Inter-task transfer of force gains is facilitated by motor imagery.

Introduction: There is compelling evidence that motor imagery (MI) contributes to improve muscle strength. While strong effects have been observed for finger muscles, only few experiments with moderate benefits were conducted within applied settings targeting large upper or lower limb muscles. The aim of the present study was therefore to extend the investigation of embedded MI practice designed to improve maximal voluntary strength on a multi-joint dynamic exercise involving the lower limbs. Additionally, we tested whether targeting the content of MI on another movement than that physically performed and involving the same body parts might promote inter-task transfer of strength gains. Methods: A total of 75 participants were randomly assigned into three groups who underwent a physical training on back squat. During inter-trial recovery periods, a first MI group (n = 25) mentally rehearsed the back squat, while a second MI group (n = 25) performed MI of a different movement involving the lower limbs (deadlift). Participants from the control group (n = 25) completed a neutral cognitive task during equivalent time. Strength and power gains were assessed ecologically using a velocity transducer device at 4 different time periods. Results: Data first revealed that participants who engaged in MI of the back squat improved their back squat performance (p < 0.03 and p < 0.01, respectively), more than the control group (p < 0.05), hence supporting the positive effects of MI on strength. Data further supported the inter-task transfer of strength gains when MI targeted a movement that was not physically trained (p = 0.05). Discussion: These findings provide experimental support for the use of MI during physical training sessions to improve and transfer force development.

Autonomic-nervous-system activity during the preparation phase for the snatch in Olympic weight lifting.

PURPOSE: To examine the preparation phase for the snatch lift in Olympic weight lifting. Two behavioral periods were studied, each corresponding to specific mental processes: a stance in front of the bar and placement of hands on the bar. Each period was hypothesized to elicit different responses of autonomic-nervous-system activity. METHODS: Twelve elite male subjects completed 12 lifts at 90% to 95% of their best grade after warm-up (80% of their best grade). Because peripheral autonomic-nervous-system activity is related to arousal and activation variation, 6 variables were continuously recorded: electrodermal (skin resistance and potential), thermovascular (skin temperature and skin blood flow), and cardiorespiratory (heart rate and respiratory frequency). RESULTS: Responses (ie, phasic activities) were evident during the first behavioral period. Decrease in heart rate (mean = 19 beats/min) or in respiratory frequency (mean = 8.6 beats/min) was related to attention processes. These responses were weaker (-0.16 degrees C vs -0.25 degrees C in skin temperature) and shorter (2.7 seconds vs 4.3 seconds in skin resistance) than those recorded during execution. The second phase showed variations in basal levels (mean increase in heart rate of 25%), related to increase in activation, thus attesting the muscle system's process of preparation for effort. CONCLUSION: Weight lifters separated the preparation phase into 2 stages that were closely matched by different physiological activities. Weight lifting requires participants to share their mental resources among the 2 demanding concentration phases by first focusing their attention on the execution and then mobilizing energizing resources.

Observation of action and autonomic nervous system responses.

Observing somebody performing an action has been shown to elicit neuronal activity in the premotor cortex. This paper investigated physiological effect of observing an effortful action at the peripheral level. As Autonomic Nervous System responses reflect central nervous system processes such as movement planning and programming, it was expected that observing an action would elicit a pattern of ANS responses matching those recorded during actual movement. 12 male subjects, ages 23 to 28 years (M = 25.5, SD = 1.9), were selected as they were experienced in weight lifting. They were asked to observe a squat movement followed by returning to the upright position under 3 different conditions: (i) observation of actual movement performed by somebody else, (ii) observation of a video of the subject himself (first-person video), and (iii) observation of a video of somebody else performing the same movement (third-person video). Moreover, each movement was observed when performed at 50% and 90% of each participant's personal best mark (% of the highest weight which could be lifted). Three ANS parameters were continuously recorded: skin resistance, temperature and heart rate. ANS responses varied as a function of movement intensity: autonomic responses recorded during movement observation at 90% were significantly higher and longer than those recorded during movement observation at 50%. Thus, autonomic responses were linked to the amount of observed effort. Conversely, no difference was found among the three conditions of observation. ANS responses from observation of actual movement were shown to resemble those recorded under the two conditions of video observation.