Sensorimotor expertise influences perceptual weight judgments during observation of a sport-specific gesture

Abstract

This study aimed to investigate the role of sensorimotor expertise in evaluating relative weight of a lifted object during the observation of a sport-specific gesture, namely the deadlift. Fifty-six participants, assigned to three groups according to their experience in weight lifting, powerlifters, CrossFit® practitioners and naïve participants (controls), performed a perceptual weight judgments task. Participants observed videos showing a powerlifter executing a deadlift at the 80%, 90% and 100% of 1 repetition maximum (1RM) and answered a question about the weight of the lifted object. Participants' response accuracy and variability were evaluated. Findings showed that powerlifters were more accurate than controls. No differences appeared between powerlifter and CrossFit® practitioners, and between CrossFit® practitioners and controls. Response variability was similar in the three groups. These findings suggest that a fine sensorimotor expertise specific for the observed gesture is crucial to detect the weight of the object displayed in the observed movement, since it might allow detecting small changes in the observed movement kinematics, which we speculate are at the basis of the object weight recognition.

Keywords: action observation; motor expertise; motor resonance; sport expertise; weight estimation.

Figure 1

Experimental paradigm. (A) Each participant executed the experiment at computer. The participants filled a questionnaire that collected personal and sport-related data. After that, a video example of the deadlift was shown and a familiarization phase, consisting of 6 videos, was performed. Then, participants executed the experimental task. It consisted of 48 videos and a relative question about the magnitude of the weight lifted by the athlete. The videos showed a deadlift performed with three different weights corresponding to 80%, 90% and 100% of athlete's 1RM (16 videos/weight). After each video, the correct answer for each weight were 8 times “Yes” and 8 times “No”. (B) Illustration of the set-up during video recording. (C) Example of the questions asked to the participants (QUEST.), the number of repetitions for each question (TRIAL) and the correct answers when participants observed the video showing a weight corresponding to 80%1RM.

Figure 2

Response accuracy values at the three percentages of the 1RM displayed in the videos (80%1RM, 90%1RM, 100%1RM). Powerlifters (PL) are represented in purple, CrossFit® practitioners (CF) in orange and control participants in grey. The box depicts median and the 25th and 75th quartiles. The whiskers show the minimum and maximum. Points represent the accuracy of each participant. * Indicates a statistically significant difference between groups (p < 0.05). The significant within group differences among weights are indicated by # (within PL), § (within CF) and+(within Controls). # p < 0.05, §§§ and +++ p < 0.001.

Figure 3

Response accuracy at 90%1RM when the question mentioned the three percentages of 1RM (80%1RM, 90%1RM, 100%1RM). Powerlifters (PL) are represented in purple, CrossFit® practitioners (CF) in orange and control participants in grey. The box depicts median and the 25th and 75th quartiles. The whiskers show the minimum and maximum. Points represent the accuracy of each participant. *** Indicates a statistically significant difference between groups (p < 0.001).