Experimental knee-related pain enhances attentional interference on postural control
To quantify how postural stability is modified during experimental pain while performing different cognitively demanding tasks.
Sixteen healthy young adults participated in the experiment. Pain was induced by intramuscular injection of hypertonic saline solution (1 mL, 6%) in both vastus medialis and vastus lateralis muscles (0.9% isotonic saline was used as control). The participants stood barefoot in tandem position for 1 min on a force plate. Center of pressure (CoP) was recorded before and immediately after injections, while performing two cognitive tasks: (i) counting forwards by adding one; (ii) counting backwards by subtracting three. CoP variables—total area of displacement, velocity in anterior–posterior (AP-velocity) and medial–lateral (ML-velocity) directions, and CoP sample entropy in anterior–posterior and medial–lateral directions were displayed as the difference between the values obtained after and before each injection and compared between tasks and injections.
CoP total area ( − 84.5 ± 145.5 vs. 28.9 ± 78.5 cm2) and ML-velocity ( − 1.71 ± 2.61 vs. 0.98 ± 1.93 cm/s) decreased after the painful injection vs. Control injection while counting forward (P < 0.05). CoP total area (12.8 ± 53.9 vs. − 84.5 ± 145.5 cm2), ML-velocity ( − 0.34 ± 1.92 vs. − 1.71 ± 2.61 cm/s) and AP-velocity (1.07 ± 2.35 vs. − 0.39 ± 1.82 cm/s) increased while counting backwards vs. forwards after the painful injection (P < 0.05).
Pain interfered with postural stability according to the type of cognitive task performed, suggesting that pain may occupy cognitive resources, potentially resulting in poorer balance performance.
KeywordsPostural stability Center of pressure Attention Distraction Pain
Analysis of variance
Center of pressure
Visual analogue scale
Center for Neuroplasticity and Pain (CNAP) is supported by the Danish National Research Foundation (DNRF121). The authors thank the State of São Paulo Research Foundation (FAPESP) for the Suda scholarship (FAPESP 2017/15449–4, 2015/00214–6).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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