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OPINION article

Front. Physiol., 12 August 2021
Sec. Exercise Physiology
This article is part of the Research Topic Adaptations to Advanced Resistance Training Strategies in Youth and Adult Athletes View all 10 articles

High-Intensity Multimodal Training for Young People: It's Time to Think Inside the Box!

  • 1College of Physical Education and Dance, Federal University of Goiás, Goiânia, Brazil
  • 2College of Physical Education and Sport, Federal University of Espírito Santo, Vitoria, Brazil
  • 3Department of Physical Activity Sciences, Universidad de Los Lagos, Santiago, Chile
  • 4Centro de Investigación en Fisiología del Ejercicio, Facultad de Ciencias, Universidad Mayor, Santiago, Chile

Introduction

Studies comparing children and adolescents from different periods have shown a decrease in physical activity and fitness in the last decades (Moliner-Urdiales et al., 2010; Runhaar et al., 2010; Cohen et al., 2011; Hardy et al., 2013; Santtila et al., 2018; Masanovic et al., 2020; Fühner et al., 2021). Low physical fitness is associated with poor metabolic health, independent of central adiposity (Lätt et al., 2018). Moreover, changes in physical fitness from childhood and adolescence to adulthood are related to metabolic health, physical activity levels, and bone mineral density (García-Hermoso et al., 2019; Mäestu et al., 2020), while both low cardiorespiratory fitness and muscle strength are associated with higher risk of premature death and disability (Ortega et al., 2012; Henriksson et al., 2019a,b). Obesity is another important concern (Wijnhoven et al., 2014; Ogden et al., 2016; Bentham et al., 2017), but previous studies have shown that increased physical activity might be associated with decreased adiposity (Hui et al., 2021) and can modulate the effects of genetic predisposition to obesity in young people (Todendi et al., 2021).

The negative impact of a sedentary lifestyle during early life has been largely debated (Faigenbaum et al., 2011; Faigenbaum and Myer, 2012; Stracciolini et al., 2013). In the early 60s, Kraus and Raab (1961) stressed the importance of physical activity for preventing diseases and suggested that the adverse health effect of physical inactivity was comparable to lack of vitamins or contagious diseases. Based on this, Faigenbaum et al. (2013) proposed a population-wide approach for identifying inactive children, prescribing interventions and raising public awareness.

Notwithstanding, some important barriers for physical activity adoption among children and adolescents might be considered, like perception of lack of safety, physical environment and lack of support (Stankov et al., 2012; Lu et al., 2014; Martins et al., 2014). It is also important to consider children and adolescents particularities (e.g., biological and behavior characteristics) when prescribing and evaluating exercise programs, since exercise programs designed for adults might be inadequate for them (Faigenbaum et al., 2013).

Previous studies suggested that young people naturally engage in intermittent activities (Bailey et al., 1995) and high intensity activities might be particularly beneficial to improve cardiorespiratory fitness (Baquet et al., 2003; Costigan et al., 2015), mental health (Leahy et al., 2020), body composition (Costigan et al., 2015; D et al., 2019) cardiovascular risk and metabolic health (Cooper et al., 2016; García-Hermoso et al., 2016; MA et al., 2021) in children and adolescents.

The purpose of the current article is to present the benefits of high-intensity multimodal training (HIMT) programs, such as CrossFit, to the youth, with a critical discussion about its potential benefits and concerns.

Potential Benefits

HIMT involves exercise programs that mix many different exercise modalities (e.g., weightlifting, powerlifting, gymnastic, calisthenic, plyometrics, running, and others) and train multiple physical capacities at the same time (e.g., cardiorespiratory, muscle strength, and flexibility) (Feito et al., 2019). The performance of high-intensity exercises in an intermittent and station-based fashion, might confer to HIMT characteristics similar from existing training methods such as circuit training and high-intensity interval training (Sobrero et al., 2017; Feito et al., 2019). Probably, the most popular form of HIMT is CrossFit; however, there are many other activities and names that might be included in this definition, like high-intensity functional training, cross-training and others.

HIMT programs are usually designed for improving physical fitness and motor skills, being characterized by high levels of effort, with a great stress in cardiorespiratory and neuromuscular systems (Timón et al., 2019). These activities have been reported to promote marked increases in muscle mass and strength and cardiorespiratory fitness, and reduce body fat (Murawska-Cialowicz et al., 2015; Brisebois et al., 2018; Carnes and Mahoney, 2019; Bahremand et al., 2020), which are, in some cases, higher than conventional activities (Bahremand et al., 2020). There is evidence that HIMT participants present high levels of satisfaction and motivation (Claudino et al., 2018) and perceive it as more enjoyable than conventional training (Heinrich et al., 2014).

CrossFit Teen and CrossFit Kids are similar programs adapted from CrossFit and designed specifically to improve fitness and resistance skill of young population. In agreement with the studies involving adults, such HIMT programs have shown to improve physical fitness in children and adolescents (Eather et al., 2016b; Garst et al., 2020), with high rates of attendance (94%) and satisfaction (4.2–4.6 out of 5) (Eather et al., 2016b). HIMT like CrossFit is usually performed inside a specific facility named “Box” (Feito et al., 2019); however, programs adapted for young people involves minimal equipment and can also be easily implemented at school setting (Eather et al., 2016b; Garst et al., 2020). In this context, the effects of HIMT on health-related fitness of students are comparable to those obtained with the regular participation in physical education classes (Garst et al., 2020).

The higher intensity achieved during HIMT seems to be an important aspect for cardiorespiratory fitness in the youth, since exercising at intensities above 80% of maximal heart rate might be important for this group (Baquet et al., 2003). Previous studies have suggested that young people might particularly benefit from high-intensity physical exercise, with improvements in body composition, metabolic, and cardiovascular health (Gist et al., 2014; Cooper et al., 2016; Eddolls et al., 2017; García-Hermoso et al., 2020), but also in other components like cognitive and mental health (Leahy et al., 2020). Regarding the latter, 8 weeks of HIMT intervention brings mental health benefits among adolescents at increased risk for psychological stress (Eather et al., 2016a). Thus, HIMT can be considered a helpful strategy to manage mental health issue in school-aged individuals.

The muscle strengthening component of HIMT might also be important for the youth, since muscle strength seems to has a strong association with health benefits (García-Hermoso et al., 2019) and mitigate the worsening of metabolic health associated with insufficient levels of physical activity (Gomes et al., 2017). Children and adolescents have lower levels of sexual hormones compared to adults, and also reduced strength and power when normalized by body mass (Dotan et al., 2012; Dotan, 2016). However, besides these apparent limitations, there are many studies showing that children and adolescents are capable of increasing muscle strength and mass in response to training (Faigenbaum et al., 1996; Pikosky et al., 2002; Granacher et al., 2011; Assunção et al., 2016). Of note, some of these studies involve children as young as 5 years old (Faigenbaum et al., 1999).

According to Faigenbaum et al. (2016), education and instruction on proper resistance training techniques and procedures should start early in life. Neuromuscular performance and muscle strength might positively predict motor competence in children (Wright et al., 2020) and higher motor competence during childhood is associated with sustained physical activity practice in adolescence (Larsen et al., 2015).

Potential Concerns

Injury risk is probably the main concern regarding HIMT in adults (Claudino et al., 2018). However, data reporting the prevalence or incidence of injury in young HIMT practitioners is scarce. A retrospective study about pediatric CrossFit-related injury found that the absolute number of CrossFit-related injury in young increased over time since CrossFit foundation (Stracciolini et al., 2020). This crescent CrossFit-related injury rate could be associated with the increased participation of young people in this modality, while the absence of relative risk analyses makes difficult to classify or compare injure rate with another training modality. The profile of CrossFit-related injury in the young might differ between sex and age, with higher proportion of lower limb injury in women, higher proportion of Shoulder injury in men, and higher proportion of trunk/spine for participant younger than 20 years old (Sugimoto et al., 2020). These findings might be of particular interest in order to develop safe HIMT for young practitioners.

Other possible concerns involving HIMT for adults, like insufficient recovery between exercises and sessions, concurrent effects and lack of specificity, might not be harmful or can even be advantageous when considering young people.

It has been suggested that recovery from high-intensity exercises (i.e., all out sprints and Wingate tests) is faster in children and adolescents when compared to adults (Bar-Or, 1995; Ratel et al., 2004). Moreover, children and adolescents seem to naturally engage in intermittent activities (Bailey et al., 1995) and studies have reported that they usually consider it enjoyable (Ratel et al., 2004; Malik et al., 2017, 2018).

The faster recovery in the young has also been reported in resistance training. Faigenbaum et al. (2008) compared the performance in the bench press exercise at 10 repetitions maximum (10RM) load between children, adolescents and adults. The results showed that children recovered faster than adolescents and adults, while adolescents recovered faster than adults. Therefore, using short interval lengths might not interfere with the results in younger people (Ramirez-Campillo et al., 2014, 2019b; Drury et al., 2021).

Regarding the recovery between sessions, a previous study by Soares et al. (1996) compared the recovery of children (12 years old) and adults (28 years old) after 5 sets of bench press performed to momentary muscle failure. According to the results, there were no changes in indirect markers of muscle damage [isometric strength and creatine kinase (CK) levels] 24 h after training in children, while adults did not recover for as long as 72 h. Similar findings were reported by Chen et al. (2014), that used muscle damaging protocols (5 sets of 6 maximal eccentric elbow flexions) and found that recovery was faster in children than adolescents and adults; and in adolescents when compared to adults. Later, Deli et al. (2017) compared the responses of boys (10–12 years old) and adults (18–45 years old) to maximal eccentric knee extensions and confirmed that children are less susceptible to exercise-induced muscle damage than adults. Children and adolescents seem to require less days to recover from a resistance exercise session than adults (Ramírez-Campillo et al., 2015) and a higher training frequency promotes higher increases in muscle strength in this group (Moran et al., 2017). Therefore, the concerns regarding insufficient recovery during HIMT might not be a problem for the young.

HIMT also can involves a large component of plyometric jumps, which might improve physical performance in young people and are safe over short term (De Freitas Guina Fachina et al., 2017; Assunção et al., 2018; Ramirez-Campillo et al., 2019a,b; Vera-Assaoka et al., 2020). However, it is important to remember that overuse injuries and tendinopathies are frequent in young athletes (Le Gall et al., 2006; Johnson et al., 2020), which might be due to an imbalance between muscle and tendon adaptation (Mersmann et al., 2014, 2016, 2017). Considering that resistance training might increase tendon strength (Kongsgaard et al., 2007; Martins et al., 2018), it is recommended to design programs with an adequate balance between plyometric (particularly high-impact jumps) and resistance training volumes, specially adolescents. The combination of resistance and plyometric training might also be beneficial for increasing performance (Zghal et al., 2019; Thapa et al., 2021). Radnor et al. (2017) studied the response of children of different maturity groups (pre- or post-peak height velocity) to a plyometric training, resistance training and combined training and reported that, irrespective of maturation, combined training provided the greatest improvements in performance.

The combination of resistance and aerobic training during HIMT might be a concern because of the potential concurrent effects. However, a systematic review with meta-analysis reported that concurrent training was more effective than single mode aerobic or resistance training in improving physical fitness in children and adolescents (Gäbler et al., 2018). Interestingly, the study revealed that concurrent training promoted higher increases on muscle power in young people when compared to strength training alone, which is the opposite to what have been reported in adults (Wilson et al., 2012).

There might be some concerns with the strengthening exercises used during HIMT, because this might be associated with risk of injury in children. However, the injury risk for these activities are lower than other sports, like soccer and basketball (Hamill, 1994), being considered safe for the youth (Falk and Eliakim, 2003; Malina, 2006; Faigenbaum et al., 2009).

Myer et al. (2009) evaluated injuries seen during emergency room visits associated with resistance training (weightlifting). The results revealed that accidental injuries decreased with age, while sprain/strain injuries increased. More than two thirds of the injuries sustained in the 8–13 group occurred in the heads, hands and feet and were most often related to “dropping” and “pinching”. Therefore, it seems that children have lower risk of sprains and strains, but a higher risk of accidental injuries, suggesting the need for adequate (and qualified) supervision during training sessions.

Because of the highly fatiguing nature of HIMT, proprioception and exercise technique are likely altered, compromising safety and efficacy of such programs, particularly for those involving exercise that require complex technics such Olympic-style weightlift (e.g., snatches and clean, and jerks), as suggested by Hooper et al. (2014). Therefore, children and adolescents must be closely supervised during HIMT and, if necessary, training programs should be adapted for their individual characteristics.

The highly fatiguing nature of HIMT should also be considered when training close to academic tasks. Though HIMT might be beneficial to improve motor skills it can impair academic performance in middle school students, due to an impairment in concentration capacity (Garst et al., 2020). However, this seems to be controversial since other studies showed that high intensity training improves executive function, memory, and selective attention in children and adolescents (Ma et al., 2015; Moreau et al., 2017; Lind et al., 2019; Tottori et al., 2019). Therefore, the negative results found by (Garst et al., 2020) might be specific to the modality used (CrossFit) and not due to high intensity nature of the activity per se. There is a common belief that high effort, especially lifting weight might limit longitudinal growth in children and adolescent. However, exercise might positively influence longitudinal growth (Borer, 1995; Hills and Byrne, 2010) and there is no evidence that muscle strengthening activities have a negative impact on growth (Falk and Eliakim, 2003; Malina, 2006; Faigenbaum et al., 2009). In fact, HIMT might be even beneficial, since high intensity activities increase circulating human growth hormone in children and adolescents (Saggese et al., 1987; Eliakim and Nemet, 2008, 2013).

Final Comments

Although there is no minimum age to start exercising (Myer et al., 2011; Faigenbaum et al., 2016), it is necessary to adapt training programs to the youngsters' biological and behavioral characteristics. Children and adolescents should be able to understand and follow instructions and they should receive safety instructions on lifting weights, proper spotting and equipment use.

Considering the competitive nature of some HIMT programs, it is important to remember that untrained youth tend to overestimate their physical performance, which might increase the risk of injury (Plumert and Schwebel, 1997). This highlights the importance of qualified supervision, which is further reinforced by the fact that direct supervision improves program adherence and the results in young people (Coutts et al., 2004).

Professionals involved with HIMT for children and adolescents need to acknowledge both their biological characteristics and psychological uniqueness. Professionals should be particularly sensitive to children and adolescents who are overweight/obese and with low physical capacities. Although they are the ones who potentially will get most benefit from HIMT, they are also the ones who might be more reluctant to adhere.

Some practical suggestions to improve adherence of obese pediatric population using HIMT, should be access to a gym, initial direction by a trainer, variety, and group-based activities (Peeters et al., 2012). Other important factor are the support of family and peer (Peeters et al., 2012; Salvy et al., 2012; Sundar et al., 2018); therefore, it is important to involve them in the exercise programs as much as possible. It is also important to provide constant feedback regarding improved fitness, since obese children might join exercise initially aiming at losing weight, but focused more on fitness over time (Peeters et al., 2012). Considering that mastering the activity is associated with less motivation (Sundar et al., 2018), we suggest choosing simple exercises and progress carefully.

In technical terms, the characteristics of HIMT, such as, the simultaneous development of many physical capacities and movements and exercise diversity might be particularly interesting for training young people. HIMT involves some important aspects for exercise adherence like variety and group-based, and might easily involve others like access to exercise facilities and supervision (Peeters et al., 2012). Many concerns like an increased risk of injury, insufficient recovery might not be troublesome for this group and are not difficult to address (Figure 1).

FIGURE 1
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Figure 1. Summary of benefits (Eather et al., 2016a,b), concerns (Hooper et al., 2014; Claudino et al., 2018; Garst et al., 2020), and suggestion/comments (Myer et al., 2011; Faigenbaum et al., 2016), regarding high-intensity multimodal training in young people.

During HIMT exercise professionals might have an opportunity to promote positive changes in physical function and body composition in children and adolescents, as well as to promote improvements in mental health and psychosocial aspects. Moreover, this might be an important opportunity to educate them about the benefits of a healthy lifestyle and overcome the perceived barriers to being physically active. The increase in physical fitness might increase spontaneous participation in physical activity and sports (Eiholzer et al., 2010; Fransen et al., 2014). Therefore, HIMT might be seen as an end (to increase physical fitness) but also as a mean (to increase physical activity).

Author Contributions

PG, CABdL, RLV, RR-C, and DS: conception, drafting the article, revising it critically, and final approval of the version to be published. All authors contributed to the article and approved the submitted version.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher's Note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Acknowledgments

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. PG receives a Research Grand from CNPq (304435/2018-0).

References

Assunção, A. R., Bottaro, M., Cardoso, E. A., Dantas Da Silva, D. P., Ferraz, M., Vieira, C. A., et al. (2018). Effects of a low-volume plyometric training in anaerobic performance of adolescent athletes. J. Sports Med. Phys. Fitness 58, 570–575. doi: 10.23736/S0022-4707.17.07173-0

PubMed Abstract | CrossRef Full Text | Google Scholar

Assunção, A. R., Bottaro, M., Ferreira-Junior, J. B., Izquierdo, M., Cadore, E. L., and Gentil, P. (2016). The chronic effects of low- and high-intensity resistance training on muscular fitness in adolescents. PLoS ONE 11:650. doi: 10.1371/journal.pone.0160650

PubMed Abstract | CrossRef Full Text | Google Scholar

Bahremand, M., Hakak Dokht, E., and Moazzami, M. (2020). A comparison of CrossFit and concurrent training on myonectin, insulin resistance and physical performance in healthy young women. Arch. Physiol. Biochem. 1–7. doi: 10.1080/13813455.2020.1853173

PubMed Abstract | CrossRef Full Text | Google Scholar

Bailey, R. C., Olson, J., Pepper, S. L., Porszasz, J., Barstow, T. J., and Cooper, D. M. (1995). The level and tempo of children's physical activities: an observational study. Med. Sci. Sports Exerc. 27, 1033–1041. doi: 10.1249/00005768-199507000-00012

PubMed Abstract | CrossRef Full Text | Google Scholar

Baquet, G., Van Praagh, E., and Berthoin, S. (2003). Endurance training and aerobic fitness in young people. Sport. Med. 33, 1127–1143. doi: 10.2165/00007256-200333150-00004

PubMed Abstract | CrossRef Full Text | Google Scholar

Bar-Or O. (1995). The young athlete: some physiological considerations. J. Sports Sci. 13, S31–S33. doi: 10.1080/02640419508732274

PubMed Abstract | CrossRef Full Text | Google Scholar

Bentham, J., Di Cesare, M., Bilano, V., Bixby, H., Zhou, B., Stevens, G. A., et al. (2017). Worldwide trends in body-mass index, underweight, overweight, and obesity from 1975 to 2016: a pooled analysis of 2416 population-based measurement studies in 128·9 million children, adolescents, and adults. Lancet 390, 2627–2642. doi: 10.1016/S0140-6736(17)32129-3

PubMed Abstract | CrossRef Full Text | Google Scholar

Borer, K. T. (1995). The effects of exercise on growth. Sport. Med. 20, 375–397. doi: 10.2165/00007256-199520060-00004

PubMed Abstract | CrossRef Full Text | Google Scholar

Brisebois, M., Rigby, B., and Nichols, D. (2018). Physiological and fitness adaptations after eight weeks of high-intensity functional training in physically inactive adults. Sports 6:146. doi: 10.3390/sports6040146

PubMed Abstract | CrossRef Full Text | Google Scholar

Carnes, A. J., and Mahoney, S. E. (2019). Polarized versus high-intensity multimodal training in recreational runners. Int. J. Sports Physiol. Perform. 14, 105–112. doi: 10.1123/ijspp.2018-0040

PubMed Abstract | CrossRef Full Text | Google Scholar

Chen, T. C., Chen, H. L., Liu, Y. C., and Nosaka, K. (2014). Eccentric exercise-induced muscle damage of pre-adolescent and adolescent boys in comparison to young men. Eur. J. Appl. Physiol. 114, 1183–1195. doi: 10.1007/s00421-014-2848-3

PubMed Abstract | CrossRef Full Text | Google Scholar

Claudino, J. G., Gabbett, T. J., Bourgeois, F., Souza, H., de, S., Miranda, R. C., et al. (2018). crossfit overview: systematic review and meta-analysis. Sport. Med. Open 4, 1–14. doi: 10.1186/s40798-018-0124-5

PubMed Abstract | CrossRef Full Text | Google Scholar

Cohen, D., Voss, C., Taylor, M., Delextrat, A., Ogunleye, A., and Sandercock, G. (2011). Ten-year secular changes in muscular fitness in English children. Acta Paediatr. Int. J. Paediatr. 100. doi: 10.1111/j.1651-2227.2011.02318.x

PubMed Abstract | CrossRef Full Text | Google Scholar

Cooper, S. B., Dring, K. J., and Nevill, M. E. (2016). High-Intensity intermittent exercise: effect on young people's cardiometabolic health and cognition. Curr. Sports Med. Rep. 15, 245–251. doi: 10.1249/JSR.0000000000000273

PubMed Abstract | CrossRef Full Text | Google Scholar

Costigan, S. A., Eather, N., Plotnikoff, R. C., Taaffe, D. R., and Lubans, D. R. (2015). High-intensity interval training for improving health-related fitness in adolescents: a systematic review and meta-analysis. Br. J. Sports Med. 49, 1253–1261. doi: 10.1136/bjsports-2014-094490

PubMed Abstract | CrossRef Full Text | Google Scholar

Coutts, A. J., Murphy, A. J., and Dascombe, B. J. (2004). Effect of direct supervision of a strength coach on measures of muscular strength and power in young rugby league players. J. Strength Cond. Res. 18, 316–323. doi: 10.1519/00124278-200405000-00021

PubMed Abstract | CrossRef Full Text | Google Scholar

D, T, J, M., G, B., BW, T., B, P., S, B., et al. (2019). High-intensity interval training in overweight and obese children and adolescents: systematic review and meta-analysis. J. Sports Med. Phys. Fitness 59, 310–324. doi: 10.23736/S0022-4707.18.08075-1

PubMed Abstract | CrossRef Full Text | Google Scholar

De Freitas Guina Fachina, R. J., Martins, D. S., Montagner, P. C., Borin, J. P., Vancini, R. L., Dos Santos Andrade, M., et al. (2017). Combined plyometric and strength training improves repeated sprint ability and agility in young male basketball players. Gazz. Medica Ital. Arch. per le Sci. Mediche 176, 75–84. doi: 10.23736/S0393-3660.16.03341-6

CrossRef Full Text | Google Scholar

Deli, C. K., Fatouros, I. G., Paschalis, V., Georgakouli, K., Zalavras, A., Avloniti, A., et al. (2017). A comparison of exercise-induced muscle damage following maximal eccentric contractions in men and boys. Pediatr. Exerc. Sci. 29, 316–325. doi: 10.1123/pes.2016-0185

PubMed Abstract | CrossRef Full Text | Google Scholar

Dotan, R. (2016). Children's neuromotor and muscle-functional attributes—Outstanding issues. Pediatr. Exerc. Sci. 28, 202–209. doi: 10.1123/pes.2015-0248

PubMed Abstract | CrossRef Full Text | Google Scholar

Dotan, R., Mitchell, C., Cohen, R., Klentrou, P., Gabriel, D., and Falk, B. (2012). Child-adult differences in muscle activation—a review. Pediatr. Exerc. Sci. 24, 2–21. doi: 10.1123/pes.24.1.2

PubMed Abstract | CrossRef Full Text | Google Scholar

Drury, B., Peacock, D., Moran, J., Cone, C., and Ramirez-Campillo, R. (2021). Effects of different inter-set rest intervals during the nordic hamstring exercise in young male athletes. J. Athl. Train. 31. doi: 10.4085/318-20

PubMed Abstract | CrossRef Full Text | Google Scholar

Eather, N., Morgan, P. J., and Lubans, D. R. (2016a). Effects of exercise on mental health outcomes in adolescents: Findings from the CrossFitTM teens randomized controlled trial. Psychol. Sport Exerc. 26, 14–23. doi: 10.1016/j.psychsport.2016.05.008

CrossRef Full Text | Google Scholar

Eather, N., Morgan, P. J., and Lubans, D. R. (2016b). Improving health-related fitness in adolescents: the CrossFit TeensTM randomised controlled trial. J. Sports Sci. 34, 209–223. doi: 10.1080/02640414.2015.1045925

PubMed Abstract | CrossRef Full Text | Google Scholar

Eddolls, W. T. B., McNarry, M. A., Stratton, G., Winn, C. O. N., and Mackintosh, K. A. (2017). High-Intensity interval training interventions in children and adolescents: a systematic review. Sport. Med. 47, 2363–2374. doi: 10.1007/s40279-017-0753-8

PubMed Abstract | CrossRef Full Text | Google Scholar

Eiholzer, U., Meinhardt, U., Petr,ò, R., Witassek, F., Gutzwiller, F., and Gasser, T. (2010). High-intensity training increases spontaneous physical activity in children: a randomized controlled study. J. Pediatr. 156, 242–246. doi: 10.1016/j.jpeds.2009.08.039

PubMed Abstract | CrossRef Full Text | Google Scholar

Eliakim, A., and Nemet, D. (2008). Exercise provocation test for growth hormone secretion: methodologic considerations. Pediatr. Exerc. Sci. 20, 370–378. doi: 10.1123/pes.20.4.370

PubMed Abstract | CrossRef Full Text | Google Scholar

Eliakim, A., and Nemet, D. (2013). The endocrine response to exercise and training in young athletes. Pediatr. Exerc. Sci. 25, 605–615. doi: 10.1123/pes.25.4.605

PubMed Abstract | CrossRef Full Text | Google Scholar

Faigenbaum, A. D., Kraemer, W. J., Blimkie, C. J., Jeffreys, I., Micheli, L. J., Nitka, M., et al. (2009). Youth resistance training: updated position statement paper from the national strength and conditioning association. J. Strength Cond. Res. 23, S60–79. doi: 10.1519/JSC.0b013e31819df407

PubMed Abstract | CrossRef Full Text | Google Scholar

Faigenbaum, A. D., Lloyd, R. S., MacDonald, J., and Myer, G. D. (2016). Citius, altius, fortius: beneficial effects of resistance training for young athletes: narrative review. Br. J. Sports Med. 50, 3–7. doi: 10.1136/bjsports-2015-094621

PubMed Abstract | CrossRef Full Text | Google Scholar

Faigenbaum, A. D., Lloyd, R. S., and Myer, G. D. (2013). Youth resistance training: past practices, new perspectives, and future directions. Pediatr. Exerc. Sci. 25, 591–604. doi: 10.1123/pes.25.4.591

PubMed Abstract | CrossRef Full Text | Google Scholar

Faigenbaum, A. D., and Myer, G. D. (2012). Exercise deficit disorder in youth: play now or pay later. Curr. Sports Med. Rep. 11, 196–200. doi: 10.1249/JSR.0b013e31825da961

PubMed Abstract | CrossRef Full Text | Google Scholar

Faigenbaum, A. D., Ratamess, N. A., McFarland, J., Kaczmarek, J., Coraggio, M. J., Kang, J., et al. (2008). Effect of rest interval length on bench press performance in boys, teens, and men. Pediatr. Exerc. Sci. 20, 457–469. doi: 10.1123/pes.20.4.457

PubMed Abstract | CrossRef Full Text | Google Scholar

Faigenbaum, A. D., Stracciolini, A., and Myer, G. D. (2011). Exercise deficit disorder in youth: a hidden truth. Acta Paediatr. Int. J. Paediatr. 100, 1423–1425. doi: 10.1111/j.1651-2227.2011.02461.x

PubMed Abstract | CrossRef Full Text | Google Scholar

Faigenbaum, A. D., Westcott, W. L., Loud, R. L., and Long, C. (1999). The effects of different resistance training protocols on muscular strength and endurance development in children. Pediatrics 104. doi: 10.1542/peds.104.1.e5

PubMed Abstract | CrossRef Full Text | Google Scholar

Faigenbaum, A. D., Westcott,2, W. L., Micheli, L. J., Outerbridge, A. R., Long, C. J., LaRosa-Loud, R., et al. (1996). The effects of strength training and detraining on children. J. Strength Cond. Res. 10:109. doi: 10.1519/1533-4287(1996)010andlt

CrossRef Full Text | Google Scholar

Falk, B., and Eliakim, A. (2003). Resistance training, skeletal muscle and growth. Pediatr. Endocrinol. Rev. 1, 120–127.

Google Scholar

Feito, Y., Brown, C., and Olmos, A. (2019). A content analysis of the high-intensity functional training literature: a look at the past and directions for the future. Hum. Mov. 20, 1–15. doi: 10.5114/hm.2019.81020

CrossRef Full Text | Google Scholar

Fransen, J., Deprez, D., Pion, J., Tallir, I. B., D'Hondt, E., Vaeyens, R., et al. (2014). Changes in physical fitness and sports participation among children with different levels of motor competence: a 2-year longitudinal study. Pediatr. Exerc. Sci. 26, 11–21. doi: 10.1123/pes.2013-0005

PubMed Abstract | CrossRef Full Text | Google Scholar

Fühner, T., Kliegl, R., Arntz, F., Kriemler, S., and Granacher, U. (2021). An update on secular trends in physical fitness of children and adolescents from 1972 to 2015: a systematic review. Sport. Med. 51, 303–320. doi: 10.1007/s40279-020-01373-x

PubMed Abstract | CrossRef Full Text | Google Scholar

Gäbler, M., Prieske, O., Hortobágyi, T., and Granacher, U. (2018). The effects of concurrent strength and endurance training on physical fitness and athletic performance in youth: a systematic review and meta-analysis. Front. Physiol. 9:1057. doi: 10.3389/fphys.2018.01057

PubMed Abstract | CrossRef Full Text | Google Scholar

García-Hermoso, A., Alonso-Martínez, A. M., Ramírez-Vélez, R., Pérez-Sousa, M. Á., Ramírez-Campillo, R., and Izquierdo, M. (2020). Association of physical education with improvement of health-related physical fitness outcomes and fundamental motor skills among youths: a systematic review and meta-analysis. JAMA Pediatr. 174, 1–11. doi: 10.1001/jamapediatrics.2020.0223

PubMed Abstract | CrossRef Full Text | Google Scholar

García-Hermoso, A., Cerrillo-Urbina, A. J., Herrera-Valenzuela, T., Cristi-Montero, C., Saavedra, J. M., and Martínez-Vizcaíno, V. (2016). Is high-intensity interval training more effective on improving cardiometabolic risk and aerobic capacity than other forms of exercise in overweight and obese youth? a meta-analysis. Obes. Rev. 17, 531–540. doi: 10.1111/obr.12395

PubMed Abstract | CrossRef Full Text | Google Scholar

García-Hermoso, A., Ramírez-Campillo, R., and Izquierdo, M. (2019). Is muscular fitness associated with future health benefits in children and adolescents? a systematic review and meta-analysis of longitudinal studies. Sport. Med. 49, 1079–1094. doi: 10.1007/s40279-019-01098-6

PubMed Abstract | CrossRef Full Text | Google Scholar

Garst, B. A., Bowers, E. P., and Stephens, L. E. (2020). A randomized study of CrossFit Kids for fostering fitness and academic outcomes in middle school students. Eval. Program Plann. 83:101856. doi: 10.1016/j.evalprogplan.2020.101856

PubMed Abstract | CrossRef Full Text | Google Scholar

Gist, N. H., Fedewa, M. V., Dishman, R. K., and Cureton, K. J. (2014). Sprint interval training effects on aerobic capacity: a systematic review and meta-analysis. Sport. Med. 44, 269–279. doi: 10.1007/s40279-013-0115-0

PubMed Abstract | CrossRef Full Text | Google Scholar

Gomes, T. N., dos Santos, F. K., Katzmarzyk, P. T., and Maia, J. (2017). Active and strong: physical activity, muscular strength, and metabolic risk in children. Am. J. Hum. Biol. 29, 1–8. doi: 10.1002/ajhb.22904

PubMed Abstract | CrossRef Full Text | Google Scholar

Granacher, U., Muehlbauer, T., Doerflinger, B., Strohmeier, R., and Gollhofer, A. (2011). Promoting strength and balance in adolescents during physical education: effects of a short-term resistance training. J. Strength Cond. Res. 25, 940–949. doi: 10.1519/JSC.0b013e3181c7bb1e

PubMed Abstract | CrossRef Full Text | Google Scholar

Hamill, B. P. (1994). relative safety of weightlifting and weight training. J. Strength Cond. Res. 8:53. doi: 10.1519/1533-4287(1994)008andlt

CrossRef Full Text | Google Scholar

Hardy, L. L., Barnett, L., Espinel, P., and Okely, A. D. (2013). Thirteen-year trends in child and adolescent fundamental movement skills: 1997–2010. Med. Sci. Sports Exerc. 45, 1965–1970. doi: 10.1249/MSS.0b013e318295a9fc

PubMed Abstract | CrossRef Full Text | Google Scholar

Heinrich, K. M., Patel, P. M., O'Neal, J. L., and Heinrich, B. S. (2014). High-intensity compared to moderate-intensity training for exercise initiation, enjoyment, adherence, and intentions: an intervention study. BMC Public Health 14, 1–6. doi: 10.1186/1471-2458-14-789

PubMed Abstract | CrossRef Full Text | Google Scholar

Henriksson, H., Henriksson, P., Tynelius, P., and Ortega, F. B. (2019a). Muscular weakness in adolescence is associated with disability 30 years later: a population-based cohort study of 1.2 million men. Br. J. Sports Med. 53, 1221–1230. doi: 10.1136/bjsports-2017-098723

PubMed Abstract | CrossRef Full Text | Google Scholar

Henriksson, P., Henriksson, H., Tynelius, P., Berglind, D., Löf, M., Lee, I. M., et al. (2019b). Fitness and body mass index during adolescence and disability later in life. Ann. Intern. Med. 170, 230–239. doi: 10.7326/M18-1861

PubMed Abstract | CrossRef Full Text | Google Scholar

Hills, A. P., and Byrne, N. M. (2010). An overview of physical growth and maturation. Med. Sport Sci. 55, 1–13. doi: 10.1159/000321968

PubMed Abstract | CrossRef Full Text | Google Scholar

Hooper, D. R., Szivak, T. K., Comstock, B. A., Dunn-Lewis, C., Apicella, J. M., Kelly, N. A., et al. (2014). Effects of fatigue from resistance training on barbell back squat biomechanics. J. Strength Cond. Res. 28, 1127–1134. doi: 10.1097/JSC.0000000000000237

PubMed Abstract | CrossRef Full Text | Google Scholar

Hui, S. S., chuen, Zhang, R., Suzuki, K., Naito, H., Balasekaran, G., Song, J. K., et al. (2021). The associations between meeting 24-hour movement guidelines and adiposity in Asian Adolescents: the Asia-Fit Study. Scand. J. Med. Sci. Sport. 31, 763–771. doi: 10.1111/sms.13893

PubMed Abstract | CrossRef Full Text | Google Scholar

Johnson, D. M., Williams, S., Bradley, B., Sayer, S., Murray Fisher, J., and Cumming, S. (2020). Growing pains: maturity associated variation in injury risk in academy football. Eur. J. Sport Sci. 20, 544–552. doi: 10.1080/17461391.2019.1633416

PubMed Abstract | CrossRef Full Text | Google Scholar

Kongsgaard, M., Reitelseder, S., Pedersen, T. G., Holm, L., Aagaard, P., Kjaer, M., et al. (2007). Region specific patellar tendon hypertrophy in humans following resistance training. Acta Physiol 191, 111–121. doi: 10.1111/j.1748-1716.2007.01714.x

PubMed Abstract | CrossRef Full Text | Google Scholar

Kraus, H., and Raab, W. (1961). Hypokinetic Disease. Springfield, IL: Charles C. Thomas.

Larsen, L. R., Kristensen, P. L., Junge, T., Rexen, C. T., and Wedderkopp, N. (2015). Motor performance as predictor of physical activity in children: the CHAMPS Study-DK. Med. Sci. Sports Exerc. 47, 1849–1856. doi: 10.1249/MSS.0000000000000604

PubMed Abstract | CrossRef Full Text | Google Scholar

Lätt, E., Jürimäe, J., Harro, J., Loit, H. M., and Mäestu, J. (2018). Low fitness is associated with metabolic risk independently of central adiposity in a cohort of 18-year-olds. Scand. J. Med. Sci. Sport. 28, 1084–1091. doi: 10.1111/sms.13002

PubMed Abstract | CrossRef Full Text | Google Scholar

Le Gall, F., Carling, C., Reilly, T., Vandewalle, H., Church, J., and Rochcongar, P. (2006). Incidence of injuries in elite French youth soccer players: a 10-season study. Am. J. Sports Med. 34, 928–938. doi: 10.1177/0363546505283271

PubMed Abstract | CrossRef Full Text | Google Scholar

Leahy, A. A., Mavilidi, M. F., Smith, J. J., Hillman, C. H., Eather, N., Barker, D., et al. (2020). Review of high-intensity interval training for cognitive and mental health in youth. Med. Sci. Sports Exerc. 52, 2224–2234. doi: 10.1249/MSS.0000000000002359

PubMed Abstract | CrossRef Full Text | Google Scholar

Lind, R. R., Beck, M. M., Wikman, J., Malarski, K., Krustrup, P., Lundbye-Jensen, J., et al. (2019). Acute high-intensity football games can improve children's inhibitory control and neurophysiological measures of attention. Scand. J. Med. Sci. Sport. 29, 1546–1562. doi: 10.1111/sms.13485

PubMed Abstract | CrossRef Full Text | Google Scholar

Lu, W., McKyer, E. L. J., Lee, C., Goodson, P., Ory, M. G., and Wang, S. (2014). Perceived barriers to children's active commuting to school: a systematic review of empirical, methodological and theoretical evidence. Int. J. Behav. Nutr. Phys. Act. 11:140. doi: 10.1186/s12966-014-0140-x

PubMed Abstract | CrossRef Full Text | Google Scholar

Ma, J. K., Mare, L., Le, and Gurd, B. J. (2015). Four minutes of in-class high-intensity interval activity improves selective attention in 9- to 11-year olds. Appl. Physiol. Nutr. Metab. 40, 238–244. doi: 10.1139/apnm,-2014-0309

PubMed Abstract | CrossRef Full Text | Google Scholar

MA, M., L, L., EA, E., JP, H., G, D., et al. (2021). Asthma and high-intensity interval training have no effect on clustered cardiometabolic risk or arterial stiffness in adolescents. Eur. J. Appl. Physiol. 121, 1967–1978. doi: 10.1007/s00421-020-04590-4

PubMed Abstract | CrossRef Full Text | Google Scholar

Mäestu, E., Harro, J., Veidebaum, T., Kurrikoff, T., Jürimäe, J., and Mäestu, J. (2020). Changes in cardiorespiratory fitness through adolescence predict metabolic syndrome in young adults. Nutr. Metab. Cardiovasc. Dis. 30, 701–708. doi: 10.1016/j.numecd.2019.12.009

PubMed Abstract | CrossRef Full Text | Google Scholar

Malik, A. A., Williams, C. A., Bond, B., Weston, K. L., and Barker, A. R. (2017). Acute cardiorespiratory, perceptual and enjoyment responses to high-intensity interval exercise in adolescents. Eur. J. Sport Sci. 17, 1335–1342. doi: 10.1080/17461391.2017.1364300

PubMed Abstract | CrossRef Full Text | Google Scholar

Malik, A. A., Williams, C. A., Weston, K. L., and Barker, A. R. (2018). Perceptual responses to high- and moderate-intensity interval exercise in adolescents. Med. Sci. Sports Exerc. 50, 1021–1030. doi: 10.1249/MSS.0000000000001508

PubMed Abstract | CrossRef Full Text | Google Scholar

Malina, R. M. (2006). Weight training in youth-growth, maturation, and safety: an evidence-based review. Clin. J. Sport Med. 16, 478–487. doi: 10.1097/01.jsm.0000248843.31874.be

PubMed Abstract | CrossRef Full Text | Google Scholar

Martins, J., Marques, A., Sarmento, H., and Carreiro Da Costa, F. (2014). Adolescents' perspectives on the barriers and facilitators of physical activity: a systematic review of qualitative studies. Health Educ. Res. 30, 742–755. doi: 10.1093/her/cyv042

PubMed Abstract | CrossRef Full Text | Google Scholar

Martins, W. R., Blasczyk, J. C., Soares, S., de Paula, W. D., Bottaro, M., and Gentil, P. (2018). A novel approach for rehabilitation of a triceps tendon rupture: a case report. Phys. Ther. Sport 32:16. doi: 10.1016/j.ptsp.2018.05.016

PubMed Abstract | CrossRef Full Text | Google Scholar

Masanovic, B., Gardasevic, J., Marques, A., Peralta, M., Demetriou, Y., Sturm, D. J., et al. (2020). Trends in physical fitness among school-aged children and adolescents: a systematic review. Front. Pediatr. 8. doi: 10.3389/fped.2020.627529

PubMed Abstract | CrossRef Full Text | Google Scholar

Mersmann, F., Bohm, S., Schroll, A., Boeth, H., Duda, G., and Arampatzis, A. (2014). Evidence of imbalanced adaptation between muscle and tendon in adolescent athletes. Scand. J. Med. Sci. Sport. 24:1266. doi: 10.1111/sms.12166

PubMed Abstract | CrossRef Full Text | Google Scholar

Mersmann, F., Bohm, S., Schroll, A., Boeth, H., Duda, G. N., and Arampatzis, A. (2017). Muscle and tendon adaptation in adolescent athletes: a longitudinal study. Scand. J. Med. Sci. Sport. 27, 75–82. doi: 10.1111/sms.12631

PubMed Abstract | CrossRef Full Text | Google Scholar

Mersmann, F., Bohm, S., Schroll, A., Marzilger, R., and Arampatzis, A. (2016). Athletic training affects the uniformity of muscle and tendon adaptation during adolescence. J. Appl. Physiol. 121, 893–899. doi: 10.1152/japplphysiol.00493.2016

PubMed Abstract | CrossRef Full Text | Google Scholar

Moliner-Urdiales, D., Ruiz, J. R., Ortega, F. B., Jiménez-Pavón, D., Vicente-Rodriguez, G., Rey-López, J. P., et al. (2010). Secular trends in health-related physical fitness in Spanish adolescents: the AVENA and HELENA studies. J. Sci. Med. Sport 13, 584–588. doi: 10.1016/j.jsams.2010.03.004

PubMed Abstract | CrossRef Full Text | Google Scholar

Moran, J., Sandercock, G. R. H., Ramírez-Campillo, R., Meylan, C., Collison, J., and Parry, D. A. (2017). A meta-analysis of maturation-related variation in adolescent boy athletes' adaptations to short-term resistance training. J. Sports Sci. 35, 1041–1051. doi: 10.1080/02640414.2016.1209306

PubMed Abstract | CrossRef Full Text | Google Scholar

Moreau, D., Kirk, I. J., and Waldie, K. E. (2017). High-intensity training enhances executive function in children in a randomized, placebo-controlled trial. Elife 6:e25062. doi: 10.7554/eLife.25062

PubMed Abstract | CrossRef Full Text | Google Scholar

Murawska-Cialowicz, E., Wojna, J., and Zuwala-Jagiello, J. (2015). Crossfit training changes brain-derived neurotrophic factor and irisin levels at rest, after wingate and progressive tests, and improves aerobic capacity and body composition of young physically active men and women. J. Physiol. Pharmacol. 66, 811–821.

PubMed Abstract | Google Scholar

Myer, G., Faigenbaum, A., Chu, D., Falkel, J., Ford, K., Best, T., et al. (2011). Integrative training for children and adolescents: techniques and practices for reducing sports-related injuries and enhancing athletic performance. Phys. Sportsmed. 39, 74–84. doi: 10.3810/psm.2011.02.1864

PubMed Abstract | CrossRef Full Text | Google Scholar

Myer, G. D., Quatman, C. E., Khoury, J., Wall, E. J., and Hewett, T. E. (2009). Youth versus adult “weightlifting” injuries presenting to United States emergency rooms: accidental versus nonaccidental injury mechanisms. J. Strength Cond. Res. 23, 2054–2060. doi: 10.1519/JSC.0b013e3181b86712

PubMed Abstract | CrossRef Full Text | Google Scholar

Ogden, C. L., Carroll, M. D., Lawman, H. G., Fryar, C. D., Kruszon-Moran, D., Kit, B. K., et al. (2016). Trends in obesity prevalence among children and adolescents in the United States, 1988–1994 through 2013–2014. JAMA— J. Am. Med. Assoc. 315, 2292–2299. doi: 10.1001/jama.2016.6361

PubMed Abstract | CrossRef Full Text | Google Scholar

Ortega, F. B., Silventoinen, K., Tynelius, P., and Rasmussen, F. (2012). Muscular strength in male adolescents and premature death: cohort study of one million participants. BMJ 345:e7279. doi: 10.1136/bmj.e7279

PubMed Abstract | CrossRef Full Text | Google Scholar

Peeters, C., Marchand, H., Tulloch, H., Sigal, R. J., Goldfield, G. S., Hadjiyannakis, S., et al. (2012). Perceived facilitators, barriers, and changes in a randomized exercise trial for obese youth: a qualitative inquiry. J. Phys. Act. Heal. 9, 650–660. doi: 10.1123/jpah.9.5.650

PubMed Abstract | CrossRef Full Text | Google Scholar

Pikosky, M., Faigenbaum, A., Westcott, W., and Rodriguez, N. (2002). Effects of resistance training on protein utilization in healthy children. Med. Sci. Sports Exerc. 34, 820–827. doi: 10.1097/00005768-200205000-00015

PubMed Abstract | CrossRef Full Text | Google Scholar

Plumert, J. M., and Schwebel, D. C. (1997). Social and temperamental influences on children's overestimation of their physical abilities: links to accidental injuries. J. Exp. Child Psychol. 67, 317–337. doi: 10.1006/jecp.1997.2411

PubMed Abstract | CrossRef Full Text | Google Scholar

Radnor, J. M., Lloyd, R. S., and Oliver, J. L. (2017). Individual response to different forms of resistance training in school-aged boys. J. Strength Cond. Res. 31, 787–797. doi: 10.1519/JSC.0000000000001527

PubMed Abstract | CrossRef Full Text | Google Scholar

Ramirez-Campillo, R., Andrade, D. C., Alvarez, C., Henríquez-Olguín, C., Martínez, C., Báez-Sanmartín, E., et al. (2014). The effects of interset rest on adaptation to 7 weeks of explosive training in young soccer players. J. Sports Sci. Med. 13, 287–96.

PubMed Abstract | Google Scholar

Ramirez-Campillo, R., Alvarez, C., García-Pinillos, F., Gentil, P., Moran, J., Pereira, L. A., et al. (2019a). Effects of plyometric training on physical performance of young Male soccer players: Potential effects of different drop jump heights. Pediatr. Exerc. Sci. 31:207. doi: 10.1123/pes.2018-0207

PubMed Abstract | CrossRef Full Text | Google Scholar

Ramirez-Campillo, R., Alvarez, C., Sanchez-Sanchez, J., Slimani, M., Gentil, P., Chelly, M. S., et al. (2019b). Effects of plyometric jump training on the physical fitness of young male soccer players: Modulation of response by inter-set recovery interval and maturation status. J. Sports Sci. 37, 2645–2652. doi: 10.1080/02640414.2019.1626049

PubMed Abstract | CrossRef Full Text | Google Scholar

Ramírez-Campillo, R., Meylan, C. M. P., Álvarez-Lepín, C., Henriquez-Olguín, C., Martinez, C., Andrade, D. C., et al. (2015). The effects of interday rest on adaptation to 6 weeks of plyometric training in young soccer players. J. Strength Cond. Res. 29, 972–979. doi: 10.1519/JSC.0000000000000283

PubMed Abstract | CrossRef Full Text | Google Scholar

Ratel, S., Lazaar, N., Dore, E., Baquet, G., Williams, C. A., Berthoin, S., et al. (2004). High-intensity intermittent activities at school: controversies and facts. J. Sports Med. Phys. Fitness 44, 272–280.

PubMed Abstract | Google Scholar

Runhaar, J., Collard, D. C. M., Singh, A. S., Kemper, H. C. G., van Mechelen, W., and Chinapaw, M. (2010). Motor fitness in Dutch youth: Differences over a 26-year period (1980–2006). J. Sci. Med. Sport 13, 323–328. doi: 10.1016/j.jsams.2009.04.006

PubMed Abstract | CrossRef Full Text | Google Scholar

Saggese, G., Meossi, C., Cesaretti, G., and Bottone, E. (1987). Physiological assessment of growth hormone secretion in the diagnosis of children with short stature. Pediatrician 14, 121–137.

PubMed Abstract | Google Scholar

Salvy, S. J., Bowker, J. C., Germeroth, L., and Barkley, J. (2012). Influence of peers and friends on overweight/obese youths' physical activity. Exerc. Sport Sci. Rev. 40, 127–132. doi: 10.1097/JES.0b013e31825af07b

PubMed Abstract | CrossRef Full Text | Google Scholar

Santtila, M., Pihlainen, K., Koski, H., Vasankari, T., and Kyröläinen, H. (2018). Physical fitness in young men between 1975 and 2015 with a focus on the years 2005–2015. Med. Sci. Sports Exerc. 50, 292–298. doi: 10.1249/MSS.0000000000001436

PubMed Abstract | CrossRef Full Text | Google Scholar

Soares, J. M. C., Mota, P., Duarte, J. A., and Appell, H. J. (1996). Children are less susceptible to exercise-induced muscle damage than adults: a preliminary investigation. Pediatr. Exerc. Sci. 8, 361–367. doi: 10.1123/pes.8.4.361

CrossRef Full Text | Google Scholar

Sobrero, G., Arnett, S., Schafer, M., Stone, W., Tolbert, T. A., Salyer-Funk, A., et al. (2017). A Comparison of high intensity functional training and circuit training on health and performance variables in women: a pilot study. Women Sport Phys. Act. J. 25, 1–10. doi: 10.1123/wspaj.2015-0035

CrossRef Full Text | Google Scholar

Stankov, I., Olds, T., and Cargo, M. (2012). Overweight and obese adolescents: what turns them off physical activity? Int. J. Behav. Nutr. Phys. Act. 9, 53. doi: 10.1186/1479-5868-9-53

PubMed Abstract | CrossRef Full Text | Google Scholar

Stracciolini, A., Myer, G. D., and Faigenbaum, A. D. (2013). Exercise-deficit disorder in children: are we ready to make this diagnosis? Phys. Sportsmed. 41, 94–101. doi: 10.3810/psm.2013.02.2003

PubMed Abstract | CrossRef Full Text | Google Scholar

Stracciolini, A., Quinn, B., Zwicker, R. L., Howell, D. R., and Sugimoto, D. (2020). Part I: crossfit-related injury characteristics presenting to sports medicine clinic. Clin. J. Sport Med. 30, 102–107. doi: 10.1097/JSM.0000000000000805

PubMed Abstract | CrossRef Full Text | Google Scholar

Sugimoto, D., Zwicker, R. L., Quinn, B. J., Myer, G. D., and Stracciolini, A. (2020). Part II: comparison of crossfit-related injury presenting to sports medicine clinic by sex and age. Clin. J. Sport Med. 30, 251–256. doi: 10.1097/JSM.0000000000000812

PubMed Abstract | CrossRef Full Text | Google Scholar

Sundar, T. K. B., Løndal, K., Lagerløv, P., Galvin, K., and Helseth, S. (2018). Overweight adolescents' views on physical activity—experiences of participants in an internet-based intervention: a qualitative study. BMC Public Health 18:5324. doi: 10.1186/s12889-018-5324-x

PubMed Abstract | CrossRef Full Text | Google Scholar

Thapa, R. K., Lum, D., Moran, J., and Ramirez-Campillo, R. (2021). Effects of complex training on sprint, jump, and change of direction ability of soccer players: a systematic review and meta-analysis. Front. Psychol. 11, 1–15. doi: 10.3389/fpsyg.2020.627869

PubMed Abstract | CrossRef Full Text | Google Scholar

Timón, R., Olcina, G., Camacho-Cardeñosa, M., Camacho-Cardenosa, A., Martinez-Guardado, I., and Marcos-Serrano, M. (2019). 48-hour recovery of biochemical parameters and physical performance after two modalities of CrossFit workouts. Biol. Sport 36, 283–289. doi: 10.5114/biolsport.2019.85458

PubMed Abstract | CrossRef Full Text | Google Scholar

Todendi, P. F., Brand, C., Silveira, J. F., de, C., Gaya, A. R., Agostinis-Sobrinho, C., et al. (2021). Physical fitness attenuates the genetic predisposition to obesity in children and adolescents. Scand. J. Med. Sci. Sport. 31, 894–902. doi: 10.1111/sms.13899

PubMed Abstract | CrossRef Full Text | Google Scholar

Tottori, N., Morita, N., Ueta, K., and Fujita, S. (2019). Effects of high intensity interval training on executive function in children aged 8–12 years. Int. J. Environ. Res. Public Health 16:4127. doi: 10.3390/ijerph16214127

PubMed Abstract | CrossRef Full Text | Google Scholar

Vera-Assaoka, T., Ramirez-Campillo, R., Alvarez, C., Garcia-Pinillos, F., Moran, J., Gentil, P., et al. (2020). Effects of maturation on physical fitness adaptations to plyometric drop jump training in male youth soccer players. J. strength Cond. Res. 34:3151. doi: 10.1519/JSC.0000000000003151

PubMed Abstract | CrossRef Full Text | Google Scholar

Wijnhoven, T. M., Van Raaij, J. M., Spinelli, A., Starc, G., Hassapidou, M., Spiroski, I., et al. (2014). WHO European childhood obesity surveillance initiative: body mass index and level of overweight among 6-9-year-old children from school year 2007/2008 to school year 2009/2010. BMC Public Health 14:806. doi: 10.1186/1471-2458-14-806

PubMed Abstract | CrossRef Full Text | Google Scholar

Wilson, J. M., Loenneke, J. P., Jo, E., Wilson, G. J., Zourdos, M. C., and Kim, J. S. (2012). The effects of endurance, strength, and power training on muscle fiber type shifting. J. Strength Cond. Res. 26, 1724–1729. doi: 10.1519/JSC.0b013e318234eb6f

PubMed Abstract | CrossRef Full Text | Google Scholar

Wright, K. E., Furzer, B. J., Licari, M. K., Dimmock, J. A., Jackson, B., and Thornton, A. L. (2020). Exploring associations between neuromuscular performance, hypermobility, and children's motor competence. J. Sci. Med. Sport 23, 1080–1085. doi: 10.1016/j.jsams.2020.06.007

PubMed Abstract | CrossRef Full Text | Google Scholar

Zghal, F., Colson, S. S., Blain, G., Behm, D. G., Granacher, U., and Chaouachi, A. (2019). Combined resistance and plyometric training is more effective than plyometric training alone for improving physical fitness of pubertal soccer players. Front. Physiol. 10, 1–11. doi: 10.3389/fphys.2019.01026

PubMed Abstract | CrossRef Full Text | Google Scholar

Keywords: sedentary behavior, pediatric obesity, resistance training, high-intensity interval training, plyometric exercise, human physical conditioning, physical exercise, interval training

Citation: Gentil P, Lira CABd, Vancini RL, Ramirez-Campillo R and Souza D (2021) High-Intensity Multimodal Training for Young People: It's Time to Think Inside the Box! Front. Physiol. 12:723486. doi: 10.3389/fphys.2021.723486

Received: 10 June 2021; Accepted: 23 July 2021;
Published: 12 August 2021.

Edited by:

Atle Hole Saeterbakken, Western Norway University of Applied Sciences, Norway

Reviewed by:

Philip Chilibeck, University of Saskatchewan, Canada
Wladimir Rafael Beck, Federal University of São Carlos, Brazil
Fabiano Francisco de Lima, Universidade de São Paulo, Brazil
Andre Nyberg, Ume University, Sweden

Copyright © 2021 Gentil, Lira, Vancini, Ramirez-Campillo and Souza. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Paulo Gentil, cGF1bG9nZW50aWwmI3gwMDA0MDtob3RtYWlsLmNvbQ==

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