The impact of a mid-season FIFA World Cup™ on injury occurrence and patterns in French professional soccer clubs

ABSTRACT

This study retrospectively compared the effect of holding the 2022 FIFA World Cup™ (WC) mid-season (season 2022/23) on injury rates and patterns in French Ligue 1 soccer clubs. Epidemiological data in 17 clubs were prospectively recorded by their physicians. Time-loss injuries (injuries leading to a player being unable to fully participate in play over the following 72-hour period) were compared with those reported during a regular season (2021–22). In the WC season, an increase of approximately 23% (training + match-play) was observed for both the total number of injuries and knee, ankle and muscle injuries combined. Incidences for match-play injury overall and for the knee, ankle and muscle regions combined and the hamstrings and calf regions specifically also rose significantly (range: p < 0.05-p < 0.01). These results suggest that injury occurrence and patterns in French L1 soccer clubs were substantially affected during the 2022/23 season when a mid-season WC was held.

KEYWORDS:

• Injury
• incidence
• epidemiology
• football
• World Cup

Introduction

In 2010, FIFA announced that Qatar would be the host country for its 2022 World Cup (WC). In addition to concerns about the country’s climatic conditions, notably the increased physiological strain associated with high temperatures, the tournament was subsequently scheduled to take place mid-season; across the months of November and December (winter for professional European football). This would be the first time that European-based players would participate in a mid-season WC. In addition to the major risk of injury commonly observed in international soccer tournaments (Sprouse et al., 2020), concerns were raised concerning the potential compounding effects of both the congested pre-tournament club competition schedules and an unusually short preparatory pre-WC period (Zouhal et al., 2022). Indeed, prior to the 2022 WC, professional European teams had played substantially more games at the same time point than during the previous season (Whitehead, 2022). At professional standards, players are typically at greater risk of sustaining injury (Page et al., 2023) and notably soft-tissue injuries such as muscle strains and joint sprains (Carling et al., 2016) when matches are played successively following a reduced recovery time. Regarding preparation time, players from the top European leagues were only released approximately 1 week prior to the tournament start and consequently may have had insufficient time to prepare optimally for the upcoming matches (FIFAPRO, 2022a).

In addition to the above points, concerns were also raised about how a mid-season WC might impact the rest of the competitive season, possibly leading to an exacerbated risk of fatigue and injury (Varley & Sprouse, 2022). European domestic championships and competitions were put on hold for a substantial duration (>40 days). Consequently, a major challenge for clubs would be how to reintegrate their players, in a short time frame, while accounting for how far their respective national teams had progressed, their exposure time, injuries sustained and returning fitness levels (Zouhal et al., 2022). This transition was important for players with reduced match time during the tournament and conversely for those with extensive match exposure time during the WC. Furthermore, the major European leagues typically integrate a winter break which was not the case following this WC. Injury risk in professional soccer is reportedly greater when there is no winter break (Ekstrand et al., 2019). Conversely, another challenge was managing the extended break from competition for players who remained in their clubs and who were accustomed to a substantially shorter mid-season pause typically placed later in the season. As such, comparison of injury rates and patterns with those from regular seasons would be pertinent to help determine the effects, if any, of holding a WC mid-season.

The purpose of this study was to retrospectively compare injury occurrence, with a specific focus on match-play injuries and muscle and knee and ankle joint injuries, in professional soccer clubs and specifically those participating in UEFA European competitions from a major European League (France’s Ligue 1) during the 2022–23 season, when the FIFA Qatar World Cup took place mid-season. Results were compared with equivalent data recorded during a regular season (2021–22).

Material and methods

This retrospective descriptive epidemiological study investigated injury occurrence and muscle and knee and ankle/foot injuries specifically, in French professional football (top-flight clubs from Ligue 1 [L1]) over two seasons. The aim was to compare the potential effects of a mid-season WC on injury risk. For this, a regular season 1 (S1, 2021–22) was compared with the WC season (S2, 2022–23). Only clubs participating in both seasons were conserved for analysis (n = 17).

The present data arose as a contractual condition of player employment (Winter & Maughan, 2009) and French regulations (règlement de la Ligue de Football Professionel [LFP], article 584) in which Ligue 1 clubs’ epidemiological and health data are systematically monitored and recorded in a national database. Data are made available by each club’s physician for exploratory analysis, usage and publication by the French Association of Physicians in Professional Football and the Medical Department of the French Football Federation. All individual participating clubs and the Federation’s Medical Council nevertheless provided permission for analysis and publication of the data, and this study follows the principles of the Declaration of Helsinki. To ensure strict team and player confidentiality and respect national privacy regulations for individuals, all information in the national database is systematically anonymized.

Match-play exposure time (hours) for each club was calculated using information from the LFP and internet media sources. This was derived by multiplying the total number of matches played (including League, French Cups and European competition) by 1.5 hours (based upon 90-minute play). When extra-time was played, an additional 0.5 hours (30-minute play) was included.

As part of the LFP’s epidemiological monitoring process, all injuries sustained by players in training and match-play were prospectively diagnosed by their club’s sports physician and documented in the Askamon athlete injury monitoring system (SAM IMSPro, Monaco) over the entire study period. Here, only injuries resulting in time-loss were included (Fuller et al., 2006), with all club physicians using the same definition to record injuries: an injury resulting from playing football and leading to a player being unable to fully participate in play over the following 72-hour period (Dauty & Collon, 2011; Feller et al., 2019), irrespective of whether a training session actually took place on the day following injury or whether the player was selected to play in the next match. Players were considered injured until they were able to fully participate in collective training and available for match selection. The type and location of each injury were documented and those diagnosed as muscle and joint injuries (knee and ankle specifically) injuries were extracted and their subsequent incidence rates reported.

Data are presented as frequencies, means and percentages unless otherwise stated. Training injuries were only reported as frequencies as exposure time in training-related activities was not systematically documented. The incidence of match-play injury (number of injuries per 1000 hours exposure to play) and incidence rate ratios (IRR) were calculated for all L1 clubs and specifically in clubs that participated in UEFA European competitions or not. Season 2021/22 was used as the regular (benchmark) season. Match injury incidences were also compared for the pre- and post-WC period during the 2022/23 season. Muscle and knee and ankle joint injuries were compared using the same analyses. 95% confidence intervals (95%CI) values were calculated for incidence and IRR values. The IRR were tested for statistical significance using the Z statistic (Hayen & Finch, 2010). A statistically significant difference was observed when p < 0.05 and if the 95% confidence interval of the incidence rate ratio did not include 1.0. All statistical procedures were performed using Excel (Microsoft, Richmond, USA).

Results

The season duration (number of days between the first and last match) was longer in the regular season: 255 days in S1 (2021/22) versus 288 in S2 (2022/23). Overall exposure time to match-play across all clubs was similar between the two seasons: 12391.5 hours in S1 and 12,243 hours in S2 (Table 1).

Table 1. Inter-seasonal match exposure time in French Ligue 1 teams during the 2022 World Cup season versus a regular season (2021/22).

Season	Regular season 2021–22		World Cup season 2022–23		Pre–World Cup period 2022–23		Post-World Cup period 2022–23
Match-play exposure	N° Matches	Exposure (h)	N° Matches	Exposure time	N° Matches	Exposure time	N° Matches	Exposure time
Clubs participating in Europe (n = 6)	301	4966.5	297	4900.5	130	2145	167	2755.5
Club not participating in Europe (n = 11)	450	7425	445	7342.5	165	2722.5	280	4620
All clubs (n = 17)	751	12391.5	742	12243	295	4867.5	447	7375.5

Respectively, a total of 850 (match: n = 467 [54.9%], training: n = 383 [45.1%]) versus 696 injuries (match: n = 385 [55.3%], training: n = 311 [44.7%]) was observed in S2 versus S1: a + 22.6% increase overall. For knee, ankle and muscle injuries combined, a total of 528 (match: n = 301 [57.0%], training: n = 227 [43.0%]) versus 431 injuries (match: n = 231 [53.6%], training: n = 200 [46.4%]) was observed in S2 compared with S1 respectively: a + 22.5% increase.

The overall risk of incurring an injury was higher in S2 than in S1 across all 17 L1 clubs (IRR: 1.2 [1.1–1.4], p < 0.01) and specifically in those participating in European competitions (IRR: 1.3 [1.1–1.6], p < 0.05) (Table 2). Clubs participating in European competitions in S2 also observed a greater overall risk of match injury in the post- versus pre-WC period (IRR: 1.4 [1.1–1.8], p < 0.05). Table 2 also reports the combined knee, ankle and muscle injuries sustained in match-play. The overall risk of incurring one of these injuries was greater in S2 versus S1 across all the L1 clubs (IRR: 1.3 [1.1–1.6], p < 0.01) and specifically in those participating in European competitions (IRR: 1.6 [1.2–2.1], p < 0.001). No differences were observed in the risk of incurring one of these injuries for the post- versus pre-WC period in S2.

Table 2. Frequency and incidence of all injuries and muscle and knee and ankle injuries combined in French Ligue 1 teams during the 2022 World Cup season versus a regular season (2021/22).

Season	Regular season 2021–22			World Cup season 2022–23			Pre-World Cup period2022–23			Post-World Cup period2022–23			2022–23 vs2021–22		Post- vs Pre-World Cup 2023
All injuries	Total N°	N° per match	Incidence	Total N°	N° per match	Incidence	Total N°	N° per match	Incidence	Total N°	N° per match	Incidence	IRR (95%CI)	p value	IRR (95%CI)	p value
Clubs participating in Europe (n = 6)	143	0.48	28.8 (24.1–33.5)	187	0.63	38.2 (32.7–43.7)	68	0.52	31.7 (24.1–39.2)	119	0.71	43.2 (35.5–51.0)	1.3 (1.1–1.6)	0.0110*	1.4 (1.1–1.8)	0.0417*
Clubs not participating in Europe (n = 11)	242	0.54	32.6 (28.5–36.7)	280	0.63	38.1 (33.6–42.6)	116	0.70	42.6 (34.8–50.4)	164	0.59	35.5 (30.1–40.9)	1.2 (1.0–1.4)	0.0757	0.8 (0.7–1.1)	0.1329
All clubs (n = 17)	385	0.51	31.1 (27.8–34.5)	467	0.63	38.1 (34.6–41.6)	184	0.62	37.8 (32.3–43.3)	283	0.63	38.4 (33.9–42.9)	1.2 (1.1–1.4)	0.0031*	1.0 (0.8–1.2)	0.8679
Muscle, knee & ankle injuries	Total N°	N° per match	Incidence	Total N°	N° per match	Incidence	Total N°	N° per match	Incidence	Total N°	N° per match	Incidence	IRR (95%CI)	p value	IRR (95%CI)	p value
Clubs participating in Europe (6)	82	0.27	16.5 (12.9–20.1)	131	0.44	26.7 (22.2–31.3)	51	0.39	23.8 (17.3–30.3)	80	0.62	29.0 (22.7–35.4)	1.6 (1.2–2.1)	0.0006*	1.2 (0.9–1.7)	0.2701
Clubs not participating in Europe	149	0.33	20.1 (16.8–23.3)	170	0.38	23.2 (19.7–26.6)	69	0.42	25.3 (19.4–31.3)	101	0.61	21.9 (17.6–26.1)	1.2 (0.9–1.4)	0.2012	0.9 (0.6–1.2)	0.3555
All clubs	231	0.31	18.6 (16.2–21.0)	301	0.41	24.6 (21.8–27.4)	120	0.41	24.7 (20.2–29.1)	181	0.61	24.5 (21.0–28.1)	1.3 (1.1–1.6)	0.0014*	1.0 (0.8–1.2)	0.9449

Injury incidence (number of injuries per 1000 hours play) and Incidence Rate Ratio (IRR) comparisons across seasons are presented with 95% Confidence Intervals (95%CI).

*= Significant difference.

No differences were observed across seasons for injuries incurred in the knee or ankle regions (Table 3). In contrast, there was a significantly greater risk of sustaining a muscle injury overall (IRR: 1.4 [1.1–1.7], p < 0.01) and specifically in the hamstring (IRR: 1.4 [1.1–1.9], p < 0.05) and calf (IRR: 2.3 [1.2–4.2], p < 0.05) regions in S2. Additional analysis of these muscle injuries (Table 4) showed that clubs participating in UEFA European competitions (IRR: 1.6 [1.1–2.2, p < 0.01] and those that were not (IRR: 1.3 [1.0–1.7, p < 0.05] both reported a significantly greater risk of muscle injuries overall during S2 versus S1. Clubs participating in European competitions specifically were at greater risk of sustaining a hamstring injury (IRR: 1.6 [1.1–2.3, p < 0.01] in S2, while this was the case for calf injuries in clubs not participating in European competitions (IRR: 2.4 [1.0–5.4, p < 0.05].

Table 3. Frequency and incidence of muscle injuries and location and knee and ankle/foot ligament injuries in French Ligue 1 teams (n = 17) during the 2022 World Cup season versus a regular season (2021/22).

Season	Regular season 2021–22			World Cup season 2022–23			2022–23 vs 2021–22
Muscle. ankle & knee injuries	Total	Per match	Incidence	Total	Per match	Incidence	IRR (95%CI)	p value
Total muscle injuries	163	0.22	13.2 (11.2–15.2)	226	0.30	18.5 (16.1–20.9)	1.4 (1.1–1.7)	0.0010*
Hamstrings	75	0.10	6.1 (4.7–7.4)	108	0.15	8.8 (7.1–10.5)	1.4 (1.1–1.9)	0.0148*
Groin	29	0.04	2.3 (1.4–3.1)	38	0.05	3.1 (2.1–4.1)	1.4 (0.8–2.1)	0.2261
Quadriceps	28	0.04	2.3 (1.5–3.1)	27	0.04	2.2 (1.4–3.0)	1.0 (0.6–1.6)	0.8691
Calf	14	0.02	1.1 (0.5–1.7)	31	0.04	2.5 (1.6–3.4)	2.3 (1.2–4.2)	0.0108*
Other	17	0.02	1.4 (0.7–2.1)	22	0.03	1.8 (1.0–2.5)	1.3 (0.7–2.4)	0.4364
Total knee & ankle/foot ligament injuries	68	0.09	5.5 (4.2–6.8)	75	0.10	6.1 (4.7–7.5)	1.1 (0.8–1.5)	0.5364
Knee	21	0.03	1.7 (1.0–2.4)	26	0.04	2.1 (1.3–2.9)	1.2 (0.7–2.2)	0.4714
Medial collateral	15	0.02	1.2 (0.6–1.8)	12	0.02	1.0 (0.4–1.6)	0.8 (0.4–1.4)	0.6378
Lateral collateral	0	0.00	0.0	3	0.00	0.2 (−0.1–0.5)
Cruciate	3	0.00	0.2 (−0.1–0.5)	7	0.01	0.6 (0.2–1.0)	3.0 (0.8–11.6)	0.1114
Other	3	0.00	0.2 (−0.1–0.5)	4	0.01	0.3 (0.0–0.6)	1.5 (0.3–6.7)	0.5955
Ankle	47	0.06	3.8 (2.7–4.9)	49	0.07	4.0 (2.9–5.1)	1.1 (0.7–1.5)	0.8016
Internal lateral ligament	9	0.01	0.7 (0.2–1.2)	5	0.01	0.4 (0.0–0.8)	0.6 (0.2–1.7)	0.3016
External lateral ligament	15	0.02	1.2 (0.6–1.8)	23	0.03	1.9 (1.1–2.7)	1.6 (0.8–3.3)	0.1662
Posterior talofibular	13	0.02	1.0 (0.4–1.6)	6	0.01	0.5 (0.0–1.0)	0.5 (0.2–1.3)	0.1602
Other	10	0.01	0.8 (0.3–1.3)	15	0.02	1.2 (0.6–1.8)	1.5 (0.7–3.3)	0.3206

Injury incidence (number of injuries per 1000 hours play) and Incidence Rate Ratio (IRR) comparisons across seasons are presented with 95% Confidence Intervals (95%CI).

*= Significant difference.

Table 4. Frequency and incidence of muscle strains during the 2022 World Cup season versus a regular season in French Ligue 1 teams participating or not in UEFA European competitions.

Season	Regular season 2021–22			World Cup season 2022–23			2022–23 vs 2021–22
Muscle injuries	N° muscle injuries	N° per match	Incidence	N° muscle injuries	N° per match	Incidence	IRR (95%CI)	p value
Total injuries
Clubs participating in Europe (n = 6)	60	0.20	12.1 (9.0–15.1)	93	0.31	19.0 (15.1–22.8)	1.6 (1.1–2.2)	0.0064*
Clubs not participating in Europe (n = 11)	103	0.23	13.9 (11.2–16.6)	133	0.30	18.1 (15.0–21.2)	1.3 (1.0–1.7)	0.0443*
Hamstring region
Clubs participating in Europe (n = 6)	29	0.10	5.8 (3.7–8.0)	45	0.15	9.2 (6.5–11.9)	1.6 (1.1–2.3)	0.0098*
Clubs not participating in Europe (n = 11)	46	0.10	6.2 (4.4–8.0)	63	0.14	8.6 (6.5–10.7)	1.4 (0.9–2.0)	0.0916
Calf region
Clubs participating in Europe (n = 6)	6	0.02	1.2 (0.2–2.2)	12	0.04	2.4 (1.1–3.8)	2.0 (0.8–5.3)	0.1657
Clubs not participating in Europe (n = 11)	8	0.02	1.1 (0.3–1.8)	19	0.04	2.6 (1.4–3.8)	2.4 (1.0–5.4)	0.0413*

Injury incidence (number of injuries per 1000 hours play) and Incidence Rate Ratio (IRR) comparisons across seasons are presented with 95% Confidence Intervals (95%CI).

*= Significant difference.

Discussion

The present report is, to our knowledge, the first to investigate the impact of a mid-season FIFA 2022 World Cup on injury rates and patterns in one of the “Big-5” European soccer leagues. The total number of injuries sustained in French Ligue 1 clubs was > 20% higher in the World Cup season (S2) compared with that for a regular season (S1) with a rise observed in both training and match-play. In S2, the total combined number of muscle injuries and injuries occurring in the knee and ankle regions also increased by > 20%. While exposure time was unavailable to calculate incidence rates in training and overall (match + training), these results imply that the risk of sustaining injury across a domestic French soccer season increased substantially when a FIFA World Cup was scheduled mid-season. Supporting this finding using actual exposure time to play, a statistically significant higher risk was observed in S2 for match-play incidence rates for all injuries sustained while muscle and knee and ankle joint injuries combined also augmented (range for the differences = IRR: 1.2–2.3, p < 0.05-p < 0.01). Further analyses showed that the incidence of muscle injury and injuries occurring in the hamstring and calf regions also increased statistically. Interestingly, comparisons of overall incidence of injury in match-play in L1 clubs reported previously by the same authors (Orhant et al., 2023) during a regular season (2018/19) and a Covid-affected season (2020–21) show that these were also substantially lower than the rate observed during the present World Cup season (respectively 29.4 & 24.9 vs 38.8/1000 hours play). While these results diverge with the declining trend for overall injury occurrence recently reported in professional European club soccer (Ekstrand et al., 2021), they partly confirm the trend for a greater risk of hamstring injury (Ekstrand et al., 2022) and generally demonstrate the considerable impact of holding a WC mid-season on injury risk in French football clubs.

Several reasonable explanations can be forwarded to explain these observations. First, while the total number of matches played by the clubs were similar across the two seasons (S1: 751 vs S2: 742), these were played across a substantially shorter time span (−33 days) in S2. As such, the average interval, hence time for players to recover and regenerate between consecutive matches, was generally shorter to what clubs were used to. This shorter delay between matches may have exacerbated the potential risk of competing while not fully recovered (e.g., strength imbalances, decreased range of motion, neuromuscular fatigue, perception of fatigue) and thereby sustaining a soft-tissue injury (Wollin et al., 2018). However, on average, across all clubs, the interval between matches remained >5 days which is generally sufficient to regain physical deficits post-match (Carling et al., 2015) and therefore possibly refutes any overall association with match congestion. Second, international tournaments are typically played end-season and are associated with a heightened risk of injury (Sprouse et al., 2020); which can be linked to chronic fatigue experienced following a ten-month season. Placing a WC mid-season would, in theory, have enabled players to participate in a “fresher” state. However, the pre-tournament competition schedule, during which more matches than usual were played (although mean interval between successive matches across all clubs was again >5 days), in combination with the rapid preparation pre-WC period (~1 week), could have contributed towards the greater overall rates of injury across the entire season. The duration of the preparation period may have been too short to enable players to adapt to international environments and thereby prepare optimally (e.g., travel, training content and workload management, tactical planning) for the demands of the ensuing matches. Indeed, related research in elite soccer has shown the importance of pre-season preparation on subsequent injury risk (Ekstrand et al., 2020). As such, it is noteworthy that a post–World Cup survey reported that two-thirds of the participating players interviewed post-tournament felt that a longer preparation period would have been necessary (FIFAPRO, 2023b). Finally, injury risk is linked to the quality of the communication between medical and coaching staff, as well as load management and training content (Ekstrand et al., 2023). Following the mid-season World Cup, practitioners encountered a new and complex context that may have impacted injury risk. Players transitioned directly back into their clubs at different dates, with diverging training and match load exposure and varying levels of physical and psychological fatigue and fitness. Post-tournament mental health might also have been an issue (FIFAPRO, 2022c) although to our knowledge no scientific research in elite soccer players exists to confirm this latter point and research is warranted. There was also a need to prepare non-selected players to return to the intensive demands of competition and avoid exposure to spikes in loads. A survey to glean information on how club practitioners managed players in these situations is also merited.

Professional teams regularly participating in UEFA club European competitions are frequently exposed to intensive schedules and, consequently, certain players to the danger of over-play. Indeed, feedback from a recent survey conducted in high-performance coaches and professional soccer players (FIFAPRO, 2022b) reported a need to reduce match exposure time and the number of back-to-back matches to attenuate the risk of overload and injury occurrence. It is therefore noteworthy that the present French teams participating in UEFA club European competitions and exposed to congested schedules reported a significantly higher rate for overall injuries sustained, muscle, ankle/knee joint injuries combined, and muscle and hamstring injuries specifically in S2. However, the incidence for muscle injuries overall and those affecting the calf region specifically were also higher in S2 in clubs not participating in European competitions. Combined, these results would suggest that the present cohort of French Ligue 1 clubs was, as a whole, negatively impacted by a major mid-season international tournament. Contextual data notably regarding the causes of injuries and when these occurred across the season would have provided useful information to help elucidate these findings.

Finally, one of the main challenges after the conclusion of the 2022 WC was the short turnaround between the end of the tournament and the resumption of club football. This interval was potentially insufficient to enable players to readjust physically and mentally to the demands of domestic professional soccer (Zouhal et al., 2022). Indeed, following the tournament, a survey of players who had participated in the WC showed that many were suffering from greater levels of physical and mental fatigue than habitually felt in the month of January while half of the cohort interviewed reported an injury or felt more likely to sustain an injury (FIFAPRO, 2023a). The removal of the winter break could partly explain these findings. However, although match injury incidence across all clubs was higher both prior to and after the WC compared with the overall rate observed during the regular season, it did not increase post-tournament. This finding suggests that the risk generally, was not amplified over the remainder of the season. In contrast, a significant increase (IRR: 1.4 [1.1–1.8], p < 0.05) in the second part of the season was observed in clubs participating in UEFA European competitions. Match congestion cannot be forwarded as an explanation for this rise as these teams played a match every 5.7 days compared with 4.5 days after the WC. The aforementioned challenges in optimally preparing players for return to competition, irrespective of whether they participated or not in the WC, might again be a more plausible explanation. Comparisons of injury rates at an individual level and specifically in players who participated or not in the WC would have provided more precise information to help elucidate the impact of the mid-season tournament on injury risk. However, this information was unavailable in the national injury database due to the need to guarantee full anonymity.

This study is not without limitations. Ideally, comparison with additional “benchmark” seasons would have strengthened comparisons. Here, only one baseline season was used for comparison as the structure and duration of the two previous L1 seasons were considerably different owing to the COVID-19 pandemic (Orhant et al., 2021). Research has nevertheless shown that a single entire season can provide a satisfactory assessment of injury incidence (Stubbe et al., 2015). Finally, information on exposure time in training was unavailable and therefore the effects of a mid-season World Cup on training-related injury risk using exposure-derived incidence values could not be determined.

To conclude, the present results suggest that both injury occurrence and patterns in French L1 soccer clubs were substantially affected during the 2022/23 season during which the 2022 FIFA World Cup™ took place. The risk of match-play injury overall and muscle injuries specifically was greater compared with a regular season (2021/22). Additional epidemiological investigations in other major European soccer leagues are arguably necessary to verify these findings and help inform the game’s governing bodies, national federations and domestic leagues in the future planning of international tournaments.

Acknowledgements

The authors would like to thank all the participating Ligue 1 clubs and their respective medical staff for their help with this study.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.