Team sports, such as soccer, basketball, rugby, and handball, are intermittent-type activities characterized by a high number of repetitive high-intensity efforts interspersed with low-intensity actions or rest (Mohr et al., 2003; Narazaki et al., 2009; Povoas et al., 2017). For instance, most team sports matches include 150-400 high-intensity movement patterns mostly consisting of running, sprinting, jumping, acceleration, deceleration, changes of direction and various sport-specific actions such as tackling, shuffling and throwing (Mohr et al., 2003; Narazaki et al., 2009; Povoas et al., 2017). All these actions though, incorporate a strong eccentric component associated with exercise-induced muscle damage (EIMD) that results in an acute inflammatory response and performance deterioration for as long as 24-72 h (Ispirlidis et al., 2008; Fatouros et al., 2010; Chatzinikolaou et al., 2014a; 2014b; Draganidis et al., 2015; Mohr et al., 2016).
Characteristically, muscle damage induced by match-play results in marked deterioration of strength (concentric and eccentric force of knee flexors and extensors), lower limb muscle power (jumping, speed, agility), and repeated sprint ability (Ispirlidis et al., 2008; Fatouros et al., 2010; Chatzinikolaou et al., 2014a; 2014b; Draganidis et al., 2015; Mohr et al., 2016). This performance deterioration is accompanied by a rise in delayed onset of muscle soreness (DOMS), immune system activation, inflammatory response and EIMD markers such as creatine kinase activity (CK) and C-reactive protein (CRP), pro-inflammatory cytokines, adhesion molecules and oxidative stress markers (Ispirlidis et al., 2008; Fatouros et al., 2010; Chatzinikolaou et al., 2014a; 2014b; Draganidis et al., 2015; Mohr et al., 2016). However, professional athletes in these sports follow a congested match schedule of three matches/week and daily practices (> 50 matches annually) that allows them only a 3- or 4-day recovery period between successive matches. Research indicates that this time may be inadequate to restore normal homeostasis resulting in prolonged performance deterioration and increased likelihood for occurrence of musculoskeletal injuries (Ekstand et al., 2004; Montgomery et al., 2008; Dupont et al., 2010). Therefore, increased attention has been focused on recovery strategies able to treat symptoms of EIMD and to restore muscles' function. These strategies are applied as either lifestyle (e.g., sleep), exercise (e.g., active recovery), physiological (e.g., cooling, massage, compression), nutritional [e.g. protein supplements, carbohydrate (CHO) feeding], or pharmacological interventions (e.g. anti-inflammatory medications) aiming to blunt the inflammatory response, enhance muscle regeneration and thus overall performance recovery (Minett and Costello, 2015).
Amongst nutritional strategies, protein supplements are widely used by athletes and physically active individuals to increase their muscle mass and enhance post-exercise recovery and performance, representing up to 70% of the sport supplement industry (5 billion dollars) (Petroczi and Naughton, 2008; Pasiakos et al., 2013; Draganidis et al., 2017). These consumers have been convinced that protein supplements will offset EIMD, facilitate skeletal muscle repair and contribute to an upregulated glycogen re-synthesis when co-administered with CHO during recovery (Pasiakos et al., 2014). Indeed, numerous studies have addressed this proof of concept (Cockburn et al., 2008; 2010; 2013; Cooke et al., 2010; Shenoy et al., 2016) providing evidence that protein-based supplementation following acute damaging exercise protocols, attenuates the decrease in muscle performance, mitigates the rise in DOMS and muscle damage markers such as CK, myoglobin (Mb) and lactate dehydrogenase, and enhances muscle regeneration and remodeling process by increasing the proliferation of satellite cells (Farup et al., 2014) during recovery. This protein-mediated effect is primarily attributed to the fact that protein supplementation during recovery increases the rate of muscle protein synthesis (Lunn et al., 2012; Breen et al., 2011) and as such facilitates muscle repair and remodeling (Breen et al., 2011) and accelerates performance recovery (Saunders, 2007). In the absence of protein or insufficient feeding following damaging exercise, EIMD accelerates muscle protein turnover by upregulating both its synthesis and degradation (Draganidis et al., 2017; Pitkanen et al., 2003), however, degradation increases over synthesis thereby resulting in a negative protein balance (Koopman et al., 2005).
An earlier systematic review on the effects of protein supplementation on recovery from endurance exercise concluded that protein supplements may promote protein synthesis acutely but no meaningful improvement in EIMD and performance recovery has been observed (Pasiakos et al., 2014). Team sports, on the other hand, such as soccer, basketball, and handball are probably the most popular sports worldwide attracting the largest number of professional and amateur participants and have a unique activity profile which is associated with a specific pattern of EIMD and recovery distinguishing them from other athletic activities such as running, biking, resistance training etc. (Ispirlidis et al., 2008; Fatouros et al., 2010; Chatzinikolaou et al., 2014a; 2014b; Draganidis et al., 2015; Mohr et al., 2016). However, a systematic review of the available evidence that supports or refutes the use of protein supplements as a post-match recovery strategy in these sports is lacking. Therefore, this paper reviews all available investigations that examined the effects of protein-based supplementation on EIMD markers and performance restoration following team sport activity.
The Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines were applied for this review.
To review whether protein supplementation affects recovery following team sport match or training activity, a search was performed with no date restriction up to 2018 in PubMed to identify relevant peer-reviewed articles. Key-terms were grouped and searched within the article title, abstract, and keywords using the conjunctions 'OR' and 'AND'. The terms that were used in the search were: "Protein", "exercise-induced muscle damage", "exercise-induced inflammation", "recovery", "redox status", "glutathione", "casein', "cysteine", "whey protein", "soy protein", "team sports", "soccer", "basketball", and "team handball". Reviews previously published were also screened for similar headings and key-words. Search was limited to articles published in the English language and studies that utilized protein supplementation/feeding during recovery following match-play. References of these articles were also searched to find potential relevant articles.
Study selection, inclusion and exclusion
Articles were included if: 1) they involved healthy, nonsmoking adults (18-40 years) classified as professional, semi-professional or amateur athletes (training experience [greater than or equal to]2 years) who did not consume performance-enhancing supplements and medications; 2) athletes participated in [greater than or equal to]3 training sessions/week and played at least one match/week; 3) participants had a baseline dietary protein consumption of [greater than or equal to]0.8 g/kg/day; 4) examined the effects of protein supplementation on [greater than or equal to]1 muscle damage, inflammatory, and performance markers following match and/or training activity for [greater than or equal to]2 h of recovery; 5) used a single- or double-blind, repeated measures design; 6) protein supplementation was utilized before and/or immediately after match or training activity and throughout recovery; and 6) examined the effects of either protein supplementation/feeding alone or in combination with CHO supplementation. Articles were excluded if they: 1) involved animals, youth (
Data extraction and management
The following data were extracted from the selected studies: study design, participants' characteristics, the type of exercise or training in which the participants were submitted (match, simulated match, training), the type of protein supplement, performance indicators, and EIMD, oxidative stress, inflammatory and metabolic markers.
Assessment of methodological quality
The reviewers used the Cochrane Collaboration Tool (CCT) to characterize the quality of the selected studies as low, high or unclear risk of bias or applicability (Tables 1 and 2) (Higgins et al., 2011). A study that satisfied all criteria for low risk it was rated with an A. A study that satisfied all criteria for high risk it was rated with a C. A study that satisfied all criteria for unclear it was rated with a D. Studies with mixed criteria were rated with a B.
The flowchart of the search is presented in Figure 1. In total, 69 abstracts were screened for eligibility. A total of 44 abstracts were excluded (63.7%), mostly because the study population did not participate in team sports or the exercise protocol did not resemble a team sport (88.6%). Furthermore, five abstracts did not contain original data (11.4%). The full-text examination of the 25 remaining articles excluded 15 (60%) more studies (three studies were not accessible, three studies examined another type of exercise, two studies did not use protein supplementation for recovery, three studies did not include team sports, one study did not contain original data, one investigation utilized questionnaires, and four studies did not use an acute exercise protocol). Consequently, ten studies were analyzed for this systematic review (Arent et al., 2010; Betts et al., 2009; Cockburn et al., 2013; Gentle et al., 2014; Gilson et al., 2010; Gunnarsson et al., 2013; Highton et al., 2013; Naclerio et al., 2015; 2014; Poulios et al., 2018).
Quality of the...