This review examines the measurement of motor imagery (MI) processes. First, self-report measures of MI are evaluated. Next, mental chronometry measures are considered. Then, we explain how physiological indices of the autonomic nervous system can measure MI. Finally, we show how these indices may be combined to produce a measure of MI quality called the Motor Imagery Index.

Motor imagery (MI) has received a lot of interest during the last decades as its chronic or acute use has demonstrated several effects on improving sport performances or skills. The development of neuroimagery techniques also helped further our understanding of the neural correlates underlying MI. While some authors showed that MI, motor execution and action observation activated similar motor cortical regions, transcranial magnetic stimulation (TMS) studies brought great insights on the role of the primary motor cortex and on the activation of the cortico‐spinal pathway during MI. After defining MI and describing the TMS technique, a short report of MI activities only at cortical level is provided. Then, a main focus on the specificities of cortico‐spinal modulations during MI, investigated by TMS, is provided. Finally, a brief overview of sub‐cortical mechanisms gives importance to the activation of peripheral neural structures during MI.

Motor imagery (MI) increases corticomotor excitability and modulates intracortical inhibition. This study aimed to relate these neurophysiological mechanisms to imagery quality. Twenty‐three healthy adults participated. First, the ability to vividly and accurately imagine performing a finger‐to‐thumb opposition task was evaluated by calculating a MI index (MII) based on psychological, behavioural and psychophysiological measurements. These scores were used to distinguish good from poor imagers. Transcranial magnetic stimulation was then used to assess modulation of corticomotor excitability, short‐interval intracortical inhibition (sICI) and short‐interval intracortical facilitation (sICF). Participants imagined abduction of their right thumb paced by a 1‐Hz metronome. Single and paired magnetic stimuli were delivered at rest, while listening to the metronome, and during or between imagined movements. Corticomotor excitability was facilitated in the right opponens pollicis for good and poor imagers during MI, and this was positively correlated to the MII score. Poor imagers also facilitated corticomotor excitability of the right abductor digiti minimi, which was not involved in the movement. No interactions were found with sICI and sICF for good imagers, whereas poor imagers recruited intracortical facilitation while imagining. Accurate MI performance was characterised by muscle‐specific temporal modulation of corticomotor excitability.

May benefit from MI training, mainly when movements are under the control of large cortical areas in the primary motor cortex. The purpose of this experiment is to assess whether MI might improve upper and lower limbs' strength through an ecological approach and validation, with complex and multijoint exercises. Nine participants were included in the MI group and 10 in the control (CTRL) group. The 2 groups performed identical bench press and leg press exercises. The MI group was instructed to visualize and feel the correspondent contractions during the rest period, whereas the CTRL group carried out a neutral task. The maximal voluntary contraction (MVC) and the maximal number of repetitions (MR) using 80% of the pre-test MVC weight were measured. Although both MI and CTRL groups enhanced their strength through the training sessions, the leg press MVC was significantly higher in the MI group than in the CTRL group (p < 0.05). The interaction between the leg press MR and the group was marginally significant (p = 0.076). However, we did not find any difference between the MI and CTRL groups, both in the bench press MVC and MR. MI-related training may contribute to the improvement of lower limbs performance by enhancing the technical execution of the movement, and the individual intrinsic motivation. From an applied and practical perspective, we state that athletes may perform imagined muscles contractions, most especially during the rest periods of their physical training, to contribute to the enhancement of concentric strength....