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Journal of Geriatric Physical Therapy:
doi: 10.1519/JPT.0b013e31821cb0ed
Research Reports

Effect of Sitting Pause Times on Postural Stability After Supine-to-Standing Transfer in Dimly Lit Environments

Johnson, Eric G. PT, DSc, NCS; Meltzer, Jonathan D. BA

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Author Information

Department of Physical Therapy, Loma Linda University, California.

Address to Eric G. Johnson, PT, DSc, NCS, Loma Linda University School of Allied Health Professions, Nichol Hall Office 1900, Loma Linda CA 92350 (ejohnson@llu.edu).

This research was funded by a research seed money grant from Loma Linda University School of Allied Health Professions. The authors declare no conflict of interest.

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Abstract

Background and Purpose: Falls are common and often take place in the home. Risk of fall increases if the environment is dimly lit. Longer sitting pause times, before standing, might improve postural stability after standing from a supine position. The purpose of this investigation was to measure the effects of sitting pause times on postural sway velocity immediately following a supine-to-standing transfer in a dimly lit room in older and younger adult women.

Methods: Five women aged 65 to 70 years and 5 aged 23 to 30 years participated in the study. On each of 2 consecutive days, study participants lay on a mat table with their eyes closed for 45 minutes before performing a supine-to-standing transfer in a dimly lit room. Sitting pause times of 2 seconds and 30 seconds preceded the transfers.

Results: Mean postural sway velocity for the whole sample and for younger and older groups was less after a 30-second pause time than that after a 2-second pause time (sample, P = .001; young, P = .019; old, P = .021). No significant difference in mean postural sway velocity was observed between the 2 groups (P > .05).

Conclusions: Total mean postural sway velocity was less when study participants performed a sitting pause of 30 seconds before standing in a dimly lit room. These results suggest that longer sitting pause times may provide improved adaptability to dimly lit environments contributing to improved postural stability.

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INTRODUCTION

Each year in the United States, 25% to 35% of community-dwelling older adults (65 years and older) fall.13 This is likely a conservative figure of actual fall occurrence, as many older adults do not realize their potential fall risk and the majority fail to report falling episodes to their physicians.4,5 Falls in the older adult population account for highest rate of hospital admissions because of trauma and nearly two-thirds of all deaths from unintentional injuries.13 In 2000, the total direct cost of all fall injuries for people 65 years and older exceeded $19 billion and by 2020, the cost is expected to exceed $54 billion dollars.6,7 Research in the area of fall prevention in older adults is widespread including functional performance testing, strength and balance training programs, and walking speed.813 Contributing factors include decreased sensorimotor function, reduced gait speed, fear of falling, postural instability, visual impairment, and dim light conditions.1419

An estimated 20% to 55% of reported falls in individuals 65 years and older occur at night in their own homes.1416,20 Intrinsic factors including visual impairments, urinary incontinence (UI), dynamic sleep disorder, and difficulty in walking and getting up are all associated with home-based nighttime falls in older women.1416,20 Research suggests that visual impairments and the degree of lighting in a room have a direct relationship on postural stability and gait.1719 In a study of 156 community-dwelling older adults, postural stability was significantly decreased when participants stood on a compliant surface during visual testing of edge-contrast sensitivity and stereopsis.17 The investigators suggested that in the presence of reduced proprioceptive input from the lower kinematic chain, postural stability is largely dependent on a person's ability to perceive accurate visual-spatial relationships. Brooke-Wavell et al18 reported that in ambient or dim light conditions, anteroposterior body sway and sway velocity (speed in which a person moves over their base of support within their limits of postural stability) were significantly increased in older adults as measured by computerized dynamic posturography. The authors reported that dim lighting levels appear to be associated with increased fall risk in the older adult population. A primary risk factor that contributes to humeral fractures that occurs secondary to a fall is ambulating in a dimly lit environment.19 With regard to hospitalization, Owens et al21 reported that the rate of fall related admissions and emergency room visits for older women is more than twice than the rate for older males.21

In our review of the literature, we were unable to find any previous studies that simultaneously investigated the components of immediate poststanding postural stability afteran extended period of eyes closed in dimly lit environments in the older adult population. These multifactorial and realistic environmental aspects of postural stability appear to directly influence fall risk in older adults. We theorized that longer sitting pause times, before standing, might improve postural stability after standing from a supine position. Therefore, the primary purpose of this investigation was to measure the effects of sitting pause times on postural sway velocity immediately following a supine-to-standing transfer in a dimly lit room in older adult women. A secondary purpose of this investigation was to compare postural sway velocity of the older female adult population to a younger female adult population. Sitting pause time was operationally defined as the number of seconds study participants sat at the edge of the mat table before standing. The practical implication of this investigation was to create an environment similar to waking up at night and getting out of bed. Because the supine-to-standing transfers followed a period of lying quietly with eyes closed, we hypothesized that longer sitting pause times would result in reduced postural sway velocity during initial standing. We also hypothesized that the younger female adults would demonstrate less postural sway velocity than older female adults.

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METHODS

Participants

A convenience sample of 5 women aged 65 to 70 years (mean = 67.60; SD = 2.07) and 5 women aged 23 to 30 years (mean = 25.8; SD = 2.77) were recruited from the local community by flyers and word of mouth. Study participants had to be healthy and able to independently perform supine-to-sit transfers. Exclusion criteria include any neurological, orthopedic, vestibular condition, or medications that impaired balance. Inclusion and exclusion criteria were determined by interview. Prior to data collection, all study participants read and signed an informed consent document, approved by the institution review board at Loma Linda University.

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Procedures

Pretest positioning was performed with each participant. Study participants lay supine on a standard hi-lo mat table adjusted to the approximate self-reported height of their bed at home. This height was measured and recorded for subsequent testing. A NeuroCom® Long Force Plate was positioned adjacent to the mat table to obtain measurements of postural stability once in standing.22 The NeuroCom® calculates a total mean sway velocity in units of degree per second.22 Study participants then performed 5 practice supine-to-standing transfers while several investigators adjusted the NeuroCom® Long Force Plate to the appropriate position using standardized foot positioning protocol.22 Participants were instructed to perform the supine-to-sit transfer as if they were getting up from participants bed at home. This pause allowed standing postural sway velocity to be measured after a transfer sequence that was customary for each study participant. The only variation from their customary transfer routine was the standardized sitting pause times of 2 and 30 seconds. The sequence of the sitting pause times were randomized after 2 consecutive days of testing.

All testing was done in a dimly lit room (defined as 1 Lux via Digital Lux Light Meter). Study participants lay quietly on the mat table with eyes closed in preparation for testing. When prompted, participants opened their eyes and moved from supine to standing, pausing either 2 or 30 sections as instructed by the tester. This allowed dark adaptation to occur prior to each measured transfer. Dark adaptation is a process where the eyes adjust from a setting of high luminance to a setting of low luminance.23 It is well established that the cones of each eye reach maximum dark adaptation within 5 to 7 minutes; however, it takes 30 to 45 minutes for this process to occur in the entire eye. This time difference can be explained by slower rod adaptation rates to changes in light sensitivity.2327 The same amount of dark adaptation for each of 2 testing conditions (2 second and 30 second sitting pause times), measurements were carried out over the course of 2 consecutive days of testing and study participants attended both testing sessions at the same time of day. Sitting pause times of 2 seconds and 30 seconds preceded each standing transfer. The sitting pause time order was randomized for all participants and a 45-minute eyes closed period preceded each supine-to-standing transfer. A Digital Lux Light Meter was used to measure lighting and the room was set to a dim light condition of 1 Lux (approximately the equivalent of a night light or small table light in a bed-room).18 Immediately upon transferring from supine to sitting, the investigators positioned the participants feet on the NeuroCom® Long Force Plate before standing using the NeuroCom® foot positioning protocol.22 The NeuroCom® Long Force Plate has a grid that allows for reliable and reproducible foot placement over successive trials.22 Total mean postural sway velocity during each standing trial was measured for a period of 10 seconds.22

The researchers selected a 2-second sitting pause time because that was the minimal amount of time needed to properly position the study participant's feet on the force-plate once in sitting. The rationale for selecting a 30-second sitting pause time was that when a person wakes up at night to use the bathroom, waiting more than 30 seconds might be an unrealistic expectation depending upon the urgency. As many as 63% of women older than 60 years have some form of UI.28 The researchers theorized that a 30-second sitting pause would allow for a level of accommodation to the dimly lit environment that would afford a more stable standing posture as measured by sway velocity. All study participants performed a single transfer for each of the sitting pause times versus taking the mean of several trials to minimize the learning curve of repeated practice. The intention was to measure initial standing postural sway velocity in a manner that most realistically resembled waking up at night and getting up from bed. The fact that all study participants performed 5 practice trials of the supine-to-standing transfer during force plate positioning served to condition them to the research environment.

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Data Analysis

Means and standard deviations were used to describe the characteristics of the study participants and outcome measures. Paired t test was used to compare the total mean sway velocity (degrees per second) following 2- and 30-second sitting pause times for all study participants. Paired t test was also used for the analysis that stratified by age category. All statistical calculations were performed with SPSS Version 18.0 for Windows (SPSS Inc, Chicago, Illinois).

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RESULTS

The mean postural sway velocity for all study participants, regardless of age, was less after a 30-second sitting pause time than that after a 2-second sitting pause time (P = .001) (Figure 1). Post hoc analysis indicated adequate power (0.995). The mean postural sway velocity was also less after a 30-second sitting pause time than after a 2-second sitting pause time for individual groups, younger adults (P = .019), and older adults (P = .021) (Table 1). Post hoc analysis indicated adequate power (0.814 and 0.783, respectively). No significant difference in mean postural sway velocity was observed between the 2 groups during the 2-second or 30- second sitting pause times (P > .05 and power 0.052).

Figure 1
Figure 1
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Table 1
Table 1
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DISCUSSION

In a case-control study of 448 cases, Chu et al19 identified difficulty walking in dimly lit rooms as one of the primary risk factors contributing to humeral fractures post falls. Brooke-Wavell et al18 reported that in dim light conditions, postural sway velocity was significantly increased in older adults as measured by computerized dynamic posturography. The authors also suggested that dim lighting levels appear to be associated with increased fall risk in the older adult population.

In the present investigation, the authors measured the effects of sitting pause times on postural sway velocity after transferring from supine-to-standing in a dimly lit room. The mean postural sway velocity for groups combined, and individual groups, was significantly less after a 30-second sitting pause time than after a 2-second sitting pause time. The authors are not aware of any other studies that quantified the optimal prestanding sitting pause time after an extended period of eyes closed in a dimly lit environment. Because a common reason for getting out of bed at night is to use the bathroom, we considered a prestanding 30-second sitting pause to be a sensible period of time. Urinary incontinence is a common problem in the older adult population and is typically classified as stress UI (leakage caused by increased abdominal pressure such as coughing or sitting up), urgency UI (leakage resulting from a strong urge to urinate), and mixed UI (a combination of both).28 The practical implication of the study findings suggest that when a person awakes at night and plans to get out of bed, they should sit at bedside for 30 seconds before standing to have better postural stability. This is a more important consideration in the older adult population given their high fall occurrence in the home during dimly lit conditions.18,19,2931

A plausible explanation for the reduced postural sway velocity in standing after the 30-second sitting pause time is an increased opportunity for visual adjustment to the dimly lit environment. Longer sitting pause times afford greater opportunity for the eyes to regulate their specific type of visual activation necessary for improved acuity. Various degrees of light are regulated by 3 different types of visual activation. In well-lit environments, photopic vision is activated to increase the ability of the cones to enhance colors of an individual's surroundings.32 At the other end of the spectrum, scotopic vision is activated in darkness, or in minimal light environments, where rod stimulation is needed.32 Between the two, in low ambient light environments, mesotopic vision is activated where both the cones and rods are needed to help an individual navigate their visual surroundings.32 In the current study, a low-ambient light environment was used. The longer sitting pause times provided more opportunity for the eyes to adjust from sco-topic vision (complete darkness while eyes were closed) to mesotopic vision (low-ambient light environment) once the eyes were opened. The increased time for adjustment from scotopic to mesotopic vision could have contributed to the significantly reduced postural sway velocities observed in this study after the longer sitting pause times.

Significant differences in mean postural sway velocities were not observed between the older and younger female adult groups (P > .05). This was an interesting observation given the fact that falls commonly occur in older women but not in younger women. We expected to see much lower postural sway velocities after both sitting pause times in the younger adult women than in the older adult women. In fact, the postural sway velocities in both groups were nearly the same. We rationalize this finding by considering likely strength differences between the younger and older female study participants.

There were several limitations in this study including the narrow age range of older adult female participants. The authors assume that longer sitting pause times will reduce postural sway velocity in women older than 70 years but cannot generalize the findings at this time. Also, the authors only measured the benefit of a 30-second sitting pause time on postural sway velocity compared to a 2-second sitting pause time. Perhaps sitting pause times shorter than 30 seconds would have similar findings. If future research demonstrates that sitting pause times closer to 15 seconds have similar positive effects on postural sway velocity after transferring from supine-to-standing in a dimly lit room, this would be beneficial given the common occurrence of UI in the older adult female population.28

Another limitation of this study was that we did not consider orthostatic hypotension (OH). Orthostatic hypotension is a very common occurrence in older adults.3335 It is defined as a 20-mm Hg reduction in systolic blood pressure (BP) or a 10-mm Hg reduction in diastolic BP after standing and is very common in older adults.34 Symptoms of OH include dizziness, lightheadedness, and blurred vision; all of which can increase postural sway velocity leading to greater fall risk.34 Mussi et al33 reported a prevalence of 12.4% of OH syncope in 259 consecutive patients, 65 years and older, who were admitted to the emergency room because of loss of consciousness. Perhaps longer sitting pause times before standing may reduce the risk for falls and subsequent injury due to OH syncope. Because OH was not a consideration in the present investigation, future research is needed to determine whether a 30-second sitting pause time before standing will reduce postural sway velocity in older adults with confirmed OH.

Also, we did not measure muscle strength. Muscle weakness, particularly in the hips and lower extremities, has been identified as a primary contributing factor of falls in older adults.5,36 It is a reasonable assumption that younger women are better able to recover from a breach, or near breach, of their limits of stability during postural sway because they are stronger, thus preventing a fall. The older participants in the present investigation were on the “younger” side of the “older” age range. It is possible that the muscle strength for both groups was similar, accounting for the lack of difference in mean postural sway velocity between groups. Future investigations should include participants in older age ranges to determine whether differences in mean postural sway velocity between younger and older populations exists.

Finally, it is possible that similar differences in postural sway velocity between 2- and 30-second sitting pause times would be observed in well-lit environments. The authors did not include baseline testing in a well-lit room. Helbostad et al37 reported no gait alterations in a sample of 24 older adults who walked 10 m in dimly light environments as compared to other levels of lighting.

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CONCLUSION

Postural sway velocity was significantly less when study participants performed a sitting pause time of 30 seconds before standing in a dimly lit room; however, significant differences in postural sway velocity were not observed between younger and older female adult groups. In consideration of increased fall risk in older adults, results of this investigation demonstrated that longer sitting pause times may afford improved adaptability to dimly lit environments contributing to improved postural stability and reduced fall risk in older adult women aged 65 to 70 years.

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ACKNOWLEDGMENTS

The authors thank Khaled Bahjri, MD, MPH, for his input and guidance with statistical analyses. They also thank the following physical therapy graduate students, who contributed to portions of this research effort: Sameer Arora, Saurabh Bhowmick, Sunit Kapoor, Vidhya Rajagopal, and Ankur Shah.

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dimly lit environments; falls; older adults; postural sway velocity

Copyright © 2012 the Section on Geriatrics of the American Physical Therapy Association

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