STRENGTH OPTIMISATION BY USING CROSS-TRAINING IN THE PHYSICAL EDUCATION LESSON FOR MILITARY STUDENTS

. Cross-training is one of the most revolutionary training methods, which has become increasingly popular at international and national levels. Cross-training includes aerobic and anaerobic exercises, functional exercises, weight training exercises, Total (Body) Resistance Exercises (TRX), gymnastics and athletics exercises, and the key to this training method is the way of combining the exercises and the intensity at which they are performed. Military physical education aims at improving the overall physical development, exercise capacity and health status of military students, all of this leading to the formation of a well-trained military person able to withstand the stress and tensions existing in this profession. The purpose of the study is to provide effective solutions for modernising the military physical education lesson and to analyse the effects of using the specific cross-training method on strength as a motor ability. The research participants were 60 male military students aged between 18 and 23 years, who were divided into two groups, namely the experimental group and the control group. The research methods used in this study are: observation, experiment, mathematical statistics and graphical method. The experiment highlights that students using the specific cross-training intervention have significantly improved their strength in the main muscle groups. In conclusion, the interpretation of the results obtained by participants reveals that the use of this training method in the military physical education lesson, as a compulsory subject in military higher education, is an effective solution for strength optimisation.


Introduction
Progress in higher education is related to the regular educational reforms caused by the continuous development of society; thus, the emergence of new information in every field of knowledge contributes to restructuring educational programmes, academic curricula and the general structure of education (Druz et al., 2017).
The physical education of students is one of the priority directions in the formation and promotion of a nation's health; it is an integral part of the humanitarian education system of students and plays an important role in building the general and professional knowledge but also the personality traits of future specialists in the field (Yarmak et al., 2017).
One of the challenges faced by physical education teachers during lessons is to give students the opportunity to improve their motor potential according to each one's individual characteristics (Tudor et al., 2014).Istrate and Bălăceanu (2021) also believe that modernising the current military physical education system should be a priority, given that it is a basic component of the educational process.
Systematic exercise is known to improve health and shape temperament and attitudes, thus contributing to the formation of personality.
Physical education specialists from all over the world highlight that physical education plays an important role in health promotion and that the use of its specific means "promotes the development of physical qualities, stimulates the work of functional systems of the body, which are an effective factor in preparing for professional activity, and affects the formation of a healthy lifestyle" (Petrova et al., 2022).Listkova (2019) states that the working capacity of students can be improved or maintained at an increased level through a physical training process adapted to the curriculum, which is nowadays quite exhausting.The above author emphasises that university physical education classes do not provide the necessary level of physical training, suggesting that the solution to this problem would be to either attend additional lessons based on various forms of physical training or get engaged in sports activities.
In recent years (due to NATO membership), there has been an attempt to refresh the field of physical education in public defence institutions, and participation in international missions with our allies has been a good opportunity to observe the role of physical training and how to prepare modern armies.
"A physically ready and resilient military is essential for national security, and the military places a premium on physical fitness training and testing."(Nindle et al., 2015) Kyröläinen et al. ( 2017) also think that "maintaining or improving physical performance among professional soldiers in various military environments is crucial for overall military readiness".
Physical training in the military field should be designed so as to provide the military with the exercise capacity necessary to meet the specific objectives of the activity carried out.(Băiţan, 2019).
"The exercise regime known as CrossFit appears to have sparked one of the biggest fitness trends in the twenty-first century."(Dawson, 2017) According to Partridge et al. (2014), "CrossFit is a growing fitness trend in the United States" and is nowadays increasingly used in the military physical training process at the international level.McCarthy (2021) states that "cross-training is trademarked, high-intensity exercise program combining gymnastics, weight lifting, and metabolic movement".Petrova et al. (2022) have noted that this training method is gaining increasing popularity among modern young people.These authors add that the uniqueness of cross-training is given by the many variations in the combination of exercises, specifying that each training session is significantly different from the previous one.
Cross-training can provide effective solutions to optimise the military physical education lesson, given that it improves the physical training of young students and increases their interest in physical education classes because this method differs from classic lessons, being a modern and attractive option.
These training methods can be competitive events during which an individual can compete against themselves (i.e., comparing with their previous workout time, repetitions or lifted weight) or others doing the same workout (Feito et al., 2018).
The cross-training method contributes to the improvement of physical training by developing strength, power, speed, endurance, mobility, agility, balance, coordination, etc. (Han et al., 2021).
Cross-training is a reinterpretation of traditional military training, which combines aerobic and anaerobic exercises, exercises that simultaneously involve several joints and muscle groups, body weight exercises, weight training exercises as well as gymnastics and athletics exercises performed at high intensity (Glassman, 2007).
The American College of Sports Medicine (ACSM) conducted a survey of its worldwide membership and found that high-intensity training methods were the main trend in the fitness industry (Thompson, 2014).According to Haddock et al. (2016), this method of optimising physical training successfully replaces traditional workouts in US military units.At national level, the implementation of new training trends prove to be useful, their influence on physical training being revealed by recent studies conducted on military students (Tudor et al., 2020).
Motor ability is a fundamental factor in the military training process (Pelmuş, 2020).Strength, together with the other components of motor ability, is particularly important in the activity carried out by the military, being necessary in most of the actions performed and influencing their exercise capacity (Istrate, 2020).
The purpose of the study is to provide effective solutions for modernising the military physical education lesson and to analyse the effects of using the specific cross-training method on strength as a motor ability.

Participants and Procedure
The research participants were 60 male military students aged between 18 and 23 years, who were divided into two groups, namely the experimental group (30 students) and the control group (30 students).They were assessed twice through an initial test and a final test, which included five strength exercises specific to the field of military physical education, namely: push-ups, pull-ups, sit-ups, standing long jump and Vertical jump test (Sargent jump test).
The study was conducted between September 2021 and March 2022.During this period, the experimental group performed three cross-training workouts per week, while the control group engaged in three bodybuilding workouts per week.Overall, the experimental group attended 40 training sessions using five specific cross-training programmes that were repeated eight times each.Physical training programmes largely consisted of body weight exercises and disc or kettlebell exercises.
It should be noted that, in addition to the three weekly workouts, a number of participants trained individually performing four to five training session per week, which led to much more significant progress for some of them.We will describe below one of the five programmes used by the experimental group throughout the study period: 600 m run; 50 pullups; 100 push-ups; 150 squats; 600 m run.
Ways of approaching the programme: it begins and ends with the 600 m run.Pull-ups, push-ups and squats are performed until each set is completed (exactly in the specified order, namely 50 pull-ups, 100 push-ups and 150 squats) or they can be split but keeping the same order (e.g.: 5 pull-ups -10 push-ups -15 squats or 10 pull-ups -20 push-ups -30 squats).

Methods
The research methods used in this study are: observation, experimental method with two variables (to verify the effects of the experimental intervention on the behaviour of participants), mathematical statistics and graphical method (to analyse, interpret and visualise the results).We also used descriptive indicators such as arithmetic mean, median, standard deviation (which provides details about the homogeneity of the sample), range, coefficient of variation, the Dependent t test or Paired Samples t Test (which provides the examiner with information about the initial test -IT and final test -FT for a group of participants) and the Independent t test (used to compare the results obtained by the two groups).The following Information Technology Products were used for the statistical data processing: SPSS V23 (Statistical Package for the Social Sciences), Minitab V16 and Microsoft Office 2019 (Word and Excel).

Experimental group
 Test 1: Push-ups (Table 1) In the push-up test, the average number of repetitions performed by the experimental group increased by 22 (67.6%), from 32.57 in the initial test to 54.57 repetitions in the final test.With a 95% confidence interval (CI), the mean difference is in the range (19.14; 24.86).The dispersion of the results is inhomogeneous in the initial test and homogeneous in the final test.According to the Dependent t Test, the mean difference is statistically significant, with p < 0.001 (< 0.05) for t = 15.748> 2.045 (t critical value).The effect size index (2.88)reveals that this difference is very large.The average scores obtained by the experiment group in the initial and final tests are shown in Figure 1.In the pull-up test, the average number of repetitions performed by the experimental group increased by 6.50 (83.3%), from 7.80 in the initial test to 14.30 repetitions in the final test.With a 95% confidence interval (CI), the mean difference is in the range (5.95; 7.05).The dispersion of the results is inhomogeneous in the initial test and homogeneous in the final test.According to the Dependent t Test, the mean difference is statistically significant, with p < 0.001 (< 0.05) for t = 24.059> 2.045 (t critical value).The effect size index (4.39)reveals that this difference is very large.The average scores obtained by the experimental group in the initial and final tests are shown in Figure 2.
 Test 3: Sit-ups (maximum number of repetitions within one minute) (Table 3)     In the vertical jump test, the average score obtained by the experimental group increased by 9.26 cm (19.5%), from 47.42 in the initial test to 56.68 cm in the final test.With a 95% confidence interval (CI), the mean difference is in the range (7.77; 10.77).The results are homogeneously dispersed in both tests.According to the Dependent t Test, the mean difference is statistically significant, with p < 0.001 (< 0.05) for t = 12.623 > 2.045 (t critical value).The effect size index (2.30)reveals that this difference is very large.The average scores obtained by the experimental group in the initial and final tests are shown in Figure 5.

Control group
 Test 1: Push-ups (Table 6)  In the push-up test, the average number of repetitions performed by the control group increased by 0.30 (1.0%), from 31.20 in the initial test to 31.50 repetitions in the final test.With a 95% confidence interval (CI), the mean difference is in the range (-0.86; 1.46).The dispersion of the results is inhomogeneous in the initial test and homogeneous in the final test.According to the Dependent t Test, the mean difference is statistically insignificant, with p = 0.600 > 0.05 for t = 0.530 < 2.045 (t critical value).The average scores obtained by the control group in the initial and final tests are shown in Figure 6.
 Test 2: Pull-ups (Table 7)  In the pull-up test, the average number of repetitions performed by the control group increased by 0.14 (2.9%), from 4.63 in the initial test to 4.77 repetitions in the final test.With a 95% confidence interval (CI), the mean difference is in the range (-0.33; 0.60).The dispersion of the results is inhomogeneous in the initial test and homogeneous in the final test.According to the Dependent t Test, the mean difference is statistically insignificant, with p = 0.564 > 0.05 for t = 0.583 < 2.045 (t critical value).The average scores obtained by the control group in the initial and final tests are shown in Figure 7.
 Test 3: Sit-ups (maximum number of repetitions within one minute) (Table 8)  In the sit-up test, the average number of repetitions performed by the control group increased by 3 (7.0%),from 42.90 in the initial test to 45.90 repetitions in the final test.With a 95% confidence interval (CI), the mean difference is in the range (2.42; 3.58).The dispersion of the results is relatively homogeneous in the initial test and homogeneous in the final test.According to the Dependent t Test, the mean difference is statistically significant, with p < 0.001 < 0.05 for t = 10.576> 2.045 (t critical value).The effect size index (1.93)highlights that this difference is very large.The average scores obtained by the control group in the initial and final tests are shown in Figure 8.
 Test 4: Standing long jump (Table 9) In this test, the average jump length of the control group increased by 1.73 cm (0.8%), from 215.50 in the initial test to 218.23 cm in the final test.With a 95% confidence interval (CI), the mean difference is in the range (0.35; 3.11).The results are homogeneously dispersed in both tests.According to the Dependent t Test, the mean difference is statistically significant, with p = 0.016 < 0.05 for t = 2.570 > 2.045 (t critical value).The effect size index (0.47) highlights that this difference is small to medium.The average scores obtained by the control group in the initial and final tests are shown in Figure 9.
 Test 5: Vertical jump test (Sargent jump test) (Table 10) In the vertical jump test, the average score obtained by the control group decreased by 0.72 cm (1.7%), from 41.42 in the initial test to 40.70 cm in the final test.With a 95% confidence interval (CI), the mean difference is in the range (-1.34; -0.09).The dispersion of the results is relatively homogeneous in the initial test and homogeneous in the final test.According to the Dependent t Test, the mean difference is statistically significant, with p = 0.026 < 0.05 for t = 2.351 > 2.045 (t critical value).The effect size index (0.43) highlights that this difference is small to medium.The average scores obtained by the control group in the initial and final tests are shown in Figure 10.

Experimental group vs. control group (final tests)
 Test 1: Push-ups (Table 11) The average number of repetitions performed by the experimental group in the final pushup test is higher by 23.07 (42.3%) than that of the control group.The average scores of the two groups are 54.57repetitions for the experimental group and 31.50 repetitions for the control group.According to Levene's Test for Homogeneity of Variances, the two samples have equal dispersions, with Sig.= 0.138 > 0.05 for F = 2.258.The Independent Samples t Test reveals that the mean difference is statistically significant, with p < 0.001 < 0.05 for t = 7.358 and df = 58.The effect size index shows that the mean difference is very large.The average scores obtained by the two groups in the final push-up test are shown in Figure 11.
 Test 2: Pull-ups (Table 12) The average number of repetitions performed by the experimental group in the final pullup test is higher by 9.53 (66.7%) than that of the control group.The average scores of the two groups are 14.30 repetitions for the experimental group and 4.77 repetitions for the control group.According to Levene's Test for Homogeneity of Variances, the two samples do not have equal dispersions, with Sig.< 0.001 < 0.05 for F = 19.517.The Independent Samples t Test reveals that the mean difference is statistically significant, with p < 0.001 < 0.05 for t = 8.058 and df = 40.The effect size index shows that the mean difference is very large.The average scores obtained by the two groups in the final pull-up test are shown in Figure 12.
 Test 3: Sit-ups (maximum number of repetitions within one minute) (Table 13) The average number of repetitions performed by the experimental group in the final sit-up test is higher by 10 (17.9%) than that of the control group.The average scores of the two groups are 55.90 repetitions for the experimental group and 45.90 repetitions for the control group.According to Levene's Test for Homogeneity of Variances, the two samples have equal dispersions, with Sig.= 0.791 > 0.05 for F = 0.071.The Independent Samples t Test reveals that the mean difference is statistically significant, with p < 0.001 < 0.05 for t = 4.439 and df = 58.The effect size index shows that the mean difference is very large.The average scores obtained by the two groups in the final sit-up test are shown in Figure 13.
 Test 4: Standing long jump (Table 14) The average jump length of the experimental group is higher by 18.34 cm (7.7%) than that of the control group.The average scores of the two groups are 236.93cm for the experimental group and 218.23 cm for the control group.According to Levene's Test for Homogeneity of Variances, the two samples have equal dispersions, with Sig.= 0.347 > 0.05 for F = 0.898.The Independent Samples t Test reveals that the mean difference is statistically significant, with p < 0.001 < 0.05 for t = 4.873 and df = 58.The effect size index shows that the mean difference is very large.The average scores obtained by the two groups in the final standing long jump test are shown in Figure 14.
 Test 5: Vertical jump test (Sargent jump test) (Table 15) In the vertical jump test, the final average score of the experimental group is higher by 15.98 cm (28.2%) than that of the control group.The average scores of the two groups are 56.68 cm for the experimental group and 40.70 cm for the control group.According to Levene's Test for Homogeneity of Variances, the two samples have equal dispersions, with Sig.= 0.965 > 0.05 for F = 0.002.The Independent Samples t Test reveals that the mean difference is statistically significant, with p < 0.001 < 0.05 for t = 9.934 and df = 58.The effect size index shows that the mean difference is very large.The average scores obtained by the two groups in the final vertical jump test are shown in Figure 15.

Discussion and Conclusion
The purpose of this study was to provide solutions to optimise the physical training of students in military higher education, given that it is an essential component for the personnel working in this field.By introducing cross-training in military physical education lessons, we will help young military people become stronger and more physically fit (Băiţan, 2021).
The training method proposed in the present paper has become very popular among military and professional athletes but, also, among people who voluntarily engage in exercise.Cross-training has multiple benefits (improved health, body composition, strength and agility, increased cardiovascular fitness) but also involves the risk of injury (because very highintensity levels are required during the workouts).
Cross-training proves its usefulness due to the following advantages: low costs (minimum equipment is needed), shorter training time, constant exercise variations (which forces the body to continuously adapt to new challenges and combats boredom).On the other hand, the exercises simultaneously engage several muscle groups and several joints, thus increasing the operational capacity of the military.
Currently, the scientific literature does not provide large-scale studies regarding the implementation of these programmes in military education and the benefits/risks of this training method; however, the existing studies reveal important data about the strengths of using this method in order to improve the physical training not only of the military but also of all those who use these training programmes.
In a study conducted on students from a university in Bari (Italy), the results obtained by the experimental group after performing a cross-training programme over a period of eight weeks highlight significant physical and mental improvements for all participants (Cataldi et al., 2021).
Using the cross-training method can be an effective solution for the physical training of athletes, not only of the military, which is demonstrated by studies conducted on kickboxing (Ambrozy et al., 2022) and judo fighters (Arman et al., 2022).In the studies carried out, the inclusion of cross-training in the training of athletes had a positive effect, improving both their general and specific physical fitness.
In the field of physical education and sport, new methods of practice should be implemented because traditional methods are obsolete, and the lesson content should be as varied as possible and designed so that students can test and overcome their physical and mental limits to achieve the objectives pursued, and cross-training could be a solution in this regard.Due to the very high-intensity level required by this training method, it brings new challenges to students while ensuring greater diversity in the physical education lesson and can be a very effective means of increasing their physical performance.
The results obtained in the strength tests indicate a rather large difference between the two groups of students participating in the research.By comparing the initial and final tests for the push-up, pull-up, sit-up, standing long jump and vertical jump exercises, it can be seen that the experimental group has achieved significant performance.
The interpretation of the results obtained in the present study suggests that the crosstraining method proves to be an effective solution to optimise strength in military students.
Authors' Contributions: All authors have equally contributed to this study.

Informed Consent Statement:
The participants provided their written informed consent to participate in this study.

Figure 2 .
Figure 2. Average scores for the pull-up test -Experimental group

Figure 3 .
Figure 3. Average scores for the sit-up test -Experimental group

Figure 4 .
Figure 4. Average scores for the standing long jump test -Experimental group

Figure 6 .
Figure 6.Average scores for the push-up test -Control

Figure 7 .
Figure 7. Average scores for the pull-up test -Control

Figure 8 .
Figure 8.Average scores for the sit-up test -Control

Funding:
The work of Gabriel Cracana was supported by the "PROINVENT" Project, Contract no.62487/03.06.2022 -POCU/993/6/13 -Code 153299, funded by The Human Capital Operational Programme 2014-2020 (POCU), Romania.Institutional Review Board Statement:The study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of the National University of Physical Education and Sports in Bucharest, Romania (ID: 123/2501).

Table 1 .
Interpretation of the results Repetitions  Initial test  Final test Figure 1.Average scores for the push-up test -Experimental group

Table 2 .
Interpretation of the results Repetitions Initial test  Final test

Table 3 .
Interpretation of the results Repetitions Initial test  Final test

Table 4 )Table 4 .
Interpretation of the results Centimetres Initial test  Final test

Table 5 )Table 5 .
Interpretation of the results Centimetres  Initial test  Final test Figure 5. Average scores for the vertical jump test -Experimental group

Table 6 .
Interpretation of the results Repetitions Initial test  Final test

Table 7 .
Interpretation of the results Repetitions Initial test  Final test

Table 8 .
Interpretation of the results Repetitions Initial test  Final test

Table 9 .
Interpretation of the results Centimetres  Initial test  Final test Figure 9. Average scores for the standing long jump test -Control

Table 10 .
Interpretation of the results Centimetres  Initial test  Final test Figure 10.Average scores for the vertical jump test -Control

Table 13 .
Comparative results