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We examined the influence of competitive standard of the opponent on activity profile and fatigue during preseason friendly soccer matches. Time motion analysis was performed in a male professional soccer team (N = 14) during six friendly games played against professional, semi-professional and amateur-level opponents (PL, SPL and AL). The reference team covered higher acceleration distance, acceleration and deceleration > 2 m· s -2 distance against PL than AL (ES = 0.77 to 0.91). Acceleration and deceleration distance > 2 m· s -2 was also higher (ES = 0.66 to 0.84) against SPL than AL. Greater decreases in total distance, distance> 16 km· h -1 and > 22 km· h -1 , total acceleration and deceleration, acceleration and deceleration distance > 2 m· s -2 (ES = 0.84 to 2.20) were also observed during PL compared to AL opponent. Playing against a stronger opponent seems to be more physically demanding, with special emphasis on events related with change of velocity (accelerations and decelerations). Declines in physical performance appear more evident against a higher opponent.

Introduction: The aims of the study were 1) to evaluate whether a multifaceted simulated soccer game protocol, entitled the Copenhagen Soccer Test (CST), elicited a similar physiological loading as a competitive game (CG) and 2) to determine muscle metabolites, blood variables, and sprint performance in various phases of CST., Methods: Twelve Danish Second- and Third-Division soccer players participated in the study. On separate days, HR measurements, frequent blood sampling, and physical/technical tests were performed during 60- and 90-min versions of the CST during which repeated musculus vastus lateralis biopsies were collected. A CG was also played, where HR was recorded and pre- and post-game muscle biopsies and blood samples were collected., Results: No differences were observed between CST and CG in average HR (85% ± 1% and 86% ± 1% HRmax, P > 0.05) or recovery plasma creatine kinase (24 h: 312 ± 57 and 324 ± 76 U·L, P > 0.05). Muscle glycogen decreased (P < 0.05) from 459 ± 15 to 232 ± 30 mmol·kg dry weight (d.w.) during CST, which was not different from CG (P > 0.05). The rate of glycogen utilization was 4 ± 1 mmol·kg d.w.·min during the warm-up and the first 15 min of CST and 1 ± 1 mmol·kg d.w.·min (P < 0.05) from 60 to 90 min of CST. After 15 min of CST, muscle lactate was elevated (P < 0.05) approximately fivefold (24 ± 3 mmol·kg d.w.), and creatine phosphate was lowered (P < 0.05) by ∼60% (28 ± 4 mmol·kg d.w.). Sprint velocity (2 × 20 m) decreased (P < 0.05) by 7% during CST (5.2 ± 0.6 to 4.9 ± 0.7 m·s)., Conclusions: The physiological response to the CST was reproducible and comparable to that of high-level CG. The CST allowed for rapid muscle sampling and revealed high creatine phosphate degradation throughout the test and a lowered glycogen utilization toward the end of the simulated game.

Using a video-based time-motion analysis system, a semi-automatic multiple-camera system, and two commercially available GPS systems (GPS-1; 5 Hz and GPS-2; 1 Hz), we compared activity pattern and fatigue development in the same football match. Twenty football players competing in the Spanish second and third divisions participated in the study. Total distance covered during the match for the four systems was as follows: 10.83 + or - 0.77 km (semi-automatic multiple-camera system, n = 20), 9.51 + or - 0.74 km (video-based time-motion analysis system, n = 17), 10.72 + or - 0.70 km (GPS-1, n = 18), and 9.52 + or - 0.89 km (GPS-2, n = 13). Distance covered by high-intensity running for the four systems was as follows: 2.65 + or - 0.53 km (semi-automatic multiple-camera system), 1.61 + or - 0.37 km (video-based time-motion analysing system), 2.03 + or - 0.60 km (GPS-1), and 1.66 + or - 0.44 km (GPS-2). Distance covered by sprinting for the four systems was as follows: 0.38 + or - 0.18 km (semi-automatic multiple-camera system), 0.42 + or - 0.17 km (video-based time-motion analysing system), 0.37 + or - 0.19 km (GPS-1), and 0.23 + or - 0.16 km (GPS-2). All four systems demonstrated greater (P < 0.05) total distance covered and high-intensity running in the first 15-min period and less (P < 0.05) total distance covered and high-intensity running during the last 15-min period than all other 15-min intervals, with a reduction (P < 0.05) in high-intensity running from the first to the last 15-min period of 46 + or - 19%, 37 + or - 26%, 50 + or - 26%, and 45 + or - 27% for the semi-automatic multiple-camera system, video-based time-motion analysis system, GPS-1, and GPS-2, respectively. Our results show that the four systems were able to detect similar performance decrements during a football game and can be used to study game-induced fatigue. Rather large between-system differences were present in the determination of the absolute distances covered, meaning that any comparisons of results between different match analysis systems should be done with caution.

This review describes when fatigue may develop during soccer games and the potential physiological mechanisms that cause fatigue in soccer. According to time-motion analyses and performance measures during match-play, fatigue or reduced performance seems to occur at three different stages in the game: (1) after short-term intense periods in both halves; (2) in the initial phase of the second half; and (3) towards the end of the game. Temporary fatigue after periods of intense exercise in the game does not appear to be linked directly to muscle glycogen concentration, lactate accumulation, acidity or the breakdown of creatine phosphate. Instead, it may be related to disturbances in muscle ion homeostasis and an impaired excitation of the sarcolemma. Soccer players' ability to perform maximally is inhibited in the initial phase of the second half, which may be due to lower muscle temperatures compared with the end of the first half. Thus, when players perform low-intensity activities in the interval between the two halves, both muscle temperature and performance are preserved. Several studies have shown that fatigue sets in towards the end of a game, which may be caused by low glycogen concentrations in a considerable number of individual muscle fibres. In a hot and humid environment, dehydration and a reduced cerebral function may also contribute to the deterioration in performance. In conclusion, fatigue or impaired performance in soccer occurs during various phases in a game, and different physiological mechanisms appear to operate in different periods of a game.

The aim of this study was to assess physical fitness, match performance and development of fatigue during competitive matches at two high standards of professional soccer. Computerized time-motion analyses were performed 2-7 times during the competitive season on 18 top-class and 24 moderate professional soccer players. In addition, the players performed the Yo-Yo intermittent recovery test. The top-class players performed 28 and 58% more (P < 0.05) high-intensity running and sprinting, respectively, than the moderate players (2.43 +/- 0.14 vs 1.90 +/- 0.12 km and 0.65 +/- 0.06 vs 0.41 +/- 0.03 km, respectively). The top-class players were better (11%; P < 0.05) on the Yo-Yo intermittent recovery test than the moderate players (2.26 +/- 0.08 vs 2.04 +/- 0.06 km, respectively). The amount of high-intensity running, independent of competitive standard and playing position, was lower (35-45%; P < 0.05) in the last than in the first 15 min of the game. After the 5-min period during which the amount of high-intensity running peaked, performance was reduced (P < 0.05) by 12% in the following 5 min compared with the game average. Substitute players (n = 13) covered 25% more (P < 0.05) ground during the final 15 min of high-intensity running than the other players. The coefficient of variation in high-intensity running was 9.2% between successive matches, whereas it was 24.8% between different stages of the season. Total distance covered and the distance covered in high-intensity running were higher (P < 0.05) for midfield players, full-backs and attackers than for defenders. Attackers and full-backs covered a greater (P < 0.05) distance in sprinting than midfield players and defenders. The midfield players and full-backs covered a greater (P < 0.05) distance than attackers and defenders in the Yo-Yo intermittent recovery test (2.23 +/- 0.10 and 2.21 +/- 0.04 vs 1.99 +/- 0.11 and 1.91 +/- 0.12 km, respectively). The results show that: (1) top-class soccer players performed more high-intensity running during a game and were better at the Yo-Yo test than moderate professional players; (2) fatigue occurred towards the end of matches as well as temporarily during the game, independently of competitive standard and of team position; (3) defenders covered a shorter distance in high-intensity running than players in other playing positions; (4) defenders and attackers had a poorer Yo-Yo intermittent recovery test performance than midfielders and full-backs; and (5) large seasonal changes were observed in physical performance during matches.

This study aimed to determine whether caffeine gum influenced perceptual-cognitive and physical performance during the extra-time period of simulated soccer match-play. Semiprofessional male soccer players (n = 12, age: 22 ± 3 years, stature: 1.78 ± 0.06 m, mass: 75 ± 9 kg) performed 120-min soccer-specific exercise on two occasions. In a triple-blind, randomized, crossover design, players chewed caffeinated (200 mg; caffeine) or control (0 mg; placebo) gum for 5 min following 90 min of soccer-specific exercise. Perceptual-cognitive skills (i.e., passing accuracy, reaction time, composure, and adaptability) were assessed using a soccer-specific virtual reality simulator, collected pre- and posttrial. Neuromuscular performance (reactive-strength index, vertical jump height, absolute and relative peak power output, and negative vertical displacement) and sprint performance (15 and 30 m) were measured at pretrial, half-time, 90 min, and posttrial. Caffeine gum attenuated declines in reaction time (pre: 90.8 ± 0.8 AU to post: 90.7 ± 0.8 AU) by a further 4.2% than placebo (pre: 92.1 ± 0.8 AU to post: 88.2 ± 0.8 AU; p <.01). Caffeine gum reduced composure by 4.7% (pre: 69.1 ± 0.8 AU to post: 65.9 ± 0.8 AU) versus placebo (pre: 68.8 ± 0.8 AU to post: 68.3 ± 0.8 AU; p <.01). Caffeine gum did not influence any other variables (p >.05). Where caffeine gum is consumed by players prior to extra-time, reaction time increases but composure may be compromised, and neuromuscular and sprint performance remain unchanged. Future work should assess caffeine gum mixes with substances like L-theanine that promote a relaxed state under stressful conditions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Purpose: To examine the recovery kinetics of exercise-induced muscle damage (EIMD), neuromuscular fatigue, and performance following small-sided games (SSGs) of different densities in soccer. Methods: Ten male players randomly completed 3 trials: a control trial (no SSGs), 4v4 SSGs (62.5 m2/player), and 8v8 SSGs (284.4 m2/player). External and internal load were monitored using GPS technology, heart-rate monitors, and rating of perceived exertion. Delayed-onset muscle soreness (DOMS), creatine kinase (CK), isokinetic strength, countermovement jump (CMJ), and sprint were determined at baseline, as well as at 24, 48, and 72 hours post-SSGs. Neuromuscular fatigue was assessed at baseline and at 1, 2, and 3 hours post-SSGs. Results: DOMS increased (P <.05) in 4v4 for 72 hours and in 8v8 for 24 hours with that of knee flexors being more pronounced than that of extensors. CK increased (P <.05) in 4v4 for 72 hours and in 8v8 for 24 hours. Neuromuscular fatigue increased (P <.05) in 4v4 for 2 hours and in 8v8 for 3 hours. Strength declined (P <.05) in 4v4 for 48 hours and in 8v8 for 72 hours. CMJ decreased (P <.05) in 4v4 for 24 hours and in 8v8 for 48 hours. Sprint decreased (P <.05) for 48 hours in 4v4 and for 72 hours in 8v8. Conclusions: SSGs are associated with a prolonged rise of EIMD and induce short-term neuromuscular fatigue and slow recovery kinetics of strength, jump, and sprinting performance. The time for complete recovery is longer for SSGs of lower density. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Glycogen particles are situated in key areas of the muscle cell in the vicinity of the main energy‐consumption sites and may be utilised heterogeneously dependent on the nature of the metabolic demands. The present study aimed to investigate the time course of fibre type‐specific utilisation of muscle glycogen in three distinct subcellular fractions (intermyofibrillar, IMF; intramyofibrillar, Intra; and subsarcolemmal, SS) during repeated high‐intensity intermittent exercise. Eighteen moderately to well‐trained male participants performed three periods of 10 × 45 s cycling at ∼105% watt max (EX1–EX3) coupled with 5 × 6 s maximal sprints at baseline and after each period. Muscle biopsies were sampled at baseline and after EX1 and EX3. A higher glycogen breakdown rate in type 2 compared to type 1 fibres was found during EX1 for the Intra (−72 vs. −45%) and IMF (−59 vs. −35%) glycogen fractions (P < 0.001) but with no differences for SS glycogen (−52 vs. −40%). In contrast, no fibre type differences were observed during EX2–EX3, where the utilisation of Intra and IMF glycogen in type 2 fibres was reduced, resulting in depletion of all three subcellular fractions to very low levels post‐exercise within both fibre types. Importantly, large heterogeneity in single‐fibre glycogen utilisation was present with an early depletion of especially Intra glycogen in individual type 2 fibres. In conclusion, there is a clear fibre type‐ and localisation‐specific glycogen utilisation during high‐intensity intermittent exercise, which varies with time course of exercise and is characterised by exacerbated pool‐specific glycogen depletion at the single‐fibre level. Key points: Muscle glycogen is the major fuel during high‐intensity exercise and is stored in distinct subcellular areas of the muscle cell in close vicinity to the main energy consumption sites.In the present study quantitative electron microscopy imaging was used to investigate the utilisation pattern of three distinct subcellular muscle glycogen fractions during repeated high‐intensity intermittent exercise.It is shown that the utilisation differs dependent on fibre type, subcellular localisation and time course of exercise and with large single‐fibre heterogeneity.These findings expand on our understanding of subcellular muscle glycogen metabolism during exercise and may help us explain how reductions in muscle glycogen can attenuate muscle function even at only moderately lowered whole‐muscle glycogen concentrations. [ABSTRACT FROM AUTHOR]

We combined game activity analyses with skeletal muscle phenotypes and comprehensive physiological testing to elucidate factors of importance for physical performance in elite women's football. GPS‐data from an experimental game, sprint and endurance testing, and muscle tissue analysis of metabolic enzyme activity, protein expression and fiber type composition were completed for international top‐level women players (n = 20; age; 23 ± 4 yrs, height; 166 ± 10 cm, weight; 60 ± 8 kg; VO2max; 51 ± 6 ml/min/kg). Muscle monocarboxylate transporter 4 (MCT4) protein expression explained 46% of the variance in total game distance, while the ability to maintain high‐intensity running (HIR) during the final 15 min of the game correlated to myosin heavy chain 1 (MHCI) and Na+‐K+ ATPase β1, FXYD1 (phospholemman) and superoxide dismutase 2 (SOD2) protein expression (range: r = 0.51–0.71; all p < 0.05). Total HIR distance correlated with (MHCIIa) protein expression (r = 0.51; p < 0.05), while muscle Na+/H+ exchanger 1 (NHE1) protein explained 36% of the variance in game sprint distance (p < 0.05). Total game accelerations (actions >4 m/s2) correlated with platelet endothelial cell adhesion molecule (PECAM‐1) protein expression (r = 0.51; p < 0.05), while concentric knee flexor strength explained 42–62% of the variance in intense decelerations (>4 m/s2). In conclusion, for elite women players' game endurance performance and resistance to end‐game fatigue were affected by monocarboxylate transporter expression and myosin heavy chain profile. HIR was also correlated to ion transporter expression and muscle antioxidative capacity. Finally, the importance of functional strength and measures of muscle vascularization in relation to total game decelerations and accelerations, respectively, illustrates the complex physiological demands in elite women's football. [ABSTRACT FROM AUTHOR]

The present study examined skeletal muscle metabolism and changes in repeated sprint performance during match play for n = 20 competitive elite women outfield players. We obtained musculus vastus lateralis biopsies and blood samples before, after, and following intense periods in each half of a friendly match, along with 5 × 30‐meter sprint tests and movement pattern analyses (10‐Hz S5 Global Positioning System [GPS]). Muscle glycogen decreased by 39% and 42% after an intense period of the second half and after the match, respectively, compared to baseline (p < 0.05). Post‐match, 80% type I fibers and 69% type II fibers were almost empty or completely empty of glycogen. Muscle lactate was higher (p < 0.05) after the intense period of the first half and post‐match compared to baseline (14.3 ± 4.6 (±SEM) and 12.9 ± 5.7 vs. 6.4 ± 3.7 mmol/kg d.w.). Muscle phosphocreatine was reduced (p < 0.05) by 16% and 12%, respectively, after an intense period in the first and second half compared to baseline. Blood lactate and glucose increased during the match and peaked at 8.4 ± 2.0 and 7.9 ± 1.2 mmol/L, respectively. Mean 5 × 30 m sprint time declined by 3.2 ± 1.7 and 7.0 ± 2.1% after the first and second half, respectively, and 4.7 ± 1.6% (p < 0.05) after an intense period in the first half compared to baseline. In conclusion, match play in elite female football players resulted in marked glycogen depletion in both fiber types, which may explain fatigue at the end of a match. Repeated sprint ability was impaired after intense periods in the first half and after both halves, which may be associated with the observed muscle metabolite perturbations. [ABSTRACT FROM AUTHOR]

The COVID-19 pandemic has changed the conditions for competitive football around the globe dramatically. Several competitions and leagues have been cancelled or postponed. Players have firstly been forced to training in solitude. In a second stage, players start training in small groups with strict contact restriction and return to competitive play might occur after only few weeks of normal team training preparation. These special circumstances are likely to impact football performance and injury risk in the upcoming competitions. Thus, clubs, coaching and medical staff, as well as players are challenged on the prioritization of fitness and performance, which easily can create several "catch-22-dilemmas". The present article presents views on fitness training, physical preparation and recovery during these uncommon conditions, and how elite football players can return to the competitive field well-prepared for post-crisis football endeavours around the world. Due to the multifaceted physiological demands in elite football, the long recovery requirements after match-play and an upcoming reality with many games within a short period, elite football players, managers and clubs may face extraordinary challenges associated with return to play under the current circumstances. [ABSTRACT FROM AUTHOR]

Elite women volleyball players (n = 25; mean ± SD: age, 19 ± 5 years; height, 171 ± 7 cm; weight, 63 ± 1 0 kg) volunteered to participate in the study. They were randomized into a high-intensity training (HIT; n = 13) group and a control (CON; n = 12) group. In addition to the normal team training and games, HIT performed 6-10 x 30-seconds all-out running intervals separated by 3-minute recovery periods 3 times per week during a 4-week in-season period whereas CON only completed the team training sessions and games. Preintervention and postintervention, all players completed the arrowhead agility test (AAT), a repeated sprint test (RST; 5 x 30 meters separated by 25 seconds of recovery), and the Yo-Yo Intermittent Recovery level 2 test (Yo-Yo IR2) followed by a-10 minute rest period and the Yo-Yo IR1 test. Mean running distance during HIT in week 1 was 152 ± 4 m and increased (p ≤ 0.05) by 4.6% (1 59 ± 3 m) in week 4. The AAT performance improved (p ≤ 0.05) by 2.3% (1 8.87 ± 0.97-1 8.44 ± 1.06 seconds) and RST by 4.3% postintervention in the HIT group only. Baseline RST fatigue index was 7.0 ± 2.9 and 6.2 ± 5.0% in HIT and CON, respectively, but was lowered (p ≤ 0.05) to 2.7 ± 3.0% posttraining in HIT and remained unaltered in CON (5.5 ± 5.0%). In HIT, Yo-Yo IR2 and Yo-Yo IR1 performance improved by 1 2.6 and 1 8.3% postintervention, respectively, with greater (p ≤ 0.05) Yo-yo IR1 change scores than in CON. In conclusion, additional high-intensity in-season training performed as interval running improved agility, repeated sprint ability, and high-intensity intermittent exercise performance in elite women volleyball players. [ABSTRACT FROM AUTHOR]

Background: Sodium bicarbonate intake has been shown to improve exercise tolerance, but the effects on high-intensity intermittent exercise are less clear. Thus, the aim of the present study was to determine the effect of sodium bicarbonate intake on Yo-Yo intermittent recovery test level 2 performance in trained young men. Method: Thirteen men aged 23 ± 1 year (height: 180 ± 2 cm, weight: 78 ± 3 kg; VO2max: 61.3 ± 3.3 mlO2 · kg−1 · min−1; means ± SEM) performed the Yo-Yo intermittent recovery test level 2 (Yo-Yo IR2) on two separate occasions in randomized order with (SBC) and without (CON) prior intake of sodium bicarbonate (0.4 g · kg−1 body weight). Heart rate and rating of perceived exertion (RPE) were measured during the test and venous blood samples were taken frequently. Results: Yo-Yo IR2 performance was 14 % higher (P = 0.04) in SBC than in CON (735 ± 61 vs 646 ± 46 m, respectively). Blood pH and bicarbonate were similar between trials at baseline, but higher (P = 0.003) immediately prior to the Yo-Yo IR2 test in SBC than in CON (7.44 ± 0.01 vs 7.32 ± 0.01 and 33.7 ± 3.2 vs 27.3 ± 0.6 mmol · l−1, respectively). Blood lactate was 0.9 ± 0.1 and 0.8 ± 0.1 mmol · l−1 at baseline and increased to 11.3 ± 1.4 and 9.4 ± 0.8 mmol · l−1 at exhaustion in SBC and CON, respectively, being higher (P = 0.03) in SBC. Additionally, peak blood lactate was higher (P = 0.02) in SBC than in CON (11.7 ± 1.2 vs 10.2 ± 0.7 mmol · l−1). Blood glucose, plasma K+ and Na+ were not different between trials. Peak heart rate reached at exhaustion was 197 ± 3 and 195 ± 3 bpm in SBC and CON, respectively, with no difference between conditions. RPE was 7 % lower (P = 0.003) in SBC than in CON after 440 m, but similar at exhaustion (19.3 ± 0.2 and 19.5 ± 0.2). Conclusion: In conclusion, high-intensity intermittent exercise performance is improved by prior intake of sodium bicarbonate in trained young men, with concomitant elevations in blood alkalosis and peak blood lactate levels, as well as lowered rating of perceived exertion. [ABSTRACT FROM AUTHOR]

Background: Caffeine and sodium bicarbonate ingestion have been suggested to improve high-intensity intermittent exercise, but it is unclear if these ergogenic substances affect performance under provoked metabolic acidification. To study the effects of caffeine and sodium bicarbonate on intense intermittent exercise performance and metabolic markers under exercise-induced acidification, intense arm-cranking exercise was performed prior to intense intermittent running after intake of placebo, caffeine and sodium bicarbonate. Methods: Male team-sports athletes (n = 12) ingested sodium bicarbonate (NaHCO3; 0.4 g.kg−1 b.w.), caffeine (CAF; 6 mg.kg−1 b.w.) or placebo (PLA) on three different occasions. Thereafter, participants engaged in intense arm exercise prior to the Yo-Yo intermittent recovery test level-2 (Yo-Yo IR2). Heart rate, blood lactate and glucose as well as rating of perceived exertion (RPE) were determined during the protocol. Results: CAF and NaHCO3 elicited a 14 and 23% improvement (P < 0.05), respectively, in Yo-Yo IR2 performance, post arm exercise compared to PLA. The NaHCO3 trial displayed higher [blood lactate] (P < 0.05) compared to CAF and PLA (10.5 ± 1.9 vs. 8.8 ± 1.7 and 7.7 ± 2.0 mmol.L−1, respectively) after the Yo-Yo IR2. At exhaustion CAF demonstrated higher (P < 0.05) [blood glucose] compared to PLA and NaHCO3 (5.5 ± 0.7 vs. 4.2 ± 0.9 vs. 4.1 ± 0.9 mmol.L−1, respectively). RPE was lower (P < 0.05) during the Yo-Yo IR2 test in the NaHCO3 trial in comparison to CAF and PLA, while no difference in heart rate was observed between trials. Conclusions: Caffeine and sodium bicarbonate administration improved Yo-Yo IR2 performance and lowered perceived exertion after intense arm cranking exercise, with greater overall effects of sodium bicarbonate intake. [ABSTRACT FROM AUTHOR]

Physiological responses and performance were examined during and after a simulated trampoline competition (STC). Fifteen elite trampoline gymnasts participated, of which eight completed two routines (EX1 and EX2) and a competition final (EX3). Trampoline-specific activities were quantified by video-analysis. Countermovement jump (CMJ) and 20 maximal trampoline jump (20-MTJ) performances were assessed. Heart rate (HR) and quadriceps muscle temperature (Tm) were recorded and venous blood was drawn. A total of 252 ± 16 jumps were performed during the STC. CMJ performance declined (P < 0.05) by 3.8, 5.2 and 4.2% after EX1, EX2 and EX3, respectively, and was 4.8% lower (P < 0.05) than baseline 24 h post-competition. 20-MTJ flight time was ~1% shorter (P < 0.05) for jump 1–10 after EX2 and 24 h post STC.Tmincreased (P < 0.05) to ~39°C after the warm-up, but declined (P < 0.05) 1.0 and 0.6ºC before EX2 and EX3, respectively. Peak HR was 95–97%HRmaxduring EX1-3. Peak blood lactate, plasma K+and NH3were 6.5 ± 0.5, 6.0 ± 0.2 mmol · l−1and 92 ± 10 µmol · l−1, respectively. Plasma CK increased (P < 0.05) by ~50 and 65% 0 and 24 h after STC. In conclusion, a trampoline gymnastic competition includes a high number of repeated explosive and energy demanding jumps, which impairs jump performance during and 24 h post-competition. [ABSTRACT FROM PUBLISHER]

The article describes a study which looked at the effect of heat stress on repeat jumping performance in Scandinavian elite soccer players after competitive matches. Researchers evaluated countermovement jump (CMJ) test performance following games in average or hot conditions, as well as net body mass loss. Degeneration of jumping performance was strongly correlated to body mass loss after games in hot temperatures, attributed to severe dehydration and muscle fatigue.

The effect of oral caffeine ingestion on intense intermittent exercise performance and muscle interstitial ion concentrations was examined. The study consists of two studies (S1 and S2). In S1, 12 subjects completed the Yo-Yo intermittent recovery level 2 (Yo-Yo IR2) test with prior caffeine (6 mg/kg body wt; CAF) or placebo (PLA) intake. In S2, 6 subjects performed one low-intensity (20 W) and three intense (50 W) 3-min (separated by 5 min) one-legged knee-extension exercise bouts with (CAF) and without (CON) prior caffeine supplementation for determination of muscle interstitial K+ and Na+ with microdialysis. In S1 Yo-Yo IR2 performance was 16% better (P < 0.05) in CAF compared with PLA. In CAF, plasma K+ at the end of the Yo-Yo IR2 test was 5.2 ± 0.1 mmol/1 with no difference between the trials. Plasma free fatty acids (FFA) were higher (P < 0.05) in CAF than PLA at rest and remained higher (P < 0.05) during exercise. Peak blood glucose (8.0 ± 0.6 vs. 6.2 ± 0.4 mmol/1) and plasma NH3 (137.2 ± 10.8 vs. 113.4 ± 13.3 µmol/l) were also higher (P < 0.05) in CAF compared with PLA. In S2 interstitial K+ was 5.5 ± 0.3, 5.7 ± 0.3, 5.8 ± 0.5, and 5.5 ± 0.3 mmol/1 at the end of the 20-W and three 50-W periods, respectively, in CAF, which were lower (P < 0.001) than in CON (7.0 ± 0.6, 7.5 ± 0.7, 7.5 ± 0.4, and 7.0 ± 0.6 mmol/1, respectively). No differences in interstitial Na+ were observed between CAF and CON. In conclusion, caffeine intake enhances fatigue resistance and reduces muscle interstitial K+ during intense intermittent exercise. [ABSTRACT FROM AUTHOR]

The article reports on research conducted to compare movement pattern, fatigue development, and heart rate for top class elite female players when playing international versus domestic league games. Researchers evaluated 17 players. They found that the elite female soccer players performed more high intensity running when playing in international games than in domestic league games and that there was no difference in heart rate between the two types of games.

The article presents the study conducted regarding the match performance and physical demands of the elite women soccer players. The study, administered to top-class and high-level players, will examine the effect of their changing locomotor activities on their performance. It shows that the greater the standard of the players the greater their running intensity becomes.

The article examines muscle and blood metabolites during soccer match play, which are then related to possible changes in sprint performance. The study used 31 Danish fourth division players, who took part in three friendly soccer games. Blood samples were frequently collected from the test subjects during the game, and muscle biopsies were taken before and after the game as well as immediately after each half or after an intense exercise period in each half. Muscle lactate and blood lactate levels were measured during the first and second halves of the soccer games.

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 Ca2+ 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% W max) 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 Ca2+ 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. [ABSTRACT FROM AUTHOR]

Highlights: [•] Male players covered more distance in total and at higher speed thresholds. [•] Gender differences were more pronounced in the second half. [•] Female players had lower pass completion rates than male players. [•] Male full-backs and midfielders covered more distance in higher speed thresholds than females. [•] More research is warranted to establish gender-specific speed thresholds. [Copyright &y& Elsevier]

Highlights: [•] The Copenhagen Soccer test has now been modified and applied for high-level female football players. [•] The physiological response and decrease in sprint performance during CSTw is comparable to competitive matches. [•] The CSTw can be used for investigation of metabolite response and fatigue mechanisms in female football. [•] The CSTw can also be used for intervention studies and for training and testing of injured female players. [ABSTRACT FROM AUTHOR]