduce leg swelling here by 3.2%. Summarizing the studies mentioned above, a positive influence of different types of exercise on the leg volume has been observed.
Limitations
The assumption concerning the reduction of the lower leg volume due to the movement at the end of the standing load could be confirmed but without significance. The mean volume reduction of 6 ml measured was too small for a significant effect and, in some subjects, no volume reduction could be detected at all. A measurement duration of about 50 s with the Bodytronic 600 was too long to be able to detect the expected effect of the volume reduction because the physiological refilling time of the veins is ≥25 s, but in many cases remains below 50 s. [21, 22]. Thus, the blood that has been pumped out of the veins has already been refilled at the end of the measurement. The recording of the intensity of the subjects’ sensations of discomfort and urge to move was done verbally on demand with the NRS and without the use of a visual scale. Although the NRS is considered very valid and reliable [23], a scale completed by the subjects themselves with visual illustration of the range of response options, such as the VAS, could have simplified the assessment of symptoms for the subjects and increased the accuracy of the ratings to avoid any kind of bias.
Conclusions
Prolonged standing with lack of movement leads to an increase in the lower leg volume and sensations of discomfort in venous-healthy subjects. A correlation between the increase in the volume and the development of lower leg discomfort can be mathematically demonstrated in the majority of cases. The association between the volume of the lower leg and the sensations of discomfort/ the urge to move that was shown by the linear mixed model in presented study implies a causal relationship in this controlled setting. Certain movements lead to a decrease in the lower leg volume and symptoms. Consequently, people with mainly sitting or standing occupational activities should perform intermittent movement exercises during breaks and in their free time, and generally integrate physical activity into their daily routine.
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