COMPARING EFFECTS OF DETERIORATED SENSORY INFORMATION ON SIT‐TO‐STAND PERFORMANCE OF YOUNG AND OLDER ADULTS—A PILOT STUDY

To the Editor: Sit-to-stand (STS) is a commonly performed movement that is crucial for independence of older persons. Inability to rise quickly from a sitting position is associated with institutionalization and risk of falling in community-living older adults.1 Ironically, STS is neuromechanically one of the most demanding mobility tasks, because it involves transition of posture that requires a large displacement of the body center of mass while the base of support is becoming smaller in size.2 It is not known how the availability of the sensory information affects this critical but complex task. This study compared the effects of deteriorated sensory inputs on the global performance and kinetic and kinematic parameters of STS of young (YAs) and older adults (OAs). Six young (aged 19–31) and six older (aged 65–85) healthy and physically active adults participated. The University of Waterloo research ethics board approved the study, and participants provided written informed consent. Subjects were instructed to stand up as quickly as possible without using hand support from a standard chair under six sensory conditions: hard surface+normal vision (control condition), hard surface+blurring vision (using custom-made goggles simulating dense cataracts3), hard surface+eyes closed, compliant surface (that disrupts lower limb proprioception4)+normal vision, compliant surface+blurring vision, and compliant surface+eyes closed. The trials were blocked according to the surface condition, and vision manipulation was randomized. All conditions were completed twice (total 12 trials). A force platform (AMTI, Newton, MA) placed beneath the participants' feet collected kinetic data. An infrared-emitting diode (IRED) placed on the participants' body on the sternal head provided trunk kinematic data. The IRED was tracked using two OPTOTRAK (Northern Digital, Waterloo, ON) cameras. Each participant's self-selected comfortable foot placement was determined, marked, and kept constant for all trials. Kinetic and kinematic data (sampled at 60 Hz) provided the following outcome measures: duration of the transition phase of STS (TransTime, defined using the sternal marker as the duration between peak horizontal velocity and peak vertical velocity), peak and time to peak vertical and horizontal momentums, and peak braking force (pkBrForce, obtained from the horizontal ground reaction force normalized to body weight). Mixed-factor analysis of variance identified the effects of age and sensory manipulations for each outcome measure. The significance level was P<.05. TransTime was longer in OAs (P=.02), and increase in TransTime on the compliant surface was higher (P=.004). Unlike in YAs, with eyes closed, TransTime increased further in OAs, irrespective of the surface condition (P=.04). Time to peak vertical momentum was longer in OAs (P=.03) and increased further on the compliant surface (P=.005). Conversely, peak vertical momentum was lower in OAs (P=.04) and reduced further on the compliant surface (P=.02). Vision manipulation had no effect. pkBrForce was lower in OAs (P=.02) and reduced further when vision was absent (P=.005), irrespective of the surface condition. A similar effect was also found in YAs but only on the compliant surface (P=.04) (Figure 1). No age or sensory effect was detected for measures of horizontal momentum. (A) Mean duration of the transition phase (TransTime, seconds), (B) peak vertical momentum (kg.m/s), (C) time to peak vertical momentum (seconds), and (D) mean peak braking force (N/kg) in young adults and older adults across vision conditions (V=full vision; BV=blurred vision; NV=no vision) and surface conditions (black=hard surface (HS); light gray=compliant surface (CS)). Error bars represent 1 standard deviation from the mean. Global performance during the transition phase depends on the available sensory information, particularly in OAs. Spending longer in this highly destabilizing phase5 may increase the risk of falling during STS. Lower magnitude and longer time to achieve peak vertical momentum in OAs could be due to weakness of lower limb muscles and slower development of muscle forces, respectively. Further effects of sensory manipulations on these parameters may suggest a maladaptive cautious strategy in challenging environments. Tight regulation of the magnitude and time required to achieve peak horizontal momentum supports the proposed invariant characteristics of horizontal parameters during STS,6 although lower pkBrForce in OAs in deteriorated sensory conditions indicates inefficiency in dynamic postural control for reducing horizontal momentum to terminate the forward transfer.7 Overall, these results indicate significant decline in the adaptive capacity of the central nervous system to suboptimal sensory inputs during STS even in highly active healthy OAs. As adults age, there is a much greater prevalence of comorbid conditions that affect peripheral sensations (e.g., peripheral neuropathies and peripheral arterial diseases, impairing somatosensory function, or cataract and macular degeneration, affecting vision) and may further magnify the effect of age-related deterioration.8 Considering the high prevalence of sensory degradations, coupled with the high functional relevance of the STS movement for the autonomy of OAs, further investigation is warranted in general older population and particularly in at-risk OAs. Conflict of Interest: The editor in chief has reviewed the conflict of interest checklist provided by the authors and has determined that the authors have no financial or any other kind of personal conflicts with this paper. Funding was received from the Ontario Neurotrauma Foundation (Deshpande) and National Sciences and Engineering Research Council, PGS Doctoral Award (Novak). Author Contributions: Alison Novak and Nandini Deshpande: conception and design; data collection, processing, analysis, and interpretation; and manuscript preparation. Sponsor's Role: None.

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