Predictors of perceived effort in the shoulder during load transfer tasks

Abstract

The mechanism of muscular effort perception in the shoulder was examined in this experiment. Two shoulder biomechanical models and experimental muscle activity data were used to assess physical exposure for a series of reaching tasks. Effort perception was quantitatively correlated to these measures of physical loading, both at the resultant torque (r(2) = 0.50) and muscle activity model-based muscle force predictions (MFPs): r(2) = 0.42, electromyography (EMG): r(2) = 0.26) levels. Muscle data did not explain variation in effort perception more fully than torque data. The inclusion of subject and task variables improved the ability of each model to explain variability in effort perception (torque: r(2) = 0.74; MFP: r(2) = 0.67, EMG: r(2) = 0.64). These results suggest that effort perception may not be fully explained by only an image of the motor command, but is rather a complex integrative quantity that is affected by other factors, such as posture and task goals, which may be dependent on sensory feedback.

Relation between Perceived Effort and the Electromyographic Signal in Localized Effort Activities of Forearm Muscles

“…We believe that the reason for the difference between the performances of the EMG models in the two studies might be due to the fact that in our experiment the task had less variability (hand grip vs. reaching to several different locations). This premise is in line with Dickerson et al [14], who found that when the reaching location was part of the model, the EMG model had an average R squared value of 0.64. It should be noted here that in all three of our experiments, only about one third of the muscles that are involved in producing the motion were measured.…”

“…In our experiments (handgrip force), the R-squared value for the applied load based model was 0.572 and the values for the EMG model were up to 0.511, while the respective values that appear in Dickerson et al [14] were 0.51 and 0.27. We believe that the reason for the difference between the performances of the EMG models in the two studies might be due to the fact that in our experiment the task had less variability (hand grip vs. reaching to several different locations).…”

“…We compared the predictive abilities of models based on load (force and torque) to those based on EMG in our experiments and in the experiments of Dickerson et al [14]. In our experiments (handgrip force), the R-squared value for the applied load based model was 0.572 and the values for the EMG model were up to 0.511, while the respective values that appear in Dickerson et al [14] were 0.51 and 0.27.…”

“…To the best of our knowledge, the study of Dickerson et al [14], which researched shoulder load during reaching tasks, is the only study of the combined effect of multiple muscles (as measured by EMG) and load level on perceived effort. The study illustrates the importance of the relationship between EMG and perceived effort for understanding the factors that determine human perception of effort.…”

Magnitude of force perception errors during static contractions of the knee extensors in healthy young and elderly individuals

“…Cooper et al (1979) and Pincivero et al (2000) assessed the MVC at 90º and 60º of knee flexion, respectively, whereas we used an angle of 75º. At the shoulder, previous studies have shown that the shoulder angle modified the perceived effort during load transfer tasks (Dickerson, Martin, & Chaffin, 2006, 2007.…”