Reliability of Smartphone Accelerometers for Measuring Gait During Data Collection Over Zoom.

This study examined whether gait data could be reliably collected by homebound participants using iPhones under online supervision. Eighteen healthy young adults met with investigators through Zoom and installed an app to record acceleration from their iPhones' accelerometers. Half of the subjects walked normally; the other half walked while spelling words backward. During the gait tasks subjects recorded their anterior-posterior (AP), medial-lateral (ML), and vertical (V) accelerations. Data collection was repeated the following week. Seven maximum and minimum peak accelerations in the AP, ML, and vertical directions associated with events in gait were determined. Significant main effects of week and direction were observed for the first and second vertical acceleration measures. Cronbach alpha values were >0.60 for all acceleration measures, but the maximum and minimum AP accelerations that showed fair to good levels of consistency. The findings suggest gait data collected inside the home setting may be of clinical use.

The effect of music on body sway when standing in a moving virtual environment.

Movement of the visual environment presented through virtual reality (VR) has been shown to invoke postural adjustments measured by increased body sway. The effect of auditory information on body sway seems to be dependent on context with sounds such as white noise, tones, and music being used to amplify or suppress sway. This study aims to show that music manipulated to match VR motion further increases body sway. Twenty-eight subjects stood on a force plate and experienced combinations of 3 visual conditions (VR translation in the AP direction at 0.1 Hz, no translation, and eyes closed) and 4 music conditions (Mozart's Jupiter Symphony modified to scale volume at 0.1 Hz and 0.25 Hz, unmodified music, and no music) Body sway was assessed by measuring center of pressure (COP) velocities and RMS. Cross-coherence between the body sway and the 0.1 Hz and 0.25 Hz stimuli was also determined. VR translations at 0.1 Hz matched with 0.1Hz shifts in music volume did not lead to more body sway than observed in the no music and unmodified music conditions. Researchers and clinicians may consider manipulating sound to enhance VR induced body sway, but findings from this study would not suggest using volume to do so.

Effects of quadriceps and hamstrings proprioceptive neuromuscular facilitation stretching on knee movement sensation.

Stretching before competition has traditionally been thought to benefit performance; however, recent evidence demonstrating reduced muscle force and power immediately after stretching suggests otherwise. We hypothesized that knee joint position sense would be diminished immediately after proprioceptive neuromuscular facilitation (PNF) stretching to the hamstrings and quadriceps. Eighteen subjects (aged 18-30 years) were seated with their dominant foot attached to a motorized arm with the knee flexed at 135 degrees . To block external cues, the subjects wore a blindfold, earplugs, and headphones providing white noise. The knee was displaced in either the flexion or the extension direction at a velocity of 0.4 degrees .s, and subjects pressed a button when they sensed motion. The knee was returned to 135 degrees , and the test was repeated for a total of 10 trials. The PNF group received PNF stretching to the hamstrings and quadriceps of the dominant leg. The SHAM group had the dominant leg passively moved within each subject's functional range of motion. The ability to detect knee movement was retested in the PNF and SHAM groups. Pre- and posttest latencies between movement onset and subject response were analyzed. Results indicated that the PNF group had significantly increased latencies after stretching (from 2.56 +/- 0.83 to 3.46 +/- 1.90 seconds) compared with the SHAM group (3.93 +/- 2.40 to 3.72 +/- 2.15 seconds). It is concluded that PNF stretching of the hamstrings and quadriceps may acutely diminish sensitivity to knee movement. For coaches and trainers, these findings are consistent with previous reports of loss in muscle force and power immediately after stretching, suggesting that stretching just before competition may diminish performance.

Field of view and base of support width influence postural responses to visual stimuli during quiet stance.

We explored the destabilizing effect of visual field motion as the base of support (BOS) and the field of view (FOV) were narrowed. Visual field motion was achieved using an immersive virtual environment (scene) that moved realistically with head motion (natural motion) and translated sinusoidally at 0.1Hz in the fore-aft direction (augmented motion). Natural motion was presented in stereo while augmented motion was presented in both stereo and non-stereo. Subjects viewed scene motion under wide (90 degrees and 55 degrees in the horizontal and vertical directions) and narrow (25 degrees in both directions) FOV conditions while standing flatfooted (100% BOS) and on two blocks (45% and 35% BOS). Head and whole body center of mass (COM) and ankle angle root mean square (RMS) were determined as were head, whole body, and shank COM FFTs. During natural motion, the primary effect emerged in the head RMS which was significantly smaller with a 35% BOS and the wide FOV compared to the narrow FOV. However, the primary effect of augmented motion emerged in the power analysis of head and whole body COM which significantly increased with the wide FOV for a 35% BOS compared to 100% BOS. Statistical analysis indicated an effect of BOS on depth perception for head and whole body RMS; however, post hoc comparisons revealed no significant differences between stereo and non-stereo augmented motion. We conclude that reducing the BOS increased reliance on peripheral visual information to stabilize the head in space even when the augmented visual motion promoted postural instability.

Visual motion combined with base of support width reveals variable field dependency in healthy young adults.

We previously reported responses to induced postural instability in young healthy individuals viewing visual motion with a narrow (25 degrees in both directions) and wide (90 degrees and 55 degrees in the horizontal and vertical directions) field of view (FOV) as they stood on different sized blocks. Visual motion was achieved using an immersive virtual environment that moved realistically with head motion (natural motion) and translated sinusoidally at 0.1 Hz in the fore-aft direction (augmented motion). We observed that a subset of the subjects (steppers) could not maintain continuous stance on the smallest block when the virtual environment was in motion. We completed a posteriori analyses on the postural responses of the steppers and non-steppers that may inform us about the mechanisms underlying these differences in stability. We found that when viewing augmented motion with a wide FOV, there was a greater effect on the head and whole body center of mass and ankle angle root mean square (RMS) values of the steppers than of the non-steppers. FFT analyses revealed greater power at the frequency of the visual stimulus in the steppers compared to the non-steppers. Whole body COM time lags relative to the augmented visual scene revealed that the time-delay between the scene and the COM was significantly increased in the steppers. The increased responsiveness to visual information suggests a greater visual field-dependency of the steppers and suggests that the thresholds for shifting from a reliance on visual information to somatosensory information can differ even within a healthy population.

The role of task difficulty in the control of dynamic balance in children and adults.

Although several studies have explored the development of balance control in children, few have addressed the influence of task difficulty on balance control under dynamic and ecologically valid conditions. In this study, reaching tasks in three directions to two distances enabled the examination of balance control in the context of graded task difficulty. Balance control was measured in younger (6 years) and older (10-11 years) children and adults using center of pressure (COP) measures (initial position, excursion, and amplitude) and reach distance. Measures of the initial position of the COP and the excursion of the COP revealed no age-related differences in balance control. Furthermore, balance control, measured by the amplitude of COP movement over the course of the reaching tasks, indicated no differences between the age groups for the least difficult and most difficult tasks. For tasks of moderate difficulty, however, older children displayed levels of balance control similar to younger children for some tasks and higher levels of balance control, similar to adults, for others. This study suggests that (1) process-based measures of balance control are more sensitive in detecting age-related differences, and (2) balance control depends upon both age and the difficulty of the task being performed.