Article

Insoles are known to alter plantar loads and thus plantar sensory input. We
therefore hypothesised that plantar somatosensory sensation could be modified
over time by use of hard metatarsal pads. A sample of 12 healthy female
participants was randomly allocated to either soft metatarsal pads (n=6, latex
foam, Shore A11) or hard metatarsal pads groups (n = 6, thermoplastic, ShoreA65).
All wore the same shoe type and pedometers measured daily activities. Using a
bespoke actuated device, multiple mechanical stimuli were applied to the forefoot
and rearfoot before and after 8 and 30 days of wearing the pads. A control test
comprised estimation of multiple auditory sensations at day 0, 8 and 30. Changes
in detection of the mechanical and sound stimuli were estimated using the Stevens
power function, Psi = k x Phi(n) (estimate = Psi; stimulus = Phi). The k
coefficient measured the sensitivity, i.e. the lowest detectable load/sound, and
the n coefficient the gain in perception over time. After 30 days, hard
metatarsal pads group had increased plantar sensitivity in the forefoot but not
the rearfoot. The soft metatarsal pads group showed no changes in plantar
sensitivity and the detection of auditory sensation remained stable over the 30
days.Metatarsal pads with relatively high hardness increased the perception of
the lowest mechanical stimulus in the forefoot compared to soft metatarsal pads.
This provides initial evidence of the potential for changes in plantar
somatosensory sensation due to choice of orthotic designs in patients with
foot-related problems.
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