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

Ashleigh Marchant ^1* Jeremy Witchalls ¹ Sarah B Wallwork ² Nick Ball ¹ Gordon Waddington ¹

• ¹ Research Institute for Sport and Exercise, Faculty of Health, University of Canberra, Canberra, Australian Capital Territory, Australia
• ² IIMPACT in Health, University of South Australia, Adelaide, Australia

Ankle somatosensation appears to be negatively affected when in simulated hypogravity (gravity, 1>g<0). Developing counter measures to reduce this negative effect is important for sensorimotor control as astronauts prepare to explore the Moon. Head-elevated supine lying has been found to be an effective method to simulate the physiological impact of hypogravity by reducing weight-bearing through the lower limbs. This study investigated whether wearing a combined compression sock with plantar textured sole is associated with enhanced somatosensory acuity of the lower limbs in a simulated hypogravity environment.Ankle somatosensory acuity was assessed on fifty-five healthy participants between the ages of 18 and 65 years (Female 28, Male 27; mean age 41 years ± 14). The active movement extent discrimination assessment (AMEDA) was used to assess somatosensory acuity on participants’ non-dominant foot across four conditions: (1) upright standing in barefoot; (2) upright standing wearing compression-tactile socks; (3) simulated hypogravity (head-elevated supine) in barefoot; (4) simulated hypogravity (head-elevated supine) 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 see the greatest gains when wearing the sock, compared to barefoot.When assessing the whole group, AMEDA scores were significantly reduced in the 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 the compression-tactile socks had no effect on AMEDA scores when compared to barefoot (p=0.173). When analyzed by 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-performance 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 in simulated hypogravity for individuals with below average somatosensory acuity. Further research is warranted to assess the effect of the compression-tactile socks in an actual hypogravity environment to determine whether the compression-tactile socks can maintain one’s somatosensory acuity.