THE ROLE OF ISOINERTIAL TRAINING IN IMPROVING LOWER LIMBS STRENGTH

: The role of isoinertial training in improving lower limbs strength is the aim of this study, because, although the place and the role of isoinertial training is still debated in specialized literature, in practice it is gaining more and more consideration. Methods . We used the CMJ test from Optojump as a measurement method, and the intensive training was carried out over a period of 12 weeks with Romanian sprinters (N=10). As a way of comparison, the test, retest method was used. During the training, modern devices were used to monitor the training of Romanian sprinters, by introducing a device that acts mainly on the eccentric strength. The data were processed using the SPSS program. Significant statistical differences were found in the value of the height of the vertical jump (CMJ), (Z= 3.51, p=0.00).


Introduction
The concept of isoinertial training using flywheel devices has been developed in the recent past, with the first evidence supporting its effectiveness as a conditioning method dating back to the early 1990s [5], this study suggesting that increases in peak torque and performance parameters related to strength were greater following a program consisting of maximal concentric and eccentric muscle actions than resistance training using only concentric muscle actions.Because the increases in muscle fiber areas were small, it is also suggested that the increase in muscle strength demonstrated following short-term adapted resistance training is mainly due to neural adaptation [8].
Wheel exercises were originally proposed to alleviate neuromuscular dysfunctions and concomitant muscle atrophy of the musculoskeletal system in astronauts caused by the absence of gravity during long-duration space travel [15].Beato & Dello Iacono, in 2020, stated that the implementation of flywheel exercises, in special in the training of performance athletes requires some precise recommendations and a systematic approach and not an indiscriminate takeover of this type of training and applied in any kind of sport, and the research obtained in this regard can form the basis of work programs involving isoinertial training [2].Contemporary literature suggests that flywheel training as a valid alternative to traditional resistance training methods, but the evidence is not particularly strong [12], [17].Flywheel exercise vs. resistance exercise is analyzed throughout almost all studies involving isoinertial training [14], [1].
This practical method of quantifying isoinertial resistance training could be useful to athletes to help monitor training.

Method
We chose the CMJ test from Optojump (Microgate) to identify explosive strength in the lower limbs.The (CMJ) test is a simple, practical, valid and highly reliable test for the assessment of lower explosive strength.The vertical jump (CMJ) is one of the most popular tests to monitor an athlete's lower body muscle strength [13].
The basic research was carried out for 12 weeks and involved the application of the work program in the training of Romanian sprinters, its structure being adapted according to the competition category and the individual work plan with the device KBox4.
The subjects of the research are 10 Romanian athletes, aged between 16-25 years, who have been practicing athletics for at least 10 years and compete in the sprint events (100m and 200m).
They agreed to participate in this research and followed the established protocol, being able to withdraw from the experiment at any time, according to the consent statements.
The research sample was evaluated before and after the application of the work programs and they constantly received objective feedback as a result of the use of modern technology in training monitoring.During the research, the ethical provisions of the research, included in the Declaration of Helsinki, were also respected.
Thus, in addition to the classic means of training, modern devices were used to monitor the training of Romanian sprinters, but there was also intervention on the means aimed at the development of strength in the lower limbs, by introducing a device that acts mainly on the eccentric strength.

Descriptive statistics
Table 1   Explosive force testing with the OPTOJUMP device recorded an average value of 50.2 (±8.21cm) in the initial test, with values between 34.8 cm and 61.2cm and in the final test, the mean was 56.1 (±8.02cm), the results being between 41 and 67.2cm seconds.Skewness indices indicate a negative skew in the data (S<0) and Kurtosis indices show a flat distribution of the data (K<3).
The flight during the jump recorded an average value of 0.63 (±0.08s) in the initial test, with values between 0.53 and 0.77s, and in the final test, the arithmetic mean was 0.67 (±0.04s), the results being between 0.58 and 0.77 seconds.Skewness indices indicate a negative skew in the data (S<0) and Kurtosis indices show a flat distribution of the data (K<3).
Applying the Wilcoxon rank sum test to identify if there are significant differences between the values recorded at the initial and final testing of the explosive strength.identified by the height of the vertical jump (CMJ), a value of Z= 3.51 (Table 2) is observed, which is at a p=0.000, a value that statistically validates the applied work program.

Discussions
In our study, there were significant improvements in explosive strength (CMJ) values with the Optojump software, the non-parametric Wilcoxon test statistically validating the impact of the work program based mainly on isoinertial training on this parameter (Z=3.51,p =0.000).the modernization of the training process becomes imperative in predicting longterm sports performances, access to modern technology not being easy in Romania, at the level of sports clubs.Without a technology of the training process and without a correct and scientific monitoring of the preparation and the competition, Romanian athletes will not be able to compete on equal terms with foreign athletes who benefit from modern training devices, highperformance equipment, but also psychological monitoring.
At the same time, isoinertial training, which emphasizes the eccentric phase of the movement, applied in our research through the Kbox4 device, led to an improvement in the level of force manifestation in the lower limbs.
Another research also used a flywheel inertial device during the execution of specific soccer exercises.The isoinertial training lasted a month and a half and 34 junior football players participated in it.All the variables registered both in the test and in the pretest identified improvements in the participating athletes and emphasized the fact that using an isoinertial device to overload multidirectional movements in specific sports conditions leads to higher performance than conventional training.Skills like accuracy and speed are definitely improved by isoinertial training [7].
Another study involved 40 physically active students and proposed an isoinertial training with them, which involved 12 sessions of squats with the lower leg.The resistance was imposed by an electrical device.Their results were positive, namely that the device with a flywheel or an electric motor induced significant increases both in muscle mass and strength, but also in the students' vertical jumps [11].
Another research proposed two months of high-intensity training and isoinertial training on muscle mass and metabolic syndrome risk factors (N=12).The sample was composed of healthy adults.The isoinertial training proved to substantially increase the muscle strength and contributed to the increase of the subjects' quality of life [3].
Another 30 performance athletes were involved in a study in which their countermovement jumping performance was measured 4 times, at several times of the day.Significant differences were found in improvements in all the specific indicators in the after lunch and hours not necessarily in the morning.These results could be taken into account in the choice of training hours, as well as of the hours of the games [16].
Future research is needed to determine directions in order to gain an objective consensus on the methodological aspects of isoinertial training, so that this becomes a common language in both research and sport, regardless of the performance level and with the specifics of each sport separately [6].