Noninvasive measurement of muscle high-energy phosphates and glycogen concentrations in elite soccer players by 31P- and 13C-MRS

PURPOSE: The purpose of this study was to measure noninvasively the absolute concentrations of muscle adenosine triphosphate [ATP], phosphocreatine [PCr], inorganic phosphate (Pi), and glycogen [Gly] of elite soccer players. METHODS: Magnetic resonance spectroscopy (31P- and 13C-MRS) was used to measure the concentrations of metabolites in the calf muscles of 18 young male players [age = 17.5 +/- 1.0 (SD) yr]. RESULTS: Average muscle [PCr] and [ATP] were 17.8 +/- 3.3 and 6.0 +/- 1.2 mmol x (kg wet weight)(-1), respectively. The ratios of Pi/PCr and PCr/ATP were 0.15 +/- 0.05 and 3.00 +/- 0.26, respectively. The muscle [Gly] was 144 +/- 54 mmol x (kg wet weight)(-1). There was a high correlation (r = 0.93, P < 0.0001) between muscle ATP and PCr concentrations, but there was no correlation between [Gly] and [PCr] or [ATP]. The concentrations of the different metabolites determined in the present study with noninvasive MRS methods were within the ranges of values reported in human muscle from biochemical analysis of muscle biopsies. CONCLUSION: MRS methods can be utilized to assess noninvasively the muscle energetic status of elite soccer players during a soccer season. The high correlation between ATP and PCr might be indicative of fiber type differences in the content of these two metabolites.     

Fluid loss and body composition of elite Kuwaiti soccer players during a soccer match

AIM: The aim of this study was to assess the effect of the hot weather conditions of Kuwait on fluid loss (FL) and body composition of Kuwaiti soccer players. METHODS: During 5 preseason soccer games, 10 elite Kuwaiti soccer players participated in this study. The age and physical characteristics (mean+/-SD) of the subjects were: age 24+/-4.7 years; height 173.4+/-5.2 cm; mass 68.2+/-7 kg; and the percent body fat 12.3+/-3.7%, the mean temperature 45.4+/-2 degrees C, mean humidity was 23.6+/-4.2%. Measurements were taken at the beginning, half time, and the end of each game; FL was measured by body weight changes. Urine specific gravity was used to determine the state of hydration. Body composition was measured using Biodynamics Model 310e Body Composition Analyzer. RESULTS: There was a significant difference in body weight changes between 1st and 2nd half at P>0.05. The mean value of the FL at the end of the game was 3.1+/-1.4 L; indicating no significant difference in FL between 1st and 2nd half at P>0.05). The mean value urine specific gravity at the end game was 1.026+/-0.002; there was a significant difference between first, and second half for urine specific gravity (P>0.05). CONCLUSIONS: Results of this study indicated that the subjects did not consume enough fluid to offset FL. Players and coaches involved with activities in hot humid environments should pay closer attention to FL and body weight changes which occur during physical activity. Special care should always be taken to insure players consume extra water prior to each training session or game.     

Postural stability decreases in elite young soccer players after a competitive soccer match

ObjectiveTo investigate the effects of an official soccer match on postural stability in youth elite soccer players.DesignSingle-group pre-post design.SettingCompetitive soccer match.ParticipantsTwenty elite U-19 male soccer players (mean age: 17.7 ± 1.0 years) of which 11 completed the full experimental set-up.Main outcome measuresPostural stability evaluated by unilateral stance tests for dominant and non-dominant lower limbs on a force plate under two visual conditions: eyes opened (EO) and eyes closed (EC).ResultsAfter the match, the centre of gravity (CoG) sway velocity with EO increased on the dominant and non-dominant limbs (median [interquartile range], 0.90°/s [0.60–1.10] vs. 1.10°/s [0.60–1.60]; and 0.70°/s [0.50–0.90] vs 1.00°/s [0.70–1.30]; respectively; p < 0.05). The CoG sway velocity with eyes closed did not change pre- to post-match.ConclusionsThe soccer match decreased the postural stability only when the assessment was conducted with eyes open.     

Dynamic balance is impaired after a match in young elite soccer players

PurposeThe aim of this study is to assess the effect of actual match effort on dynamic balance abilities in young elite soccer players.MethodsSeventeen Under 15 male players who compete at national level participated in the study. Their dynamic balance was assessed by having them jump starting with both feet on the ground in a standing position and land on one foot only. Their vertical time to stabilization (vTTS) and postural sway were calculated before and after 35 min of an unofficial match. Postural sway was assessed on the basis of center-of-pressure (COP) trajectories. Parameters considered were sway area, COP displacements in the antero-posterior (AP) and medio-lateral (ML) directions and COP path length.ResultsAfter the match, a significant increase in vTTS (p = 0.007) COP path length (p = 0.001) and COP displacements in ML (p < 0.001) was observed. Such effects involve both non-dominant (vTTS, path length) and dominant limb (COP displacements).ConclusionsThe physical effort associated with the match induces significant impairments of players' dynamic balance abilities. On the basis of such findings, coaches might consider integrating training sessions with specific balance exercises as well as performing injury-prevention routines even when players are fatigued, to better adapt them to match conditions.     

Age‐related physical and technical match performance changes in elite soccer players

The age of peak performance is likely to vary between sports and competitions, affected by the specific skills and attributes needed to succeed in the particular competition. However, no studies using modern tracking techniques have examined the effects of age on competitive match play performance. Thus, the purpose of this study was to evaluate the effects of age on match physical and technical performance using a large‐scale analysis of match performance in professional soccer players. A total of 14 546 individual match observations were undertaken in the first German league (Bundesliga) during the 2012‐2013, 2013‐2014, and 2014‐2015 seasons using a computerized tracking system (VISTRACK, by Impire Corp.). Differences in physical and technical match performance of soccer players were analyzed for the following variables: total distance covered, number of fast runs, number of sprints, and percentage of successful passes. Professional soccer players aged >30 years showed a significant lower performance in the total distance covered, the number of fast runs, and the number of sprints compared with younger players (≤30 years). Conversely, the player's ability to make successful passes increased with age. These effects were observed in all positional roles except wide midfielders. These findings may help coaches and managers to better understand the effects of age on match‐related physical and technical performance and may have the potential to assist in decisions such as, when a new contract would be signed, the duration of the contract, the salary, or when to replace or transfer a player depending on their age.     

Muscle damage produced during a simulated badminton match in competitive male players

The purpose of the study was to assess the occurrence of muscle damage after a simulated badminton match and its influence on physical and haematological parameters. Sixteen competitive male badminton players participated in the study. Before and just after a 45-min simulated badminton match, maximal isometric force and badminton-specific running/movement velocity were measured to assess muscle fatigue. Blood samples were also obtained before and after the match. The badminton match did not affect maximal isometric force or badminton-specific velocity. Blood volume and plasma volume were significantly reduced during the match and consequently haematite, leucocyte, and platelet counts significantly increased. Blood myoglobin and creatine kinase concentrations increased from 26.5 ± 11.6 to 197.3 ± 70.2 µg·L^?1 and from 258.6 ± 192.2 to 466.0 ± 296.5 U·L^?1, respectively. In conclusion, a simulated badminton match modified haematological parameters of whole blood and serum blood that indicate the occurrence of muscle fibre damage. However, the level of muscle damage did not produce decreased muscle performance.     

Intensity demands and peak performance of elite soccer referees during match play

ObjectivesThis study examined the peak physical and physiological (heart rate) performance intensities andassociated decrements in elite soccer referees during match play.DesignLongitudinal study.MethodsPhysical performancevariables and heart rate were analyzed during 457 matches across two seasons. Differences between halves, and the rate ofdecline in peak performance intensities across moving average durations of 1–10 minutes were assessed using linear mixed models and power-law analysis, respectively.ResultsLarge significant differences were observed between halves for mean total distance, mean velocity, mean heart rate, and percentage of maximal heart rate (p ≤ 0.05; r = 0.51–0.64). Peak intensities (p ≤ 0.05; r = 0.15–0.17) and the rate of decline (p < 0.001; r = 0.17–0.37) were significantly higher in the 2^nd half compared to the 1^st half, for relative total distance, relative high-intensity running and mean velocity. The rate of decline was significantly greater in the 2^nd half than the 1^st half for relative distance covered by high-intensity acceleration (>2 m/s^–2/min), deceleration (<-2 m/s^–2/min), and relative mean heart rate (p < 0.001; r = 0.28–0.61). Elite soccer referees might have experienced transient fatigue during match play, as relative high-intensity running immediately following the most intense 5-minute period significantly declined by 61.2% ( p< 0.001; r = 0.94), and was 16.2% lower than the mean 5-minute period (p < 0.001; r = 0.34).ConclusionsIncreased physical and physiological demands during match play, with associated declines in the second half and transient signs of fatigue throughout the match, supports the inclusion of high-intensity interval and endurance training programs to prepare soccer referees for the intensity demands and peak performance outcomes of match play.     

Physiological profile and activity pattern of young soccer players during match play

PURPOSE: The purpose of this study was to examine aerobic demands and activity patterns during match play in young soccer players with respect to competition level, age, and biological maturity. METHODS: Ten nonelite players (NbP) and nine elite players (EbP) in their early puberty (12 yr), and seven elite players (EeP) in their late puberty (14 yr) were studied. Heart rate (HR) and activity pattern were recorded during match play, whereas corresponding .VO(2) and HR values were obtained during submaximal and maximal treadmill tests in the laboratory. The maturity status was assessed from testicular volume. RESULTS: No difference in .VO(2max) was observed between the nonelite and the elite players in the beginning of puberty (58.7 +/- 5.3 vs 58.6 +/- 5.0 mL O(2).min-1.kg(-1)), whereas the elite players in the end of puberty were significantly more fit (63.7 +/- 8.5 mL O(2).min(-1).kg(-1)). During match play, a higher HR was recorded in the elite players in the beginning of puberty than their nonelite counterparts, whereas the two elite groups showed the same HR responses (HR 1st half/2nd half-NbP: 162/157; EbP: 177/174; EeP: 178/173). The elite players in the end of puberty thus performed a higher absolute and relative .VO(2) (.VO(2).min(-1) and mL O(2).min(-1).kg(-1)) compared with the nonelite players during both halves, corresponding to more time spent in standing/walking in the nonelite group. The elite players in the end of puberty showed higher absolute .V(O2) values during match play than the young elite players but identical relative aerobic loads. It seems that the midfield/attack group had the highest absolute .VO(2max) and was performing at the highest HR during the matches. CONCLUSION: The present study shows that young soccer players are highly specialized both according to playing level and position on the field.     

No sport for old players. A longitudinal study of aging effects on match performance in elite soccer

ObjectivesThis study aimed to examine the effects of age on match-related physical and technical–tactical performance in elite soccer players using a longitudinal design.MethodsData were collected from 154 players who competed in the Spanish first division (LaLiga) between the 2012–13 and 2019–20 seasons. A total of 14,092 individual match observations were analyzed using a computerized tracking system (TRACAB, Chyronhego, New York, NY). The players were classified into five positional roles: central defenders (n = 37); external defenders (n = 44); central midfielders (n = 34); external midfielders (n = 22); and forwards (n = 17).ResultsThe main results showed that (a) soccer players decreased by an average of 0.56% their total distance covered for each year that they got older. Similarly, the number of high-intensity efforts and distance covered at high-intensity running decreased by 1.80% and 1.42% per year, respectively; (b) players significantly increased their pass accuracy by an average of 0.25% each year that they got older; (c) the detrimental effect of age on total distance and high-intensity running was greater for external defenders, external midfielders, and forwards; and (d) the positive effect of age on pass accuracy was greater for central defenders and central midfielders.ConclusionsElite soccer players with long-term careers were unable to maintain their match-related physical performance as they got older. However, players can annually improve their technical–tactical skills with increasing age as a possible compensation mechanism against physical performance declines related to aging.     

Influence of carbohydrate supplementation on skill performance during a soccer match simulation

ObjectivesThis study investigated the influence of carbohydrate supplementation on skill performance throughout exercise that replicates soccer match-play.DesignExperimentation was conducted in a randomised, double-blind and cross-over study design.MethodsAfter familiarization, 15 professional academy soccer players completed a soccer match simulation incorporating passing, dribbling and shooting on two separate occasions. Participants received a 6% carbohydrate–electrolyte solution (CHO) or electrolyte solution (PL). Precision, success rate, ball speed and an overall index (speed-precision-success; SPS) were determined for all skills. Blood samples were taken at rest, immediately before exercise, every 15 min during exercise (first half: 15, 30 and 45 min; second half: 60, 75 and 90 min), and 10 min into the half time (half-time).ResultsCarbohydrate supplementation influenced shooting (time × treatment interaction: p < 0.05), where CHO attenuated the decline in shot speed and SPS index. Supplementation did not affect passing or dribbling. Blood glucose responses to exercise were influenced by supplementation (time × treatment interaction: p < 0.05), where concentrations were higher at 45 min and during half-time in CHO compared with PL. Blood glucose concentrations reduced by 30 ± 1% between half-time and 60 min in CHO.ConclusionsCarbohydrate supplementation attenuated decrements in shooting performance during simulated soccer match-play; however, further research is warranted to optimise carbohydrate supplementation regimes for high-intensity intermittent sports.     

Incidence of injuries in elite French youth soccer players: a 10-season study

BACKGROUND: Research on age-related injury incidence in elite youth soccer is needed to identify high-risk groups. PURPOSE: To investigate the incidence of soccer-related injuries in elite French youth players based at the Clairefontaine Football Center. STUDY DESIGN: Cohort study (Prevalence); Level of evidence, 1. METHODS: Injuries sustained by players in the younger than 14-, 15-, and 16-year-old age groups during 10 seasons were diagnosed and documented by a sports physician according to type, location, severity, the date the injury occurred, and playing position. RESULTS: Altogether, 1152 injuries were documented across all age groups with 69.1% and 30.9% sustained during training and matches, respectively. A total of 4.8 injuries per 1000 hours' exposure time were recorded and 11.2 and 3.9 injuries per 1000 hours for matches and training, respectively. There was no significant difference in injury frequency between age groups. The youngest group sustained more training injuries (P < .05) and osteochondroses (P < .05) and fewer match injuries than did the oldest group. Injury incidence varied throughout the season, peaking in September in all groups. The majority of injuries lasted less than 1 week (60.2%), contusions were the predominant injury type (30.6%, P < .05), and the upper leg was the site most often injured (24.5%, P < .05). CONCLUSION: Those players younger than 14 years incurred more injuries in training and sustained more growth-related overuse disorders. Older players were more often injured during matches. Injury incidence and the frequency of overuse disorders were highest early in the season.     

Changes in bone turnover markers during the close season in elite football (soccer) players

ObjectivesBone turnover marker changes in response to physical activity are well documented. There is, however, little information on the extent and severity of skeletal de-conditioning in athletes in response to rest periods. This study analyses changes in markers of bone resorption and bone formation during the close season within the squad of an English Football Association Championship club.DesignEvaluation was performed on the first team football squad just before the end of the 2007/2008 football season and again 8 weeks later before pre-season testing and training.MethodBone resorption was measured by serum concentration of C-terminal telopeptide (CTx) and bone formation by serum concentration of the N-terminal propeptide of type I procollagen (PINP). Twenty football players aged from 18 to 36 years (mean 23.6 years) were included in the study.ResultsThe mean change in CTx during the close season was +0.14 ng/ml (95% CI: 0.21 to 0.06, p = 0.001). The mean change in PINP was ?10.8 ng/ml (95% CI: ?3.9 to ?17.7, p = 0.004).ConclusionsIn professional football players, a close season rest of 8 weeks results in an increase in bone resorption and a decrease in bone formation markers. This imbalance between formation and resorption may have negative effects on bone mass and structure. Future research should focus on understanding the many factors that could contribute to the changes found in the study during the close season.     

Development and validation of a sport-specific exercise protocol for elite youth soccer players

AIM: The aims of the current study were, firstly, to quantify the motion characteristics of professional youth soccer players and, secondly, to develop and validate a soccer-specific exercise protocol (SSEP). METHODS: The motion characteristics of 12 first team members and 12 scholars (under 19s), signed to an English Premiership club were determined via motion analysis. Motion profiles from the analysis were then used to develop a SSEP for a non-motorised treadmill. Validity of the protocol was checked with 6, healthy, male soccer players who completed the SSEP and, on a separate occasion, a soccer match. Heart rates were recorded during both trials, in addition, capillary blood and expired air samples were taken, and RPE recorded, during the SSEP. RESULTS: Youth team players covered 10274+/-609 m, compared to 9741+/-882 m by the first team players (t=1.72, p>0.05; 95% CI for the difference = -1174 m to 109 m). The trend for greater mean distance covered by youth players could be attributed to the distances covered while jogging and running. Mean heart rate response was 166+/-9 beatsxmin(-1) during match play and 166+/-12 beatsxmin(-1) during the SSEP (t=0.164, p>0.05). Mean .VO(2) during the SSEP was 70+/-3% of .VO(2max). Blood lactate concentration fell from a mean value of 5.37+/-1.15 mmol x L(-1) during the first half to 4.74+/-1.25 mmol x L(-1) during the 2(nd) half (t=2.52, p<0.05). CONCLUSION: The findings of this study suggest that the protocol developed induced a similar physiological load to soccer match play and provides the opportunity to study the physiological demands of soccer.     

Plasma antioxidant responses and oxidative stress following a soccer game in elite female players

We aimed to investigate markers of oxidative stress and levels of endogenous and dietary antioxidants in 16 elite female soccer players in response to a 90‐min game (average intensity 82±3% HRpeak). Blood samples were taken before, immediately and 21 h after the game. Plasma‐oxidized glutathione, the ratio of reduced to oxidized glutathione (GSH:GSSG) and lipid peroxidation measured by d‐ROMs were used as markers of oxidative stress. Plasma endogenous [uric acid, total glutathione (TGSH)] and dietary antioxidants (α‐tocopherol, ascorbic acid, total carotenoids and polyphenols) were analyzed using liquid chromatography and the Folin–Ciocalteu method. Exercise induced an acute increase (P<0.05) in GSSG, uric acid, TGSH, α‐tocopherol, and ascorbic acid. In parallel, the GSH:GSSG ratio and polyphenols decreased (P<0.05). GSSG, GSH:GSSG ratio, uric acid, TGSH, and ascorbic acid returned to baseline at 21 h, while polyphenols and α‐tocopherol remained altered. Total carotenoids increased above baseline only at 21 h (P<0.05). Lipid peroxidation, measured by d‐ROMs, remained unchanged throughout the study. Thus, intermittent exercise in well‐trained female athletes induces a transient increase in GSSG and a decrease in the GSH:GSSG ratio, which is effectively balanced by the recruitment of both endogenous and dietary antioxidants, resulting in the absence of lipid peroxidation measured by d‐ROMs.