Individual Torque And Neuromuscular Responses During A Sustained, Isometric Muscle Action Anchored To RPE = 7

Abstract

Purpose: Few studies have examined the neuromuscular patterns of responses during a sustained, isometric muscle action anchored to a constant rating of perceived exertion (RPE). Furthermore, previous studies have examined the mean responses for torque and the amplitude of the electromyographic signal (EMG AMP) during a sustained task anchored to RPE, but few have examined the individual responses and compared them with the composite models. Therefore, the aim of this study was to examine the individual responses and compare them to the composite models for torque and EMG AMP during a sustained, isometric forearm flexion muscle action anchored to RPE = 7. Methods: Twelve men (mean ± SD: age = 21.3 ± 1.7 yrs.; height = 181.1 ± 6.7 cm; body mass = 87.2 ± 17.0 kg) performed 2, 3 s forearm flexion maximal voluntary isometric contractions (MVIC) before a sustained, isometric, forearm flexion muscle action anchored to RPE = 7 until task failure (defined as torque that would require RPE > 7, or the torque was reduced to zero). During testing, torque was recorded on a Cybex 6000 dynamometer and surface EMG was used to record the EMG AMP of the biceps brachii (BB) and torque and EMG AMP were normalized to the greatest pre-test MVIC. Polynomial regression analyses (linear or quadratic) were used to examine the normalized torque and EMG AMP responses vs. time relationships. Results: Time to task failure was 678.0 ± 468.1 s and torque was reduced to zero for all of the subjects at task failure. For the composite models, there was a significant (p < 0.01, r = -0.84), negative linear torque relationship and a significant (p < 0.01, R = 0.97), positive quadratic EMG AMP relationship vs. Time. For torque, there was 83% (10/12) agreement with the composite model and 17% (2/12) of the subjects did not exhibit a relationship. For EMG AMP, there was 42% (5/12) agreement with the composite model, 8% (1/12) of the subjects exhibited a positive, linear relationship, 42% (5/12) of subjects exhibited negative relationships (linear or quadratic), and 8% (1/12) did not exhibit a relationship. Conclusion: The results of this study indicated that torque was continuously adjusted to maintain the predetermined RPE. In addition, there were consistent responses for torque but substantial inter-individual responses and moderate agreement with the composite model for EMG AMP.