Postural control provides insight into health concerns such as fall risk but remains relatively untapped as a vital sign of health. One understudied aspect of postural control involves transient responses within center of pressure (CoP) data to events such as vision occlusion. Such responses are masked by common whole-trial analyses. We hypothesized that the transient behavior of postural control would yield unique and clinically-relevant information for quiet stance compared to traditionally calculated whole-trial CoP estimates. Three experiments were conducted to test different aspects of this central hypothesis.

To test whether transient, epoch-based characteristics of CoP estimates provide different information than traditional whole-trial estimates, we investigated correlations between these estimates for a population of young adults performing three 60-second trials of quiet stance with eyes closed. Next, to test if transient behavior is a result of sensory reweighting after eye closure, we compared transient characteristics between eyes closed and eyes open conditions. Finally, to test if there was an effect of age on transient behavior, we compared transient characteristics during eyes closed stance between populations of young and older adults.

Negligible correlations were found between transient characteristics and whole-trial estimates (p>0.08), demonstrating limited overlap in information between them. Additionally, transient behavior was exaggerated during eyes closed stance relative to eyes open (p<0.044). Lastly, we found that transient characteristics were able to distinguish between younger and older adults, supporting their clinical relevance (p<0.029).

An epoch-based approach captured unique and potentially clinically-relevant postural control information compared to whole-trial estimates. While longer trials may improve the reliability of whole-trial estimates, including a complementary assessment of the initial transient characteristics may provide a more comprehensive characterization of postural control. 
 

Description of methods used for collection/generation of data:

Reed CA, AMW Chaudhari, LC Worthen-Chaudhari, Bigelow KE, Monfort SM (2020). A new perspective on transient characteristics of quiet stance postural control. PLOS ONE

Instrument-specific information needed to interpret the data:
Vertical force and moments about the x and y axes were recorded at 1000 Hz using a balance plate (BP5046; Bertec Corp.; Columbus, OH) and captured using custom software written in LabView (National Instruments; Austin, TX). The LabVIEW program collected data from the balance plate using the Bertec Device SDK provided on Bertec's website at: http://www.bertec.com/downloads

Standards and calibration information, if appropriate:
Before the 1st trial for every participant, the balance plate was zeroed.

Methods for processing the data:
The data was processed in MATLAB using custom-scripts. Medio-lateral and Anterior-posterior CoP time series data was calculated using Bertec guidelines. CoP parameters were obtained based on calculations described by Prieto et al. (1996). Code may be available upon request.

Participant Information:
Experiment 1-- 67 young adults (YA) (24.9 ± 3.9 years, 75.7 ± 14.7 kg, 1.77 ± 0.09 m, 42 males/25 females)
Experiment 2-- a subseet of 30 young adults (YA) from Experiment 1 (22.9 ± 2.6 years, 75.1 ± 11.6 kg, 1.77 ± 0.09 m, 18 males/12 females)
Experiment 3-- the 67 YA from Experiment 1 and 38 older adults (OA) (83.5 ± 8.4 years, 66.5 ± 12.9 kg, 1.66 ± 0.09 m, 8 males/30 females)

Inclusion/Exclusion Criteria:
YA = Individuals with a known neurological impairment, a prior lower-extremity joint replacement surgery, or a lower-extremity injury within the three months prior to testing were excluded.
OA = Individuals with any known neurological impairment or who could not stand for more than 5 minutes at a time without some form of assistance (e.g. cane, walker, etc.) were excluded.

Environmental/experimental conditions:
Environmental--
The collections were performed in 3 different settings. The 2017 American Society of Biomechanics conference, the Montana State University Neuromuscular Biomechanics Lab, and various nursing home/assisted living facilities in Bozeman, MT.

Experimental--
The data were collected in two different conditions: quiet, eyes closed (QEC) stance and quiet, eyes open (QEO) stance.

Describe any quality-assurance procedures performed on the data:
All trials were quality controlled to ensure that they had approximately the same amount of data points.

Certain trials were excluded due to a participant's failure to comply with test protocol, technical difficulties with data collection, or interruption of testing by outside noise or movement, etc. Within this dataset, the TrialNum (Trial Number) indicates the order that the trial was collected, accounting for both successful and excluded trials. This explains why certain participants may have a trial number above 1, 2, or 3, as some participants required more trials in order to obtain 3 successful trials.