Associations of prolonged standing with musculoskeletal symptoms—A systematic review of laboratory studies

Highlights

• Evidence on musculoskeletal symptoms during prolonged standing was reviewed.

• We found associations of standing with low back and lower extremity symptoms.

• Awkward postures and lower limb blood pooling may underlie this association.

• We recommend to refrain from standing >40 min to avoid symptoms development.

• Interventions should reduce standing time and should address underlying mechanisms.

Abstract

While prolonged standing has shown to be detrimentally associated with musculoskeletal symptoms, exposure limits and underlying mechanisms are not well understood. We systematically reviewed evidence from laboratory studies on musculoskeletal symptom development during prolonged (≥20 min) uninterrupted standing, quantified acute dose-response associations and described underlying mechanisms.

Peer-reviewed articles were systematically searched for. Data from included articles were tabulated, and dose-response associations were statistically pooled. A linear interpolation of pooled dose-response associations was performed to estimate the duration of prolonged standing associated with musculoskeletal symptoms with a clinically relevant intensity of ≥9 (out of 100).

We included 26 articles (from 25 studies with 591 participants), of which the majority examined associations of prolonged standing with low back and lower extremity symptoms. Evidence on other (e.g., upper limb) symptoms was limited and inconsistent. Pooled dose-response associations showed that clinically relevant levels of low back symptoms were reached after 71 min of prolonged standing, with this shortened to 42 min in those considered pain developers. Regarding standing-related low back symptoms, consistent evidence was found for postural mechanisms (i.e., trunk flexion and lumbar curvature), but not for mechanisms of muscle fatigue and/or variation in movement. Blood pooling was the most consistently reported mechanism for standing-related lower extremity symptoms.

Evidence suggests a detrimental association of prolonged standing with low back and lower extremity symptoms. To avoid musculoskeletal symptoms (without having a-priori knowledge on whether someone will develop symptoms or not), dose-response evidence from this study suggests a recommendation to refrain from standing for prolonged periods >40 min. Interventions should also focus on underlying pain mechanisms.

Introduction

Prolonged periods of standing are traditionally common in certain occupations, including in retail, food, healthcare, education, and manufacturing industries. It has been shown that 62% of a sample from the general Australian working population reported their work involved standing [1]; which is consistent with findings from a study in a Canadian working population [2].

A growing body of evidence suggests that prolonged sitting is associated with several adverse health outcomes [3], [4], [5]. Consequently, expert recommendations advise workers to replace periods of sitting at work with standing and other light activities such as walking [6]. There is a growing interest in workplaces implementing this advice [7], most notably through the introduction of sit/stand office workstations [8]. However, these alternatives to sitting, such as standing, may expose workers to other health consequences [9].

Adverse health outcomes of standing have been previously reported [10], and include lower extremity venous disorders [11], [12], perinatal health complications (such as preterm delivery and pre-eclampsia) [13] and musculoskeletal symptoms (e.g. self-reported pain, discomfort or complaints in any region of the musculoskeletal system). In a recent systematic review on epidemiological evidence, it was identified (albeit from limited high quality evidence from longitudinal studies) that occupational standing was detrimentally associated with low back symptoms [14]. Evidence regarding the association of excessive standing and lower extremity symptoms was inconclusive, while of the limited evidence with upper extremity symptoms, a significant association did not seem to be evident.

One key issue inadequately addressed to date is the dosage of prolonged standing that may induce musculoskeletal symptoms. The prolonged standing strain index developed by Halim and Omar [15], which was based on a review of (scientific and professional) occupational health literature and expert (e.g., ergonomic practitioners, medical doctors and physiotherapists) opinions, states that ≤1 h of continuous standing can be considered safe, >1 h of continuous standing is slightly unsafe and >1 h of continuous standing in combination with >4 h of standing per day as unsafe. The scientific basis of these exposure limits was, however, unclear as a systematic review of evidence on dose-response associations has not been undertaken.

Apart from the lack of understanding about exposure limits, underlying mechanisms explaining the associations of prolonged standing with musculoskeletal symptoms have not been elucidated. Such knowledge is needed for the development of interventions targeted at preventing detrimental effects of prolonged standing. Previous work has suggested mechanisms of muscle fatigue [16], static postures and lack of variation in movement [17], [18] to be possible contributors to standing-related low back symptoms. It has also been suggested that there may be different subgroups of people that do and do not develop low back symptoms during periods of prolonged standing [19], [20], [21]; often referred to as ‘pain developers’ and ‘non-pain developers’, respectively. However, factors that distinguish pain developers from non-pain developers are not well understood yet. For the association of standing and lower limb symptoms, mechanisms of muscle fatigue [22] and mechanisms from a non-musculoskeletal origin such as those of swelling [23] due to blood pooling in the lower limbs [16] have been suggested. However, a systematic overview of such mechanisms has not, as yet, been provided.

Considering the current emphasis on replacing office workplace sitting with standing, and the number of existing occupations that have traditionally been exposed to prolonged standing, a profound understanding of the health consequences of standing is needed to inform healthy work practices. Evidence-based exposure limits of standing are needed, while an understanding of the mechanisms with regards to the association of prolonged standing and musculoskeletal symptoms is required. Our prior review of epidemiological studies examined the evidence of medium to long term dose-response relationships [14] but was not able to address acute dose-response relationships and contemporaneous potential mechanism changes. In this review we therefore aimed to: 1) systematically review the evidence on the acute associations between prolonged uninterrupted standing and non-specific musculoskeletal symptoms from controlled laboratory studies; 2) describe acute dose-response associations for standing and musculoskeletal symptoms to establish exposure limits; and, 3) tabulate potential mechanisms for these associations.