Impact of COVID-19 infection on physical performance of soccer players: a systematic review

Abstract

This review sought to identify the impact of COVID-19 infection on the physical performance parameters of soccer players. The systematic review was conducted based on the PRISMA guidelines. The following databases were searched up to the end of October 2024: MEDLINE, Scopus, Mendeley, SPORTDiscus, and Google Scholar. Studies conducted on professional and semi-professional adult male soccer players were considered. For a study to be included, it had to report at least one outcome measure both before and after COVID-19 infection. At the end of the screening procedure, a total of 11 studies met the inclusion criteria. The reviewed studies on V̇O2 max showed mixed results. One study reported a significant (p<0.01) decrease 60 days post-infection, while others found no change or even an increase 1-year post-pandemic. Pulmonary function assessment revealed a significant (p<0.01) increase in respiratory work, whereas one study found no significant changes at rest. GPS (Global Positioning System) -based studies reported a significant (p<0.05) reduction in high-intensity accelerations, decelerations, and high-speed running post-COVID-19, while one study found no differences between infected and non-infected players. Strength, power, and anaerobic power showed no significant decline. These findings should be interpreted with caution due to the small sample sizes and limited number of studies.

 

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Keywords

SARS-CoV-2 - return to play - isolation - football - game performance

Introduction

Coronavirus (COVID-19), caused by SARS-CoV-2, has affected many aspects of human life, including sports. The short-term mild to moderate effects of COVID-19 infection primarily include but are not limited to fever, fatigue, muscle pain, cough, shortness of breath, headache, nausea, and loss of taste [1]. In more severe cases, patients experience pneumonia and multi-organ failure, which require hospitalization and intensive care [1] [2]. Beyond the acute phase, a subset of individuals experience long COVID symptoms after the initial recovery from SARS-CoV-2 infection [2]. The symptoms of long COVID include fatigue, muscle pain, palpitations, cognitive impairment, dyspnea, anxiety, chest pain, and arthralgia [2]. Such long-term effects can significantly impact the quality of life, daily functioning, and physical performance, especially in athletes and physically active individuals. For soccer players, COVID-19 infection created considerable challenges due to the high physical demands of the game [3]. As players returned to training after recovering from COVID-19, coaches and medical personnel realized that it was essential to understand how the virus had impacted players’ physical performance. This understanding was essential for developing appropriate, individualized recovery strategies, making training adjustments, and implementing safe return-to-play protocols based on medical and league-specific guidelines, such as FIFA’s return-to-play protocols and the Aspetar Clinical Guidelines [4] [5].

Several studies confirm that soccer players must maintain high cardiovascular fitness to meet the demands of this intense sport, where high-intensity actions are interspersed with low-intensity activities [6] [7] [8]. Considering that the most decisive and critical moments of the game require high-speed running and sprinting [8], it is clear that players are required to maintain high levels of anaerobic power, strength, and speed in addition to aerobic fitness and technical skills. Thus, the return-to-play process for soccer players following COVID-19 infection was not easy as it required not only reaching peak performance levels but also ensuring the players’ safety. Despite the urgency of the issue, only a few studies evaluated the impact of COVID-19 infection on male soccer players. The limited studies primarily focused on the cardiorespiratory system [9], game-related performance [10], and strength parameters [11] following COVID-19 infection. Parpa and Michaelides (2022) [9] demonstrated that professional soccer players experienced a significant reduction in V̇O2 max, running time on the treadmill, and velocity at V̇O2 max two months post-infection, suggesting that full recovery may take longer than anticipated. Furthermore, they demonstrated a significant reduction of V̇O2 max at the respiratory compensation point (RC) and higher heart rate values at the ventilatory threshold (VT) and RC. The authors explained that the reduction in the RC point may indicate an increased hypoxic ventilatory response [9]. Also, they emphasized that the earlier onset of the RC point, which is linked to hyperventilation due to impaired bicarbonate buffering and a subsequent increase in blood PH, should be taken into consideration, as it suggested a reduced aerobic capacity even 60-days post post-COVID-19 recovery. Similar reductions were observed in a study by Savicevic and colleagues (2021) [10], which reported a significant decline in high-intensity accelerations and decelerations post-infection. Conversely, no changes were reported in strength or power performance among male soccer players following COVID-19 infection [11]. While these studies provide valuable information, they are limited by small sample sizes, short-term follow-ups, and the assessment of only specific performance or fitness parameters, leaving a gap in our understanding of how COVID-19 affects soccer players over the different phases of recovery and return to play as well as the long-term consequences on the various performance parameters. Furthermore, while a few systematic reviews and meta-analyses have been conducted on the effects of COVID-19 infection and/or confinement on athletic performance in general athletic populations, none have specifically examined the impact of COVID-19 infection on the performance parameters of male soccer players. Considering the unique demands and characteristics of soccer, there is a clear need for a focused review to better understand the specific impact of COVID-19 infection on this group.

Therefore, this systematic review aims to present the related literature on the impact of COVID-19 on soccer players, focusing on physical performance changes after the acute and post-recovery phases. More specifically this review sought to identify and quantify the acute and post-recovery changes in strength, aerobic performance, and game-related parameters of soccer players who had been infected with COVID-19 and returned to play following the return-to-play protocols.

 

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Methodology

This systematic review followed the preferred reporting items for systematic reviews (PRISMA). The protocol was registered with the International Platform of Registered Systematic Review and Meta-Analysis Protocols with the number INPLASY202530099 and DOI 10.37766/inplasy2025.3.0099.

Furthermore, the criteria used for the conclusion of the studies followed the guidelines of the PICOS strategy ([Table 1]). A systematic literature search was conducted for articles published up to the end of October 2024, and the time frame was set between 2021 and 2024. The following databases were searched: MEDLINE (via PubMed), Scopus, Mendeley, SPORTDiscus (via EBSCOhost), and Google Scholar. Additionally, the reference lists of the selected studies were reviewed to identify eligible studies that were not captured by the electronic searchers. The search strategies included the following keywords: COVID-19, performance, soccer, football, running, strength, cardiovascular, aerobic, anaerobic respiration, and infection. The keywords were combined using the Boolean operators “AND” and “OR.”

Table 1 Definition of PICOS for inclusion and exclusion of articles.

Parameter	Definition
Population	Elite and sub-elite adult male soccer players
Intervention	Exposure to COVID-19 virus
Comparison	Pre-and post-exposure conditions
Outcomes	Cardiovascular endurance, strength, and game-related parameters of performance
Study design	No restrictions regarding the study design

Abbreviation: PICOS: population, intervention, comparison, outcomes and study design.

The selection of studies was based on the following inclusion criteria: (1) studies involving professional and semi-professional adult male soccer (football) players; and (2) investigations of performance parameters such as endurance, strength, and game-related variables before and after COVID-19 infection. Articles were excluded based on the following criteria: (1) non-peer-reviewed studies, review articles, letters to the editor, editorials, posters, conference abstracts and case studies; (2) studies not published in English; (3) studies investigating lockdown rather than infection, psychological parameters, COVID-19 incidence, injuries, sports other than soccer, female soccer players, or adolescent/ youth players; and (4) studies lacking details and quantitative information.

Initial screening was conducted by two experienced investigators (K. P. and K. I.). The two investigators independently searched for studies based on the titles and abstracts and reviewed the studies’ relevance based on the inclusion and exclusion criteria. All relevant articles were collected, and the duplicated studies were removed. If the two researchers could not agree, the opinion of a third investigator (A. P.) was obtained. Next, some articles were selected to read the full text to verify that they met the inclusion criteria as described by the PICOS strategy, demonstrated in [Table 1]. Articles that passed the screening were selected for a full review. The following information was obtained from the selected studies: authors and year of publication, the aim of the study, descriptive characteristics of the sample, instruments and methodology, analysis, results, and conclusions.

Quality assessment

The risk of bias was assessed utilizing the 16-item form that evaluates study quality based on Law and colleagues [12]. The instrument has undergone validation by multiple investigators to ensure its reliability and applicability in systematic reviews related to the performance of soccer players [13] [14]. The articles were evaluated according to the items presented in [Table 2]. The selected studies were evaluated on a binary scale (meets the criteria=1, does not meet the criteria=0). Study quality was calculated by summing the obtained score and dividing by the total number of scored items (total of 16). Studies were then classified, based on the final score, as having low methodological quality (below 50%), good methodological quality (51–75%), or excellent methodological quality (over 75%), as presented in previously published studies [13] [14].

Table 2 Assessment of methodological quality according to previous studies.

	Question	Answer	Score
Q1	Was the purpose stated clearly?	Yes=1	0–1
		No=0
Q2	Was relevant background literature reviewed?	Yes=1	0–1
		No=0
Q3	Was the design appropriate for the research question	Yes=1	0–1
		No=0
Q4	Was the sample described in detail?	Yes=1	0–1
		No=0
Q5	Was the sample size justified?	Yes=1	0–1
		No=0
Q6	Was informed consent obtained?	Yes=1	0–1
		No=0
Q7	Were the outcome measures reliable?	Yes=1	0–1
		No=0
Q8	Were the outcome measures valid?	Yes=1	0–1
		No=0
Q9	Was the methodology described in detail?	Yes=1	0–1
		No=0
Q10	Were the results reported in terms of statistical significance?	Yes=1	0–1
		No=0
Q11	Were the analysis (methods) appropriate?	Yes=1	0–1
		No=0
Q12	Was the importance reported?	Yes=1	0–1
		No=0
Q13	Were there any dropouts reported?	Yes=1	0–1
		No=0
Q14	Were the conclusions appropriate given the study methods and results?	Yes=1	0–1
		No=0
Q15	Were the study implications presented?	Yes=1	0–1
		No=0
Q16	Were the limitations presented and described by the authors?	Yes=1	0–1
		No=0
			Total: 0–16

 

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Selection process

The selection process is presented in [Fig. 1] (Flowchart), which was developed according to the PRISMA guidelines [15]. The initial search identified a total of 2,213 articles (PubMed: 74, Scopus: 76, SPORTDiscus: 16, MENDELEY: 1890, and Google Scholar: 157). Duplicates relevant to the purpose of this review (16 studies) were identified and removed. The remaining studies were screened for relevance based on titles and abstracts. Out of the 2,197 studies, 2,125 were considered ineligible as they examined endurance athletes, injury rates among female soccer players, elite pooled athletes, high school female soccer players, and young adolescent male players. Also, some studies were excluded because they examined the psychological impact of COVID-19 or the effects of lockdown rather than COVID-19 infection or because they investigated sports other than soccer. Lastly, two studies were excluded as they were published in Spanish and French. After the initial screening, 70 studies were examined due to uncertainty if they met the inclusion criteria. Out of these, 15 studies were selected for meeting most of the general inclusion criteria. Upon screening the full texts, four studies were excluded for not meeting the eligibility criteria. Of these four studies, one focused on workers, one examined the impact of the COVID-19 pandemic rather than COVID-19 infection, one investigated the incidence, relative risk, and characteristics of COVID-19 infection among high-level footballers over 12 months, and the last, although relevant, was a letter to the editor. At the end of the screening procedure, 11 studies were suitable for inclusion in the analysis. Based on the quality assessment ([Table 3]), eight studies were classified as excellent, one as good, and two as low quality. Details on the characteristics and methodologies of the included studies are presented in [Table 4].

Fig. 1 PRISMA flowchart [15] illustrating the flow of information through the different phases of a systematic review.

Table 3 A quality assessment based on the selected criteria (16 items).

Author	Year	Q1	Q2	Q3	Q4	Q5	Q6	Q7	Q8	Q9	Q10	Q11	Q12	Q13	Q14	Q15	Q16	%	Classification
Parpa and Michaelides [9]	2022	1	1	1	1	0	1	1	1	1	1	1	1	0	1	1	0	81.25	Excellent
Savicevic et al. [10]	2021	1	1	1	1	0	0	1	1	1	1	1	1	0	1	1	1	81.25	Excellent
Gattoni et al. [16]	2022	1	1	1	1	0	1	1	1	1	1	1	1	1	1	1	1	93.75	Excellent
Stavrou et al. [17]	2023	1	0	1	1	0	1	1	1	1	1	1	1	0	1	1	1	81.25	Excellent
Nincevic et al. [18]	2023	1	1	1	1	0	0	1	1	1	1	1	1	0	1	1	1	81.25	Excellent
Wagemans et al. [11]	2021	1	1	1	1	0	1	1	1	1	1	1	1	0	1	1	1	87.5	Excellent
Wezenbeek et al. [19]	2023	1	1	1	1	0	1	1	1	0	1	1	1	1	1	1	1	87.5	Excellent
Luo et al. [20]	2024	1	1	1	1	1	0	1	1	1	1	1	1	1	1	1	0	87.5	Excellent
Bruzzese et al. [21]	2023	1	0	1	0	0	1	1	1	0	1	1	0	0	1	0	0	50	Low
Muñoz et al. [22]	2024	1	0	1	1	0	0	1	1	1	1	1	1	0	1	1	1	75	Good
Mickovska et al. [23]	2022	1	1	1	0	0	1	1	0	0	1	0	0	0	1	0	1	50	Low

Note: Quality classification scale:<50%=low methodological quality, 51–75%=good methodological quality,>75% excellent methodological quality [13] [14].

Table 4 Methodology and participant characteristics of the included studies.

Authors/country	Characteristics	Duration	Post-testing and severity of symptoms	Aerobic Capacity	Running performance	Pulmonary/respiratory function	Power	Strength	Technical performance
Parpa and Michaelides (2022) [9] Cyprus	21 division-1 elite soccer players (age 24.24±5.75 years, height 178.21±5.44 cm, weight 74.12±5.21 kg	60 days	2 months post-COVID. Symptoms mild to moderate	Incremental maximal cardiopulmonary exercise testing
Savicevic et al. (2021) [10] Croatia	47 professional soccer players; 31 players positive (infected) and 16 negative.	Season 2020/2021	Athletes were 10–14 days in isolation followed by 1–4 weeks of retraining depending on symptoms. Testing was done one month (30-days) after returning to play.		GPS data (10 variables)
	Mean age: 21.6 years		74% were symptomatic, while 26% were asymptomatic.
Gattoni et al. (2022) [16] Italy	13 professional soccer players (age: 23.9±4.0 years)	Season 2020/2021	15.5±5 days post-COVID and following 10 official games.			Incremental running step test and spirometry	GPS data (accelerations, decelerations, high-speed running, total distance covered etc)
			Symptoms mild to moderate
Stavrou et al. (2023) [17] Greece	40 male professional players [divided in COVID-19 group (age:25.2±4.1) and healthy group (age:25.1±4.4)	Season 2021/2022	2 days after a negative test. Total duration of positive test (6.1±1.1) days. Asymptomatic			Cardiopulmonary exercise testing and Spirometry. Blood lactate to assess O2 utilization
Nincevic et al. (2023) [18] Croatia	First division players (N=47 in season 2020/21; N=31 in season 2021/22)	Season 2020/21	Comparison of two seasons. Mild to moderate symptoms.		GPS data (accelerations, decelerations, high-speed running, total distance covered etc.)
		Season 2021/22
Wagemans et al. (2021) [11] Belgium	33 Professional players (age: 25.37±4.11 years; height: 182.75±7.62 cm; weight: 78.90±8.97 kg)	Season 2020/21	Players were assessed weekly for up to 8 weeks post-COVID. Testing completed 2, 4, and 8 weeks after a positive test.				Jump test	Adductor, abductor tests (ForceFrame) and hamstring strength test (NordBord)
Wezenbeek et al. (2023) [19] Belgium	84 professional players (from 3 teams). Out of these 22 players got infected.	Season 2020/2021	Quarantine duration was 12.1±6.1 days. Testing was conducted 52.0±11.2 days and 127.6±33.1 days after positive PCR. 20 had mild to moderate and 2 had more severe symptoms.	YOYO test for%HR max.			Jump test	Eccentric knee flexor strength (NordBoard)
							Sprint test
Luo et al. (2024) [20] England, Spain, Germany, Italy, France	100 attacking players from the 5 Big European football leagues	2020–2023	3–4 months post-COVID with data collection spanning from 2020 to 23.						Game data (28 match technical performance indicators)
Bruzzese et al. (2023) [21] Argentina	10 professional players (22.4±6.9 years, body mass 71.5±7.1 kg and height 176.2±6.9 cm)	2021	10 days after medical discharge. 5 asymptomatic and 5 with mild to moderate symptoms	Cardiopulmonary exercise test (CPET)
Munos et al. (2024) [22] Brazil	20 professional players	Season 2020/2021	1–4 weeks upon return to play. Moderate symptoms		GPS data (accelerations, decelerations, high-speed running, total distance covered etc)
Mickovska et al. (2022) [23] Republic of North Macedonia	16 players (mean age 25.0±5.28 years)	Season 2021/2022	1-year post-pandemic.	Bruce submaximal treadmill test
	10 infected, 6 non-infected.		Asymptomatic or mild symptoms

 

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Outcome domains

The primary outcome domains included in this systematic review were (1) cardiorespiratory measurements (e.g., V̇ O2 max, V̇ O2 max at RC, V̇ O2 max at VT, heart rate values, velocities at RC, at VT and V̇ O2 max, metabolic power, metabolic needs, hyperventilation, respiratory exchange ratio, and running performance on a treadmill and/or bicycle), (2) strength and power performance measurements (e.g., muscle strength, jump performance, and anaerobic power), and (3) game related parameters (e.g., GPS data, high-intensity accelerations, high-intensity decelerations, game technical performance, and distance covered during high-intensity actions). Data were considered if measurements were obtained at baseline (before COVID-19 infection) and during follow-up assessments (no restrictions were applied to the follow-up assessment). All reported outcomes within each domain from the included studies were considered.

Studies were considered eligible for inclusion based on the predefined criteria, population characteristics, a confirmed positive for the COVID-19 virus, and reported outcome measures. For each synthesis, studies were categorized based on the three primary outcome domains. Therefore, for this systematic review, the studies were grouped based on common methodological approaches.

 

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Results

Aerobic capacity and pulmonary function

Six studies[9] [16] [17] [19] [21] [23] were identified evaluating aerobic capacity and pulmonary function ([Table 5]). Regarding the V̇ O2 max and aerobic performance, one study [9] reported a significant decrease (57.4±4.6 to 54.3±5.2, p<0.01), while two studies [17] [21] found no differences. In contrast, another study [23] observed a significant increase when the whole group was tested 1 year post-COVID-19 infection (+2.42 ml kg⁻¹ min⁻¹, p<0.05). V̇ O2 RC was significantly reduced in two studies [9] [21]. More specifically, the study by Parpa and Michaelides (2022) [9] demonstrated that V̇ O2 at RC decreased from 49.8±6.1 to 47.5±5.7 (p<0.05) when the assessment was conducted 60 days post-COVID. In agreement were the results of Bruzzese and colleagues (2023) [21], which indicated an 18% reduction in V̇ O2 at RC (p<0.05). In the same study [21], RER was significantly reduced by 5% when 10 professional players were tested 10 days after medical discharge. In addition to the aforementioned findings Parpa and Michaelides (2022) [9] demonstrated significant reductions in running time on the treadmill (p<0.01) and velocity at V̇ O2 max (p<0.05) when the players performed maximal incremental cardiorespiratory testing ([Table 5]). Furthermore, HR at VT and RC significantly increased [9] while HR max showed only a slight increase in the same study. On the contrary, three studies [17] [19] [21] indicated significant increases in maximal HR max or% HR max. More specifically the study by Stavrou and colleagues (2023) [17] indicated a significant increase in HR max (from 191.6±7.8 to 196.6±8.6, p<0.05) in asymptomatic patients with a positive test of 6.1±1.1 days. In agreement were the results by Bruzzese et al. (2022) [23] that revealed a 1.8% increase (p<0.05) in HR max when testing was conducted 10 days after medical discharge on five asymptomatic patients and five patients with mild to moderate symptoms. Additionally, a study by Wezenbeek et al. (2023) [19] revealed a significant (p<0.05) increase in%HR max on average 52.0±11.2 days after a positive test; however, this increase was no longer present after 127.6±33.1 days when the 22 professional players were tested (20 players with mild to moderate symptoms and 2 with more severe symptoms) utilizing a Yo-Yo intermittent recovery test. In the same study [19], non-infected players demonstrated a clinically significant 2–5% decrease in%HR max. With regard to respiratory function, Stavrou et al. (2023) [17] reported a compromised respiratory function in post-COVID-19 players characterized by increased respiratory work at both rest and maximum effort (137.1±15.5 vs. 109.1±18.4, p<0.01) as well as hyperventilation during exercise. On the contrary, Gattoni et al. (2022) [16] suggested no significant changes in respiratory function at rest when the players with mild to moderate symptoms were tested 15.5±5 days post-COVID-19 infection.

Table 5 Aerobic capacity and pulmonary function.

Authors	V̇O2 max and/or aerobic performance	V̇O2 RC or VT2 point	RER	Running time (min)	HR at VT	HR max or%HR max	HR at RC	Velocity at V̇O2 max (km h−1)	Respiratory function	RW
Parpa and Michaelides (2022) [9]	57.4±4.6 to 54.3±5.2**	49.8±6.1 to 47.5±5.7*		17.5±2.2 to 16.6±2.1**	150±16.6 to 158±12.9**	190±7.9 to 191±7.7	174±9.3 to 179±10.1**	17.4±1.4 to 16.9±1.4*
Gattoni et al. (2022) [16]									↔ (FEV1, PEF, FVC) pre and 15.5±5 days post COVID
Stavrou et al. (2023) [17]	55.7±4.4 to 55.4±4.6					191.6±7.8 (COVID) vs. 196.6±8.6 (Non)*			14.7±3.1(COVID) vs 11.5±2.6 (Non)**	137.1±15.5 (COVID) vs. 109.1 18.4 (Non)**±hyper ventilation
Wezenbeek et al. (2023) [19]						↑* (52.0±11.2 days after a positive test)
						↔ (127.6±33.1 days after a positive test)
Bruzzese et al. (2023) [21]	61.7±5.2 vs 59.0±5.1	↓ 18%*	↓ 5%*			↑ 1.8%*
Mickovska et al. (2022) [23]	+2.42 ml kg−1 min−1 for the whole group

Abbreviations: HR at RC: heart rate at respiratory compensation (beats min⁻¹); HR at VT: heart rate at ventilatory threshold (beats min⁻¹); RER: respiratory exchange ratio; RW: respiratory work (L min⁻¹); V̇O2 max: Maximal oxygen consumption (ml kg⁻¹ min⁻¹); V̇O2 RC or VT2: V̇O2 at respiratory compensation or second ventilatory threshold (ml kg⁻¹ min⁻¹);

Note: *p<0.05, **p<0.01, ↔ no change or absent, ↑ increased, ↓ decreased.

 

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GPS parameters and technical performance

Five studies [10] [16] [18] [20] [22] were identified evaluating GPS parameters and technical performance ([Table 6]). Regarding the GPS parameters, Savicevic et al. (2021) [10] demonstrated significantly lower high-intensity acceleration counts (28.7±11.6 to 21.2±10.8, p<0.05) and high-intensity deceleration counts (38.1±10.3 to 31.3±15.3, p<0.05), when the 31 COVID-19 positive professional players were compared to the 16 negative players. In their study, COVID-19-positive players were isolated for 10–14 days, which was followed by 1–4 weeks of return to play training based on the severity of the symptoms. Similar findings were reported by Munos et al. (2024) [22], showing a significant reduction (p<0.05) in the distance covered during high-intensity running and a significant (p<0.05) increase in the distance travelled at speeds between 0 and 7 km/h, when 20 professional players with moderate symptoms were tested 1–4 weeks after returning to play. On the contrary, the study by Nincevic et al. (2023) [18] reported that accelerations, decelerations, high-speed running, and total distance covered were not significantly different between infected and non-infected groups. It is important to note that their study [18] assessed players over two seasons. Regarding metabolic power, Gattoni et al. (2022) [16] demonstrated a significant reduction of−4.1±3.5% (p<0.05) when analyzing GPS data from 10 official games following the players’ return to play. Last but not least, a study by Luo and colleagues (2024) [20] reported changes in 76% of players’ match technical performance. More specifically, 14 indicators (five indicators linked to scoring) were significantly (p<0.05) compromised post-COVID-19. In their study [20], the elite group experienced fewer negative effects, with players returning to pre-COVID infection levels after an average of 2.64 games, while the control group required 3.55 games for recovery.

Table 6 GPS parameters and technical performance.

Authors	HI accelerations (count)	HI deceleration (count)	HI distance	Metabolic power (w/kg)	Game running performance	Game technical performance (14 indicators, five linked to scoring)
Savicevic et al. (2021) [10]	28.7±11.6 to 21.2±10.8*	38.1±10.3 to 31.3±15.3*
Gattoni et al. (2022) [16]				−4.1±3.5%*
Nincevic et al. (2023) [18]					↔ (accelerations, decelerations, high-speed running, total distance covered, etc.) were not significantly different between infected and non-infected groups.
Muños et al. (2024) [22]			↓* distance covered during high-intensity running and ↑* in distance traveled at speeds between 0 and 7 km/h.
Luo et al. (2024) [20]						Changes in 76% of players’ match technical performance. 14 indicators (five indicators linked to scoring) significantly ↓* post-COVID-19. The elite group experienced fewer negative effects, and players returned to pre-COVID infection levels on average after 2.64 games compared to the control group, which required 3.55 games.

Abbreviation: HI: high intensity.

Note: *p<0.05, **p<0.01, ↔ no change or absent, ↑ increased, ↓ decreased.

 

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Strength, power, and anaerobic performance

Two studies [11] [19] were identified evaluating strength, power, and anaerobic performance. The studies evaluated parameters such as jump performance, specifically jump height during the countermovement jump, lower extremity strength (knee flexor, hip adductors/abductors, and hamstrings), and anaerobic performance during 5- and 20-m sprint tests. The results of both studies showed no significant differences in these parameters due to COVID-19 infection. The study by Wagemans et al. (2021) [11] reported that the functional strength of the hamstring muscle improved significantly (p<0.05) at 2 weeks and 4 weeks after COVID-19 infection in the 11 players, with a mean duration of illness of 13±7 days.

 

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Discussion

The present systematic review investigated the acute and post-recovery changes in aerobic performance, strength, power, and game-related parameters of soccer players who had been infected with COVID-19 and returned to play following return-to-play protocols. In general, the effects of COVID-19 infection on athletic performance vary, with significant effects on aerobic capacity [9] [21], pulmonary function [17], GPS parameters [10] [16] [22], and technical performance [20], while strength, power, and anaerobic performance remain largely unaffected [11] [19]. V̇ O2 max showed mixed results, with one study reporting a decrease [9] two months post-COVID-19 infection, while others found no change [17] [19] or even an increase 1 year post-pandemic [23]. Studies indicated a significant reduction in V̇ O2 max at RC [9] [21] and running velocity at V̇ O2 max [9], while maximum HR generally increased [17] [19] [21] post-COVID-19 infection. Pulmonary function assessment revealed increased respiratory work and hyperventilation [17] at rest and during maximal exertion, whereas others found no significant changes at rest [16]. GPS-based studies indicated reduced high-intensity accelerations, decelerations, and high-speed running post-COVID-19 [10] [22], while one study found no differences between infected and non-infected players [18]. Furthermore, it was reported that technical performance was compromised in 76% of the players, particularly in scoring-related parameters [20]. Last but not least, strength, power [11] [19], and anaerobic power [19], including spring and jump tests, showed no significant decline, with one study even reporting improved hamstring strength 2 to 4 weeks post-infection [11].

Aerobic capacity and pulmonary function

Several studies highlight the use of incremental exercise testing to assess V̇ O2 max as a key indicator of aerobic capacity in elite male soccer players [24]. Based on this systematic review, Parpa and Michaelides (2022) [9] reported a significant reduction in V̇ O2 max from 57.4±4.6 to 54.3±5.2 ml kg⁻¹ min⁻¹ (p<0.01, d=0.61 medium effect) along with a decline in V̇ O2 at RC (p<0.05, d=0.39 small effect), velocity at V̇ O2 max (p<0.05, d=0.41, small effect), and running time on the treadmill (p<0.01, d=0.46, small effect) when the same elite soccer players with mild and moderate symptoms were tested pre and 60 days post-COVID-19 infection. Bruzzese et al. (2023) [21] reported similar findings, with a significant (p<0.05) 18% reduction in V̇ O2 at RC. Although V̇ O2 max also decreased (from 61.7±5.2 to 59.0±5.1 ml kg⁻¹ min⁻¹), the change was not statistically significant. However, it is important to note that the results of the aforementioned study [21] are based on a small sample size of only 10 professional players, and the testing was conducted 10 days after medical discharge. Concurrently, no information was available on the return-to-play protocol the players followed. While one might argue that the reductions in aerobic capacity observed in the study by Parpa and Michaelides (2022) [9] could be due to training interruptions, the authors emphasized that these declines cannot be solely due to detraining, as the professional players followed a 2-week re-training phase, a 10-day specific adaptation program, and a 20-day game adaptation program. Therefore, their study raised important concerns about players’ readiness even 60 days after recovering from COVID-19. In contrast to the findings mentioned above, Mickovska et al. (2022) [23] reported an increase in V̇ O2 max (+2.42 ml kg⁻¹ min⁻¹) across their study population. Notably, the study included 10 infected (either asymptomatic or with mild symptoms) and 6 non-infected players, with the reported improvements in V̇ O2 max observed for the whole group 1 year after the pandemic. Despite the limitations of these studies, the combined results suggest that players may not achieve full recovery 2 months after COVID-19 infection but appear to be fully recovered after 1 year.

Regarding the heart rate responses at different ventilatory thresholds, Parpa and Michaelides (2022) [9] reported that HR at VT increased significantly (from 150±16.6 to 158±12.9, p<0.01, d=0.55 medium effect) as did HR at RC (from 174±9.3 to 179±10.1, p<0.01, d=0.52 medium effect), while HR max remained stable. The authors suggested that the increases in HR at RC and VT may be linked to an elevated cardiovascular response due to hypoxemia [9]. Stavrou et al. (2023) [17] also noted significant changes in HR responses post-COVID-19 infection, where the HR max was significantly higher (from 191.6±7.8 to 196.6±8.6, p<0.05) in asymptomatic patients with a positive of 6.1±1.1 days. Similar findings were reported by Bruzzese et al. (2022) [23] as well as Wezenbeek et al. (2023) [19] who reported significant (p<0.05) increases in%HR max 52.0±11.2 days after a positive COVID-19 test. However, this increase was no longer present when the players were retested 127.6±33.1 days post-infection, which may suggest a recovery period of approximately 2–3 months [19]. Based on these results, the authors [19] suggested that the observed decline in aerobic performance may have been due to alterations in muscle enzyme activity and metabolic function, leading to capillary flow disturbances that limited oxygen uptake and reduced the endurance capacity of the elite players. They also [19] proposed that persistent fatigue following the acute phase of COVID-19 could be a contributing factor, as some athletes continue to experience symptoms such as cough, fatigue, and tachycardia. Lastly, the authors [19] noted that the early return to training (average 12.1±6.1 days) may have influenced their findings.

Regarding respiratory function and respiratory work, Stavrou et al. (2023) [17] reported a compromised respiratory function in post-COVID-19 players characterized by increased respiratory work at both rest and maximum effort (137.1±15.5 vs. 109.1±18.4, p<0.01) as well as hyperventilation during exercise. Furthermore, the authors reported significantly higher blood lactate concentrations in post-COVID-19 athletes. The authors explained that the body compensates for potential hypoxia through hyperventilation (which was evident in their study), aiding in CO₂ removal. Furthermore, considering that post-COVID-19 patients may have an impaired lung diffusion capacity for carbon monoxide, the authors suggested that this impairment could lead to an increased reliance on anaerobic metabolism, resulting in excessive blood lactate accumulation. The authors further explained that oxygen utilization may be systematically reduced due to impaired gas exchange following COVID-19 infection and that hyperventilation indicates persistent respiratory inefficiencies. In contrast to the above findings, Gattoni et al. (2022) [16] suggested no significant changes in respiratory function at rest when the players with mild to moderate symptoms were tested on average 15.5±5 days post-COVID-19 infection. However, it is important to note that the study is limited by its small sample size of only 13 professional players.

 

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GPS and game performance indicators

This review highlighted significant differences in high-intensity acceleration counts (28.7±11.6 to 21.2±10.8, p<0.05, moderate effect size) and high-intensity deceleration counts (38.1±10.3 to 31.3±15.3, p<0.05, moderate effect size) [10] when 31 COVID-19 positive professional players were compared to 16 negative players. In the above study [10], COVID-19-positive players were isolated for 10–14 days, which was followed by 1–4 weeks of return-to-play training based on the severity of the symptoms. It should be noted that competitive regulations in Croatia did not allow a longer recovery period, and therefore some of the players in the above study [10] had less available time to adapt to the full training process due to their competition calendar. In addition, the authors reported that the games were postponed only if more than seven players were infected, but in the case of individual infections games were played according to schedule, which forced some professional teams to even speed up the return-to-play protocols, which may suggest that some players did not fully recover before they returned to play.

Furthermore, the study by Munos et al. (2024) [22] reported a moderate and significant reduction (p<0.05) in the distance covered during high-intensity running and a significant (p<0.05) increase in the distance travelled at speeds between 0 and 7 km/h, when 20 professional players with moderate symptoms were tested after returning to play during the 2020–2021 season. The authors suggested that these changes might have been due to isolation periods or the players altering their movement patterns in response to suboptimal recovery periods during matches. Furthermore, the authors pointed out that the return-to-play protocols were not entirely applicable at the time of their study due to the many unpredictable, specific, and contextual factors that influenced the time required for players to return to play. Reductions were also reported in metabolic power over the 10 games played immediately after COVID-19 compared to the 10 games played immediately before, as indicated by the reduction of game intensity by 4.1%±3.5% despite covering the same distance per unit of time [16]. Furthermore, a study by Luo and colleagues (2024) [20] evaluated the impact of COVID-19 infection on technical performance indicators for soccer attacking players upon their return to play, including 100 players from the five big domestic leagues (England, Spain, Germany, Italy, and France). The data of the aforementioned study were collected over 3–4 months after completion of return-to-play protocols, with the data collection spanning from 2020 to 2023. Considering the differences in the timing of COVID-19 infection among players, the nearly 3-year data collection period, and the inclusion of players from five different countries, it is likely that the players did not follow the same return-to-play protocols. Despite this, 75% of the players had changes in at least one performance indicator compared to their pre-COVID-19 levels. Notably, 14 performance indicators (out of which 5 were related to scoring) demonstrated a significant decline, with players requiring an average of 3.09 games to return to their pre-infection levels. The researchers demonstrated that the elite players experienced a milder effect, requiring an average of 2.64 games for recovery, while the control group needed 3.55 games. Lastly, their study indicated that age did not influence these results [20].

Interestingly, a study by Nincevic et al. (2023) [18] evaluated the same players who were re-infected during the 2021–2022 season (16 out of the 31 players who had been infected during the 2020–2021 season) following the same inclusion criteria. In addition to experiencing milder symptoms during their second infection and fewer days of inactivity, the OMICRON variant did not negatively affect game performance. The authors suggested that the non-significant differences in high-intensity accelerations observed during the second infection might be attributed to the adjustments made to the return-to-play protocols that were implemented after the 2020–2021 season [18]. Considering that soccer relies heavily on high-intensity actions, these adjustments to the return-to-play protocols were expected, as reductions in high-intensity accelerations or distance covered during high-intensity running raised concerns for coaches and sports scientists.

 

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Strength and anaerobic performance

Interestingly, this systematic review revealed no impact on strength and anaerobic parameters as indicated by jump [11] [19] and sprint testing [19]. In addition, researchers demonstrated no impact of COVID-19 infection on adductor or abductor muscle strength, while the functional hamstring strength improved significantly 2 weeks and 4 weeks after COVID-19 infection [11]. These results align with other studies [25] on highly trained athletes (Shanghai Elite Sports Training Administrative Center), which indicated that after a 4-week recovery period, athletes’ maximum and explosive strength was nearly close to pre-infection levels. In the same study [25], it was, however, indicated that reactive strength and initial phase force generation capability remained significantly impaired following COVID-19 infection. Therefore, based on the results of both studies that were conducted on soccer players [11] [19] and non-soccer elite athletes [25], it may be suggested that strength and anaerobic performance are primarily dependent on neuromuscular adaptations and may not be as directly affected by COVID-19 infection as the cardiovascular system. Furthermore, considering that COVID-19 has a significant effect on the lungs and the cardiovascular system, it may not have an immediate impact on muscle strength, especially in patients with mild to moderate symptoms.

 

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Conclusions

Although most studies reported significant impairments in aerobic capacity, pulmonary function, and technical skills, with no significant negative effects on strength and anaerobic power, these findings should be interpreted with caution due to the small sample sizes and limited number of studies. It is important to consider the significant variation in return-to-play timelines, as the number of days that the players were absent from sporting activities ranged from 7 to 51 days. In addition, there was a considerable variation in the number of days infected players did not play any games, with a range spanning from 7 to 97 days. Furthermore, most of the studies did not account for changes in body composition, which could have influenced performance parameters. Also, sleep disturbances, which were prevalent during COVID-19 and may have influenced performance parameters, were not reported in any of the studies. Furthermore, variations in symptoms caused by different viral strains (mutations) should be considered when evaluating the effects of COVID-19 infection. It is important to account for differences among the Alpha, Beta, Delta, and Omicron variants, as well as the impact of vaccination status. As indicated by the reviewed studies, omicron was associated with less severe respiratory illness. Also, the vaccination status might have influenced the results, especially in studies conducted over the course of two seasons. Additionally, return-to-play protocols were not consistently applied across studies; in some cases, they were not fully implemented, while in others, the coaching staff had to accelerate the process due to competitive regulations, potentially resulting in some players returning before full recovery. Therefore, the results of our review cannot be generalized to all male soccer players, as the severity of COVID-19 and return-to-play protocols varied significantly both between subjects in different studies and within the same studies. Considerations should also be given to the level of the players, pre-infection fitness levels, playing position, and period of the season.

Despite the aforementioned discrepancies, this review may offer some insights which can be used to improve recovery protocols, minimize performance decrements, and ultimately enhance both individual athletes’ and overall team performance in the event of a future situation similar to COVID-19. Considering the variability in COVID-19 effects, it is essential to adopt an individualized approach when assessing and managing each player’s recovery, ensuring tailored interventions that take into account all the physiological, psychological, and performance-related parameters. Also, it is recommended that future reviews focus on female soccer players as well as youth players.

 

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Conflict of interest

The authors declare that they have no conflicts of interest.

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Publikationsverlauf

Eingereicht: 30. November 2024

Angenommen nach Revision: 08. Mai 2025

Artikel online veröffentlicht:
16. Juni 2025