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It is notable that, in both Bair et al.’s and Chen &
Tsai’s studies, arm configurations differed between ex-
perimental conditions (6, 7). In the NT condition, both
arms were held alongside the body. In the LT condition,
however, the dominant elbow was maintained at a cer-
tain angle of flexion (90° or 135°) when making contact
with a bar or plate using a fingertip. An earlier study has
documented that merely changing the orientation of the
arm significantly adjusts proprioceptive input, which
affects body sway, demonstrating that body kinematics
may be indirectly affected by the posture of the upper
extremity (12). Therefore, the stabilizing effects of LT
may be confounded by variations in arm configurations
between the NT and LT conditions. It is impossible to
identify the “true” effects of LT on adapting body sway
if the confounding impact of arm configuration is not
taken into account and well controlled.
It should also be noted, however, that previous stu-
dies have also shown significantly smaller effects of LT
on decreasing body sway in children with DCD than in
TDC (6, 7). In other words, the use of LT reduced the
amplitude of body sway less in children with DCD than
in TDC. A potential explanation may involve somato-
sensory deficits at the peripheral level in children with
DCD. That is to say, children with DCD may be less
sensitive (i.e. have a higher threshold) to LT, which can
result in a lower level of feedback cues/information to
the CNS, thus weakening the impact of the effects of
LT on postural stability. Unfortunately, sensitivity to
LT has not been measured in previous studies.
To investigate whether children with DCD are less
sensitive to LT, this study measured sensitivity to LT
on the fingertip. Furthermore, to determine whether
sensitivity to LT is involved in the smaller effects of LT
on reducing body sway, this study attempted to change/
increase sensitivity to LT and measure its impact on
the effects of LT. A study comparing sensitivity to LT
before and after soaking the hands in water, showed
that sensitivity to LT on the fingers was significantly
increased after 30 min of immersion (13). A study by
Verrillo et al. (14) further noted that after only 5 min
of immersion in a 2% solution of sodium dodecyl
sulphate, sensitivity to touch-related perception, i.e.
roughness and texture, was significantly enhanced, and
that this effect persisted for up to 30 min. According
to Verrillo et al.’s study (14) and our pilot experiment,
soaking in a surfactant-water solution appears to be an
effective way to achieve a marked and longer-lasting
increase in sensitivity to LT.
The aims of this study were to compare sensitivity to
LT in children with DCD and TDC, and to examine how
changes/increases in sensitivity to LT impact on the ef-
fects of LT on reducing body sway in both groups, while
controlling for the possible confounding effects of arm
www.medicaljournals.se/jrm
configuration. The 3 research questions addressed were:
(i) Are children with DCD less sensitive to LT compared
with controls? (ii) Does immersion in surfactant-water
solution alter sensitivity to LT in children with or wit-
hout DCD? (iii) Are the effects of LT on reducing body
sway in children with or without DCD altered by im-
mersing their fingertips in surfactant-water solution? It
was hypothesized: (i) that children with DCD would
exhibit a lower level of sensitivity to LT compared
with controls; (ii) that after immersing the fingertip in
surfactant-water solution, children with DCD and their
counterparts would have increased sensitivity to LT; and
(iii) enhanced effects of LT on decreasing body sway.
METHODS
Prior to entering this study, the experimental procedure was
fully explained and all participants and their legal guardians
signed informed consent forms. This study was approved by the
ethics committee of Antai Memorial Hospital, and performed in
accordance with the Declaration of Helsinki 1975.
Participants
A convenience sample of 52 children aged 11–12 years, including
26 children with DCD (12 boys and 14 girls) and 26 TDC (11
boys and 15 girls), was recruited from 3 urban elementary schools
in Kaohsiung City, Taiwan. Children with DCD all scored at or
below the 5th percentile from the 2 nd edition of the Movement
Assessment Battery for Children (MABC-2) (15). Following
Chen et al.’s study (7), the TDC group had a MABC-2 score above
the 50 th percentile. No participants had intelligent impairments
(as assessed by the score from the 2 nd edition of Kaufmann Brief
Intelligence Test > 80) (16), behavioural symptoms of attention
deficit hyperactivity disorder (ADHD) (evaluated according to
a score < 70 on Conners’ Teacher Rating Scale) (17), or recent
injuries/orthopaedic conditions that might affect postural control
capacities (as confirmed by parental reports). All participants were
strongly right-handed according to the Edinburgh Handedness
Inventory in which a –100 score denotes a complete left-handed
preference, and a +100 score denotes a complete right-handed
(18). All participants had normal or corrected-to-normal vision.
Table I presents basic data for the DCD and TDC groups.
Electromagnetic motion-tracking device
A Polhemus Fastrak (Polhemus Inc., Colchester, VT, USA)
was used to record the 3D position and orientation of each
participant’s dominant upper limb in all experimental condi-
tions. Sensors were attached to: (i) the dorsal side (nail) of the
index finger, (ii) the midpoint of the third dorsal metacarpal, (iii)
the styloid process of the ulna, and (iv) the lateral epicondyle of
the humerus, to capture the movement of the index finger, palm,
forearm, and upper arm, separately. The transmitter was fitted
to a 100-cm high plastic stand, located 30 cm behind the force
plate. All kinematic data were recorded at 30 Hz.
Assessment of sensitivity to light touch
Sensitivity to LT on the dominant index fingertip was evaluated
using von Frey filaments, with forces ranging from 0.008 to