Active sitting with backrest support: Is it feasible?

Abstract

Ergonomics science recommends office chairs that promote active sitting to reduce sitting related complaints. Since current office chairs do not fulfill this recommendation, a new chair was developed by inverting an existing dynamic chair principle. This study compares active sitting on the inverted chair during a simulated computer-based office task to two existing dynamic office chairs (n?=?8). Upper body stability was analysed using Friedman ANOVA (p?=?.01). In addition, participants completed a questionnaire to rate their comfort and activity after half a working day.

The inverted chair allowed the participants to perform a substantial range of lateral spine flexion (11.5°) with the most stable upper body posture (≤11?mm, ≤2°, p?≤?.01). The results of this study suggest that the inverted chair supports active sitting with backrest support during computer-based office work. However, according to comfort and activity ratings, results should be verified in a future field study with 24 participants.

Practitioner Summary: This experimental laboratory study analyses the feasibility of active sitting with a backrest support during common office work on a new type of dynamic office chair. The results demonstrate that active sitting with a backrest support is feasible on the new but limited on existing chairs.     

The effect of a dynamic chair on seated energy expenditure

Abstract

Dynamic sitting approaches have been advocated to increase seated energy expenditure with the view of lessening the sedentary nature of the task. This study compared energy expenditure (EE) and overall body discomfort on a novel dynamic chair with a standard office chair. Fifteen pain-free participants completed a DVD viewing task on both chairs in a randomised order. Energy expenditure and discomfort were collected simultaneously. Linear mixed models were used to analyse steady-state EE recorded on each of the chairs. Differences in discomfort were analysed using Wilkoxon Signed Rank Tests. Sitting on the novel dynamic chair significantly (p = 0.005) increased energy expenditure compared to a standard office chair. The discomfort experienced was mild overall, but was significantly greater on the dynamic chair (p = 0.004). Whilst the EE was seen to be significantly higher on the dynamic chair, the MET values are still below 1.5 METS. Thus, the use of a dynamic chair does not seem to be the most effective measure to prevent sedentary behaviour.

Practitioner Summary: Sitting on a dynamic chair increased energy expenditure compared to sitting on a standard office chair among pain-free participants. Whilst the EE was seen to be significantly higher on the dynamic chair, the MET values are still below 1.5 METS (low level EE).     

Stability ball versus office chair: comparison of muscle activation and lumbar spine posture during prolonged sitting

OBJECTIVE: The objective of the study was to evaluate the differences between sitting on a stability ball and in an office chair in terms of trunk muscle activation and lumbar spine posture. BACKGROUND: Stability balls have become increasingly popular as an alternative to office chairs to help reduce the prevalence of low back pain; however, little research has been conducted on their use as office chairs. METHODS: The 14 participants (7 men, 7 women) were required to sit on both a stability ball and an office chair for 1 hour each while performing various computer workstation tasks throughout the sitting periods. The activation of eight muscles and lumbar spine posture were measured and analyzed. RESULTS: Increased muscle activation in thoracic erector spinae (p = .0352), decreased pelvic tilt (p = .0114), and increased perceived discomfort (p < .0001) while sitting on the stability ball were observed. CONCLUSIONS: The small changes in biological responses when sitting on a stability ball as compared with an office chair, combined with the increased reported discomfort while on the ball, suggests its use for prolonged sitting may not be advantageous. APPLICATION: Prolonged sitting on a stability ball does not greatly alter the manner in which an individual sits, yet it appears to increase the level of discomfort. Therefore, it is important to fully explore a new chair design and consult scientific research before implementing its use.     

Lumbar posture and trunk muscle activation during a typing task when sitting on a novel dynamic ergonomic chair

Low back pain (LBP) is a common musculoskeletal disorder and prolonged sitting often aggravates LBP. A novel dynamic ergonomic chair (‘Back App’), which facilitates less hip flexion while sitting on an unstable base has been developed. This study compared lumbar posture and trunk muscle activation on this novel chair with a standard backless office chair. Twelve painfree participants completed a typing task on both chairs. Lumbar posture and trunk muscle activation were collected simultaneously and were analysed using paired t-tests. Sitting on the novel dynamic chair significantly (p < 0.05) reduced both lumbar flexion and the activation of one back muscle (Iliocostalis Lumborum pars Thoracis). The discomfort experienced was mild and was similar (p > 0.05) between chairs. Maintaining lordosis with less muscle activation during prolonged sitting could reduce the fatigue associated with upright sitting postures. Studies with longer sitting durations, and in people with LBP, are required.

Practitioner Summary: Sitting on a novel dynamic chair resulted in less lumbar flexion and less back muscle activation than sitting on a standard backless office chair during a typing task among pain-free participants. Facilitating lordotic sitting with less muscle activation may reduce the fatigue and discomfort often associated with lordotic sitting postures.     

Specific flexion-related low back pain and sitting: comparison of seated discomfort on two different chairs

No study has examined the effectiveness of prescribing seating modifications according to the individual clinical presentation of people with low back pain (LBP). A dynamic, forward-inclined chair (‘Back App’) can reduce seated paraspinal muscle activation among pain-free participants. This study examined 21 participants whose LBP was specifically aggravated by prolonged sitting and was eased by standing. Low back discomfort (LBD) and overall body discomfort (OBD) were assessed every 15 min while participants sat for 1 h on both the dynamic, forward-inclined chair and a standard office chair. LBD increased significantly more (p = 0.005) on the standard office chair, with no significant difference (p = 0.178) in OBD between the chairs. The results demonstrate that, in a specific flexion-related subgroup of people with LBP, increased LBD during sitting can be minimised through modifying chair design. Mechanisms that minimise seated discomfort may be of relevance in LBP management, as part of a biopsychosocial management plan.

Practitioner summary: This study examined low back discomfort (LBD) during a typing task among people with low back pain (LBP). Sitting on a dynamic, forward-inclined chair resulted in less seated LBD than sitting on a standard office chair. Further research is required to examine the long-term effectiveness of ergonomics interventions in LBP.     

Is active sitting as active as we think?

The aim of this study was to compare the biomechanical characteristics of sitting on a stool without a backrest (so as to encourage active sitting), sitting on a conventional office chair and standing in healthy participants. Thirteen healthy participants performed a keyboard-writing task during four (stable and unstable) sitting conditions and standing. Body segment positions and posture, postural sway and muscle activity of neck and trunk muscles were assessed with a motion capture system, a force plate and surface electromyography. The results showed that body segment positions, postural sway and trunk muscle activity were relatively similar for the stools without backrests compared with standing. All sitting conditions showed lower vertical upper body alignment, less anterior pelvic tilt and larger hip angles, compared with standing (p = 0.000). Unexpectedly, the muscle activity levels and total postural sway, sway velocity and sway in M/L and A/P directions were lower (p = 0.000) for the conditions that encouraged active sitting and standing, compared with the conventional office chair conditions.

Practitioner Summary: Thirteen healthy participants performed a keyboard-writing task during different sitting conditions and standing and were analysed regarding posture, postural sway and trunk muscle activity. Surprisingly, less postural sway and less muscle activity were observed during the conditions that encourage active sitting, compared with sitting on a conventional office chair.     

Evaluation of a prototype multi-posture office chair

Office chairs have often been designed to promote a single ‘correct’ rather rigid and upright posture, yet it is acknowledged that allowing changes in posture is good ergonomics practice. The present study investigated office worker's preferences for a standard shaped typist's chair (ST) and a prototype multi-posture (PMP) office chair designed to allow its users a variety of sitting positions. Forty-two (22 male and 20 female) telesales personnel (12), clerical staff (12) and researchers (18) used ST or PMP in their workplace for the first week of a 2-week study (with an even number in each work area). The PMP chair was introduced to participants with a brief lecture on how to use it and with an information booklet. Following this, each participant completed a chair comfort questionnaire. In the second week, participants swapped chairs and again completed the chair comfort questionnaire. At the end of the second week participants were also asked to complete a separate questionnaire about the usability of the information booklet that accompanied the PMP chair. Statistically significant differences in subject's rating of the two chairs were observed in 7 out of 19 questions. On a 100 mm scale, the ST chair was rated as having a greater mean overall acceptability, desirability and suitability for body build than the PMP chair. Participants also claimed to achieve better posture in the ST chair, that they tipped forward less and were more satisfied with its width. Although the participants generally preferred the ST chair, the PMP chair received more favourable ratings among the researchers who were quite mobile in their work, and in whom there was a trend for less neck, shoulder and upper back discomfort. More participants reported an overall preference for the PMP chair. The findings suggest that a more aesthetically acceptable PMP chair should be developed, peoples' reasons for preferring a more traditionally designed chair should be explored, and that the effect of postural stability education on personal preconceptions should be examined to obtain an optimal combination of healthy sitting habits, comfort and aesthetic qualities in an office chair.     

Evaluation of a prototype multi-posture office chair

Office chairs have often been designed to promote a single 'correct' rather rigid and upright posture, yet it is acknowledged that allowing changes in posture is good ergonomics practice. The present study investigated office worker's preferences for a standard shaped typist's chair (ST) and a prototype multi-posture (PMP) office chair designed to allow its users a variety of sitting positions. Forty-two (22 male and 20 female) telesales personnel (12), clerical staff (12) and researchers (18) used ST or PMP in their workplace for the first week of a 2-week study (with an even number in each work area). The PMP chair was introduced to participants with a brief lecture on how to use it and with an information booklet. Following this, each participant completed a chair comfort questionnaire. In the second week, participants swapped chairs and again completed the chair comfort questionnaire. At the end of the second week participants were also asked to complete a separate questionnaire about the usability of the information booklet that accompanied the PMP chair. Statistically significant differences in subject's rating of the two chairs were observed in 7 out of 19 questions. On a 100 mm scale, the ST chair was rated as having a greater mean overall acceptability, desirability and suitability for body build than the PMP chair. Participants also claimed to achieve better posture in the ST chair, that they tipped forward less and were more satisfied with its width. Although the participants generally preferred the ST chair, the PMP chair received more favourable ratings among the researchers who were quite mobile in their work, and in whom there was a trend for less neck, shoulder and upper back discomfort. More participants reported an overall preference for the PMP chair. The findings suggest that a more aesthetically acceptable PMP chair should be developed, peoples' reasons for preferring a more traditionally designed chair should be explored, and that the effect of postural stability education on personal preconceptions should be examined to obtain an optimal combination of healthy sitting habits, comfort and aesthetic qualities in an office chair.     

Lipoatrophia semicircularis and the relation with office work.

The relation between lipoatrophia semicircularis (LS--band-like circular depressions and isolated atrophy of the subcutaneous fatty tissue on the anterior thighs and sitting posture or pressure on the seat surface of office chairs was investigated in an office environment. A questionnaire was presented to 21 subjects and electromyographic measurements, video analysis and pressure measurements were performed. Remarkable posture differences between the LS group and the group without LS were found: less use of the lumbar support of the chair, static sitting postures and a too high seat surface of the office chair were characteristics of the subjects with LS. These observations were confirmed by higher pressure measurements for the subjects with LS. In addition, highly significant pressure differences were found between different chairs.     

Electromyography and office-chair design; a pilot study

Abstract

A pilot study is described which investigates the feasibility of using spinal electromyography as a means of discriminating between the effects of various office-chair designs on spinal muscle activity. The results support the view that the use of a backrest reduces spinal muscle activity but also suggest that when working (typing), the technique adopted by the worker has a greater effect on muscle activity than the design of the chair. Simple electromyographic studies may not be sufficiently sensitive to discriminate between the effects of individual chairs on spinal health, but it is suggested that ergonomic considerations may be more important than individual design concepts of office chairs.     

Static and dynamic postural loadings during computer work in females: Sitting on an office chair versus sitting on an exercise ball

Seated computer work results in prolonged static loading, which has been associated with the development of musculoskeletal disorders. A popular alternative to sitting on an office chair while performing computer work is to sit on an exercise ball. Sitting on an exercise ball might affect static and dynamic aspects of working posture. We monitored posture, muscle activation and spinal shrinkage in 10 females performing a 1-h typing task, while sitting on an office chair with armrests and while sitting on an exercise ball. Sitting on an exercise ball resulted in 33% more trunk motion and in 66% more variation in lumbar EMG. Both of these findings can be considered to be an advantage for the exercise ball. However, the fifth percentile and average lumbar EMG were also higher when sitting on an exercise ball, with 38% and 78%, respectively. In addition, more spinal shrinkage occurred when sitting on an exercise ball than when sitting on an office chair. Arm flexion was reduced, but trapezius activation was unaffected when sitting on an exercise ball. It is concluded that the advantages with respect to physical loading of sitting on an exercise ball may not outweigh the disadvantages.     

The impact of office chair features on lumbar lordosis,intervertebral joint and sacral tilt angles: a radiographic assessment

Abstract

Background: The purpose of this study was to determine which office chair feature is better at improving spine posture in sitting. Method: Participants (n = 28) were radiographed in standing, maximum flexion and seated in four chair conditions: control, lumbar support, seat pan tilt and backrest with scapular relief. Measures of lumbar lordosis, intervertebral joint angles and sacral tilt were compared between conditions and sex. Results: Sitting consisted of approximately 70% of maximum range of spine flexion. No differences in lumbar flexion were found between the chair features or control. Significantly more anterior pelvic rotation was found with the lumbar support (p = 0.0028) and seat pan tilt (p < 0.0001). Males had significantly more anterior pelvic rotation and extended intervertebral joint angles through L1–L3 in all conditions (p < 0.0001). Conclusion: No one feature was statistically superior with respect to minimising spine flexion, however, seat pan tilt resulted in significantly improved pelvic posture.

Practitioner Summary: Seat pan tilt, and to some extent lumbar supports, appear to improve seated postures. However, sitting, regardless of chair features used, still involves near end range flexion of the spine. This will increase stresses to the spine and could be a potential injury generator during prolonged seated exposures.     

Increasing surfboard volume reduces energy expenditure during paddling

Abstract

The purpose of this study was to investigate how altering surfboard volume (BV) affects energy expenditure during paddling. Twenty surfers paddled in a swim flume on five surfboards in random order twice. All surfboards varied only in thickness and ranged in BV from 28.4 to 37.4 L. Measurements of heart rate (HR), oxygen consumption (VO₂), pitch angle, roll angle and paddling cadence were measured. VO₂ and HR significantly decreased on thicker boards [VO₂: r = ?0.984, p = 0.003; HR: r = ?0.972, p = 0.006]. There was also a significant decrease in pitch and roll angles on thicker boards [Pitch: r = ?0.995, p < 0.001; Roll: r = ?0.911, p = 0.031]. Results from this study suggest that increasing BV reduces the metabolic cost of paddling as a result of lower pitch and roll angles, thus providing mechanical evidence for increased paddling efficiency on surfboards with more volume.

Practioner Summary: This study investigated the impact of surfboard volume on energy expenditure during paddling. Results from this study suggest that increasing surfboard volume reduces the metabolic cost of paddling as a result of lower pitch and roll angles, thus providing mechanical evidence for increased paddling efficiency on surfboards with more volume.     

Safer chairs for elderly patients: design evaluation using electromyography and force measurement

A vast majority of patient fall events in hospitals involve the elderly. In inpatient care settings, despite the risk of fall, patients are encouraged to leave their bed, move around their room, and sit on their chair to progress in their healing. Despite the vital role of patient chair design in improving recovery, few studies have examined the ergonomic requirements of safe patient chairs. This study examined the impact of manipulating horizontal and vertical positions of armrests in a test chair on required physical effort during Stand-to-Sit-to-Stand (St-Si-St) transitions among 15 elderly women. Physical effort was measured using: (1) surface electromyography (sEMG); (2) force measurement by load cells; (3) video recording. Findings showed non-linear patterns of change in required physical effort due to changes in armrests’ height and distance. It was also found that minimum effort is associated with armrests higher and farther apart than those in typical patient chairs.

Practitioner Summary: Safe chairs are essential for inpatient recovery, yet their ergonomic features are not investigated. Impact of changes in chair armrests on required physical effort was examined using electromyography, force measurement and video recording. Armrests higher and farther apart than those in typical patient chairs may be safer for elderly patients.     

Spinal shrinkage with three different types of chair whilst performing video display unit work

The aim of the study was to investigate the magnitude of spinal shrinkage during video display unit (VDU) work when subjects were sitting on chairs with different design with forward-sloping seats with or without backrest, armrest or knee support and when using a conventional chair with horizontal seat. Three different chairs were investigated: A “Conventional chair” with horizontal seat, B “Ullman chair” with front half of seat sloping forward and back half horizontal, and C “Balans chair” with forward-sloping seat plus knee support. Eight healthy subjects used to professional VDU work volunteered to participate in this field study, which was performed at their own workplaces. The median shrinkage after a three-hour period was 1.3, 1.8 and 3.1 mm for chairs A, B and C, respectively. All subjects shrank more (p < 0.05) when sitting on the chair with knee support (C) than when sitting on the conventional chair. There was no statistically significant difference in shrinkage between chairs A and B, or between chairs B and C.     

Assessing sedentary body movement with accelerometers and domain specific cognitive function during active sitting

The potential physiological and psychological consequences of active sitting are not self-evident. The purpose of this study was to determine how active sitting affects hip motion, as well as domain specific cognitive function. Thirty-seven participants sat for 10 min in three different sitting conditions including a chair with a backrest, chair without a backrest, and an exercise ball. Hip acceleration was monitored using an ActiGraph GT9X Link triaxial accelerometer, and cognitive function was assessed using three different tasks including typing, reading comprehension, and spatial direction estimates. A significant difference in hip acceleration was found between participants that sat on the exercise ball compared to a stool. Additionally, the participants sitting on the ball attempted fewer total direction estimates and fewer egocentric-based direction estimates than the participants who sat on the stool. There may be little or no cognitive benefit to active sitting for many typical work tasks.     

Sitting patterns at work: objective measurement of adherence to current recommendations

Long uninterrupted sedentary periods, independent of total sedentary time, are risk factors for poor health. There is little objective data relating to workplace sedentary behaviour and adherence to current recommendations. The sitting behaviour of office workers (n = 83) was quantified objectively using body-worn accelerometers (activPAL?) over a working week. Adherence to three different recommendations (maximum length of a sitting event of: 20 min; 30 min; 55 min) were assessed. Participants were seated at work for 5.3 ± 1.0 h/d (mean ± 1 SD), equivalent to 66 ± 12% of the working day, accrued in 27 ± 7events/d individual sitting events. Dependent on the recommendation applied, 5–20% of sitting events and 25–67% of time was accumulated in sitting events longer than current guidelines. No participants met the 20 or 30 min recommendations on every working day but seven (8%) participants met the 55 min recommendation. In conclusion, office workers spend a considerable period of their day sitting, accumulated in uninterrupted sitting events longer than current recommendations.

Statement of Relevance: Emerging evidence suggests prolonged sitting has negative health effects. In this study of office workers, 25–67% of time sitting was accumulated in events longer than minimum recommended durations. Adverse sitting behaviour is prevalent in the office, making it an appropriate setting to target the reduction of this behaviour.     

Body movements and muscle activity in sitting cross-legged

Abstract

Assuming the cross-legged (SCL) sitting posture on the ground is possible in two different ways. One which is being termed ‘normal’ does not have an intermediate squatting position, while the other has. In the normal mode, four phases may be discerned, although the transition of postures are smooth. By means of cinematographic observation, the position of the body segments during different instants of the SCL movement and the squatting cycle have been obtained. Electromyographic study shows that the muscles exert greater force during the squatting-arising cycle than during the normal SCL rising cycle. Also, based on heart rate data, the energy expenditure in the squatting mode of SCL appears to be higher than in the normal mode of SCL.     

Evaluation of foot swelling and lower-limb temperatures in relation to leg activity during long-term seated office work

Seven healthy females were studied during three experimental days, each comprising 8 hours of seated office work at different well-defined levels of leg activity. The mean foot swelling was 4·8% in the case of no leg activity (‘inactive sitting’), 2·3% when the legs were moved freely (‘ semi-active sitting’) and 0·8% at the highest activity level (‘active sitting’). The activity of the soleus muscle was evaluated by EMG and discussed in relation to the function of the musculovenous pump. The decrease in skin temperature (T_sk ) of the foot and lower leg was completed after half the working day, and on average it was 4·6°C/2·8°C (foot) and 3·3°C/l·6°C (lower leg) during ‘inactive sitting’/‘active sitting’. The mean temperature in the flexor hallucis longus muscle (T_m ) decreased by 3·7°C during the 8 hours of ‘inactive sitting’, but was almost constant during ‘active sitting’. The discomfort of the lower leg and foot was significantly correlated to foot swelling and T_m , but not to T_sk . The mean heart rate was highest during ‘inactive sitting’.

The results indicate that it is possible to reduce physiological and discomfort problems in the lower legs and feet during prolonged sedentary work by introducing modest leg activity as a natural part of the seated work.     

The effects of helmet design and bowling speed on indices of stress in cricket batting

Abstract

Elite cricketers believe that the use of helmets may help to reduce anxiety when facing fast bowling although they risk visual impairment in time-stressed circumstances. This study aimed to determine the effects of helmet design and bowling speed on heart rate (HR), anxiety arid batting performance.

Elite batsman (n=12) faced 20 deliveries from a bowling machine at slow (21 m s^?1) and fast (42ms^?1 ) speeds under three different headgear conditions— helmet with bars, visorless helmet and no-helmet. State measures of anxiety were taken before and after each batting condition by questionnaire. Heart rate (HR) was monitored throughout the test session. Batting performance was filmed and rated for quality by expert coaches on the basis of bat contact, foot movement, element of attack and timing.

Repeated measures analysis of variance revealed no significant differences in HR or performance between helmet conditions. Batting performance was significantly better against slow bowling than fast (p<0·01) and no significant differences were found for HR between the bowling speeds. No significant correlations were found between HR, performance and state anxiety scores but there was a significant negative relationship between perceived quality of performance and post-batting A-state (r= ?0·62; p<0·05) in the barred helmet condition only.

It is concluded that elite cricketers experienced little change in the level of performance-related anxiety when wearing helmets of varying designs, even when faced with bowling of considerable speed. There was no evidence of performance decrements when wearing helmets with bars and visors which suggests that the use of maximum protection against the possibility of facial damage does not seriously affect the batsman's ability to track and play the ball.