Effects of a single habituation session on neuromuscular isokinetic profile at different movement velocities

Abstract

Single training session (STS) may increase the power output (i.e., maximal torque) in different contraction types; however, little is known about the neuromuscular adaptations to reach this enhancement. In this way, the present study examined the differences between knee extensors EMG, kinematics, and dynamometry at 60 and 180° s(-1) before (PRE) and after (POST) a STS. Seventeen healthy males completed three different tasks: (1) 5-maximal isokinetic knee extensions, without previous habituation (PRE) at 60 and 180° s(-1); (2) in the same day and after a proper rest, two bouts of 5-maximal isokinetic contractions (STS) at 60 and 180° s(-1); and (3) in a new visit, POST consisted in new 5-maximal isokinetic contractions at 60 and 180° s(-1). The main parameters examined were: knee extensors peak torque (PT), total work (TW), EMG (prior to the movement onset, agonist and antagonist activation), rate of force (RFD), and velocity development (RVD). There was significant increase in PT [12% (60° s(-1)) and 8.7% (180° s(-1))] and TW [13.5% (60° s(-1)) and 10.7% (180° s(-1))] from PRE to POST sessions. Increases in RFD were found for both velocities (p < 0.05); however, RVD and vastus lateralis EMG prior to the movement onset were significantly higher for POST only at 60° s(-1). The RFD percentage of change (%change) was significantly correlated to %change for PT at 60° s(-1) (r(2) = 0.53) and 180° s(-1) (r(2) = 0.45). In conclusion, STS improves neural strategies to contract muscles stronger and faster at the slowest velocity, while higher velocities present different adaptations and might need more practice to further adaptations.

Maximal isokinetic peak torque and emg activity determined by shorter ranges of motion

“…In the same way, as was previously verified [2,14], there were minimal changes in EMG related to movement velocity. This issue as of yet has no consensus in the literature on the subject, primarily because of the wide range of studied velocities [7].…”

“…However, existing literature presents some divergent results on maximal torque and joint positions: (1) the use of short RoMs (partitions of 15° to 30° throughout the full RoM) provides similar results compared to full RoM at low and moderate speeds, but also presents noteworthy inconsistencies [5,6], while (2) other studies have verified that the further from the optimized length-tension joint position, the lower the maximal torque [3,4,7].…”

“…Contraction speed, which affects generating peak torque, has also been widely investigated, but EMG activity was found not to follow the same pattern and shows no changes among different contraction speeds [2,7,9].…”

“…Even modest sports associations have procedures for measuring maximal capacity (using standard resistance training equipment), while more sophisticated centers may make use of iso kinetic equipment (which provides constant velocity throughout the entire range of motion). In addition, an evaluation of muscular activity by use of electromyography [EMG] during maximal effort provides more accurate results and optimizes readings during testing and training [1,2]. This isokinetic procedure usually requires a full range of motion (RoM) from which the moment of maximal torque is selected for analysis.…”

Balance Exercises Circuit improves muscle strength, balance, and functional performance in older women

“…Data were collected from the Biodex software and analyzed in MATLAB R2010a software. Data were butterworth-filtered at 10 Hz and calculation of RFD was performed according to procedures described elsewhere (Corvino 2009;Oliveira et al 2010). Briefly, throughout the contraction, RFD was derived as the average slope of the moment-time curve (Δtorque/Δtime) over time.…”