Can complex contrast training interventions improve aerobic endurance, maximal strength, and repeated sprint ability in soccer players? A systematic review and meta-analysis

his systematic review and meta-analysis aimed to assess the effects of complex contrast training (CT) on aero- bic endurance, maximal strength, and repeated sprint ability (RSA) in soccer players. After an electronic search, nine peer-reviewed articles were considered, including soccer players from junior to professional-level (age 14 – 23 years). One study was conducted during the pre-season, seven studies during the in-season, and one study during the off-season period of a competitive schedule. The studies included were of moderate to high meth - odological quality (PEDro scale) and incorporated CT with soccer practice. Large significant improvements (ES = 1.30; 95% CI = 0.61 – 2.00; p < 0.001; I 2 = 80.6%) for maximal strength, and small non-significant improve- ments for aerobic endurance (ES = 0.33; 95% CI = -0.19 – 0.85; p = 0.209; I 2 = 0.0%) and RSA (ES = 0.32; 95% CI = -0.12 – 0.75; p = 0.156; I

significant improvements (ES = 1.30; 95% CI = 0.61 – 2.00; p < 0.001; I 2 = 80.6%) for maximal strength, and small non-significant improve- ments for aerobic endurance (ES = 0.33; 95% CI = -0.19 – 0.85; p = 0.209; I 2 = 0.0%) and RSA (ES = 0.32; 95% CI = -0.12 – 0.75; p = 0.156; I 2 = 0.0%) were noted for CT groups when compared to active or specific-active control groups. Therefore, supplementing regular soccer training with CT induces adaptations to improve maximal strength. CT may be implemented during the pre-season and in-season to induce adaptations similar to tradi - tional strength training (e.g., maximal strength gains), although alternative training strategies may be needed to further improve aerobic endurance and RSA. The use of CT may be applicable during different periods of the season to achieve certain goals, e.g., pre- and in-season for maximal strength development, and off-season to attenuate the decline of strength or power. Keywords: football, plyometric exercise, human physical conditioning, resistance training, muscle strength, movement Cite this article: Thapa, R.K., Narvariya, P., Weldon, A., Talukdar, K., & Ramirez-Campillo, R. (2022) Can complex contrast training interventions improve aerobic endurance, maximal strength, and repeated sprint ability in soccer players? A systematic review and meta-analysis. Montenegrin Journal of Sports Science and Medicine, 11 (2), Ahead of print. https://doi.org/10.26773/mjssm.220906 REVIEW ARTICLE @MJSSMontenegro COMPLEX CONTRAST TRAINING IN SOCCER http://mjssm.me/?sekcija=article&artid=241

4 DOI 10.26773/mjssm.220906COMPLEX CONTRAST TRAINING IN SOCCER | R. K. THAPA ET AL. Introduction Soccer requires a combination of aerobic and high-in- tensity demands (e.g., sprints, changes of direction) (Barnes et al., 2014; Bush et al., 2015), which defines the match run- ning performance among professional soccer players (Modric et al., 2022; Modric, Versic, et al., 2021). Indeed, these de- mands during training sessions may also determine the out- comes of matches (Modric, Jelicic, et al., 2021). A common method to assess these demands in soccer players is the Yo-Yo intermittent recovery test (Yo-Yo IRT) (Castagna et al., 2020; Deprez et al., 2015). Indeed, elite players show better Yo-Yo IRT performance compared to sub-elite (2,420 m versus 2,030 m) (Bangsbo et al., 2008). In addition to aerobic endurance, short-duration maximal- and near-maximal physical efforts (e.g., vertical jumps) are prevalent in soccer, and are required to overcome opponents during play (Stølen et al., 2005). These maximal- or near-maximal efforts have shown to be positive- ly associated with the strength of lower limbs (e.g., maximal squat strength) (Arnason et al., 2004; Requena et al., 2009; Thapa et al., 2019; Wisløff et al., 2004). Moreover, maximal strength of lower limbs (e.g., one repetition maximum [1RM]) may also be used to differentiate the player’s playing level (e.g., professional versus amateur) (Cometti et al., 2001). Another relevant aptitude in soccer players is the ability to repeatedly produce maximal sprints with brief recovery periods (Ramp- inini et al., 2007), considering the ever-increasing high-inten- sity running demands (e.g., ~30 % increase in high-intensity running distance between 2006 versus 2012) (Barnes et al., 2014; Bush et al., 2015; Dellal et al., 2011). Based on the avail- able evidence aerobic endurance (Bangsbo et al., 2008), mus- cle strength (Gissis et al., 2006; Reilly et al., 2000), and repeat- ed sprint ability (RSA) (Chaouachi et al., 2010; Stølen et al., 2005) are important physical characteristics for soccer players. Traditional strength training with exercises such as heavy squat (McKinlay et al., 2018; Silva et al., 2015) and plyometric jump training with exercises implicating a fast stretch-short- ening cycle muscle action (Ramirez-Campillo,

et al., 2006; Reilly et al., 2000), and repeat- ed sprint ability (RSA) (Chaouachi et al., 2010; Stølen et al., 2005) are important physical characteristics for soccer players. Traditional strength training with exercises such as heavy squat (McKinlay et al., 2018; Silva et al., 2015) and plyometric jump training with exercises implicating a fast stretch-short- ening cycle muscle action (Ramirez-Campillo, Gentil, et al., 2021; Sánchez et al., 2020; van de Hoef et al., 2019) may im- prove aerobic endurance, strength, and RSA. However, com- pared to a single training mode, a combination of resistance and plyometric/ballistic exercise (i.e., complex contrast train- ing [CT]) may further improve aerobic endurance, strength, and RSA in soccer players (Faude et al., 2013; Hammami et al., 2017a). CT involves the performance of a high-load low- speed resistance training exercise, followed immediately by the execution of a low-load high-speed plyometric/ballistic exercise (Carter & Greenwood, 2014; Cormier et al., 2022; Ebben, 2002; Fleck & Kontor, 1986). This training format usually involves performing biomechanically similar exercis- es with a high-load resistance exercise performed first (e.g., squat at 90% of one-repetition maximum [1RM]), followed by a low-load plyometric/ballistic exercise (e.g., squat jump) (Do- cherty et al., 2004; Fleck & Kontor, 1986). Sequencing exercis- es in such a format stimulates the post-activation potentiation of performance (Carter & Greenwood, 2014; Docherty et al., 2004; Hodgson et al., 2005; Prieske et al., 2020), subsequently increasing motor unit recruitment and force-production po- tential of the used musculature (Healy & Comyns, 2017; Tha- pa et al., 2020). Furthermore, CT may induce neuromuscular adaptations, such as enhanced stretch-shortening cycle func- tion, motor unit recruitment, firing frequency, intra- and in- ter-muscular coordination, and morphological changes (e.g., fiber type, pennation angle) (Cormie et al., 2011; Markovic & Mikulic, 2010), thus broadly enhancing athletic performance. Another benefit of CT is it provides a time-efficient combi- nation of traditional resistance and plyometric exercise into a single session, which may assist strength and conditioning coaches in overcoming congested weekly micro-cycles (Lim & Barley, 2016; Weldon et al., 2021). In the last decade, a considerable number of studies have analyzed the

Mikulic, 2010), thus broadly enhancing athletic performance. Another benefit of CT is it provides a time-efficient combi- nation of traditional resistance and plyometric exercise into a single session, which may assist strength and conditioning coaches in overcoming congested weekly micro-cycles (Lim & Barley, 2016; Weldon et al., 2021). In the last decade, a considerable number of studies have analyzed the effects of CT on soccer player’s athletic perfor- mance. However, aggregated literature in the form of system- atic reviews with meta-analysis are only available for a limited number of physical abilities such as sprint, jump, and change of direction ability (Thapa et al., 2021). Indeed, a recent sur- vey study by Weldon et al. (2021) on the practices of strength and conditioning coaches in professional soccer found the most common application (52%) of plyometric training was in the form of CT when compared to other formats (e.g., before weights, separate days, after weights). However, it is yet to be determined whether CT may favor other key physical abilities such as aerobic endurance, maximal strength, and RSA. In- deed, some studies suggested a greater improvement in aero- bic endurance (Miranda et al., 2021), maximal strength (Brito et al., 2014), and RSA (Spineti et al., 2016) after CT compared to single-mode training (e.g., soccer training), but others re- ported contrasting findings (Faude et al., 2013; Hammami et al., 2017a; Kobal et al., 2017). Part of the controversy in some studies may be related to insufficient statistical power in their analyses, arising from a reduced sample size. Indeed, most studies involving CT among soccer players recruited reduced sample sizes in the experimental interventions (e.g., n=10) (Faude et al., 2013; Kobal et al., 2017; Spineti et al., 2016). A reduced number of participants precludes generalization of findings to other soccer athlete groups (Abt et al., 2020). As an alternative to experimental studies, meta-analysis allows the aggregation of sample sizes from different studies, providing more robust conclusions (Murad et al., 2016). To the author’s knowledge, no study has attempted to aggregate the available literature regarding the effects of CT on soccer player's aerobic endurance, maximal

generalization of findings to other soccer athlete groups (Abt et al., 2020). As an alternative to experimental studies, meta-analysis allows the aggregation of sample sizes from different studies, providing more robust conclusions (Murad et al., 2016). To the author’s knowledge, no study has attempted to aggregate the available literature regarding the effects of CT on soccer player's aerobic endurance, maximal strength, and RSA. Therefore, this sys- tematic review with meta-analysis aims to assess the available body of peer-reviewed articles related to the effects of CT on aerobic endurance, maximal strength, and RSA among soccer players compared to active control groups. The results arising from this systematic review may be useful for practitioners to make evidence-based decisions regarding CT interventions for soccer players in relation to the optimization of aerobic en- durance, maximal strength, and RSA. Methods This systematic review with meta-analysis was conducted following the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) (Page et al., 2021). The lead author conducted preliminary electronic searches in PubMed and Google Scholar databases. Articles published up to February 15 th , 2022 were considered. The key- words were selected based on a previous meta-analysis study conducted on CT for similar population (Thapa et al., 2021). The following combination of keywords (Using Boolean log- ic) was used in the search databases: “complex training” or “contrast training” and “soccer”. An example of search strat- egy used in PubMed was: ((complex training) OR (contrast training)) AND (soccer). For Google Scholar database, the

COMPLEX CONTRAST TRAINING IN SOCCER | R. K. THAPA ET AL. DOI 10.26773/mjssm.220906 5 author used the advanced search option. An example of search strategy in Google Scholar was: with all of the words (complex training soccer); where my words occur (in the title of the arti- cle). The same author retrieved the list of articles and removed duplicates. Thereafter, the search results were analyzed accord- ing to the eligibility criteria (Table 1). Table 1. Selection criteria used in the systematic review with meta-analysis. Category Inclusion criteria Exclusion criteria Population Apparently healthy soccer players, with no restrictions on their playing level, sex, or age. Soccer players with health problems (e.g., injuries, recent surgery). Intervention A complex contrast training programme, defined as a combination of heavy load strength exercise followed by low load plyometric/power exercise, set by set. Exercise interventions not involving complex contrast training or exercise interventions involving descending training, where strength training exercises were conducted first and plyometric/power exercises were conducted at the end or during a different session. Comparator Active control group (i.e., players participating in regular soccer training) or specific-active control group (i.e., players participating in regular soccer training combined with traditional strength training). Absence of active control group or specific-active control group. Outcome At least one measure related to lower body strength, repeated sprint ability and endurance before and after the training intervention. Lack of baseline and/or follow-up data. Study design Controlled trials. Non-controlled trials. For the inclusion of studies two authors (RKT and PN) independently screened the titles, abstracts, and full-text versions of the retrieved studies. Any potential discrepancies between the same two authors regarding the inclusion and ex- clusion criteria were resolved through the consensus with a third author (RRC). From selected articles, the reference lists were examined to identify further articles for inclusion in the meta-analysis. Inclusion and exclusion criteria A PICOS (participants, intervention, comparators, out- comes, and study design) approach was used to rate studies’ el- igibility (Liberati et al., 2009). Table 1 shows the inclusion/ex- clusion criteria adopted in this study, with only peer-reviewed articles in English. Articles only published in

reference lists were examined to identify further articles f

This study reviews the impact of complex contrast training on soccer players' performance.