Date Published: April 23, 2018
Publisher: Public Library of Science
Author(s): Naiandra Dittrich, Daniel Agostino, Roberta Antonini Philippe, Luiz Guilherme A. Guglielmo, Nicolas Place, William D Phillips.
The aim of this study was to investigate whether hypnotic suggestions can alter knee extensor neuromuscular function at rest and during exercise.
Thirteen healthy volunteers (8 men and 5 women, 27 ± 3 years old) took part in this counterbalanced, crossover study including two experimental (hypnosis and control) sessions. Knee extensor neuromuscular function was tested before and after hypnosis suggestion by using a combination of voluntary contraction, transcutaneous femoral nerve electrical stimulation and transcranial magnetic stimulation (TMS). A fatiguing exercise (sustained submaximal contraction at 20% maximal voluntary contraction (MVC) force) was also performed to evaluate the potential influence of hypnosis on the extent and origin of neuromuscular adjustments.
Hypnosis did not (p>0.05) alter MVC force or knee extensor neural properties. Corticospinal excitability, assessed with the amplitude of knee extensor motor evoked potentials, was also unchanged (p>0.05), as was the level of intracortical inhibition assessed with paired pulse TMS (short-interval intracortical inhibition, SICI). Time to task failure (~300 s) was not different (p>0.05) between the two sessions; accordingly, hypnosis did not influence neuromuscular adjustments measured during exercise and at task failure (p>0.05).
Hypnotic suggestions did not alter neuromuscular properties of the knee extensor muscles under resting condition or during/after exercise, suggesting that hypnosis-induced improvement in exercise performance and enhanced corticospinal excitability might be limited to highly susceptible participants.
Hypnosis can be defined as an altered state of consciousness in which one person is guided to respond to suggestions aiming at altering perception, sensation, emotion, thought or behavior [1–2]. The efficacy of hypnosis has been well established in the medical field as a pain-reduction intervention [3–4] and also as an anesthesia method before surgery procedures [5–6]. In the field of sport science, hypnosis has been used to reinforce the effects of mental imagery  or to overcome the mental discomfort associated with injury . In athletes, the combination of hypnosis and relaxation has been shown to improve precision and thus performance in archery, basketball and golf [9–11].
The present study was designed to test the hypothesis that hypnotic suggestions would increase knee extensor corticospinal excitability and, therefore, increase time to task failure of a sustained isometric contraction. Contrary to our hypothesis, we found no effect of hypnosis on knee extensor neuromuscular function at rest and during exercise. In agreement with these findings, time to task failure was similar for both sessions.