Effect of hypnotic suggestion on knee extensor neuromuscular properties in resting and fatigued states
Place N (2018) Effect of
hypnotic suggestion on knee extensor
neuromuscular properties in resting and fatigued
states. PLoS ONE 13(4): e0195437. https://doi.org/
10.1371/journal.pone.0195437
Effect of hypnotic suggestion on knee extensor neuromuscular properties in resting and fatigued states
Naiandra Dittrich 0 1 2
Daniel Agostino 0 2
Roberta Antonini Philippe 2
Luiz Guilherme A. Guglielmo 1 2
Nicolas Place 0 2
0 Institute of Sport Sciences, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland, 3 Institute of Sport Sciences, Faculty of Social and Political Sciences, University of Lausanne , Lausanne , Switzerland
1 Sports Center, Federal University of Santa Catarina, Physical Effort Laboratory , Florian oÂpolis , Brazil
2 Editor: William D Phillips, University of Sydney , AUSTRALIA
Purpose
Methods
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.
Results
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).
Conclusion
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.
Introduction
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 [
7
]
or to overcome the mental discomfort associated with injury [
8
]. In athletes, the combination
of hypnosis and relaxation has been shown to improve precision and thus performance in
archery, basketball and golf [9±11].
Some time ago, an interesting study of Ikai and Steinhaus [
12
] showed an impressive
average increase of 25% in the maximum voluntary contraction (MVC) force of the forearm flexor
muscles following hypnotic suggestion. These results were in line with previous observations
of hypnosis-induced increased strength and endurance observed in upper limb muscles [
13
].
However, the underlying mechanisms were not identified in those early studies. More recently,
Takarada and Nozaki [
14
] investigated the consequences of hypnotic suggestions on
corticospinal excitability by measuring motor evoked potentials (MEP) evoked by transcranial magnetic
stimulation (TMS). Contrary to the findings of Ikai and Steinhaus [
12
], the authors did not
find any change in maximal voluntary handgrip force. However, they found enhanced MEP
amplitude and increased force exertion when task-motivating suggestions were provided
during hypnotic induction. Collectively, these results suggest that hypnosis might alter
neuromuscular function and exercise performance.
In the present study, we aimed at investigating whether hypnotic suggestions can alter knee
extensor neuromuscular function at rest and during exercise. Specifically, in addition to
electrical stimulation of the femoral nerve, we used TMS-induced single and paired stimuli to get
insights into potential changes in corticospinal excitability and intracortical inhibition. A
sustained isometric knee extension at 20% MVC force was chosen as the exercise model, because
task failure in this paradigm has recently been attributed to neural factors [
15
], which can be
modulated by hypnosis. We hypothesized that hypnotic induction would enhance time to task
failure of a sustained submaximal isometric contraction through increased corticospin (...truncated)