Muscle and blood metabolites during a soccer game: implications for sprint performance

Third-Man-Passing Small-Sided Games Induce Higher Anaerobic Energy Contributions Than Regular-Passing Small-Sided Games in Football Players

PURPOSE

This study compared the physiological profiles and energy-system contributions of trained football players engaged in regular-passing and third-man-passing small-sided games (SSGs) that included 4 versus 4 and a goalkeeper.

METHODS

Ten male trained football players participated in this crossover study. All participants were randomly assigned to either regular-passing SSG or third-man-passing SSG (4 vs 4 with a goalkeeper, 35-m × 17-m pitch size, and 6-min match duration). During these SSGs, physiological parameters including peak and mean heart rate, oxygen uptake (V˙O2peak and V˙O2mean), metabolic equivalents in V˙O2peak and V˙O2mean, and blood lactate concentrations (peak La- and delta La- [Δ La-]), were measured. Energy contributions (oxidative [WOxi], glycolytic [WGly], and phosphagen [WPCr] systems) and Global Positioning System (GPS) variables (total distance, total acceleration counts, mean speed, and maximum speed) were also analyzed.

RESULTS

No significant differences in physiological parameters and GPS variables were found between regular- and third-man-passing SSGs. WOxi in kilojoules and percentages was significantly higher during both SSGs than WPCr and WGly (P < .0001, respectively). WPCr and WPCr + WGly values during third-man-passing SSGs were significantly higher than those during regular-passing SSGs (P < .05). Additionally, low to moderate positive correlations were observed between WOxi, WGly in kilojoules, V˙O2peak, V˙O2mean, peak La-, Δ La-, total acceleration counts, and mean speed (r = .39-.64).

CONCLUSIONS

Third-man-passing SSGs may be useful for increasing anaerobic capacity. More third-man-passing SSG sessions in preparation for football games may support high metabolic power and repeated powerful anaerobic performances in trained football players.

Influence of Carbohydrate Intake on Different Parameters of Soccer Players' Performance: Systematic Review

BACKGROUND

The objective of this systematic review is to analyze the influence of carbohydrate (CHO) intake on physical and technical aspects, glucose and muscle glycogen levels, fatigue, cognition, and gastrointestinal comfort involved in the performance of soccer players, as well as to examine whether there are any differences between men and women.

METHODS

A bibliographic search was conducted in PubMed, Web of Science, Scopus, and SportDiscus, resulting in 61 selected articles. The PRISMA recommendations and the Cochrane Handbook for Systematic Reviews guidelines were followed.

RESULTS

The results indicate that CHO intake before and during the match improves speed and the number of sprints, attenuates the decrease in shooting accuracy and speed, increases time to fatigue, and enhances cognitive function. There is no consensus on passing, dribbling, jumping, or agility improvements. Glucose levels drop during the first 15 min of the second half without affecting performance.

CONCLUSIONS

It is recommended that players ingest 6-8 g/kg/d of CHO the day before, a meal with 1-3 g/kg 3-4 h before, and 30-60 g/h during the match. Muscle glycogen drops drastically at the end of the match, remaining low at 48 h. Hence, 1-1.5 g/kg/h is recommended during the first 4 h, starting from the first 20 min. Female soccer players have a similar physical demand to men, and energy availability is low, especially in the post-match periods, as they underestimate their energy expenditure and do not consume enough CHO. Therefore, the recommended guidelines should be followed, individualized, and periodized according to each athlete's energy needs.

On-field concurrent validity of flight time-based countermovement jump height during fatigue: A comparison between inertial measurement units worn at different locations on the body

We explored the feasibility of utilizing immediate changes in flight time-based vertical countermovement jump height as an on-field measure for fatigue-induced decrements in performance. Comparing Inertial Measurement Units (IMUs) worn at five body locations (feet, shorts for thighs and pelvis, waist strap, and thorax in a standard GPS vest) with a force plate as a reference, we enlisted 19 amateur football players who performed a series of 10 maximal 30 m sprints (initiated every minute). Maximal jumps were executed immediately before and after each sprint, with the latter jumps recorded on a force plate integrated into the field. Bland Altman's bias (-0.49 cm) and limits of agreement (1.01 cm) were minimal for the feet IMUs. The thorax IMU had the highest bias (-6.35 cm), but the limits of agreement (2.73 cm) were similar to the other locations. Repeated measures correlations (rmcorr) between force plate and IMUs were excellent for the feet (rmcorr = 0.98) and good for the thorax (rmcorr = 0.86) and other locations except for the waist strap. In the fatigued state, within-session coefficients of variation ranged from 4.0% (pelvis in shorts) to 6.5% (waist strap). These findings suggest that body-worn IMUs possess the potential for a prompt and straightforward on-field vertical jump assessment to monitor acute fatigue.

Nutritional habits of professional team sport athletes: An insight into the carbohydrate, fluid, and caffeine habits of English Premier League football players during match play

To better understand the in-match fuelling practices of elite football players and compare against current guidelines, we quantified the carbohydrate, fluid, and caffeine intake of players from an English Premier League club (n = 22) during 90 min of competitive match-play. Mean carbohydrate intake across match-play was 17 ± 11 g.h-1 with players demonstrating a preference towards CHO-containing fluids (58%) when compared with semi-solids (38%) and solids (14%), respectively. CHO intake was significantly lower than reported by players (17 ± 11 vs 24.8 ± 11 g.h-1, p < 0.001) during initial consultation. Fluid was ingested at a rate of 0.45 ± 0.14 L.h-1, with 54, 40 and 6% of ingested fluid coming from water, carbohydrate, and electrolyte-only solutions, respectively. The majority of players (91%) met the UEFA guidelines for fluid consumption. Of the players who consumed caffeine across match-play (55%) the average dose was 233 ± 148 mg (2.8 ± 1.1 mg.kg-1 body mass [BM]), which meets the UEFA consensus guidelines for caffeine intake. Caffeine capsules (42%) and caffeine containing fluids (30%) were the preferred format prior to the warm-up whilst caffeine gum was exclusively used prior to kick-off and during the half-time period (100%). We conclude that 81% of the total playing squad failed to meet the current UEFA CHO intake recommendations of 30-60 g.h-1, which may be attributed to the preference towards fluid-based CHOs as the chosen format of delivery.

Testing in Intermittent Sports-Importance for Training and Performance Optimization in Adult Athletes

ABSTRACT

Performance in intermittent sports relies on the interplay between multiple physiological systems determining the capacity to perform short explosive efforts as well as repeated intense actions with limited recovery over the course of an entire game. Testing should reflect these demands to allow for sport- and position-specific capacity analyses that eventually may translate into optimized training and improved performance. This may include individual load management and optimized training prescription, intensity targeting for specific positions or individual athletes, as well as benchmarking for monitoring of training progression and enhanced engagement of athletes. This review provides an overview of available tests in different exercise domains identified as relevant (from assessment of single explosive actions to intermittent endurance capacity), forming the basis for recommendations on how to compose a comprehensive yet feasible test battery that may be integrated into the seasonal competition and training plan. The test procedures should cover the performance spectrum of relevance for the individual athlete-also in team sports to account for positional differences. We emphasize the benefits of sport-specific tests, highlight parameters of importance for test standardization, and discuss how the applied test battery may be supplemented with secondary tests directed toward specific energy systems to allow for more in-depth analyses when required (e.g., in terms of an underperforming athlete). The synergy between testing and tracking of match performance (utilizing time-motion or global positioning systems) is highlighted, and although tracking cannot substitute for testing, combining the tools may provide a comprehensive overview of the physiological demands and performance during competition contextualized to the athletes' maximal exercise capacity.

Influence of Substitutions and Roles on Kinematic Variables in Professional Soccer Players

In soccer, roles and substitutions can make it unclear how different physical capacities decrease over time and impact performance. This investigation aimed to analyze kinematic parameters and their changes over game time, and provide information to effectively prescribe training programs. Data from four professional teams were analyzed, and all the teams competed in the Italian First Division (Serie A). Average metabolic power and high-intensity activities associated with critical moments in the match were considered in the comparisons. The video analysis system STATS SportVU collected the data during official matches. Players were assigned to a specific group according to their time played, categorized as follows: 0-15', 15-30', 30-45', 45-60', 60-75', 75-90', and > 90 min. Different roles, including forwards and wingers (FW), midfielders (MF), center-backs (CB), and side-backs (SB) were also considered. Significant differences (p<0.05) were found in different roles and within roles at different times played. The results highlighted how MF performance decreased over time, whereas CB was unaffected by time. SB spent more time at very high velocity than other roles, independently from the time played. These findings provide valuable information about the physical demands of official soccer matches and could be used to review training prescriptions.

Acute inorganic nitrate ingestion does not impact oral microbial composition, cognitive function, or high-intensity exercise performance in female team-sport athletes

The purpose of this study was to investigate the effects of acute nitrate (NO3-)-rich beetroot juice ingestion on explosive and high-intensity exercise performance, oral microbiota composition, and cognitive flexibility (i.e., function), before and after maximal intermittent running exercise. Fifteen women team-sport athletes were assigned in a randomized, double-blind, crossover design to consume concentrated NO3--depleted beetroot juice (PL; 0.1 mmol NO3-) and NO3--rich beetroot juice (BR; 12.0 mmol NO3-) 2.5 h prior to performing a battery of exercise performance tasks and cognitive testing before and after the Yo-Yo intermittent recovery level 1 (YYIR1) running test. Resting plasma [NO3-] and plasma nitrite ([NO2-]) were elevated following BR (P < 0.001). BR did not impact global composition or relative abundance of taxa in the oral microbiome (P > 0.05) or cognitive flexibility before or after exercise (P > 0.05). There was no significant difference in performance during 20-m (PRE, PL: 4.38 ± 0.27 vs. BR: 4.38 ± 0.32 s; POST, PL: 4.45 ± 0.29 vs. BR: 4.43 ± 0.35 s) and 10-m sprints (PRE, PL 2.78 ± 0.15 vs. BR 2.79 ± 0.18 s; POST, PL: 2.82 ± 0.16 vs. BR: 2.81 ± 0.19 s), isokinetic handgrip dynamometry, medicine ball throw, horizontal countermovement jump, or YYIR1 (PL: 355 ± 163 m vs. BR: 368 ± 184 m) between BR and PL (P > 0.05). These findings indicate that acute dietary NO3- may not influence the oral microbiome, explosive and high-intensity exercise performance, or cognitive function in women team-sport athletes.

Using Bar Velocity to Assess Post-match Neuromuscular Fatigue in Young Soccer Players

This study aimed to investigate the recovery of neuromuscular performance using mechanical parameters collected during jump (vertical and horizontal) and strength-power exercises in youth soccer players after official soccer matches. Twenty-one outfield highly trained youth male soccer athletes (age: 18.23±0.73 years; weight: 72.12±6.99 kg; height: 1.78±0.08 m) from two teams competing in the 1st division of U-19 Portuguese National Championship participated in this study. Players completed a battery of physical tests at -2 h, + 30 min, +24 h, and +48 h in relation to the match. Countermovement jump height, horizontal jump distance, and bar velocity during the half squat, bench press, and hip thrust exercises, at fixed loads, were recorded. Countermovement jump was impaired until 24 h post-match (-: 1.7% from pre- to 24 h post-match, p=0.050; ES=-: 0.82). Half-squat bar velocity was reduced immediately following the match (-: 6.8% from pre-match, p=0.004; ES=-: 0.64) but recovered at +24 h (+2.9%, p=1.00; ES=0.02). Hip-thrust bar velocity was reduced for up to 48 h post-match (-: 7.4% from pre- to 48 h post-match, p<0.001; ES=-: 0.80). No impairments were found in the horizontal jump and bench press at any moment. Our findings show prolonged decrements in strength of the posterior chain following a soccer match, measured in the hip thrust exercise, while the other exercises displayed faster recovery dynamics.

Recovery during Successive 120-min Football Games: Results from the 120-min Placebo/Carbohydrate Randomized Controlled Trial

PURPOSE

This study aimed to examine the recovery kinetics (i.e., time-dependent changes) of performance-related variables between two 120-min male football games performed 3 d apart with and without carbohydrate supplementation.

METHODS

Twenty male players (20 ± 1 yr; body fat, 14.9% ± 5.1%; maximal oxygen consumption, 59.4 ± 3.7 mL·kg -1 ·min -1 ) participated in two 120-min football games (G1, G2) according to a randomized, two-trial, repeated-measures, crossover, double-blind design. Participants received carbohydrate/placebo supplements during recovery between games. Field activity was monitored during the games. Performance testing and blood sampling were performed before and at 90 and 120 min of each game. Muscle biopsies were collected at baseline and at 90 and 120 min of G1 and pre-G2.

RESULTS

Compared with G1, G2 was associated with reduced total distance (10,870 vs 10,685 m during 90 min and 3327 vs 3089 m during extra 30 min; P = 0.007-0.038), average (6.7 vs 6.2 km/h during extra 30-min game-play; P = 0.007) and maximal speed (32.2 vs 30.2 km/h during 90 min and 29.0 vs 27.9 km/h during extra 30 min; P < 0.05), accelerations/decelerations ( P < 0.05), and mean heart rate ( P < 0.05). Repeated sprint ability ( P < 0.001), jumping ( P < 0.05), and strength ( P < 0.001) performance were compromised before and during G2. Muscle glycogen was not restored at G2 baseline ( P = 0.005). Extended game-play reduced lymphocyte, erythrocyte counts, hematocrit, hemoglobin, reduced glutathione ( P < 0.05) and increased delayed onset of muscle soreness, creatine kinase activity, blood glycerol, ammonia, and protein carbonyls ( P < 0.05) before and during G2. Pax7 + ( P = 0.004) and MyoD + cells ( P = 0.019) increased at baseline G2. Carbohydrate supplementation restored performance and glycogen, reduced glycerol and delayed onset of muscle soreness responses, and increased leukocyte counts and Pax7 + and MyoD + cells.

CONCLUSIONS

Results suggest that extended football games induce a prolonged recovery of performance, which may be facilitated by carbohydrate supplementation during a congested game fixture.

Peak fat oxidation, peak oxygen uptake, and running performance increase during pre-season in sub-elite male football players

PURPOSE

In Football, the high-intensity running bouts during matches are considered decisive. Interestingly, recent studies showed that peak fat oxidation rates (PFO) are higher in football players than other athletes. This study aimed to investigate whether PFO increases following a pre-season. Secondarily, and due to COVID-19, we investigated whether PFO is related to the physical performance in a subgroup of semi-professional male football players.

METHODS

Before and after 8 weeks of pre-season training, 42 sub-elite male football players (18 semi-professionals and 24 non-professionals) had a dual-energy x-ray absorptiometry scan and performed a graded exercise test on a treadmill for the determination of PFO, the exercise intensity eliciting PFO (Fatmax) and peak oxygen uptake (V̇O2peak). Additionally, the semi-professional players performed a Yo-Yo Intermittent Recovery Test level 2 (YYIR2) before and after pre-season training to determine football-specific running performance.

RESULTS

PFO increased by 11 ± 10% (mean ± 95% CI), p = 0.031, and V̇O2peak increased by 5 ± 1%, p < 0.001, whereas Fatmax was unchanged (+12 ± 9%, p = 0.057), following pre-season training. PFO increments were not associated with increments in V̇O2peak (Pearson's r2 = 0.00, p = 0.948) or fat-free mass (FFM) (r2 = 0.00, p = 0.969). Concomitantly, YYIR2 performance increased in the semi-professional players by 39 ± 17%, p < 0.001, which was associated with changes in V̇O2peak (r2 = 0.35, p = 0.034) but not PFO (r2 = 0.13, p = 0.244).

CONCLUSIONS

PFO, V̇O2peak, and FFM increased following pre-season training in sub-elite football players. However, in a subgroup of semi-professional players, increments in PFO were not associated with improvements in YYIR2 performance nor with increments in V̇O2peak and FFM.

Relationships among Physical Fitness, External Loads, and Heart Rate Recovery: A Study on Futsal Players during an Overseas Congested-Weeks Training Camp

This study examined relationships among players' physical characteristics, match external loads, and heart rate recovery (HRR) during match substitutions in a congested fixture of an overseas futsal training camp. Eleven under-20 national futsal players' anthropometric characteristics (age, body height, body mass, % fat, and % muscle) and physical fitness [HRmax, VO2max, maximal aerobic speed (MAS) during the 30-15 intermittent fitness test (IFT)] were determined. Additionally, locomotion profiles during field play and HRR sitting on the bench were recorded during five matches. A repeated-measures analysis of variance and Pearson's correlation coefficient were used for statistical analysis. The results revealed that the overall observed correlations among anthropometry, body composition, physical fitness, and HRR were inconsistent across all the matches and substitutions. However, the numbers of moderate (1.00-1.99 m/s2), moderate-to-high (2.00-2.99 m/s2), and high (3.00-50.00 m/s2) intensities of acceleration presented negative correlations in the last match (r < -0.76; p < 0.05). HRR during match substitutions may have been influenced by uncontrolled factors across all the match play and recovery. HRR measures may be affected mainly by fatigue caused by the accumulation of accelerations throughout a congested fixture during a congested-schedule of a futsal training camp.

Variability of External Load Measures During Soccer Match Play: Influence of Player Fitness or Pacing?

PURPOSE

The aims of this study were to examine the variability of selected external load metrics within 15-minute intervals during soccer match play and examine their relationship with players' high-intensity intermittent fitness.

METHODS

A total of 18 male soccer players were monitored for their external load metrics during 26 matches, which included total distance, high-metabolic-load distance, and mechanical work (defined as the sum of accelerations and decelerations >3 m2). Additionally, players completed the 30-15 Intermittent Fitness Test.

RESULTS

Total distance had lower coefficients of variation than high-metabolic-load distance and mechanical work (effect size [ES]: 5.2 to 6.4; very large). Within-player Δ-15min showed moderate to large decreases (ES: -0.7 to -1.6) and increases (ES: 0.9 to 1.8) in absolute and coefficient-of-variation values, respectively. Large relationships (r = .55 to .61) were observed between the Intermittent Fitness Test and 15-minmean and 15-minbest in all selected external load metrics. However, small to moderate (0.27 to 0.41) associations were observed between the Intermittent Fitness Test and Δ-15min in selected external load metrics.

CONCLUSIONS

These findings suggest that players with relatively lower intermittent running capacity might show lower variability during matches, as evidenced by smaller reductions in high-intensity actions during the final 15 minutes. We attribute these observations to players' possessing better pacing strategies.

Sleep architecture of elite soccer players surrounding match days as measured by WHOOP straps

This study aimed to quantify and compare sleep architecture before and after home and away matches in elite soccer players from the English Premier League. Across two seasons, 6 male players (age 28 ± 5 y; body mass 85.1 ± 9.5 kg; height 1.86 ± 0.09 m) wore WHOOP straps to monitor sleep across 13 matches that kicked off before 17:00 h. For each, sleep was recorded the night before (MD-1), after (MD) and following the match (MD +1). Across these 3 days total sleep time (TST), sleep efficiency (SE), sleep disturbances, wake time, light sleep, deep sleep, REM sleep, sleep and wake onsets, alongside external load, were compared. TST was reduced after MD versus MD +1 (392.9 ± 76.4 vs 459.1 ± 66.7 min, p = 0.003) but no differences existed in any other sleep variables between days (p > 0.05). TST did not differ after home (386.9 ± 75.7 min) vs. away matches (401.0 ± 78.3 min) (p = 0.475), nor did other sleep variables (p > 0.05). GPS-derived external load peaked on MD (p < 0.05). In conclusion, despite reduced TST on MD, sleep architecture was unaffected after matches played before 17:00 h, suggesting sleep quality was not significantly compromised.

Elite Soccer Players Do Not Cover Less Distance in the Second Half of the Matches When Game Interruptions Are Considered

ABSTRACT

Rey, E, Kalén, A, Lorenzo-Martínez, M, López-Del Campo, R, Nevado-Garrosa, F, and Lago-Peñas, C. Elite soccer players do not cover less distance in the second half of the matches when game interruptions are considered. J Strength Cond Res 38(4): 709-713, 2024-This study aimed to analyze quantitative differences in the physical demands of male elite soccer players between the first and second halves during official matches, accounting for effective playing time (the duration of play after subtracting the game interruptions) and playing positions. A total of 4,249 individual match observations of 412 outfield players competing in the Spanish first division league (LaLiga) were undertaken during the 2018-2019 season, using a computerized tracking system (TRACAB, Chyronhego, New York, NY). The players were classified into 5 positional roles: central defenders (CD), external defenders (ED), central midfielders (CM), external midfielders (EM), and forwards (F). The main results showed that in contrast to those observed when total playing time was considered, independent of playing position, there were no significant differences on high-speed running (HSR) (5.5 ± 2.4 vs. 5.5 ± 2.4 m·min -1 ) and sprint (5.3 ± 3.3 vs. 5.4 ± 3.3 m·min -1 ) distances between the first and second halves in professional soccer players when the effective playing time was considered. However, differences in match running performance at HSR and sprint distances between the first and second halves were dependent on players' playing position. Whereas ED and EM maintained HSR and sprint efforts during the second half, CD and CM significantly increased ( p < 0.001) the distance covered at sprint during the second period of the match. Contrarily, F were unable to maintain their HSR (6.2 ± 2.3 vs. 5.9 ± 3.3 m·min -1 ) and sprint (7.0 ± 3.5 vs. 6.5 ± 3.4 m·min -1 ) match running performances during the second half. Such findings demonstrate that total playing time could overestimate fatigue-induced performance declines. Thus, effective playing time and playing position should be taken into account when interpreting the match running performance of professional soccer players.

Ketone Monoester Followed by Carbohydrate Ingestion after Glycogen-Lowering Exercise Does Not Improve Subsequent Endurance Cycle Time Trial Performance

Relative to carbohydrate (CHO) alone, exogenous ketones followed by CHO supplementation during recovery from glycogen-lowering exercise have been shown to increase muscle glycogen resynthesis. However, whether this strategy improves subsequent exercise performance is unknown. The objective of this study was to assess the efficacy of ketone monoester (KME) followed by CHO ingestion after glycogen-lowering exercise on subsequent 20 km (TT20km) and 5 km (TT5km) best-effort time trials. Nine recreationally active men (175.6 ± 5.3 cm, 72.9 ± 7.7 kg, 28 ± 5 y, 12.2 ± 3.2% body fat, VO2max = 56.2 ± 5.8 mL· kg BM-1·min-1; mean ± SD) completed a glycogen-lowering exercise session, followed by 4 h of recovery and subsequent TT20km and TT5km. During the first 2 h of recovery, participants ingested either KME (25 g) followed by CHO at a rate of 1.2 g·kg-1·h-1 (KME + CHO) or an iso-energetic placebo (dextrose) followed by CHO (PLAC + CHO). Blood metabolites during recovery and performance during the subsequent two-time trials were measured. In comparison to PLAC + CHO, KME + CHO displayed greater (p < 0.05) blood beta-hydroxybutyrate concentration during the first 2 h, lower (p < 0.05) blood glucose concentrations at 30 and 60 min, as well as greater (p < 0.05) blood insulin concentration 2 h following ingestion. However, no treatment differences (p > 0.05) in power output nor time to complete either time trial were observed vs. PLAC + CHO. These data indicate that the metabolic changes induced by KME + CHO ingestion following glycogen-lowering exercise are insufficient to enhance subsequent endurance time trial performance.

Hypoxia Does Not Impair Resistance Exercise Performance or Amplify Post-Exercise Fatigue

Purpose: To determine whether performing resistance exercise in hypoxia acutely reduces performance and increases markers of fatigue, and whether these responses are exaggerated if exercising at high versus low work rates (i.e., exercising to failure or volume matched non-failure). Methods: Following a within-subject design, 20 men completed two trials in hypoxia (13% oxygen) and two in normoxia (21% oxygen). The first session for hypoxic and normoxic conditions comprised six sets of bench press and shoulder press to failure (high work rate), while subsequent sessions involved the same volume distributed over 12 sets (low work rate). Physical performance (concentric velocity) and perceptual responses were measured during exercise and for 72 hr post-exercise. Neuromuscular performance (bench throw velocity) was assessed pre- and post-session. Results: Hypoxia did not affect physical performance, neuromuscular performance, and perceptual recovery when exercising at high or low work rates. Higher work rate exercise caused greater acute decrements in physical performance and post-exercise neuromuscular performance and increased perceived exertion and muscle soreness (p ≤ 0.006), irrespective of hypoxia. Conclusions: Hypoxia does not impact on resistance exercise performance or increase markers of physical and perceptual fatigue. Higher exercise work rates may impair physical performance, and exaggerate fatigue compared to low work rate exercise, irrespective of environmental condition. Practitioners can prescribe hypoxic resistance exercise without compromising physical performance or inducing greater levels of fatigue. For athletes who are required to train with high frequency, decreasing exercise work rate may reduce post-exercise markers of fatigue for the same training volume.

A century of exercise physiology: effects of muscle contraction and exercise on skeletal muscle Na+,K+-ATPase, Na+ and K+ ions, and on plasma K+ concentration-historical developments

This historical review traces key discoveries regarding K+ and Na+ ions in skeletal muscle at rest and with exercise, including contents and concentrations, Na+,K+-ATPase (NKA) and exercise effects on plasma [K+] in humans. Following initial measures in 1896 of muscle contents in various species, including humans, electrical stimulation of animal muscle showed K+ loss and gains in Na+, Cl- and H20, then subsequently bidirectional muscle K+ and Na+ fluxes. After NKA discovery in 1957, methods were developed to quantify muscle NKA activity via rates of ATP hydrolysis, Na+/K+ radioisotope fluxes, [3H]-ouabain binding and phosphatase activity. Since then, it became clear that NKA plays a central role in Na+/K+ homeostasis and that NKA content and activity are regulated by muscle contractions and numerous hormones. During intense exercise in humans, muscle intracellular [K+] falls by 21 mM (range - 13 to - 39 mM), interstitial [K+] increases to 12-13 mM, and plasma [K+] rises to 6-8 mM, whilst post-exercise plasma [K+] falls rapidly, reflecting increased muscle NKA activity. Contractions were shown to increase NKA activity in proportion to activation frequency in animal intact muscle preparations. In human muscle, [3H]-ouabain-binding content fully quantifies NKA content, whilst the method mainly detects α2 isoforms in rats. Acute or chronic exercise affects human muscle K+, NKA content, activity, isoforms and phospholemman (FXYD1). Numerous hormones, pharmacological and dietary interventions, altered acid-base or redox states, exercise training and physical inactivity modulate plasma [K+] during exercise. Finally, historical research approaches largely excluded female participants and typically used very small sample sizes.

Dietary Intake of Soccer Players before, during and after an Official Game: Influence of Competition Level and Playing Position

Physical demands in soccer differ according to league level and playing position and may influence nutritional requirements. This study examined the effect of competition level and playing position on dietary intake in male soccer players (SP). Diet was weighed and recorded by 123 SP for 3 days; before, on the day, and the day after an official match. SP in the Super League (SL, n = 33) division reported higher (p < 0.05) average three-day energy (195 ± 36 kJ/kg), carbohydrate (6.0 ± 1.1 g/kg), and protein (2.2 ± 0.5 g/kg) intakes compared to the intakes reported by SP in the 2nd (n = 30) (energy: 159 ± 31 kJ/kg; carbohydrate: 4.6 ± 1.2 g/kg; protein: 1.9 ± 0.4 g/kg), 3rd (n = 30) (energy: 153 ± 34 kJ/kg; carbohydrate: 4.5 ± 1.2 g/kg; protein: 1.7 ± 0.4 g/kg), and 4th (n = 30) (energy: 152 ± 36 kJ/kg; carbohydrate: 4.2 ± 1.2 g/kg; protein: 1.7 ± 0.5 g/kg) national leagues (mean ± SD). Furthermore, when data were analyzed by playing position (pooled data), wide midfielders reported higher (p < 0.05) energy (183 ± 33 kJ/kg), carbohydrate (5.4 ± 1.2 g/kg), and fat (1.5 ± 0.4 g/kg) intakes compared to central defenders (energy: 147 ± 37 kJ/kg; carbohydrate: 4.1 ± 1.1 g/kg; fat: 1.2 ± 0.4 g/kg). The dietary intake of SP may differ according to the playing position and competition level, possibly due to different metabolic demands in training and competition.

Changes in Physical Performance Throughout Professional Soccer Match-Play

ABSTRACT

Oliva-Lozano, JM, Granero-Gil, P, and Panascì, M. Changes in physical performance throughout professional soccer match-play. J Strength Cond Res 38(1): 123-127, 2024-The aim of this study was to explore the changes in physical performance by playing position throughout professional soccer match-play. Global Positioning Systems were used for the collection of external load measures during 35 matches. Each match was divided into 15-minute periods. Physical performance varied according to the period in distance covered ( F = 25.69; p < 0.001; partial eta-squared [ηp 2 ] = 0.11), sprinting distance (SPD, F = 4.35; p < 0.001; ηp 2 = 0.02), sprinting actions (SPAs, F = 5.19; p < 0.001), high-intensity accelerations (Acc+3, F = 2.18; p = 0.05; ηp 2 = 0.01), high-intensity decelerations (Dec+3, F = 4.51; p < 0.001; ηp 2 = 0.02), and high-metabolic load distance (HMLD, F = 5.59; p < 0.001; ηp 2 = 0.03). The period with the greatest mean physical performance was usually from the first half of the matches: 0-15 minutes (distance, Acc+3, and Dec+3) and 30-45 minutes (HMLD, SPA, and SPD). However, the lowest mean physical performance compared with the rest of 15-minute periods was observed in the 60-75-minute period (distance, HMLD, Acc+3, and Dec+3), except for SPA and SPD (15-30 minutes and 75-90 minutes). Overall, no significant differences ( p > 0.05) were observed in the physical performance between the extratime periods. In addition, the playing position had a significant effect on all performance variables ( F = 39.99-133.29; p < 0.001; ηp 2 = 0.14-0.34). Central defenders showed the lowest physical performance throughout the periods of match-play, whereas wide midfielders showed the greatest physical performance in all variables, except for distance covered, in which midfielders had the greatest performance. In conclusion, there were changes in physical performance during the matches depending on the period of match-play and playing position.

The physiology of ice hockey performance: An update

Ice hockey is an intense team sport characterized by repeated bursts of fast-paced skating, rapid changes in speed and direction and frequent physical encounters. These are performed in on-ice shifts of ~30-80 s interspersed with longer sequences of passive recovery, resulting in about 15-25 min on-ice time per player. Nearly 50% of the distance is covered at high-intensity skating speeds and with an accentuated intense activity pattern in forwards compared to defensemen. During ice hockey match-play, both aerobic and anaerobic energy systems are significantly challenged, with the heart rate increasing toward maximum levels during each shift, and with great reliance on both glycolytic and phosphagen ATP provision. The high-intensity activity pattern favors muscle glycogen as fuel, leading to pronounced reductions despite the relatively brief playing time, including severe depletion of a substantial proportion of individual fast- and slow-twitch fibers. Player-tracking suggests that the ability to perform high-intensity skating is compromised in the final stages of a game, which is supported by post-game reductions in repeated-sprint ability. Muscle glycogen degradation, in particular in individual fibers, as well as potential dehydration and hyperthermia, may be prime candidates implicated in exacerbated fatigue during the final stages of a game, whereas multiple factors likely interact to impair exercise tolerance during each shift. This includes pronounced PCr degradation, with potential inadequate resynthesis in a proportion of fast-twitch fibers in situations of repeated intense actions. Finally, the recovery pattern is inadequately described, but seems less long-lasting than in other team sports.

Simulated Soccer Game Protocols: A Systematic Review on Validated Protocols That Represent the Demands of the Game

ABSTRACT

Brito, P, Costa, J, Figueiredo, P, and Brito, J. Simulated soccer game protocols: A systematic review on validated protocols that represent the demands of the game. J Strength Cond Res 38(1): 192-205, 2024-Several laboratory and field testing protocols have been developed attempting to simulate the activity pattern and physiological demands of soccer. In the present systematic review, we aimed to analyze and discuss the appropriateness, strengths, and limitations of soccer-specific simulated tests. A systematic review of the literature was conducted based on the PRISMA guidelines. Studies conducted in soccer, simulated soccer match tests, and validated simulation protocols performed on-the-field or on a treadmill were considered. No sex restriction was applied, and age >18 years (i.e., adults) was considered. At least 1 outcome measure (e.g., neuromuscular performance, external load, internal load, or psychometric state) of post-simulated-match test or protocol had to be reported. Within the 14 studies included, the average methodological quality of the included articles was 0.61 ± 0.09 (mean ± SD) of 1. Overall, 9 validated protocols were identified. In the protocols, only amateur, university, or semiprofessional soccer players were analyzed. Only one study evaluated female soccer players. None of the studies evaluated the effect on performance over the 2-3 days after the protocol. Accelerations and decelerations, and changes in direction typically present in a game have not been clearly described in any protocol. Future research should address this issue and validate soccer-specific protocols in women.

The Effects of Players' Rotations on High-Intensity Activities in Professional Futsal Players

The current study aimed to investigate the effects of interchange rotations on players` physical performance during competition, with special reference to high-intensity activity (HIA) according to the playing position. Physical performance data, collected from 19 professional players during seven official matches from the Spanish futsal league using a portable local positioning system, included the number of high-speed running activities (>18 km·h-1), high-intensity accelerations (>3 m·s-2), and high-intensity decelerations (>3 m·s-2). Statistically significant (p ≤ 0.05) differences were observed in the number of HIA efforts across rotations and between positions. Players performed more HIA efforts in the first rotation (n = 17.6), suggesting that their first rotation was more demanding than all subsequent rotations. Wingers demonstrated a higher HIA effort and frequency of HIA efforts when compared to defenders (p ≤ 0.05) and pivots (p ≤ 0.001). For all positions, the first rotation was more physically demanding as the number of HIA efforts per rotation decreased with an increased number of rotations throughout the match. Furthermore, higher HIA profile positions, such as wingers and defenders, were less likely to maintain consistent HIA properties (repetition number, time-frequency, and the work-rate) across subsequent rotations during the match. The findings of the study can inform coaching decisions regarding players' rotations to maintain consistent HIA performance throughout the match.

Monitoring load, wellness, and psychological variables in female and male youth national team football players during international and domestic playing periods

Aim

To study differences in total load exposure, wellness, and psychological variables in youth female (N = 19) and male (N = 20) national team football players during domestic and international playing periods, respectively.

Procedures

The players filled out questionnaires on well-being, stress, and resilience before and after both playing periods lasting 8 days each. The Hooper index was used to monitor daily wellness levels during both playing periods. The number of training sessions and matches were recorded, and the session rating of perceived exertion was collected. Training load, monotony, and strain were calculated. Daily measurements were used to evaluate in-period changes, and composite scores were used to describe differences between periods.

Results

The international compared to the domestic playing period was for both groups characterized by more matches played, longer field training session durations, and of fewer gym-based sessions (P < 0.05). The male players increased total exposure time (25%; P < 0.05), monotony (P < 0.001), and strain (P < 0.001), which was not changed in the female players. Well-being decreased (P < 0.05) during the international playing period in male players. Stress levels were higher (P < 0.05) for both genders during the international compared to the domestic playing period. During the international playing period, positive correlations were found between the initial levels of stress, and the change in stress (P = 0.03; r2 = 0.12), and between the changes in total load and changes in well-being (P = 0.02; r2 = 0.12), whereas a negative correlation was found between the changes in wellness and stress (P = 0.03; r2 = 0.14).

Conclusion

A playing period characterized by increased match focus, longer field training sessions, and fewer gym-based training activities may lead to changes in the physical and mental profiles of youth national team football players. Alterations to load exposure and wellness may influence mental health. Players with high initial stress levels may be subjected to greater changes compared to other players. Sports scientists and medical staff may benefit from initiating structured monitoring systems to track alterations in physical load and mental health in youth national team players.

The lactate response to a second bout of exercise is not reduced in a concurrent lower-limb exercise program

We aimed to evaluate the blood lactate level in response to two bouts of exercise. First, we hypothesized that blood lactate elevation in response to moderate-intensity aerobic exercise (MIAE) would be lower at the end of the second bout of MIAE than the first bout of MIAE. In this context, we also hypothesized that lactate accumulation at the end of resistance exercise (RE) would be reduced if MIAE is performed before RE (i.e., concurrent exercise; CE). If so, we hypothesized that the order of the CE (i.e., RE + MIAE vs. MIAE + RE) influences blood lactate kinetics. To test the hypotheses, forty-three healthy men participated in three studies. In study 1, 20 men (age 21 ± 2 years) performed two bouts of a 20-min MIAE separated by a 20-min rest interval. In study 2, 11 men (age 22 ± 1 years) performed RE only and CE (MIAE + RE; ARCE) with a 20-min rest interval in a crossover design. In study 3, 12 men (age 21 ± 2 years) performed both CEs, which were ARCE and RE + MIAE (RACE), with a 20-min rest interval in a crossover design. We measured blood lactate before and at the end of each exercise session. In study 1, the blood lactate response to the second bout of MIAE was lower than that of the first bout (P < 0.001, r = 0.68). However, the blood lactate response to the ARCE trial was not lower than the response to the RE trial in study 2 (P = 0.475, r = 0.22). The results of study 3 showed that the RACE and ARCE trials induced a similar lactate response (MIAE P = 0.423, r = 0.28; RE P = 0.766, d = 0.03). These observations indicate that whereas lactate accumulation might be diminished by a second bout of MIAE, a different type of exercise (i.e., aerobic/resistance) did not result in a diminished lactate accumulation in response to a second bout of exercise.

The potassium-glycogen interaction on force and excitability in mouse skeletal muscle: implications for fatigue

A reduced muscle glycogen content and potassium (K+ ) disturbances across muscle membranes occur concomitantly during repeated intense exercise and together may contribute to skeletal muscle fatigue. Therefore, we examined whether raised extracellular K+ concentration ([K+ ]o ) (4 to 11 mM) interacts with lowered glycogen to reduce force production. Isometric contractions were evoked in isolated mouse soleus muscles (37°C) using direct supramaximal field stimulation. (1) Glycogen declined markedly in non-fatigued muscle with >2 h exposure in glucose-free physiological saline compared with control solutions (11 mM glucose), i.e. to <45% control. (2) Severe glycogen depletion was associated with increased 5'-AMP-activated protein kinase activity, indicative of metabolic stress. (3) The decline of peak tetanic force at 11 mM [K+ ]o was exacerbated from 67% initial at normal glycogen to 22% initial at lowered glycogen. This was due to a higher percentage of inexcitable fibres (71% vs. 43%), yet without greater sarcolemmal depolarisation or smaller amplitude action potentials. (4) Returning glucose while at 11 mM [K+ ]o increased both glycogen and force. (5) Exposure to 4 mM [K+ ]o glucose-free solutions (15 min) did not increase fatiguability during repeated tetani; however, after recovery there was a greater force decline at 11 mM [K+ ]o at lower than normal glycogen. (6) An important exponential relationship was established between relative peak tetanic force at 11 mM [K+ ]o and muscle glycogen content. These findings provide direct evidence of a synergistic interaction between raised [K+ ]o and lowered muscle glycogen as the latter shifts the peak tetanic force-resting EM relationship towards more negative resting EM due to lowered sarcolemmal excitability, which hence may contribute to muscle fatigue. KEY POINTS: Diminished muscle glycogen levels and raised extracellular potassium concentrations ([K+ ]o ) occur simultaneously during intense exercise and together may contribute to muscle fatigue. Prolonged exposure of isolated non-fatigued soleus muscles of mice to glucose-free physiological saline solutions markedly lowered muscle glycogen levels, as does fatigue then recovery in glucose-free solutions. For both approaches, the subsequent decline of maximal force at 11 mM [K+ ]o , which mimics interstitial [K+ ] levels during intense exercise, was exacerbated at lowered compared with normal glycogen. This was mainly due to many more muscle fibres becoming inexcitable. We established an important relationship that provides evidence of a synergistic interaction between raised [K+ ]o and lowered glycogen content to reduce force production. This paper indicates that partially lowered muscle glycogen (and/or metabolic stress) together with elevated interstitial [K+ ] interactively lowers muscle force, and hence may diminish performance especially during repeated high-intensity exercise.

The recovery of muscle function and glycogen levels following game-play in young elite male ice hockey players

Despite the frequent occurrence of congested game fixtures in elite ice hockey, the postgame recovery pattern has not previously been investigated. The purpose of the present study was therefore to evaluate the acute decrements and subsequent recovery of skeletal muscle glycogen levels, muscle function and repeated-sprint ability following ice hockey game-play. Sixteen male players from the Danish U20 national team completed a training game with muscle biopsies obtained before, postgame and following ~38 h of recovery (day 2). On-ice repeated-sprint ability and muscle function (maximal voluntary isometric [MVIC] and electrically induced low- (20 Hz) and high-frequency (50 Hz) knee-extensor contractions) were assessed at the same time points, as well as ~20 h into recovery (day 1). Muscle glycogen decreased 31% (p < 0.001) postgame and had returned to pregame levels on day 2. MVIC dropped 11%, whereas 50 and 20 Hz torque dropped 21% and 29% postgame, respectively, inducing a 10% reduction in the 20/50 Hz torque ratio indicative of low-frequency force depression (all p < 0.001). While MVIC torque returned to baseline on day 1, 20 and 50 Hz torque remained depressed by 9%-11% (p = 0.010-0.040), hence restoring the pre-exercise 20/50 Hz ratio. Repeated-sprint ability was only marginally reduced by 1% postgame (p = 0.041) and fully recovered on day 1. In conclusion, an elite youth ice hockey game induces substantial reductions in muscle glycogen content and muscle function, but only minor reductions in repeated-sprint ability and with complete recovery of all parameters within 1-2 days postgame.

Improved physical performance of elite soccer players based on GPS results after 4 days of carbohydrate loading followed by 3 days of low carbohydrate diet

BACKGROUND

Carbohydrate loading is an established sports nutrition strategy for endur- 16 ance exercise performance. We tested if carbohydrate loading could improve the performance of 17 elite soccer players under ecologically valid circumstances using Global Positioning System (GPS) data.

METHODS

Twenty-two adult Iran Premier league soccer players were divided into a carbohydrate-loading group (CLG) and Control group (CG). The carbohydrate loading group restricted carbohydrate intake for three days to 1.5 g/kg/d while increasing exercise intensity. From days four to seven, exercise intensity was decreased and carbohydrate intake was considerably increased up to 7.5 g/kg/d on the day of the match, during which performance was analyzed using GPS data. The control group performed the same exercise training but maintained their habitual carbohydrate intake of 5-6 g/kg/d. The data were analyzed using a univariate ANCOVA with baseline data from a pre-intervention match as the control variable.

RESULTS

The carbohydrate loading team scored significantly higher on running distance, maximum speed and the number of top and repeated sprints; the carbohydrate loading group scored significantly lower on player load, metabolic power and running imbalance compared to the control team during their match.

CONCLUSIONS

Our findings suggest carbohydrate loading enabled elite soccer players to achieve greater running outputs with greater metabolic efficiency and lower fatigue compared to their habitual diets.

Acute beetroot juice supplementation did not enhance intermittent running performance in trained rugby players

ABSTRACTPurpose: Since the effect of dietary nitrate (NO3-) supplementation on rugby performance is unclear, the aim of the present study was to determine the effect of acute NO3- supplementation, on the modified Yo-Yo intermittent recovery level 1 (IR1) performance test in trained male rugby players.Methods: In a randomised, counterbalanced, double-blind, placebo-controlled crossover design, 12 trained rugby union players performed two experimental trials three hours after supplementation of either 140 mL NO3--rich (BRJ; ∼12.8 mmol NO3-) or NO3--depleted (PLA) BRJ. After blood sampling, players performed the modified Yo-Yo IR1 test. Countermovement jumps (CMJ) were also measured before (pre-CMJ) and after (post-CMJ) the prone Yo-Yo IR1 test.Results: Plasma NO3- (BRJ: 570 ± 146 µM vs. PLA: 72 ± 23 µM) and nitrite (NO2-) concentrations (BRJ: 320 ± 123 nM vs. PLA: 103 ± 57 nM) were increased after BRJ compared to PLA supplementation (both P < 0.001). Performance in the modified Yo-Yo IR1 test did not differ between BRJ (542 ± 209 m) and PLA (498 ± 185 m, P = 0.3). The jump height in pre-CMJ and in post-CMJ were similar between trials (both P > 0.05).Conclusions: Acute BRJ supplementation increased plasma NO3- and NO2- concentrations but had no benefit on an intermittent running test that reflects the demands of rugby performance, and CMJ performances. The findings do not support acute high-dose NO3- supplementation as an ergogenic aid to enhance physical performance in trained male rugby players.

Effects of exchange vs. controlled diet on biochemical, body composition and functional parameters in elite female soccer players

Due to the increasing level of professionalism, the high frequency of competitions, and the alarming injury rate observed in elite female soccer players, multidisciplinary strategies, including nutritional monitoring, need to be implemented. This study aimed to quantify energy, macronutrient and micronutrient intakes during the competitive period and to analyze the effects of two different nutritional interventions on nutritional knowledge, anthropometric data, biochemical values and physical performance. 19 elite female soccer players were randomly divided into two groups: the controlled-diet group (CG, n = 10), that followed a diet based on pre-established menus, and the exchange-diet group (EG, n = 9), that designed their own menus with an exchanged list. A cross-sectional study was designed to evaluate the dietary intake, while an experimental randomized controlled trial was designed to compare the effects of both 12-week nutritional interventions. Total energy, CHO, PROT, fibre and micronutrients intakes were below the general recommendations for athletes while, total and saturated fat intakes were above these. Moreover, there were no differences in diet during weekdays, pre-competition and competition days. The study also revealed a low nutritional knowledge and exchanged diet has demonstrated to be a better strategy to improve this. Biochemical monitoring showed that participants presented decreased concentration of haemoglobin and controlled diet may lead to greater effects on haemoglobin concentration and in anemia prevention. Both EG and CG showed significant reduction on skinfolds sum after intervention, but no significant differences were observed in thigh and calf indices. However, no significant changes were observed in soccer-related skills for any group.

Continuous Monitoring of Interstitial Fluid Glucose Responses to Endurance Exercise with Different Levels of Carbohydrate Intake

We compared the 24 h changes in interstitial fluid glucose concentration (IGC) following a simulated soccer match between subjects consuming a high-carbohydrate (HCHO; 8 g/kg BW/day) diet and those consuming a moderate-carbohydrate (MCHO; 4 g/kg BW/day) diet. Eight active healthy males participated in two different trials. The subjects were provided with the prescribed diets from days 1 to 3. On day 3, the subjects performed 90 min (2 bouts × 45 min) of exercise simulating a soccer match. The IGC of the upper arm was continuously monitored from days 1 to 4. No significant difference in the IGC was observed between trials during exercise. The total area under the curve (t-AUC) value during exercise did not significantly differ between the HCHO (9719 ± 305 mg/dL·90 min) and MCHO (9991 ± 140 mg/dL·90 min). Serum total ketone body and beta-hydroxybutyrate concentrations were significantly higher in the MCHO than in the HCHO after a second bout of exercise. No significant differences in the IGC were observed between trials at any time point during the night after exercise (0:00-7:00). In addition, t-AUC value during the night did not significantly differ between the HCHO (32,378 ± 873 mg/dL·420 min) and MCHO (31,749 ± 633 mg/dL·420 min). In conclusion, two days of consuming different carbohydrate intake levels did not significantly affect the IGC during a 90 min simulated soccer match. Moreover, the IGC during the night following the exercise did not significantly differ between the two trials despite the different carbohydrate intake levels (8 vs. 4 g/kg BW/day).

Exploring the impact of professional soccer substitute players on physical and technical performance

BACKGROUND

Substitutions are generally used to promote the match performance of the whole team. This study aimed to analyze the performance of substitute players and explore the performance difference among substitute players, completed players, and replaced players across each position.

METHODS

Chinese Super Soccer League (CSL) matches in the season 2018 including 5871 individual observation from 395 professional soccer players were analyzed by establishing linear mixed models to quantify the performance difference among substitute players (SP) (n = 1,071), entire match players (EMP) (n = 3,454), and replaced players (RP) (n = 1,346), and then separately for each position (central defenders, fullbacks, central midfielders, wide midfielders, and attackers).

RESULTS

The results show SP display higher high intensity distance and sprint distance significantly (p < 0.05) relative to playing time than RP and EMP. SP in offensive positions (attackers, wide midfielders) showed significantly higher (p < 0.05) passing and organizing performance such as passes, ball control, short passes, and long passes than RP or EMP. The scoring performances of central midfielders of SP including goals, shots, and shots on target are significantly higher (p < 0.05) than RP or EMP. Central defenders of SP showed higher shot blocks and pass blocks (p < 0.05) while lower passing and organizing performance (p < 0.05).

CONCLUSION

Depending on different playing positions, substitute players could indeed improve physical and technical performance related to scoring, passing, and defending as offensive substitute players can boost organizing performance and substitute defenders enhance defending performance. These could help coaches better understand substitute players' influence on match performance and optimize the substitution tactic.

Blood Lactate Responses of Male and Female Players Across an International Rugby Sevens Tournament

PURPOSE

This study investigated within- and between-matches blood lactate (La-) responses across an international Rugby Sevens tournament (5 matches over 2 d) in male and female players.

METHODS

Earlobe blood samples were taken from 25 professional players around matches: before warm-up (PRE), immediately upon finishing match participation (POST), and 30 minutes postmatch (30 min).

RESULTS

POST [La-] (mean [SD], range) for males was 10.3 (3.2; 2.9-20.2) mmol·L-1 and for females was 9.1 (2.3; 3.4-14.6) mmol·L-1. Linear mixed-effects models revealed a decrease in POST [La-] after match 5, compared to match 1. Increased PRE [La-] was found before match 2 (+0.8 [0.6-1.1] mmol·L-1), match 3 (+0.8 [0.5-1.1] mmol·L-1), and match 5 (+0.6 [0.4-0.9] mmol·L-1) compared to match 1 (all P < .001). The [La-] remained elevated at 30 min, compared to PRE (+1.7 [1.4-2.0] mmol·L-1, P < .001), with ∼20% of values persisting >4 mmol·L-1. Higher POST was observed in males compared to females (+1.6 [0.1-3.2] mmol·L-1, P = .042); however, no differences between sexes were found across 30 min or PRE [La-]. No [La-] differences between positions (backs and forwards) were identified.

CONCLUSIONS

Lactate concentrations above 10 mmol·L-1 are required to effectively simulate the anaerobic demands of international Rugby Sevens matches. Practitioners are advised to individualize anaerobic training prescription due to the substantial variability observed within positional groups. Additionally, improving athletes' metabolic recovery capacity through training, nutrition, and recovery interventions may enhance physical preparation for subsequent matches within a day, where incomplete lactate clearance was observed.

The Acute Demands of Repeated-Sprint Training on Physiological, Neuromuscular, Perceptual and Performance Outcomes in Team Sport Athletes: A Systematic Review and Meta-analysis

BACKGROUND

Repeated-sprint training (RST) involves maximal-effort, short-duration sprints (≤ 10 s) interspersed with brief recovery periods (≤ 60 s). Knowledge about the acute demands of RST and the influence of programming variables has implications for training prescription.

OBJECTIVES

To investigate the physiological, neuromuscular, perceptual and performance demands of RST, while also examining the moderating effects of programming variables (sprint modality, number of repetitions per set, sprint repetition distance, inter-repetition rest modality and inter-repetition rest duration) on these outcomes.

METHODS

The databases Pubmed, SPORTDiscus, MEDLINE and Scopus were searched for original research articles investigating overground running RST in team sport athletes ≥ 16 years. Eligible data were analysed using multi-level mixed effects meta-analysis, with meta-regression performed on outcomes with ~ 50 samples (10 per moderator) to examine the influence of programming factors. Effects were evaluated based on coverage of their confidence (compatibility) limits (CL) against elected thresholds of practical importance.

RESULTS

From 908 data samples nested within 176 studies eligible for meta-analysis, the pooled effects (± 90% CL) of RST were as follows: average heart rate (HRavg) of 163 ± 9 bpm, peak heart rate (HRpeak) of 182 ± 3 bpm, average oxygen consumption of 42.4 ± 10.1 mL·kg-1·min-1, end-set blood lactate concentration (B[La]) of 10.7 ± 0.6 mmol·L-1, deciMax session ratings of perceived exertion (sRPE) of 6.5 ± 0.5 au, average sprint time (Savg) of 5.57 ± 0.26 s, best sprint time (Sbest) of 5.52 ± 0.27 s and percentage sprint decrement (Sdec) of 5.0 ± 0.3%. When compared with a reference protocol of 6 × 30 m straight-line sprints with 20 s passive inter-repetition rest, shuttle-based sprints were associated with a substantial increase in repetition time (Savg: 1.42 ± 0.11 s, Sbest: 1.55 ± 0.13 s), whereas the effect on sRPE was trivial (0.6 ± 0.9 au). Performing two more repetitions per set had a trivial effect on HRpeak (0.8 ± 1.0 bpm), B[La] (0.3 ± 0.2 mmol·L-1), sRPE (0.2 ± 0.2 au), Savg (0.01 ± 0.03) and Sdec (0.4; ± 0.2%). Sprinting 10 m further per repetition was associated with a substantial increase in B[La] (2.7; ± 0.7 mmol·L-1) and Sdec (1.7 ± 0.4%), whereas the effect on sRPE was trivial (0.7 ± 0.6). Resting for 10 s longer between repetitions was associated with a substantial reduction in B[La] (-1.1 ± 0.5 mmol·L-1), Savg (-0.09 ± 0.06 s) and Sdec (-1.4 ± 0.4%), while the effects on HRpeak (-0.7 ± 1.8 bpm) and sRPE (-0.5 ± 0.5 au) were trivial. All other moderating effects were compatible with both trivial and substantial effects [i.e. equal coverage of the confidence interval (CI) across a trivial and a substantial region in only one direction], or inconclusive (i.e. the CI spanned across substantial and trivial regions in both positive and negative directions).

CONCLUSIONS

The physiological, neuromuscular, perceptual and performance demands of RST are substantial, with some of these outcomes moderated by the manipulation of programming variables. To amplify physiological demands and performance decrement, longer sprint distances (> 30 m) and shorter, inter-repetition rest (≤ 20 s) are recommended. Alternatively, to mitigate fatigue and enhance acute sprint performance, shorter sprint distances (e.g. 15-25 m) with longer, passive inter-repetition rest (≥ 30 s) are recommended.

SARS-CoV-2 Infection Increases the Risk of Muscle Injury in Professional Male Soccer Players-A Retrospective Analysis of the Italian and Spanish Major Leagues

A retrospective cohort study on professional soccer players from the Serie A and LaLiga was conducted to investigate the correlation between SARS-CoV-2 infection and muscle injuries. Players were divided into two groups based on whether they contracted the SARS-CoV-2 infection (C+) or not (C-) during the 2020/2021 season. In the 2019-2020 season, both championships showed a similar number of muscular injuries (MI) between C+ and C- (Serie A: p = 0.194; 95% CI: -0.044 to 0.215, LaLiga p = 0.915; 95% CI: -0.123 to 0.137). In the 2020-2021 season, C+ had a significantly higher number of MI compared to C- in both championships (Serie A: p < 0.05; 95% CI 0.731 to 1.038; LaLiga: p < 0.05; 95% CI: 0.773 to 1.054). Multiple linear regression analysis confirmed that belonging to C+ in the season 2020/2021 was the variable that most strongly influenced the probability of having a muscle injury. Survival analysis revealed a hazard ratio of 3.73 (95% CI 3.018 to 4.628) and of 5.14 (95% CI 3.200 to 8.254) for Serie A and LaLiga respectively. We found an association between SARS-CoV-2 infection and increased risk of muscle injury, emphasizing the importance of carefully considering the infection in the decision-making process for returning to sport. Therefore, SARS-CoV-2 infection should be judged as a real injury requiring specific assessment and training programs.

Estimated Energy Expenditures and Energy Intakes of International Female Rugby Sevens Players in Five Days of a Training Camp and Competition Preparation

To understand the energy balance of international female rugby sevens (R7s) players in applied environments, this study estimated the energy intakes (EI) and total daily estimated energy expenditures (TDEE) during a five-day training camp (TRAIN) and phase of competition preparation (COMP) of equal duration. Tri-axial accelerometer devices were worn throughout both scenarios to estimate TDEE, whereas EI was estimated via self-reported food diaries. Energy deficits of -47% (TDEE_TRAIN: 14.6 ± 1.6 MJ·day^-1, EI_TRAIN: 7.7 ± 0.9 MJ·day^-1, p ≤ 0.001, d = 5.1) and -50% (TDEE_COMP: 15.5 ± 1.6 MJ·day^-1, EI_COMP: 7.7 ± 1.0 MJ·day^-1, p ≤ 0.001, d = 5.7) were observed throughout TRAIN (n = 11; age: 25 ± 4 years, height: 170 ± 6 cm, weight: 71 ± 7 kg) and COMP (n = 8; age: 25 ± 3 years, height: 172 ± 5 cm, weight: 72 ± 6 kg), respectively. Carbohydrate intakes were below the lower range of sports nutrition recommendations in both TRAIN (-62%; 2.3 ± 0.3 g·kg^-1 BM, p ≤ 0.001) and COMP (-60%; 2.4 ± 0.5 g·kg^-1 BM, p ≤ 0.001). For protein (TRAIN: 1.7 ± 0.4 g·kg^-1 BM, COMP: 1.5 ± 0.1 g·kg^-1 BM), intakes met the lower range of recommendations. Fat intake exceeded recommendations of the percentage of total EI (COMP: 39 ± 5%). Accordingly, the dietary strategies of international female R7s players may warrant optimization, as carbohydrate and fat intakes were less than optimal when compared to current performance-based sports nutrition guidelines.

High-intensity Actions in Elite Soccer: Current Status and Future Perspectives

Over the years, soccer has become more physically demanding; the number and frequency of high-intensity actions have increased, and these activities are decisive in determining the match outcome. Importantly, the reductionist approach commonly used to analyze high-intensity actions does not contemplate a more contextualized perspective on soccer performance. Traditionally, most investigations have only provided quantitative data regarding sprints (i. e. time, distances, frequency) without examining "how" (e. g. type of trajectory or starting position) and "why" (e. g. tactical role) soccer players sprint. In fact, other high-intensity actions, apart from running, are not even mentioned (i. e. curve sprints, change of direction, and specific-jump tasks). This has led to the use of tests and interventions that do not accurately reflect real game actions. Given the true technical-tactical-physical demands of each playing position, this narrative review collected a wide-spectrum of current soccer-related articles and provided a discussion regarding high-intensity actions, with a positional-based approach. In this narrative review, practitioners are encouraged to contemplate and consider the different elements that characterize high-intensity actions in soccer, in order to assess and train soccer players under a more sport-specific and integrative perspective.

Effects of Concurrent High-Intensity and Strength Training on Muscle Power and Aerobic Performance in Young Soccer Players during the Pre-Season

The aim of the present study was to evaluate two different intervention programs applied during a 4-week pre-season period. Twenty-nine players participated in this study and were divided into two groups. One group (BallTrain, n = 12, age: 17.8 ± 0.4 years, body mass: 73.9 ± 7.6 kg, height: 178 ± 0.1 cm, body fat: 9.6 ± 5.3%) performed a higher percentage of aerobic training with ball and strength training using plyometrics and exercises with body weight. The other group (HIITTrain, n = 17, age: 17.8 ± 0.7 years, body mass: 73.3 ± 5.0 kg, height: 179 ± 0.1 cm, body fat: 8.0 ± 2.3%) trained with high-intensity interval training (HIIT) without the ball and performed resistance training with weights in the same session. Both groups trained for strength (two times/week) and performed aerobic–anaerobic fitness without the ball, passing games, and tactical and small-sided games. Lower limb power (CMJ) and aerobic fitness (Yo-Yo intermittent recovery test level 1-IR1) were evaluated before and after the four-week training program. Yo-Yo IR1 performance was improved in both groups, but the improvement was greater for the HIITTrain than BallTrain group (468 ± 180 vs. 183 ± 177 m, p = 0.07). CMJ showed a non-significant improvement in the BallTrain group (5.8 ± 8.8%, p = 0.16), but it decreased by 8.1 ± 9% (p = 0.001), in the HIITTrain group. In conclusion, we have shown that a short pre-season period of training results in improvements in aerobic fitness in both groups, with high-intensity interval training showing superior adaptations than training with the ball. However, CMJ performance was reduced in this group, possibly suggesting higher fatigue levels and overload, and/or showing the effects of concurrent HIITTrain and strength training in soccer.

Effects of short bout small-sided game training on acid-based balance markers in youth male soccer players

This study aimed to compare the effects of 1 × 1 small-sided games (SSGs) with different bout durations on external (ETL) and internal training loads (ITL) in youth soccer players. Twenty U18 players were divided into two groups performing six 1 × 1 SSGs with 30 and 45 s bout durations on a playing field of 10 by 15 m. ITL indices, including the percentage of maximum heart rate (HR), blood lactate (BLa) level, pH, bicarbonate (HCO₃^-) level, and base excess (BE) level, were measured at rest, after each SSG bout, and 15 and 30 min after the entire exercise protocol. ETL (Global Positioning System metrics) was recorded during all six SSG bouts. The analysis showed that the 45 s SSGs had a greater volume (large effect) but a lower training intensity (small to large effect) than the 30 s SSGs. A significant time effect (p < 0.05) was observed in all ITL indices and a significant group effect (F_{1, 18} = 8.84, p = 0.0082, ƞ² = 0.33) in the HCO₃^- level only. Finally, the changes in the HR and HCO₃^- level were smaller in the 45 s SSGs than in the 30 s SSGs. In conclusion, 30-s games, characterized by a higher intensity of training effort, are more physiologically demanding than 45-s games. Secondly during short-bout SSG training the HR and BLa level have limited diagnostic value for ITL. Extending ITL monitoring using other indicators, such as the HCO₃^- and BE levels, appears reasonable.

Comparison of external load indicators between official matches and sport-specific training in semi-professional soccer players: focus on intensity and strength

BACKGROUND

The aim of this study was to investigate any differences in external load indicators (ELi) between official matches (OM) and sport-specific tasks in semi-professional soccer players.

METHODS

Among 28 semi-professional soccer players, 1932 observations (age: 25±6 years, height: 183±6 cm, weight: 75.2±7 kg; FC Palermo, Palermo, Italy) were collected through GPS devices (Qstarz BT-Q1000EX, 10 Hz; Qstarz International Co., Ltd., Taipei, Taiwan) and the related software (LaGalaColli V: 8.6.4.3; Spinitalia Srl, Rome, Italy) during the season 2019-2020. Participants were monitored during OM, friendly matches (FM), small sided games (SSG), and match-based exercises (MBE), considering the percentage of intense accelerations (%int. acc.), percentage of intense decelerations (%int. dec.), and passive recovery time /min (PrT/m) as Eli.

RESULTS

We detected the highest mean value for PrT/m in OM and the lowest in MBE and SSG (18.36±4.38 and 13.4±5.26 and 13.4±4.29 (s/min), respectively). The lowest mean values of %int. acc. and %int. dec. were found in OM and the highest in SSG (8.64±1.52 vs. 13.02±3.14 and 9.25±1.56 vs. 15.68±3.14, for %int. acc. and %int. dec., respectively). Significant differences between the four tasks for all the ELi considered (P<0.001). The post-hoc pairwise comparisons revealed significant differences for all the ELi between all tasks (P<0.001) except for the %int. acc. between MBE vs. FM (P=0.003). No significant difference was found in PrT/m between MBE vs. FM and SSG vs. FM.

CONCLUSIONS

ELi are in accordance with the performance model by achieving better values in training than OM, suggesting the fundamental role of GPS for monitoring external load in soccer.

Performance Adaptations to Intensified Training in Top-Level Football

Because physical demands are surging in football (soccer, USA), clubs are more and more seeking players who have a high capacity to perform repeated intense exercise. High-intensity interval training (HIIT), comprising exercise performed at intensities near or exceeding the capacity of aerobic energy systems, effectively enhances the physical conditioning of players. But given that HIIT imposes high loads, it increases the risk of overload-associated match performance decline and injury. This makes some coaches inclined to conduct HIIT in the weeks leading up to the season and during the season. Therefore, the challenge is how to optimize and dose HIIT during these phases, as they can be decisive. Studies have highlighted the utility of conducting periods of intensified training to overcome the risk of overload while at the same time enhancing performance. During intensified training periods of typically a few weeks, intensity is increased by enlarging the amount of HIIT, for example, aerobic high-intensity training or speed endurance training, while volume at low-to-moderate intensity is significantly reduced. The outcome depends on training composition and prescription-most notably, intensity and duration of bouts and recovery. When work intervals are prescribed for a few minutes at intensities > 90% heart rate max (i.e., aerobic high-intensity training), then beneficial adaptations pertaining to aerobic power and capacity are apparent. But when work intervals are conducted at much higher intensities, as all-out efforts or sprinting of typically 10- to 40-s duration with longer recovery periods (i.e., speed endurance training), beneficial adaptations pertaining to anaerobic energy systems, ion handling, and fatigue resilience are commonly observed. In this review, we discuss the utility of conducting intensified training periods to enhance performance in elite football players during the late preparation phase and competitive season.

When and How Do Soccer Players From a Semi-Professional Club Sprint in Match Play?

The aims of this study were to investigate the periods in which sprints occurred during official matches and analyze these sprints considering the effect of the playing position and different contextual variables. Electronic performance and tracking systems were used for the analysis of all sprints performed by players. Matches were recorded by video and synchronized with performance tracking data. A total of 252 sprints were analyzed. The greatest frequency of sprints was observed in the period 1 (0’–15’), followed by period 2 (15’–30’) and period 6 (75’–90’), regardless of the playing position (χ2 = 31.35; p = 0.051). Most sprints were non-linear (non-linear sprints: 97.6%; linear sprints: 2.4%) and without ball possession (without ball possession: 95.2%; with ball possession: 4.8%) for all playing positions, but the role of the sprint and the field area in which the sprint occurred were dependent on the position (p < 0.001). Specifically, players covered ~17.55 m per sprint, starting at ~10.34 km/h, reaching ~26.74 km/h, maximally accelerating at ~2.73 m/s2, and decelerating at ~3.61 m/s2. Overall, the playing position and contextual variables had no significant effect on physical performance variables analyzed during these sprints. Therefore, this study allows performance practitioners to have a better understanding of when and how soccer players sprint in match-play. In this regard, this study presents some training and testing strategies that may be considered to improve performance and decrease injury risk.

Extended Match Time Exacerbates Fatigue and Impacts Physiological Responses in Male Soccer Players

PURPOSE

This study evaluated how extended match time (90 + 30 min) affected physiological responses and fatigue in male soccer players.

METHODS

Twenty competitive players (mean ± SD: age, 20 ± 1 yr; maximal oxygen uptake, 59 ± 4 mL·min -1 ·kg -1 ) completed an experimental match with their activity pattern and heart rate assessed throughout the game, whereas countermovement jump performance and repeated sprint ability were tested and quadriceps muscle biopsies and venous blood samples were taken at baseline and after 90 and 120 min of match play.

RESULTS

Less high-intensity running (12%) was performed in extra time in association with fewer intense accelerations and decelerations per minute compared with normal time. Peak sprint speed was 11% lower in extra time compared with normal time, and fatigue also manifested in impaired postmatch repeated sprint ability and countermovement jump performance (all P < 0.05). Muscle glycogen declined from 373 ± 59 mmol·kg -1 dry weight (dw) at baseline to 266 ± 64 mmol·kg -1 dw after 90 min, with a further decline to 186 ± 56 mmol·kg -1 dw after extra time ( P < 0.05) and with single-fiber analyses revealing depleted or very low glycogen levels in ~75% of both slow and fast twitch fibers. Blood glucose did not change during the first 90-min but declined ( P < 0.05) to 81 ± 8 mg·dL -1 after extra time. Plasma glycerol and ammonia peaked at 236 ± 33 mg·dL -1 and 75 ± 21 μmol·L -1 after the extra period.

CONCLUSIONS

These findings demonstrate exacerbated fatigue after extra time compared with normal time, which seems to be associated with muscle glycogen depletion, reductions in blood glucose levels, and hyperammonemia. Together, this points to metabolic disturbances being a major part of the integrated and multifaceted fatigue response during extended soccer match play.

When and how do elite soccer players sprint in match play? A longitudinal study in a professional soccer league

The aims of this study were to examine the periods in which the maximum speed actions occurred during elite soccer matches and analyse these actions considering the effect of playing position and different contextual variables. Performance-related variables (V_MAX: maximum speed; Vo: starting speed; SPD: sprinting distance; ACC_MAX: maximum acceleration; DEC_MAX: maximum deceleration) and sprint-related contextual variables (trajectory, ball possession, role, field area in which the action occurred) from each maximum speed action were collected. The first 15 minutes of each match half elicited most maximum speed actions (44.6% of cases), regardless of playing position (likelihood ratio, LR=13.95; p=0.95). However, playing position had a significant effect on the role of the action (Chi-Squared, χ²=50.68; p=0.001) and the field area in which the sprint occurred (χ²=26.54; p=0.001). Regarding the effect of different contextual variables on the sprint-related performance variables, no significant effect from any contextual variable on ACC_MAX, DEC_MAX or Vo was found (p > 0.05). Nevertheless, the contextual variables had a significant effect on SPD (from ball possession: sprints without ball > sprints with ball; trajectory: non-linear sprints > linear sprints; role: offensive sprints > defensive sprints) and V_MAX (from ball possession: sprints without ball > sprints with ball; playing position: midfielders < other positions).

The Role of Muscle Glycogen Content and Localization in High-Intensity Exercise Performance: A Placebo-Controlled Trial

PURPOSE

We investigated the coupling between muscle glycogen content and localization and high-intensity exercise performance using a randomized, placebo-controlled, parallel-group design with emphasis on single-fiber subcellular glycogen concentrations and sarcoplasmic reticulum Ca 2+ kinetics.

METHODS

Eighteen well-trained participants performed high-intensity intermittent glycogen-depleting exercise, followed by randomization to a high- (CHO; ~1 g CHO·kg -1 ·h -1 ; n = 9) or low-carbohydrate placebo diet (PLA, <0.1 g CHO·kg -1 ·h -1 ; n = 9) for a 5-h recovery period. At baseline, after exercise, and after the carbohydrate manipulation assessments of repeated sprint ability (5 × 6-s maximal cycling sprints with 24 s of rest), neuromuscular function and ratings of perceived exertion during standardized high-intensity cycling (~90% Wmax ) were performed, while muscle and blood samples were collected.

RESULTS

The exercise and carbohydrate manipulations led to distinct muscle glycogen concentrations in CHO and PLA at the whole-muscle (291 ± 78 vs 175 ± 100 mmol·kg -1 dry weight (dw), P = 0.020) and subcellular level in each of three local regions ( P = 0.001-0.046). This was coupled with near-depleted glycogen concentrations in single fibers of both main fiber types in PLA, especially in the intramyofibrillar region (within the myofibrils). Furthermore, increased ratings of perceived exertion and impaired repeated sprint ability (~8% loss, P < 0.001) were present in PLA, with the latter correlating moderately to very strongly ( r = 0.47-0.71, P = 0.001-0.049) with whole-muscle glycogen and subcellular glycogen fractions. Finally, sarcoplasmic reticulum Ca 2+ uptake, but not release, was superior in CHO, whereas neuromuscular function, including prolonged low-frequency force depression, was unaffected by dietary manipulation.

CONCLUSIONS

Together, these results support an important role of muscle glycogen availability for high-intensity exercise performance, which may be mediated by reductions in single-fiber levels, particularly in distinct subcellular regions, despite only moderately lowered whole-muscle glycogen concentrations.

Comparison of the Physical, Physiological, and Psychological Responses of the High-Intensity Interval (HIIT) and Small-Sided Games (SSG) Training Programs in Young Elite Soccer Players

We investigated the effects of high-intensity interval (HIIT) and small-sided games (SSG) training programs on physiological and psychological responses in young soccer players. Twenty-four male soccer players (age 16.7 ± 0.9 years) were divided into two groups (HIIT and SSG) and completed a 6-week training programs consisting of two training sessions a week. HIIT consisted of intermittent runs lasting 15 s at the 110% maximum aerobic speed followed by a passive recovery lasting 15 s; SSG was instead structured in a 4 versus 4 players games on a playing field of 25 × 35 m. The muscular power of the lower body was assessed before and after each training session using the 5-jump test to leg length, and two incremental field tests (VAMEVAL test and modified agility t-test). Our results show that HIIT and SSG have similar beneficial effects on the variables connected to the soccer-specific performance and the endurance with little influence on neuromuscular performances. Psychological responses were assessed using the "physical activity enjoyment scale", the Hooper index and the POMS variables. Results showed that SSG offers greater perceived enjoyment than what can be achieved with HIIT. In conclusion, SSG can be considered an effective, more motivating, and fun soccer-specific training that brings about physiological responses and neuromuscular adjustments in young soccer players.

Ketone Ester Supplementation Improves Some Aspects of Cognitive Function during a Simulated Soccer Match after Induced Mental Fatigue

Ketone supplementation has been proposed to enhance cognition during exercise. To assess whether any benefits are due to reduced cognitive fatigue during the latter portions of typical sport game action, we induced cognitive fatigue, provided a ketone monoester supplement (KME) vs. a non-caloric placebo (PLAC), and assessed cognitive performance during a simulated soccer match (SSM). In a double-blind, balanced, crossover design, nine recreationally active men (174.3 ± 4.2 cm, 76.6 ± 7.4 kg, 30 ± 3 y, 14.2 ± 5.5 % body fat, V˙O2 max = 55 ± 5 mL·kg BM−1·min−1; mean ± SD) completed a 45-min SSM (3 blocks of intermittent, variable intensity exercise) consuming either KME (25 g) or PLAC, after a 40-min mental fatiguing task. Cognitive function (Stroop and Choice Reaction Task [CRT]) and blood metabolites were measured throughout the match. KME reduced concentrations of both blood glucose (block 2: 4.6 vs. 5.2 mM, p = 0.02; block 3: 4.7 vs. 5.3 mM, p = 0.01) and blood lactate (block 1: 4.7 vs. 5.4 mM, p = 0.05; block 2: 4.9 vs. 5.9 mM, p = 0.01) during the SSM vs. PLAC, perhaps indicating a CHO sparing effect. Both treatments resulted in impaired CRT performance during the SSM relative to baseline, but KME displayed a reduced (p < 0.05) performance decrease compared to PLAC (1.3 vs. 3.4% reduction in correct answers, p = 0.02). No other differences in cognitive function were seen. These data suggest that KME supplementation attenuated decrements in CRT during repeated, high intensity, intermittent exercise. More study is warranted to assess fully the potential cognitive/physical benefits of KME for athletes.

Decline in Running Performance in Highest-Level Soccer: Analysis of the UEFA Champions League Matches

It is widely recognized that there is a decline in match running performance (MRP) towards the end of matches. To clarify whether it is primarily a consequence of fatigue, pacing or situational influences, this study aimed to examine MRP across 15-min match periods for players on different playing positions. Players’ MRP (n = 244) were examined from the UEFA Champions League matches (n = 20) using a semiautomatic optical tracking system. Linear mixed models for repeated measures were adjusted to analyze MRP over the six 15-min match periods while controlling the influence of situational factors. No effects of match outcome, match location, team, and opponent quality on total distance (TD) and high-intensity running (HIR) for players in all playing positions were found (F = 0.03−2.75; all p > 0.05). Significant differences in TD (F = 17.57−53.01; η2 = 0.39−0.52, all large effect sizes) and HIR (F = 3.67−7.64; η2 = 0.05−0.19, small to medium effect sizes) among six 15-minute match periods were found for players in all playing positions. In addition, players in all playing positions covered less TD (d = 1.41−2.15, large to very large effect sizes) and HIR (d = 0.16−0.6, trivial to medium effect sizes) in the last compared to the first 15-min match period. No differences in TD and HIR between the last two match periods in the second half were observed. This study confirmed that soccer players reduce MRP towards the end of matches, and suggest that the decline of MPR in highest-level soccer may be a consequence of pacing strategies.

Effects of an experimental short-time high-intensity warm-up on explosive muscle strength performance in soccer players: A pilot study

Objective: This study aimed to evaluate the effects of an experimental short-time warm-up consisting of a small number of intermittent high-intensity sprints on explosive muscle strength performance in soccer players and to identify recovery times after performing the sprints. Furthermore, we evaluated the reliability of a smartphone app in jumping performance.

Methods: Twenty male soccer players were given the following tests: 1) the counter-movement jump (CMJ) test with the Microgate system, 2) the counter-movement jump (CMJ) test with the MyJump smartphone app, and 3) the handgrip strength test. The experimental short-time high-intensity warm-up was carried out 1 week after test administration. The warm-up consisted of three maximum sprints over 60 m with 120 s of recovery between sprints. Then, the tests were administered again: the vertical jump height (VJH) performances (five trials) were measured 90 s after the last sprint; the handgrip strength performances (three trials) were measured 120 s after the last vertical jump test.

Results: The maximum VJH was found in the third trial of the CMJ test, 330 s after the last sprint (p < 0.01), the result closest to the baseline. The lowest VJH was found in the first trial of the CMJ test, 90 s after the last sprint (p < 0.05). Pearson’s analysis between the CMJ test with the Microgate system and the CMJ test with MyJump showed a strong correlation (R = 0.96). Lin’s concordance correlation coefficient showed a substantial concordance (ρc = 0.959) between measures.

Conclusion: This experimental short-time warm-up of high-intensity intermittent sprints appears to be a simple, quick, and efficient activity to accelerate soccer players’ optimal performance.

Breaking new grounds in injury risk screening in soccer by deploying unsupervised learning with a special focus on sex and fatigue effects

In injury prevention, a vertical drop jump (DJ) is often used for screening athletes at risk for injury; however, the large variation in individual movement patterns might mask potentially relevant strategies when analysed on a group-based level. Two movement strategies are commonly discussed as predisposing athletes to ACL injuries: a deficient leg axis and increased leg stiffness during landing. This study investigated the individual movement pattern of 39 female and male competitive soccer players performing DJs at rest and after being fatigued. The joint angles were used to train a Kohonen self-organising map. Out of 19,596 input vectors, the SOM identified 700 unique postures. Visualising the movement trajectories and adding the latent parameters contact time, medial knee displacement (MKD) and knee abduction moment allow identification of zones with presumably increased injury risk and whether the individual movement patterns pass these zones. This information can be used, e.g., for individual screening and for feedback purposes. Additionally, an athlete's reaction to fatigue can be explored by comparing the rested and fatigued movement trajectories. The results highlight the ability of unsupervised learning to visualise movement patterns and to give further insight into an individual athlete's status without the necessity of a priori assumptions.