Light Touch Contact Improves Pain-Evoked Postural Instability During Quiet Standing

Objective To investigate if attention to additional sensory information from the fingertip can improve postural stability during pain, which is known to impair balance. Methods In 16 healthy volunteers, experimental pain was induced by intramuscular injection of hypertonic saline in the right vastus medialis muscle (isotonic saline used as nonpainful control, intramuscular injection in the same location). Pain intensity was assessed on an 11-point numeric rating scale (NRS; 0 representing "no pain" and 10 "maximum pain"). Subjects were asked to stand as still as possible on a force plate for 40 seconds with their eyes closed. Their postural stability was quantified by the area and velocity of center of pressure (CoP) displacement. The CoP was recorded with and without pain during two different conditions: 1) no touch and 2) the subjects were asked to lightly touch a curtain with their right index finger and focus their attention on keeping it as still as possible. Results Hypertonic injections induced higher NRS scores compared with control injections (P