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Our second hypothesis, that finger soaking enhances
sensitivity to LT, was also confirmed, since the present
data show, for the first time, that children with or without
DCD exhibited increased sensitivity to LT after their
fingers had been soaked in surfactant-water solution.
These results corroborate those of Verrillo et al., who
found that immersing fingers or hands in a surfactant-
water solution enhances the sensitivity of touch-related
perception in young adults (14). Nevertheless, our data
were insufficient to illustrate the mechanism behind
the changes in sensitivity to LT resulting from finger
soaking. We propose that the effects of finger soaking on
increasing sensitivity to LT could be caused by modifi-
cations in mechanical characteristics, i.e., skin softness,
as a result of increased hydration of the corneal layers of
the fingers (27–29). Further studies measuring hydration
and/or hardness of the fingertip will help to identify the
factors responsible for the effects of surfactant-water
immersion on sensitivity to LT in children with or with
out DCD. Briefly, this study demonstrates that finger
soaking can effectively increase sensitivity to LT in the
fingertips of children in both DCD and TDC groups.
Our third hypothesis, that finger soaking would
modulate the body sway response during LT in both
groups, was partially confirmed. The data revealed the
novel finding that, after the fingertips had been soaked
in surfactant-water solution, the stabilizing effects of
LT were augmented only in the DCD group. Regar-
ding the mechanism of how variations in sensitivity
to LT may affect the control of body sway, Jeka et al.
(8) and Balden et al. (9) proposed that light fingertip
contact on an external reference location could pro-
vide additional and useful somatosensory informa-
tion about body motion, thus enhancing individuals’
postural stability. Indeed, during maintenance of LT,
the cutaneous receptor could not only detect skin
stretching and force at the contact location, but also
receive proprioceptive signals of the in-contact upper
extremity and provide further cues concerning body
sway direction and amplitude regarding the reference
location (12). In addition, Kouzaki & Masani (30)
found the stabilizing effects of LT were mitigated when
removing sensory cues elicited from the fingertip by
tourniquet ischaemia. A more recent study indicated
that individuals with a higher level of sensitivity to
LT were capable of reducing their body sway to a
greater extent when executing a LT compared with
those with lower level sensitivity to LT (21). Finally,
the present study indicated that, when the sensitivity
to LT of children with DCD increased, the stabilizing
effects of LT on body sway were enhanced. Given that
a lower-threshold (higher-sensitivity) sensory receptor
is easier to trigger via peripheral stimuli, children with
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DCD should have a greater, or at least equal, number
of afferent signals arising from LT leading to the CNS
in the LTAS condition compared with the LT condition.
Combining these considerations, it seems reasonable
to suggest that extra sensory information arising from
sensitivity-enhanced touch receptors in the fingertips
facilitates the stabilizing effects of LT.
Interestingly and unexpectedly, the results of the
current study showed that, while finger soaking in-
creased sensitivity to LT in both groups, body sway
was reduced only in the DCD population. We surmised
that this was simply due to a floor effect of body sway
in TDC. As they already have low amplitude of body
sway, TDC may have less “space” to decrease their
own body sway, therefore leading to an interaction
effect in which, after finger soaking, children with
DCD exhibited relatively more evident changes/de-
creases regarding body sway while performing a LT
compared with TDC. Bair et al.’s study indicated that
children with DCD tended to be less effective in using
cues from LT to reduce body sway compared with
TDC (6). Based on the present results, it appears that
immersion in surfactant-water solution can potentially
benefit children with DCD by promoting sensitivity
to LT, thus in turn compensating for smaller effects of
LT (reducing body sway). A rehabilitation programme
often involves practicing while therapists alter the
availability of sensory information. Therefore, we
suggest that therapists can employ finger soaking as a
rehabilitation strategy to immediately augment sensory
inputs obtained through LT, as well as to enhance the
effects of LT on reducing body sway. Further research
is needed to determine how long the effects of finger
soaking persist, and whether the use of finger soaking
applied in rehabilitation routines induces long-lasting
improvements in sensitivity to LT and the effects of
LT in children with DCD.
The strengths of this study were the implementation
of an evidence-based intervention (finger soaking in
surfactant-water solution) (14) and employing a well-
established study design that requires arm posture be
kept the same across experimental conditions to avoid
the confounding effects of different arm configurations
(21, 22).
A limitation of the current study was that the motion-
tracking device used was equipped with only 4 chan-
nels or sensors, thus it was not feasible to record the
movement of the non-dominant limbs (finger, palm,
forearm, and upper arm). Therefore, it is not known
whether non-dominant limb movement differed bet-
ween groups and/or differed among experimental
conditions, and it is uncertain whether non-dominant
limb movements substantially influenced the results.