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.18,19,29–31
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.33–35 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.
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.
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