The Effect of Acute Body Unloading on Somatosensory Performance, Motor Activation, and Visuomotor Tasks

The effect of combined compression and tactile stimulation on ankle somatosensation in a lunar gravity lower limb load analog

Ankle somatosensation appears to be negatively affected when in simulated hypogravity (gravity, 1 > g < 0). Developing countermeasures to reduce this negative effect is necessary for sensorimotor control as astronauts prepare to explore the Moon. Head-elevated supine lying has been found to be an effective method in simulating the physiological impact of hypogravity by reducing the weight-bearing capacity through the lower limbs. This study investigated whether wearing a combined compression sock with plantar textured sole (compression-tactile sock) is associated with enhanced somatosensory acuity of the lower limbs in a simulated hypogravity environment. Ankle somatosensory acuity was assessed on 55 healthy participants between the ages of 18 and 65 years (female subjects 28, male subjects 27; mean age 41 years ±14). The active movement extent discrimination assessment (AMEDA) was used to assess somatosensory acuity on participants' non-dominant foot under four conditions: (1) upright standing in barefoot; (2) upright standing wearing compression-tactile socks; (3) simulated hypogravity (head-elevated supine position) in barefoot; and (4) simulated hypogravity (head-elevated supine position) wearing compression-tactile socks. Analysis was conducted for (i) the whole participant group, (ii) high (above-average) performers, (iii) medium (average) performers, and (iv) low (below average) performers. It was hypothesized that low performers would experience the greatest gains when wearing the sock, compared to those in barefoot. When assessing the group as a whole, AMEDA scores were significantly reduced in the simulated hypogravity (head-elevated supine) conditions when compared to upright standing conditions (p < 0.001; 3% decline when barefoot; 2.9% decline when wearing the socks). Wearing compression-tactile socks had no effect on AMEDA scores when compared to barefoot (p = 0.173). When analyzed by the performance group, somatosensory acuity was enhanced in the compression-tactile sock condition, when compared to barefoot (upright, p = 0.009, 4.7% increase; head-elevated supine, p = 0.022, 3% increase) in the low performers only. In the medium and high-performer groups, there was no difference between the compression-tactile sock conditions and barefoot conditions (p > 0.05 for all). Compression-tactile socks may be associated with enhanced somatosensory acuity in upright standing and simulated hypogravity for individuals with below-average somatosensory acuity. Further research is warranted to assess the effect of compression-tactile socks in an actual hypogravity environment to determine whether the compression-tactile socks can maintain one's somatosensory acuity.

A Pilot Study to Evaluate the Relationships between Supine Proprioception Assessments and Upright Functional Mobility

Long-duration bedrest impairs upright postural and locomotor control, prompting the need for assessment tools to predict the effects of deconditioning on post-bedrest outcome measures. We developed a tilt board mounted vertically with a horizontal air-bearing sled as a potential supine assessment tool for a future bedrest study. The purpose of this pilot study was to examine the association between supine proprioceptive assessments on the tilt board and upright functional mobility. Seventeen healthy participants completed variations of a supine tilt board task and an upright functional mobility task (FMT), which is an established obstacle avoidance course. During the supine tasks, participants lay on the air-bearing sled with axial loading toward the tilt board. Participants tilted the board to capture virtual targets on an overhead monitor during 30 s trials. The tasks included two dynamic tasks (i.e., double-leg stance matching mediolateral tilt targets over ±3° or ±9° ranges) and two static tasks (i.e., single-leg stance maintaining a central target position). The performances during the dynamic tasks were significantly correlated with the FMT time to completion. The dominant-leg static task performance showed a moderate trend with the FMT time to completion. The results indicate that supine proprioceptive assessments may be associated with upright ambulation performance, and thus, support the proposed application in bedrest studies.

The effect of compression and combined compression-tactile stimulation on lower limb somatosensory acuity

Background

Lower limb somatosensation and proprioception are important for maintaining balance. Research has shown that compression garments or exposure to textured surfaces, can enhance somatosensation however, little is known about the effect of combined compression and texture on somatosensory acuity in the lower limb. This study aimed to assess the effects of combined compression socks with a plantar textured sole, on lower limb somatosensory acuity.

Methods

Thirty participants completed a somatosensory acuity task (active movement extent discrimination apparatus; AMEDA) under three conditions: barefoot (control condition), standard knee-high compression sock (compression sock), and knee-high compression sock with internal rubber nodules situated on the sole (textured-compression sock). Somatosensory acuity was assessed between the different sock conditions for the (i) entire group, (ii) high performers, and (iii) low performers. It was hypothesized that low performers would see gains wearing either sock, but the greatest improvement would be in the textured-compression sock condition.

Results

AMEDA scores were not significantly different between conditions when the entire group was analyzed (p = 0.078). The low performers showed an improvement in somatosensory acuity when wearing the compression sock (p = 0.037) and the textured compression sock (p = 0.024), when compared to barefoot, but there was no difference between the two sock conditions (p > 0.05). The high performers did not show any improvement (p > 0.05 for all).

Conclusion

These findings demonstrate that additional sensory feedback may be beneficial to individuals with lower baseline somatosensory acuity but is unlikely to provide benefit for those with higher somatosensory acuity.

Evaluation and Utility of the King-Devick With Integrated Eye Tracking as a Diagnostic Tool for Sport-Related Concussion

Background

Eye-tracking technology for detecting eye movements has been gaining increasing attention as a possible assessment and monitoring tool for sport-related concussion (SRC).

Purpose

To determine the diagnostic accuracy of a rapid number-naming task with eye tracking, the King-Devick Eye Tracking (K-D ET) assessment, in identifying SRC.

Study Design

Cohort study.

Methods

One female and 1 male team of United States collegiate rugby-15 players competing during the 2018 season were recruited. Variables assessed were total saccades, saccade velocity, total fixations, fixation duration, fixation polyarea, and test duration. A generalized estimating equation was used to examine group (concussion vs nonconcussion), time (baseline vs postinjury/postseason), and sex-based differences for each outcome measure. In addition, the different components of diagnostic accuracy of the K-D ET were calculated.

Results

Baseline K-D ET assessment for 49 participants (25 male, 24 female) were assessed at the beginning of the season, with 28 participants who did not sustain a head injury during the season completing the postseason assessments and 6 participants completing a postinjury (suspected concussion) assessment. Significant differences were observed between concussed and nonconcussed groups for total saccades (P = .024), fixation duration (P = .007), and fixation polyarea (P = .030), with differences from baseline to follow-up observed for saccade velocity (P = .018) in both groups. Sex-based differences were noted for total fixations (P = .041), fixation polyarea (P = .036), and completion time (P = .035). No significant Group × Time interactions were noted. The K-D ET test duration indicated high specificity (0.86) but not high sensitivity (0.40). No other variables reported high sensitivity or specificity.

Conclusion

Other than completion time of the K-D ET test, no K-D ET oculomotor parameter was highly sensitive or specific in the diagnosis of concussion in this study.

An investigation into the measurement properties of the King-Devick Eye Tracking system

Objectives

Eye tracking has been gaining increasing attention as a possible assessment and monitoring tool for concussion. The King-Devick test (K-DT) was expanded to include an infrared video-oculography-based eye tracker (K-D ET). Therefore, the aim was to provide evidence on the reliability of the K-D ET system under an exercise condition.

Methods

Participants (N = 61; 26 male, 35 female; age range 19-25) were allocated to an exercise or sedentary group. Both groups completed a baseline K-D ET measurement and then either two 10-min exercise or sedentary interventions with repeated K-D ET measurements between interventions.

Results

The test-retest reliability of the K-D ET ranged from good to excellent for the different variables measured. The mean ± SD of the differences for the total number of saccades was 1.04 ± 4.01 and there was an observable difference (p = 0.005) in the trial number. There were no observable differences for the intervention (p = 0.768), gender (p = 0.121) and trial (p = 0.777) for average saccade’s velocity. The mean ± SD of the difference of the total fixations before and after intervention across both trials was 1.04 ± 3.63 and there was an observable difference in the trial number (p = 0.025). The mean ± SD of the differences for the Inter-Saccadic Interval and the fixation polyarea before and after intervention across both trials were 1.86 ± 22.99 msec and 0.51 ± 59.11 mm2 and no observable differences for the intervention, gender and trial.

Conclusion

The results provide evidence on the reliability of the K-D ET, and the eye-tracking components and demonstrate the relationship between completion time and other variables of the K-D ET system. This is vital as the use of the K-DT may be increasing and the combination of the K-DT and eye tracking as one single package highlights the need to specifically measure the reliability of this combined unit.

Developing Proprioceptive Countermeasures to Mitigate Postural and Locomotor Control Deficits After Long-Duration Spaceflight

Astronauts experience post-flight disturbances in postural and locomotor control due to sensorimotor adaptations during spaceflight. These alterations may have adverse consequences if a rapid egress is required after landing. Although current exercise protocols can effectively mitigate cardiovascular and muscular deconditioning, the benefits to post-flight sensorimotor dysfunction are limited. Furthermore, some exercise capabilities like treadmill running are currently not feasible on exploration spaceflight vehicles. Thus, new in-flight operational countermeasures are needed to mitigate postural and locomotor control deficits after exploration missions. Data from spaceflight and from analog studies collectively suggest that body unloading decreases the utilization of proprioceptive input, and this adaptation strongly contributes to balance dysfunction after spaceflight. For example, on return to Earth, an astronaut's vestibular input may be compromised by adaptation to microgravity, but their proprioceptive input is compromised by body unloading. Since proprioceptive and tactile input are important for maintaining postural control, keeping these systems tuned to respond to upright balance challenges during flight may improve functional task performance after flight through dynamic reweighting of sensory input. Novel approaches are needed to compensate for the challenges of balance training in microgravity and must be tested in a body unloading environment such as head down bed rest. Here, we review insights from the literature and provide observations from our laboratory that could inform the development of an in-flight proprioceptive countermeasure.

Postural Evaluation in Sports and Sedentary Subjects by Rasterstereographic Back Shape Analysis

Posture is defined as the position of the body in space, the aim of which is to maintain balance, both in static and dynamic conditions. Our purpose was to study various postural variables involved in postural adaptations of athletes practicing symmetric and asymmetric sports at professional level. Methods: Patients include sedentary subjects, competitive athletes practicing symmetrical and asymmetrical sports. Postural evaluation of the three different groups was performed using the rasterstereographic-system Formetric-4D. Results: 157 subjects were recruited. From the comparison between subjects playing symmetrical and asymmetrical sports, arises a statistically significant difference on cervical (p = 0.041) and lumbar (p = 0.047) flèche of Stagnara, with higher values for symmetrical athletes’ group. Hemipelvis torsion (p = 0.031) and lumbar flèche (p ≤ 0.001) of Stagnara are higher in symmetrical athletes’ group (sedentary). Hemipelvis torsion, cervical and lumbar flèche resulted to be higher among athletes (sedentary) (p = 0.016, p = 0.003, p = 0.027). Conclusions: In addition to the competitive sports’ medical examination, a screening with rasterstereographic-system Formetric-4D is suggested to all sedentary subjects, without serious skeletal pathologies which want to start athletic activity. Rasterstereographic-system Formetric-4D is also suggested to all athletes practicing sports, with the aim to identify eventual unknown postures, consequent to reiterated repetition of specific movements.