The Effect of 12-Week Core Strengthening and Weight Training on Muscle Strength, Endurance and Flexibility in School-Aged Athletes

s study investigates the effect of 12-week core strengthening and weight training on muscle strength, endurance and exibility in school-aged athletes. Ninety male athletes at the age of 12 were randomly divided into three equal groups (30 in each). Group 1 underwent core strengthening training, group 2 underwent weight training, and group 3 was the control. The training was for12 weeks, with three sessions per week (one hour per session). Prior to and after the training, abdominal strength, endurance, and exibility were evaluated using the sit-ups test, the Cooper 12 min run test and the sit and reach test. The analysis of variance was used to analyze pre- and post-intervention data. The results showed that both the core strength training group and the weight training group signi cantly (p= 0.00) improved in ab- dominal strength, represented by the number of sit-ups (from18.70 3.20 to22.21 3.50 and from17.60 3.29 to21.60 3.63 , respectively); endurance, represented by distance covered in 12 min(from1817 185.78 m to2008.97 214.79 m and from1806 237.25 m to2002.59 83.32 m

results showed that both the core strength training group and the weight training group signi cantly (p= 0.00) improved in ab- dominal strength, represented by the number of sit-ups (from18.70 3.20 to22.21 3.50 and from17.60 3.29 to21.60 3.63 , respectively); endurance, represented by distance covered in 12 min(from1817 185.78 m to2008.97 214.79 m and from1806 237.25 m to2002.59 83.32 m , respectively); and exibility, represented by the sit and reach distance (from23.48 2.75 cm to 25.96 2.38 cm and from23.66 2.92 cm to25.86 2.55 cm , respectively) when compared to the control group (from17.20 3.20 to16.39 2.69 ; from1813 224.69 m to1778.15 05.28 m ; from 23.46 3.06 cm to21.76 2.56 cm ). More speci cally, abdominal strength and endurance improved slightly more in the weight training group than in the core strength training group, whilst exibility increased slightly more in the core strength training group than in the weight training group. These ndings indicate that both core strengthening training and weight training are effective in improving physical tness in school-aged athletes; however, the improvement is to differing extents regarding their endurance, exibility, and abdominal strength. Keywords: Cooper 12 min run test; core strengthening exercises; resistance exercises; sit and reach test; sit-up test 1. Introduction Resistance training represents a main part of performance and health-oriented exercise programs [1]. It increases muscle strength, power, endurance, and hypertrophy, which are bene cial to improving motor performance [1]. Among potential health bene ts may be in- cluded “reduced body fat, increased basal metabolic rate, decreased blood pressure and the cardiovascular demands to exercise, improved blood lipid pro les, glucose tolerance, and insulin sensitivity, increased muscle and connective tissue cross-sectional area, improved functional capacity, and relieved low back pain” [1]. Recently, exercises that strengthen and stabilize core musculature have become a part of conditioning programs for competitive athletes as well as recreationally physically Appl. Sci.2022,12, 12550.

Appl. Sci.2022,12, 12550 2 of 10 active individuals [2]. These exercises are usually performed alone [3–7] or in combi- nation with plyometric and body strengthening exercises [8] under stable and unstable conditions [3,5,6,8] . The intervention usually takes from 4 to 8 weeks [3–8], twice per week in durations of 25–45 min when it is a part of warm-up [3,5,6,8] and 60–75 min when it is performed as part of the standard training program [4,7]. Training programs focused on the development of core muscle strength, muscular endurance, and postural and core stability [3,6–8] have been found to improve functional movements [3,5,7,8] and consequently also athletic performance [4,6]. While core strength- ening exercises increase activation of local stabilizers and global mobilizers and facilitate the transfer of muscle power, core stabilization exercises improve control of the lumbar spine [4,5,9]. A recent systematic review by Luo et al. [10] showed that overall control of motion and the transfer of force to the terminal segment during athletic tasks can be opti- mized by core strength exercises; thus, they should be included in daily training routines. Furthermore, these exercises may be bene cial for prevention of back problems in young athletes. As core musculature provides stability for effective control of body motions and force production in the lower extremities, its de ciency or imbalance can increase fatigue and decrease muscular endurance, leading to greater susceptibility to injuries [11]. Therefore, most current conditioning programs in schools also include exercises strengthening core musculature, in addition to traditional resistance exercises. Research so far has been aimed at investigations of the relationship between core stability and ath- letic performance, as well as the assessment of the effectiveness of core strengthening and stabilization exercises in children and adolescents [3–5,7–9,12–18]. Nevertheless, there are only a few studies dealing with young athletes. For instance, a 6-week core conditioning intervention enhanced endurance of the core muscles (lateral and prone plank, parallel dynamic back extension on a roman chair, static and dynamic curl-ups) in school-aged children [19]. Similarly, a 10-week Quad-Core training improved strength and endurance of the core muscles in school football players

there are only a few studies dealing with young athletes. For instance, a 6-week core conditioning intervention enhanced endurance of the core muscles (lateral and prone plank, parallel dynamic back extension on a roman chair, static and dynamic curl-ups) in school-aged children [19]. Similarly, a 10-week Quad-Core training improved strength and endurance of the core muscles in school football players [20]. Furthermore, an 8-week core training using body weights along with handball training improved vertical vault, exibility, 20 m speed, balance, right hand clutch power, agility, back-leg strength, dribbling, quick passes, and point shooting in 9–10-year-old male handball players [21]. The trunk muscle strength and dynamic balance was also improved after one year of simple core muscle training in pediatric male soccer players [22]. Moreover, one-leg, but not bipedal, vertical jump height was increased after a 4-week integrated program focused on core stabilization in prepubertal athletes [4]. Postural balance control, but not jump ability, was improved after an 8-week integrated neuromuscular training aimed at dynamic balance, core stability, and plyometrics in junior alpine skiers [8]. Throwing velocity was increased after progressive isolated unstable core stability training in young handball players [6]. Similarly, maximal throwing velocity was increased after a 6-week sling training based on core stability in young female handball players, indicating that rotational velocity in multisegmental move- ments can be improved following core stability training including unstable, closed kinetic chain motions due to a more stable and stronger lumbopelvic-hip complex [4]. Ball-exit velocity, but not throwing velocity, was increased after a 6-week isolated resistance training program in young baseball players [7]. Core muscle stability was improved after a 6-week Swiss ball training, whereas there were no signi cant changes in myoelectric activity of the back and abdominal muscles, running posture, running economy, and treadmill VO2maxin young male athletes [3]. However, in comparison with a predominant number of studies that conducted research on competitive athletes, a scarce amount of research deals with core strengthening exercises and their ef ciency in improving overall tness in school-age athletes. In order to partly ll this gap in the literature, we have investigated the

posture, running economy, and treadmill VO2maxin young male athletes [3]. However, in comparison with a predominant number of studies that conducted research on competitive athletes, a scarce amount of research deals with core strengthening exercises and their ef ciency in improving overall tness in school-age athletes. In order to partly ll this gap in the literature, we have investigated the effect of 12-week core strengthening training and weight training on physical tness among school-age athletes. Both training programs have been assumed to be effective in improvement of their physical performance; however, their effectiveness is assumed be to different extents regarding the endurance, exibility, and abdominal strength.

Appl. Sci.2022,12, 12550 3 of 10 2. Materials and Methods 2.1. Participants Ninety male school-age athletes were randomly divided into three equal groups (Table). Experimental group 1 underwent core strengthening training, experimental group 2 underwent weight training, and group 3 was the control. Participants were informed about the main purpose of this study and related procedures. They were examined by a quali ed physician and all of them were t for participating in this study. Participants were free to withdraw their consent if they felt any discomfort during training programs. There were no dropouts in this study. The procedures followed were in accordance with the ethical standards on human experimentation stated in compliance with the 1964 Helsinki Declaration and its later amendments. Table 1.Characteristics of participants (mean SD). Groups of Athletes n (1) Age (Years) Height (cm) Body Mass (kg) Core strength training group (G1)30 12.3 0.3 142.4 6.1 33.0 6.1 Weight training group (G2) 30 12.2 0.3 141.8 5.9 33.3 6.2 Control group (G3) 30 12.2 0.3 142.0 6.0 33.1 6.1 2.2. Experimental Protocol Group 1 underwent core strengthening training that included exercises such as side planks, bridges, leg-raises, utter kicks, butte y sit-ups, dead bugs, and rolling like a ball (3–4 sets). Group 2 underwent weight training that included exercises such as military presses, back presses, biceps curls, bench presses, heel raises, half squats, and lunges (2–3 sets,8–12 reps). The increase in training load re ected individual capacity to respond and adapt to particular exercise. Interventions were administrated for a duration of 12 weeks. The number of sessions per week was con ned to three alternative days and each session lasted an hour. Both experimental groups underwent their respective training program simultaneously under the supervision of the research scholar. Control group 3 was not exposed to any conditioning program. Abdominal strength, exibility, and endurance were evaluated before and after train- ing programs using the sit-ups test, the sit and reach test, and the Cooper 12 min run test. The items selected to measure these abilities were the number of sit-ups, the sit and reach distance, and the distance

scholar. Control group 3 was not exposed to any conditioning program. Abdominal strength, exibility, and endurance were evaluated before and after train- ing programs using the sit-ups test, the sit and reach test, and the Cooper 12 min run test. The items selected to measure these abilities were the number of sit-ups, the sit and reach distance, and the distance covered in 12 min. 2.2.1. Sit-Ups Test To evaluate the strength of abdominal muscles, participants performed repeated sit- ups [23]. An ICC of 0.96 (0.94–0.97) and CV of 2.02% ( 1.12–3.42%) signi es good reliability of this test [24]. Participants were instructed to lie on their backs with knees exed, feet on oor, and heels between 12 and 18 inches from the buttocks. Their arms were crossed over chest with hands on opposite shoulders. Feet were held to the mat by a partner. On “Ready” and “Go” the participants were asked to curl to a sitting position with arms contacting the chest. When their elbows touched their thighs, the sit-up was completed. Participant were then instructed to uncurl to a position where the mid-back contacts the mat. They were asked to complete as many sit-ups in this manner as possible in one minute. Only correctly performed sit-ups were counted. 2.2.2. Cooper 12 Min Run Test To evaluate their endurance, participants performed the Cooper 12 min run test [25]. Cooper [25] reported a correlation of 0.90 between VO2maxand the distance covered in a 12 min walk/run. The reported ICC (95% CI) for distance was 0.99 (0.96–0.99), for maximum heart rate it was 0.93 (0.80–0.98), and for rate of perceived exertion it was 0.68 (0.05–0.89) [26]. The reported CV for distance was 1.7%, for maximum heart rate it was 1.3%, and for rate of perceived exertion it was 7.5% [26]. Participants were asked to stand

Appl. Sci.2022,12, 12550 4 of 10 behind the start line of a 400 m track after a warm-up session. They were instructed to start running on the starter's gun. They were asked to run for 12 min as fast as possible. The distance covered in 12 min was recorded. 2.2.3. Sit and Reach Test To evaluate the lower back and hamstring exibility, participants performed the sit and reach test [27]. High values of ICC indicate that both versions, the chair sit and reach (0.92–0.96) [28] and the back saver sit and reach (0.99) [29], are reliable. An apparatus which had 25 cm mark equivalent to the point where the feet touch the box was used. Participants were asked to warm-up by performing slow stretching exercises. They were asked to “sit barefoot with the legs fully extended with the soles of the feet placed at against the horizontal cross board of the apparatus, with the inner edge of the sole placed 2 cm from the scale, keeping the knees fully extended, arms evenly stretched, and palms down”. Participants were then asked to bend and reach forward (without jerking) while pushing the sliding marker along the scale with the ngertips as far forward as possible. They held maximum exion position for approx. two seconds. The test was performed twice. The trial was not recorded if the knees exed. The record taken was the max. distance reached to the nearest 0.5 cm. 2.3. Statistical Analysis Data analysis was performed using the statistical program SPSS for Windows (SPSS, Inc., Chicago, IL, USA). The pre- and post-random group design was used as an experimen- tal design, in which ninety school-age athletes were divided into three groups. One-way analysis of variance (ANOVA) was used to estimate differences among G1, G2, and G3 prior to and after a 12-week period. Furthermore, pre- and post-intervention data was statistically analyzed by means of ANOVA to assess the discrepancies if any of the groups were to be assessed separately on a selected dependent variable. Whenever the `F' ratio for post-interventions was found to be relevant, the post hoc Scheff²test was

differences among G1, G2, and G3 prior to and after a 12-week period. Furthermore, pre- and post-intervention data was statistically analyzed by means of ANOVA to assess the discrepancies if any of the groups were to be assessed separately on a selected dependent variable. Whenever the `F' ratio for post-interventions was found to be relevant, the post hoc Scheff²test was used to assess the paired mean differences, if any. The con dence level of 0.05 was set for signi cance to test the `F' ratio obtained. Data are presented as mean standard deviation (SD). Between- group effect sizes (Cohen's d) were calculated by using a pooled standard deviation. An effect size of 0.80 and higher was considered as large, 0.50–0.79 as medium, 0.20–0.49 as small, and 0–0.19 as trivial [30]. 3. Results Table physical tness variables among school-aged athletes. Abdominal strength.The analysis of pre-intervention data showed that the obtained F value of 2.03 was less than the 0.95p-value needed. As a result, the pre-test importance of the core strength training group, the weight training group, and the control group on abdominal strength prior to respective interventions was found to be insigni cant, at the 0.05 level. This therefore con rms that the random allocation of subjects into three groups has been successful. The analysis of post-intervention data showed that the obtained F value of 28.01 was greater than the 0.00p-value. Thus, the post-test mean value of abdominal strength revealed signi cant con dence at 0.05. Accordingly, these results showed that both core strengthening training and weight training programs led to signi cant improvements in abdominal strength among intervention groups.

Appl. Sci.2022,12, 12550 5 of 10 Table 2.Pre- and post-12-week changes in physical tness variables among school-aged athletes. Test Pre-Post Group Mean SD pValues Number of sit-ups (#) Pre G1 18.70 3.20 0.13 G2 17.60 3.29 G3 17.20 3.20 Number of sit-ups (#) Post G1 22.21 3.50 0.00 G2 21.60 3.63 G3 16.39 2.69 Distance covered in 12 min run test (m)Pre G1 1817 185.78 0.97 G2 1806 237.25 G3 1813 224.69 Distance covered in 12 min run test (m)Post G1 2008.97 214.79 0.00 G2 2002.59 283.32 G3 1778.15 205.28 Sit and reach distance (cm) Pre G1 23.48 2.75 0.96 G2 23.66 2.92 G3 23.46 3.06 Sit and reach distance (cm) Post G1 25.96 2.38 0.00 G2 25.86 2.55 G3 21.76 2.56 Endurance.The analysis of pre-intervention data showed that the obtained F value of 0.02 was less than the 0.98p-value needed. As a result, the pre-test importance of the core strength training group, weight training group, and the control group on endurance prior to the respective interventions was found to be insigni cant, at the 0.05 level. This therefore con rms that the random allocation of subjects into three groups has been successful. The analysis of post-intervention data showed that the obtained F value of 9.29 was greater than the 0.00p-value. Thus, the post-test mean value of endurance showed signi - cant con dence at 0.05. Accordingly, these results showed that both the core strengthening training and weight training programs led to signi cant improvements in endurance among intervention groups. Flexibility.The analysis of pre-intervention data showed that the obtained F value of 0.04 was less than the 0.96p-value needed. As a result, the pre-test importance of the core strength training group, the weight training group, and the control group on exibility prior to respective interventions was found to be insigni cant, at the 0.05 level. This therefore con rms that the random allocation of subjects into three groups has been successful. The analysis of post-intervention data showed that the obtained F value of 27.12 was greater than the 0.00p-value. Thus, the post-test mean value of exibility showed signif- icant con

exibility prior to respective interventions was found to be insigni cant, at the 0.05 level. This therefore con rms that the random allocation of subjects into three groups has been successful. The analysis of post-intervention data showed that the obtained F value of 27.12 was greater than the 0.00p-value. Thus, the post-test mean value of exibility showed signif- icant con dence at 0.05. Accordingly, these results showed that both core strengthening training and weight training programs led to signi cant improvements in exibility among intervention groups. However, there were no signi cant differences in gains obtained after intervention programs in G1 and G2 in the number of sit-ups (3.51 and 4.0, respectively), distance covered in 12 min run test (191.97 m and 196.59 m, respectively), and the sit and reach distance (2.48 cm and 2.2 cm, respectively). This may be also corroborated by trivial Cohen's d when compared post-intervention differences between G1 and G2 in abdominal strength (0.171), endurance (0.025), and exibility (0.042). 4. Discussion Findings revealed signi cant improvements in abdominal strength, endurance, and exibility in school-aged athletes following a 12-week core strengthening training as well as weight training. However, abdominal strength and endurance improved slightly more in the weight training group than in the core strength training group, whilst exibility

Appl. Sci.2022,12, 12550 6 of 10 increased slightly more in the core strength training group than in the weight training group. This may be ascribed to adaptations to exercises used. While the core strengthening training included exercises such as side planks, bridges, leg-raises, utter kicks, butter y sit-ups, dead bugs, and rolling like a ball, the weight training included exercises such as military presses, back presses, biceps curls, bench presses, heel raises, half squats, and lunges. These ndings are in line with those of previous studies, which demonstrated a sig- ni cant increase in muscle power and strength following weight training. For instance, maximal lifting power and isometric hip and trunk extension strength increased after an 8-week training, including maximal voluntary co-contraction of abdominal muscles, in young adult men [31]. Core/torso stiffness improved more after a 6-week isometric com- pared to a dynamic core training [32]. However, core strength training can also be effective in improving various physical tness variables. Similar to our study, the endurance and strength of the core muscles improved after a 10-week Quad-Core training in school football players [20]. Regarding the exibility, spine range of motion, lateral exibility, dynamic balance, and endurance and/or strength of the back, abdominal and leg muscles improved after an 8-week core muscle training program using BOSU and a Swiss ball in male uni- versity students [33]. The range of motion in the stand and reach test also improved after an 8-week training program using a foam roll, without a decrease in muscle performance, strength endurance of the core muscles, or balance [34]. Strength of the core muscles in- creased following core stability exercises with a Swiss ball in junior swimmers [35]. Thus, a Swiss-ball core strength training program can be used for improvements in muscle strength of the lower limb exors (hamstrings), lower limb extensors (quadriceps), trunk exor (abdominal), trunk extensor (lower back), endurance of the lower limb, lower back and abdominal muscles, exibility of the lower back, and dynamic balance [36]. A 6-week program of Swiss ball training can be a suitable alternative to traditional oor exercises for improvements in

The study evaluates the impact of training on physical fitness in young athletes.