Times for Peaks of Stress in Quadriceps Muscles During the Force-Velocity Test

During the Force-Ve-locity Test. Biomed J Sci & Tech Res 39(2)-2021. The aim of this study was to examine the surface Electromyogram (EMG) power spectral during an intermittent test with increasing intensity. Methods: Eighteen sedentary participants (age, 25 ± 4 years; height, 181 ± 3 cm, and weight, 77 ± 7 kg) completed two tests each: a maximum test to determine their physical fitness and a Force-Velocity test (FVt) to examine the EMG evolution of three su perficial quadriceps muscles [anterior (RA), Vastus Lateralis (VL), Vastus Medialis (VM)] at each sprint. Results: The increases of the root-mean-square (RMS in arbitrary unit) and mean power frequency (MPF in HZ) of EMG signal were observed for all sprints in RA, VL, and VM. Rapids increase of RMS and MPF up to 4-5 th seconds and a plateau or decline towards the 6 second were observed. While for RMS these increases were similar and larger for RF and VL compared to that of VM, for MPF, the result was opposite. We showed early and great implication of RF and VL during rapids actions as sprints on bicycle with slow and low contribution of VM important to the maintenance of effort. It would be important to advise a particular training of the RF and the VL in the cyclists to improve the speed of reaction and, of the VM for the maintenance of this speed. Conclusion: We observed similar times for peaks of stress in surface quadriceps muscles at all sprints despite the increase of power output.


Introduction
Among the intermittent tests with increasing loads, there is the Force-Velocity test (FVt) which consists of successive sprints of few seconds separated by recovery periods of a few minutes on an ergo cycle as Monark ergo cycle [1] against increasing braking loads. These authors found the increases of the mechanical power with the increase in the braking loads up to a maximal Power Output (POmax) despite the decrease in the pedaling speed, then its decrease despite the increase in the braking loads. The evolution in surface Electromyogram (EMG) power spectral and the Power Output (PO) concomitant with the increased in braking loads during the FVt were reported [2]. They showed an increase in EMG from the start of FVt to the peak load (Lpic), and then its decrease at the Lpic +1 kg. Thus, during the FVt, the muscle fatigue started after Lpic. Rouffet & Hautier (2008) found the root-mean-square (RMS) of EMG of Vastus Lateralis (VL) and Rectus Femoris (RF) muscles during the Isometric Maximal Voluntary Contractions (IMVC) and torque-velocity bicycling tests (T-V) increased from zero to approximately before 4 seconds during T-V and after 5 seconds during IMVC. Their results agreed those of Vandewalle (1987) who suggested the participants to reach the peak of pedaling speed before the end of the sprint (6 seconds). Due to these variations of the time to reach the maximum peak of EMG during intense exercise [3], the other question was to localize the time of muscle fatigue during each sprint of the FVt. For that, the aim of this study was to examine the EMG evolution of RF, VL, and VM of the quadriceps superficial muscles during the FVt to localize the peak of each EMG signal during the six seconds of each sprint.

Study Design
The approach was to determine the time to attack the peak of the EMG signal during each sprint of the FVt and, to examine if this time depends to the load and to the muscle. So, EMG signal were collected during each sprint in three quadriceps superficial muscles. In order to have good results during the FVt, only athletes suitable for intense and repetitive exercises such as soccer players were selected during maximum exercise tests.

Participants
Eighteen soccer players (age, 25 ± 4 years; height, 181 ± 3 cm, and weight, 77 ± 7 kg) participated in two tests each: a maximum test to determine their physical fitness and a FVt to examine the evolution of RMS and PMF for EMG in RF, VL, and VM at each sprint. Each participant was informed to refrain from doing intense exercise at least two days before the maximal exercise test or FVt.
Both tests were performed at ~20°C between 3 and 6 p.m. in a laboratory. All participants were informed of the experimental procedures complying with the ethical standards of Helsinki Declaration as revised in 1989, before giving written their consent to the adhesion of the study.

Procedure
The maximal exercise test allowed the assessment of the maximal heart rate (HRmax), maximal power output (POmax), and maximal oxygen uptake (VO2max). The protocol consisted of 2 min cycling against a workload of 1 kg at 60 rev·min-1 on the ergometer repeating the 2nd sprint against the load increased by 2 kg. When the velocity was under 130 rev·min-1, the load was increased by only 1 kg for each sprint to attain more precise the peak load (Lpic) for the peak power output (POpic). We assumed that the participant attained the POpic if an additional + 1 kg (Lpic + 1kg) to the Lpic induced a PO decrease. An automatic system was used to determine the peak velocity (Vpic) for each load and to calculate the PO as the product of load and Vpic (F×Vpic).
Surface EMG evolution of VM, RF, and VL were examined during the FVt for each participant. The EMG signals were collected by Beckman bipolar surface electrodes (9 mm diameter, physiosystems, Noisy-le-Grand), spaced by 20 mm distance, placed over the centre of the belly of each muscle of the right leg of each participant. The ground electrode was placed at the right wrist.
EMG signals were conditioned and stored on magnetic tape (TEAC R-71, TEAC Corp., Tokyo, Japan), after differential amplification with bandwidth ranging from 2 Hz to 2 kHz along with the output signal from the dynamometer. EMG signals were sampled by a spectrum

Discussion
The main result of this study was a rapid increase of EMG signals of the three superficial muscles of the quadriceps from the start of each sprint until 4-5 seconds, then a tendency to form a plateau or a decline until the end of the 6th second. This increase of EMG signals could inform on the muscle activity illustrated by RMS which was greater for the RF and VL muscles than for the VM muscle at all sprints. On the other hand, these increases in the activities of the three muscles became more significant with the increase in loads until the peak power reached at the load peak (Lpic). Then a slight drop in the activities of the three muscles was observed with Lpic + 1kg. Muscle fatigue was illustrated by smaller increases in the MFP of RF and VL muscles compared to that of VM whose intervention in VO2max were lower than those of professional and even amateur soccer players [6][7][8][9]. This study just needed adult's participants able to participate in a rough test on an ergocycle (the forcevelocity test) to avoid as much as possible, cases of accident [10] linked to poor physical condition during this kind of exercise. At all sprints, the evolution of the RMS and MPF of RF, VL or and VM during pedaling presented in Figure 1 showed the level of participation of these three superficial quadriceps muscle. The EMG signals of these muscles were previously illustrated.