A standardization method to compare isotonic vs. isokinetic eccentric exercises

Abstract

The present study aimed to standardize isotonic (IT) and isokinetic (IK) eccentric exercises by equalizing the amount of work and the angular velocity at two intensity levels, to be able to compare specific effects of these exercise modes on the neuromuscular system. Fourteen subjects participated in three test sessions consisting of two IT and two IK sets on a customized isokinetic dynamometer. IT sets were comprised of 8 eccentric contractions of the knee extensors at 120% of the maximal repetition (1RM) in the first two sessions, and 100% in the third session. IK sets were performed at the same mean angular IT velocity and stopped when the amount of work performed corresponded to the IT set. External work, angular velocity and Root Mean Square (RMS) of electromyographic activity of three superficial muscles of the quadriceps femoris were calculated. Results showed concordance of work and angular velocity for each test session. Both modes involved the same number of repetitions at 120% and fewer repetitions in IK mode at 100% of 1RM. Work and RMS values remained steady in all sets. This study allowed the standardization of isotonic and isokinetic eccentric exercises, a first step before determining their specific effects on neuromuscular function.

A Methodologic Approach for Normalizing Angular Work and Velocity During Isotonic and Isokinetic Eccentric Training

“…This process equalizes the contraction time between modes while the specificity of IT and IK training stimulus is conserved. 2 Even standardized, both training modes elicit different torque-angle and velocity-angle relations that could induce specific effects on the neuromuscular system. Therefore, the effects of standardized training would be attributable only to the biomechanical characteristics of each exercise mode.…”

“…Applying overload in the IT condition generates higher torques and a greater amount of work in IT mode and involves the same number of repetitions in both modes. 2 The longer duration of this overload period might have eliminated potential differences during the first stage of training.…”

“…Isotonic exercise stresses the neuromuscular system mainly at the beginning and end of the muscle contraction because of the mechanical leverage points throughout the range of motion (ROM), whereas with IK exercise, muscle contraction is performed against an accommodating resistance that theoretically allows a maximal contraction throughout the entire ROM at a preset constant velocity. Therefore, these 2 exercise modes induce different mechanical stimuli on the skeletal muscle system, 2 suggesting that each mode might induce specific adaptive processes of the neuromuscular system and the muscle-tendon unit and specific changes on torque-angle and torque-velocity relationships through different loading mechanisms. 3 Attempts to determine the effects of IT and IK training on muscle strength have produced conflicting findings.…”

“…This standardization method has been adapted effectively for eccentric contractions using a test-retest design. 2 These investigators collectively have demonstrated that this standardization procedure can be applied to both concentric and eccentric muscle contractions. Although this method was established during 1 bout of exercise, 2,7 it also could be used in the long term with standardized IT and IK eccentric modes.…”

“…2 These investigators collectively have demonstrated that this standardization procedure can be applied to both concentric and eccentric muscle contractions. Although this method was established during 1 bout of exercise, 2,7 it also could be used in the long term with standardized IT and IK eccentric modes. Therefore, the purpose of our study was to examine whether the standardization protocol previously used could be adjusted adequately and applied effectively to a 9-week eccentric training program.…”