An investigation of perceived exertion via whole body exertion and direct muscle force indicators during the determination of the maximum acceptable weight of lift

The objective of this study was to identify the perceived exertion mechanis ms (direct muscle force and whole body exertion) associated with the decisi on to change the weight of lift during the determination of the maximum acc eptable weight of lift (MAWL). Fifteen males lifted a box of unknown weight at a rate of 4.3 lifts/min, and adjusted the weight until their MAWL was r eached. Variables such as the predicted muscle forces and heart rate were m easured during the lifting exertion, as well as the predicted spinal loadin g in three dimensions using an EMG-assisted biomechanical model. Multiple l ogistic regression techniques were used to identify variables that were ass ociated with the decision to change the weights up and down prior to a subs equent lift. Results indicated that the force in the left erector spinae, r ight internal oblique, and left latissimus dorsi muscles as well as heart r ate were associated with decreases in the weight prior to the next lift. It appears that a combination of local factors (muscle force) and whole body exertion factors (heart rate) provide the feedback for the perceived exerti on when decreasing the weight. The up-change model indicated that the force s of the right erector spinae, left internal oblique, and the right latissi mus dorsi muscles were associated with the decision to increase the weight prior to the next lift. Thus, local factors provide feedback during the dec ision to increase the weight when starting from light weights. Collectively , these findings indicate that psychophysically determined weight limits ma y be more sensitive to muscular strain rather than spinal loading.