Food for thought: Physiological considerations for nutritional ergogenic efficacy.

Top-class athletes have optimized their athletic performance largely through adequate training, nutrition, recovery, and sleep. A key component of sports nutrition is the utilization of nutritional ergogenic aids, which may provide a small but significant increase in athletic performance. Over the last decade, there has been an exponential increase in the consumption of nutritional ergogenic aids, where over 80% of young athletes report using at least one nutritional ergogenic aid for training and/or competition. Accordingly, due to their extensive use, there is a growing need for strong scientific investigations validating or invalidating the efficacy of novel nutritional ergogenic aids. Notably, an overview of the physiological considerations that play key roles in determining ergogenic efficacy is currently lacking. Therefore, in this brief review, we discuss important physiological considerations that contribute to ergogenic efficacy for nutritional ergogenic aids that are orally ingested including (1) the impact of first pass metabolism, (2) rises in systemic concentrations, and (3) interactions with the target tissue. In addition, we explore mouth rinsing as an alternate route of ergogenic efficacy that bypasses the physiological hurdles of first pass metabolism via direct stimulation of the central nervous system. Moreover, we provide real-world examples and discuss several practical factors that can alter the efficacy of nutritional ergogenic aids including human variability, dosing protocols, training status, sex differences, and the placebo effect. Taking these physiological considerations into account will strengthen the quality and impact of the literature regarding the efficacy of potential ergogenic aids for top-class athletes.

Internal Load of Female Varsity Ice Hockey Players During Training and Games During a Season.

This study quantified internal load, using sessional rating of perceived exertion (sRPE) and heart-rate derived training impulse (TRIMP), of female varsity ice hockey players throughout a season. Twenty-four female (19.8±1.4 yr, 68.0±6.9 kg) varsity ice hockey players participated in this prospective cohort study. Internal load was captured using sRPE and TRIMP for each on-ice session. Internal load was significantly higher (p<0.05) for games (sRPE: 324±202 AU, TRIMP: 95±60 AU) compared to training (sRPE: 248±120 AU, TRIMP: 68±32 AU). Overall, goalies had a higher internal load than forwards (sRPE and TRIMP) and defence (TRIMP), with no differences between forwards and defence. Micro-cycle periodization was present, with training sessions several days prior to game days having the highest internal load (sRPE and TRIMP) and tapering down as subsequent training sessions approached game day. For the meso-cycle assessment, for both training and competition combined, the post-season sRPE was greater than the pre-season (p=0.002) and regular season (p<0.001). Lastly, the association between sRPE and TRIMP, revealed a large, statistically significant relationship (r=0.592, p<0.001). Internal load was greater during competitions, training sessions and subsequent internal loads suggested prioritization around game days, the post-season phase demanded the highest internal load and there was a strong correlation between sRPE and TRIMP.

External Training Demands in Women's Varsity Rugby Union Players Quantified by Wearable Microtechnology With Individualized Speed Thresholds.

ABSTRACT: Nyman, DLE and Spriet, LL. External training demands in women's varsity rugby union players quantified by wearable microtechnology with individualized speed thresholds. J Strength Cond Res 36(11): 3151-3158, 2022-This study used wearable Global Positioning System (GPS) microtechnology with individualized speed thresholds to examine external training demands in 29 female varsity rugby union athletes during competitive season practices. Players were categorized as forwards or backs and observed during fitness, game-based, or skill training days (FT/GT/ST). Global Positioning System-derived variables included distances, high-intensity running (HIR), work-to-rest ratio, power plays, and PlayerLoad. Five speed zones categorized athlete movements and were customized according to each individual's overall maximum velocity (V̇max). Compared with backs, forwards had lower overall V̇max (6.62 ± 0.66 m·s -1 ; 7.38 ± 0.61 m·s -1 , p = 0.003) and HIR thresholds (3.97 ± 0.40 m·s -1 ; 4.43 ± 0.37 m·s -1 , p = 0.003). There were no interaction effects between position and training day for any GPS-derived variables. However, there were several effects of position ( p ≤ 0.05), with forwards being lower than backs in mean V̇max, zone 1 distance, and power plays, and greater than backs in zone 3, zone 4, and HIR distances. Effects of the training day ( p ≤ 0.05) were also observed in zone 1 distance, with FT being lower than GT and ST, and in power plays, with FT being greater than ST. In female varsity rugby union athletes, there were significant positional differences in individualized speed thresholds and external training demands. However, there were few marked differences between fitness, game-based, and skill training days.

Internal Physiological Load Measured Using Training Impulse in Varsity Men's and Women's Ice Hockey Players Between Game Periods.

ABSTRACT: Bigg, JL, Gamble, ASD, and Spriet, LL. Internal physiological load measured using training impulse in varsity men's and women's ice hockey players between game periods. J Strength Cond Res 35(10): 2824-2832, 2021-This study quantified internal load in male and female ice hockey players throughout a season, with comparisons between game periods and match outcome. Twenty-seven male and 24 female varsity ice hockey players participated in this longitudinal prospective cohort study monitoring internal load, using Banister's training impulse (TRIMP). Data were assessed according to game periods, match outcome (win or loss), and games played in noncongested (1 game/wk) or congested (2 + games/wk) weeks. Statistical significance was considered at p < 0.05. The TRIMP for period 1 for both male (25 ± 16 arbitrary units [AU]) and female (23 ± 19 AU) players was significantly lower than period 3 (males: 30 ± 21 AU; p = 0.001; females: 29 ± 21 AU; p = 0.003) but not period 2 (males: 27 ± 17 AU; p = 0.183; females: 27 ± 19 AU; p = 0.681). There were no differences in TRIMP within any period between games resulting in a win compared with a loss. Overall, there were no differences in TRIMP between male and female players. However, when stratified by position, male forwards experienced greater TRIMP than female forwards (p < 0.001 for all periods), whereas female defense had greater TRIMP than male defense (p ≤ 0.032 for all periods). There were no differences between noncongested and congested week games and no differences in TRIMP between nonback-to-back and back-to-back games, or the first and second games played of a back-to-back series. This study measured physiological demand throughout the periods of ice hockey games in men and women and concluded that internal load was highest in the third period. Understanding the demands throughout a game can provide information to coaches and players that would be useful in managing fatigue and optimizing physical performance.

Moderate Load Resisted Sprints Do Not Improve Subsequent Sprint Performance in Varsity-Level Sprinters.

ABSTRACT: Thompson, K, Whinton, AK, Ferth, S, Spriet, LL, and Burr, JF. Moderate load resisted sprints do not improve subsequent sprint performance in varsity-level sprinters. J Strength Cond Res 35(1): 72-77, 2021-Resisted sprint training (RST) is commonly used for performance enhancement in athletics and team sports to develop acceleration ability. Evidence suggests that RST may be effective as a short-term intervention to improve successive sprints. Although these improvements have been measured in team sport athletes, limited research has considered the acute effects of RST training in sprint-trained athletes. Therefore, the aim of the current study was to determine whether performing RST with varsity-level sprinters using sled-equivalent resistive loads of ∼45% body mass results in a potentiation effect, leading to improvements in subsequent maximal sprint performance over 0-5 m and 0-20 m. Competitive sprinters (n = 20) were randomly assigned to perform a pre/post maximal 20-m sprint separated by either 3 resisted (RST group) or unresisted (URS group) sprints. The RST or URS protocol was performed on 4 occasions separated by at least 7 days. No significant differences were observed between the RST and URS groups comparing changes in sprint times over 0-5 m (URS Δ <0.01 ± 0.03 seconds, RST Δ <0.01 ± 0.03 seconds) and 0-20 m (URS Δ 0.013 ± 0.04 seconds, RST Δ <0.01 ± 0.04 seconds). We conclude that resisted sprints using sled-equivalent loads of 45% body mass are ineffective at inducing a potentiating effect on subsequent sprint performance in varsity-level sprinters. In this population of trained athletes, greater loads may be necessary to induce a potentiating effect.

Sweat Loss and Fluid Intake of Female Varsity Ice Hockey Players During On-Ice Practices and Games.

Bigg, JL, Gamble, ASD, Vermeulen, TF, Bigg, LM, and Spriet, LL. Sweat loss and fluid intake of female varsity ice hockey players during on-ice practices and games. J Strength Cond Res 34(2): 389-395, 2020-Sweat losses of ∼1.5-2% body mass (BM) during exercise impairs athletic performance in stop and go sports such as ice hockey. The study examined the pre-exercise hydration status, sweat loss, fluid and carbohydrate (CHO) intake, and sodium balance of female hockey players. Twenty-four female varsity hockey players were tested during 2 practices and 4 games. Data analyses were performed using a level of significance of p ≤ 0.05. Over 70% of players arrived at the practices and ∼50% of players arrived at the game mildly dehydrated. Before the high- (P1) and low-intensity (P2) practices, players consumed an average of 0.19 ± 0.14 and 0.15 ± 0.13 L. Before the games, mean fluid intake was 0.39 ± 0.19 L. The sweat rate during P1 was significantly greater than P2 (p = 0.006), but there was no significant difference in total fluid intake between practices (p = 0.279). Consequently, the average BM loss for P1 was significantly greater than that for P2 (p = 0.016). Sweat loss during games was 1.01 ± 0.29 L and fluid intake was 0.70 ± 0.43 L, resulting in minimal BM losses (<1% BM for all players). CHO intake during games was 39.2 ± 22.8 g, with 19/20 players consuming CHO before or during the intermissions of the game. Sweat sodium losses were 0.64 ± 0.34 and 0.32 ± 0.18 g·h for P1 and P2, and 0.83 ± 0.38 g during the game. In conclusion, female ice hockey players replaced the fluid they lost through sweat during practices and games and maintained adequate hydration. Players also consumed adequate CHO during games from the CHO containing food and drinks provided.

Sweat Loss and Hydration Habits of Female Olympic, Varsity and Recreational Ice Hockey Players.

This study measured sweat losses, voluntary fluid intake, sodium balance, and carbohydrate intake of female ice hockey players during on-ice practices at the Olympic, varsity, and recreational levels. Testing was conducted on 25 Canadian Olympic players, 21 varsity, and 21 recreational players. The average sweat rate for the Olympic players (0.99±0.08 L/h) was significantly greater than both the varsity (0.67±0.05 L/h, p=0.001) and the recreational players (0.42±0.03 L/h, p<0.001), and the varsity players also had a significantly greater sweat rate than the recreational athletes (p=0.016). Total fluid intake was significantly greater for both the Olympic (p=0.001) and varsity players (p=0.007) compared to the recreational group. Only 3 of 25 Olympic players lost>1.5% BM and 4 others lost>1% BM, with no players in both the varsity and recreational teams losing>1% BM. Half of the Olympic players consumed some carbohydrate during practice, but most of the varsity and recreational players did not. In conclusion, sweat rates in female ice hockey players during practices were proportional to competitive level. Fluid intake was similar between groups and resulted in only a few athletes at the Olympic level being at risk of excess body mass loss.

Estimated Sweat Loss, Fluid and Carbohydrate Intake, and Sodium Balance of Male Major Junior, AHL, and NHL Players During On-Ice Practices.

Several previous studies have reported performance decrements in team sport athletes who dehydrated approximately 1.5-2% of their body mass (BM) through sweating. This study measured on-ice sweat loss, fluid intake, sodium balance, and carbohydrate (CHO) intake of 77 major junior (JR; 19 ± 1 years), 60 American Hockey League (AHL; 24 ± 4 years), and 77 National Hockey League (NHL; 27 ± 5 years) players. Sweat loss was calculated from pre- to post-exercise BM plus fluid intake minus urine loss. AHL (2.03 ± 0.62 L/hr) and NHL (2.02 ± 0.74 L/hr) players had higher sweat rates (p < .05) than JR players (1.63 ± 0.58 L/hr). AHL (1.23 ± 0.69%; p = .006) and NHL (1.29% ± 0.63%; p < .001) players had ∼30% greater BM losses than JR players (0.89% ± 0.57%). There was no difference in fluid intake between groups (p > .05). Sodium deficits (sodium loss - intake) were greater (p < .05) in AHL (1.68 ± 0.74 g/hr) and NHL (1.56 ± 0.84 g/hr) players compared with JR players (1.01 ± 0.50 g/hr). CHO intake was similar between groups (14-20 g CHO/hr), with 29%, 32%, and 40% of JR, AHL, and NHL players consuming no CHO, respectively. In summary, sweat rates were high in all players, but the majority of players (74/77, 54/60, and 68/77 of JR, AHL, and NHL, respectively) avoided mild dehydration (>2% BM) during 60 min of practice. However, ∼15%, 41%, and 48% of the JR, AHL, and NHL players, respectively, may have reached mild dehydration and increased risk of performance decrements in a 90-min practice.

Ablating the protein TBC1D1 impairs contraction-induced sarcolemmal glucose transporter 4 redistribution but not insulin-mediated responses in rats.

TBC1 domain family member 1 (TBC1D1), a Rab GTPase-activating protein and paralogue of Akt substrate of 160 kDa (AS160), has been implicated in both insulin- and 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/IMP cyclohydrolase-mediated glucose transporter type 4 (GLUT4) translocation. However, the role of TBC1D1 in contracting muscle remains ambiguous. We therefore explored the metabolic consequence of ablating TBC1D1 in both resting and contracting skeletal muscles, utilizing a rat TBC1D1 KO model. Although insulin administration rapidly increased (p < 0.05) plasma membrane GLUT4 content in both red and white gastrocnemius muscles, the TBC1D1 ablation did not alter this response nor did it affect whole-body insulin tolerance, suggesting that TBC1D1 is not required for insulin-induced GLUT4 trafficking events. Consistent with findings in other models of altered TBC1D1 protein levels, whole-animal and ex vivo skeletal muscle fat oxidation was increased in the TBC1D1 KO rats. Although there was no change in mitochondrial content in the KO rats, maximal ADP-stimulated respiration was higher in permeabilized muscle fibers, which may contribute to the increased reliance on fatty acids in resting KO animals. Despite this increase in mitochondrial oxidative capacity, run time to exhaustion at various intensities was impaired in the KO rats. Moreover, contraction-induced increases in sarcolemmal GLUT4 content and glucose uptake were lower in the white gastrocnemius of the KO animals. Altogether, our results highlight a critical role for TBC1D1 in exercise tolerance and contraction-mediated translocation of GLUT4 to the plasma membrane in skeletal muscle.

A review of the associations between single nucleotide polymorphisms in taste receptors, eating behaviors, and health.

Food preferences and dietary habits are heavily influenced by taste perception. There is growing interest in characterizing taste preferences based on genetic variation. Genetic differences in the ability to perceive key tastes may impact eating behavior and nutritional intake. Therefore, increased understanding of taste biology and genetics may lead to new personalized strategies, which may prevent or influence the trajectory of chronic disease risk. Recent advances show that single nucleotide polymorphisms (SNPs) in the CD36 fat taste receptor are linked to differences in fat perception, fat preference, and chronic-disease biomarkers. Genetic variation in the sweet taste receptor T1R2 has been shown to alter sweet taste preferences, eating behaviors, and risk of dental caries. Polymorphisms in the bitter taste receptor T2R38 have been shown to influence taste for brassica vegetables. Individuals that intensely taste the bitterness of brassica vegetables ("supertasters") may avoid vegetable consumption and compensate by increasing their consumption of sweet and fatty foods, which may increase risk for chronic disease. Emerging evidence also suggests that the role of genetics in taste perception may be more impactful in children due to the lack of cultural influence compared to adults. This review examines the current knowledge of SNPs in taste receptors associated with fat, sweet, bitter, umami, and salt taste modalities and their contributions to food preferences, and chronic disease. Overall, these SNPs demonstrate the potential to influence food preferences and consequently health.

IOC consensus statement: dietary supplements and the high-performance athlete.

Nutrition usually makes a small but potentially valuable contribution to successful performance in elite athletes, and dietary supplements can make a minor contribution to this nutrition programme. Nonetheless, supplement use is widespread at all levels of sport. Products described as supplements target different issues, including (1) the management of micronutrient deficiencies, (2) supply of convenient forms of energy and macronutrients, and (3) provision of direct benefits to performance or (4) indirect benefits such as supporting intense training regimens. The appropriate use of some supplements can benefit the athlete, but others may harm the athlete's health, performance, and/or livelihood and reputation (if an antidoping rule violation results). A complete nutritional assessment should be undertaken before decisions regarding supplement use are made. Supplements claiming to directly or indirectly enhance performance are typically the largest group of products marketed to athletes, but only a few (including caffeine, creatine, specific buffering agents and nitrate) have good evidence of benefits. However, responses are affected by the scenario of use and may vary widely between individuals because of factors that include genetics, the microbiome and habitual diet. Supplements intended to enhance performance should be thoroughly trialled in training or simulated competition before being used in competition. Inadvertent ingestion of substances prohibited under the antidoping codes that govern elite sport is a known risk of taking some supplements. Protection of the athlete's health and awareness of the potential for harm must be paramount; expert professional opinion and assistance is strongly advised before an athlete embarks on supplement use.

IOC Consensus Statement: Dietary Supplements and the High-Performance Athlete.

Nutrition usually makes a small but potentially valuable contribution to successful performance in elite athletes, and dietary supplements can make a minor contribution to this nutrition program. Nonetheless, supplement use is widespread at all levels of sport. Products described as supplements target different issues, including the management of micronutrient deficiencies, supply of convenient forms of energy and macronutrients, and provision of direct benefits to performance or indirect benefits such as supporting intense training regimens. The appropriate use of some supplements can offer benefits to the athlete, but others may be harmful to the athlete's health, performance, and/or livelihood and reputation if an anti-doping rule violation results. A complete nutritional assessment should be undertaken before decisions regarding supplement use are made. Supplements claiming to directly or indirectly enhance performance are typically the largest group of products marketed to athletes, but only a few (including caffeine, creatine, specific buffering agents and nitrate) have good evidence of benefits. However, responses are affected by the scenario of use and may vary widely between individuals because of factors that include genetics, the microbiome, and habitual diet. Supplements intended to enhance performance should be thoroughly trialed in training or simulated competition before implementation in competition. Inadvertent ingestion of substances prohibited under the anti-doping codes that govern elite sport is a known risk of taking some supplements. Protection of the athlete's health and awareness of the potential for harm must be paramount, and expert professional opinion and assistance is strongly advised before embarking on supplement use.

Ingesting A Sports Drink Enhances Simulated Ice Hockey Performance While Reducing Perceived Effort.

This study determined whether ingesting a carbohydrate-electrolyte solution (CES) vs. progressive dehydration affected skeletal muscle glycogen use and performance in ice hockey players during simulated ice hockey exercise comprised of 3 active "periods". Seven males (21.3±0.3 years, 184.7±1.2 cm, 84.2±3.9 kg, and 49.6±1.8 mL·kg-1·min-1) performed a hockey-specific protocol on two occasions and either dehydrated progressively (NF), or stayed well-hydrated by ingesting a CES. Muscle biopsies were taken at rest, before the 3rd period (P3), and after the final sprint in the protocol. Compared to dehydration in the NF trial (-1.8% BM), CES ingestion enhanced voluntary performance (151.0±8.0 vs. 144.1±8.7 kJ) and glycogen use (177.5±31.1 vs. 103.5±16.2 mmol·kg dm-1), and reduced perceived exertion (16±1 vs. 18±1) in P3. Mean core temperature was reduced by CES ingestion throughout the protocol (38.0±0.2 vs. 38.1±0.1°C). These results suggest that compared to progressive dehydration, staying hydrated by ingesting a CES helps preserve performance, while reducing thermal and perceptual strains, in P3 of cycle-based simulation of ice hockey exercise. These benefits are observed despite greater glycogen use in P3 with CES ingestion.

Mild Dehydration Does Not Influence Performance Or Skeletal Muscle Metabolism During Simulated Ice Hockey Exercise In Men.

This study determined whether mild dehydration influenced skeletal muscle glycogen use, core temperature or performance during high-intensity, intermittent cycle-based exercise in ice hockey players vs. staying hydrated with water. Eight males (21.6 ± 0.4 yr, 183.5 ± 1.6 cm, 83.9 ± 3.7 kg, 50.2 ± 1.9 ml·kg-1·min-1) performed two trials separated by 7 days. The protocol consisted of 3 periods (P) containing 10 × 45-s cycling bouts at ~133% VO2max, followed by 135 s of passive rest. Subjects drank no fluid and dehydrated during the protocol (NF), or maintained body mass by drinking WATER. Muscle biopsies were taken at rest, immediately before and after P3. Subjects were mildly dehydrated (-1.8% BM) at the end of P3 in the NF trial. There were no differences between the NF and WATER trials for glycogen use (P1+P2; 350.1 ± 31.9 vs. 413.2 ± 33.2, P3; 103.5 ± 16.2 vs. 131.5 ± 18.9 mmol·kg dm-1), core temperature (P1; 37.8 ± 0.1 vs. 37.7 ± 0.1, P2; 38.2 ± 0.1 vs. 38.1 ± 0.1, P3; 38.3 ± 0.1 vs. 38.2 ± 0.1 °C) or performance (P1; 156.3 ± 7.8 vs. 154.4 ± 8.2, P2; 150.5 ± 7.8 vs. 152.4 ± 8.3, P3; 144.1 ± 8.7 vs. 148.4 ± 8.7 kJ). This study demonstrated that typical dehydration experienced by ice hockey players (~1.8% BM loss), did not affect glycogen use, core temperature, or voluntary performance vs. staying hydrated by ingesting water during a cycle-based simulation of ice hockey exercise in a laboratory environment.

High-intensity interval and endurance training are associated with divergent skeletal muscle adaptations in a rodent model of hypertension.

Skeletal muscle is extremely adaptable to a variety of metabolic challenges, as both traditional moderate-intensity endurance (ET) and high-intensity interval training (HIIT) increases oxidative potential in a coordinated manner. Although these responses have been clearly demonstrated in healthy individuals, it remains to be determined whether both produce similar responses in the context of hypertension, one of the most prevalent and costly diseases worldwide. Therefore, in the current study, we used the Dahl sodium-sensitive rat, a model of hypertension, to determine the molecular responses to 4 wk of either ET or HIIT in the red (RG) and white gastrocnemius (WG) muscles. In the RG, both ET and HIIT increased the content of electron transport chain proteins and increased succinate dehydrogenase (SDH) content in type I fibers. Although both intensities of exercise shifted fiber type in RG (increased IIA, decreased IIX), only HIIT was associated with a reduction in endothelial nitric oxide synthase and an increase in HIF-1α proteins. In the WG, both ET and HIIT increased markers of the electron transport chain; however, HIIT decreased SDH content in a fiber-specific manner. ET increased type IIA, decreased IIB fibers, and increased capillarization, while, in contrast, HIIT increased the percentage of IIB fibers, decreased capillary-to-fiber ratios, decreased endothelial nitric oxide synthase, and increased hypoxia inducible factor-1α (HIF-1α) protein. Altogether, these data show that unlike in healthy animals, ET and HIIT have divergent effects in the skeletal muscle of hypertensive rats. This suggests ET may be optimal at improving the oxidative capacity of skeletal muscle in animals with hypertension.

Taurine and skeletal muscle function.

PURPOSE OF REVIEW: To discuss the recent work examining the importance of taurine in skeletal muscle and outline the discrepancy that exists between research findings in rodent vs. human skeletal muscle. RECENT FINDINGS: There is clear evidence that a normal taurine level is important for the normal functioning of skeletal muscle. Taurine is believed to be involved in many cellular functions, but in skeletal muscle its main roles are to facilitate Ca2+ dependent excitation-contraction processes, contribute to the regulation of cellular volume, and aid in antioxidant defense from stress responses. Most research has studied the importance of taurine in rodent skeletal muscle by downregulating and upregulating the muscle taurine content and examining the effects on the functioning of skeletal muscle at rest and during the stress of contractions (exercise). One successful research approach is to supplement the diet with taurine, which leads to increases in muscle taurine content and contractile function in rodents. However, this approach does not work in human skeletal muscle as the processes involved in the transport of taurine into the muscle are resistant to large and prolonged increases in plasma taurine following oral taurine supplementation. At present, attempts to influence muscle function with taurine supplementation can only occur through interactions outside the muscle cell in humans. SUMMARY: Future research should target the mechanisms responsible for the transport of taurine into human skeletal muscle and determine why the muscle defends the normal taurine content in the face of elevated plasma taurine levels, as opposed to the results in rodent muscle. This may lead to more fruitful usage of taurine as a skeletal muscle enhancing nutrient in athletic and clinical populations.

Investigating the Relevance of Maximal Speed and Acceleration in Varsity-Level Female Ice Hockey Players.

PURPOSE: To characterize and compare female ice hockey players' peak skating speed and acceleration ability during linear sprints and gameplay. We also sought to quantify the time spent at various speeds and the frequency of accelerations at different thresholds during games. METHODS: Seventeen varsity-level female ice hockey players (20 [1.4] y, 68.9 [4.9] kg, 167.6 [4.7] cm) participated in an on-ice practice session (performing 3 × 40-m linear sprints) and 4 regular-season games while being monitored using a local positioning system. Speed and acceleration were recorded from the sprint and within-game monitoring. Time on ice spent in relative skating speed zones and the frequency of accelerations at different intensities were recorded. RESULTS: Players' greatest peak speeds (29.5 [1.3] vs 28.3 [1.1] km/h) and accelerations (4.39 [0.48] vs 3.34 [0.36] m/s2) reached during gameplay were higher than those reached in linear sprinting (both P < .01). Peak in-game values were moderately predicted by linear sprint values for speed (r = .69, P < .01) but not for acceleration (r < .01, P = .95). Players spent little time at near-peak linear sprint speeds (≥80% [22.7 km/h], ∼3% time on ice; ≥90% [25.5 km/h], <1% of time on ice) during gameplay. However, 26% to 35% of accelerations recorded during the 4 games were ≥90% of linear sprint acceleration. CONCLUSIONS: Although skating speed may be advantageous in specific game situations, our results suggest that players spend little time at near-maximal speeds while accelerating frequently during games. This warrants further investigation of direction changes, skating transitions, repeated sprints, and other determinant variables potentially related to on-ice success and the implementation of training strategies to improve repeated acceleration or qualities beyond maximal skating speed.

AMP-activated protein kinase is required for exercise-induced peroxisome proliferator-activated receptor co-activator 1 translocation to subsarcolemmal mitochondria in skeletal muscle.

In skeletal muscle, mitochondria exist as two subcellular populations known as subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria. SS mitochondria preferentially respond to exercise training, suggesting divergent transcriptional control of the mitochondrial genomes. The transcriptional co-activator peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α) and mitochondrial transcription factor A (Tfam) have been implicated in the direct regulation of the mitochondrial genome in mice, although SS and IMF differences may exist, and the potential signalling events regulating the mitochondrial content of these proteins have not been elucidated. Therefore, we examined the potential for PGC-1α and Tfam to translocate to SS and IMF mitochondria in human subjects, and performed experiments in rodents to identify signalling mechanisms regulating these translocation events. Acute exercise in humans and rats increased PGC-1α content in SS but not IMF mitochondria. Acute exposure to 5-aminoimidazole-4-carboxamide-1-ß-ribofuranoside in rats recapitulated the exercise effect of increased PGC-1α protein within SS mitochondria only, suggesting that AMP-activated protein kinase (AMPK) signalling is involved. In addition, rendering AMPK inactive (AMPK kinase dead mice) prevented exercise-induced PGC-1α translocation to SS mitochondria, further suggesting that AMPK plays an integral role in these translocation events. In contrast to the conserved PGC-1α translocation to SS mitochondria across species (humans, rats and mice), acute exercise only increased mitochondrial Tfam in rats. Nevertheless, in rat resting muscle PGC-1α and Tfam co-immunoprecipate with α-tubulin, suggesting a common cytosolic localization. These data suggest that exercise causes translocation of PGC-1α preferentially to SS mitochondria in an AMPK-dependent manner.

Increase in skeletal-muscle glycogenolysis and perceived exertion with progressive dehydration during cycling in hydrated men.

This study investigated the effects of progressive mild dehydration during cycling on whole-body substrate oxidation and skeletal-muscle metabolism in recreationally active men. Subjects (N = 9) cycled for 120 min at ~65% peak oxygen uptake (VO2peak 22.7 °C, 32% relative humidity) with water to replace sweat losses (HYD) or without fluid (DEH). Blood samples were taken at rest and every 20 min, and muscle biopsies were taken at rest and at 40, 80, and 120 min of exercise. Subjects lost 0.8%, 1.8%, and 2.7% body mass (BM) after 40, 80, and 120 min of cycling in the DEH trial while sweat loss was not significantly different between trials. Heart rate was greater in the DEH trial from 60 to 120 min, and core temperature was greater from 75 to 120 min. Rating of perceived exertion was higher in the DEH trial from 30 to 120 min. There were no differences in VO2, respiratory-exchange ratio, total carbohydrate (CHO) oxidation (HYD 312 ± 9 vs. DEH 307 ± 10 g), or sweat rate between trials. Blood lactate was significantly greater in the DEH trial from 20 to 120 min with no difference in plasma free fatty acids or epinephrine. Glycogenolysis was significantly greater (24%) over the entire DEH vs. HYD trial (433 ± 44 vs. 349 ± 27 mmol · kg-1 · dm-1). In conclusion, dehydration of <2% BM elevated physiological parameters and perceived exertion, as well as muscle glycogenolysis, during exercise without affecting whole-body CHO oxidation.

The acute effects of fluid intake on urine specific gravity and fluid retention in a mildly dehydrated state.

Many athletes arrive at training sessions and competitions in a mildly hypohydrated (HYPO) state and are instructed to drink fluids before exercise to reach a euhydrated (HYD) state. Ten recreational athletes (6 women, 4 men; 71.9 ± 4.6 kg, 25.2 ± 0.9 years) participated in the studies to examine (a) the day-to-day variability of morning urine specific gravity (USG), (b) the effects of consuming 600 ml of water on the hydration status of HYD and HYPO (USG > 1.020) subjects, and (c) the effects of consuming water (W), salt-water (SW, 40 mM Na), a carbohydrate-electrolyte solution with 3% or light carbohydrate (CES-L, 20 mM Na) or a CES with 6% carbohydrate (CES, 20 mM Na) on the hydration status of HYPO subjects. The hydration status was assessed with USG and body mass measures and urine volume collections. The day-to-day variability in morning USG (coefficient of variation = 0.2 ± 0.1%) was low and the responses to 600 ml of W ingestion were repeatable. Pretrial USG was 1.022 ± 0.001 in the HYPO trial and decreased <1.020 by 45 minutes (1.013 ± 0.003). In the CES study, HYPO subjects reached HYD status at 45 minutes in all conditions (W 1.013 ± 0.003, SW 1.013 ± 0.003, CES-L 1.011 ± 0.003, CES 1.017 ± 0.004) because salt or CES ingestion did not affect fluid retention (W 68%, SW 72%, CES-L 68%, CES 76%). This study demonstrated that mildly HYPO subjects could reach euhydration within 45 minutes of the ingestion of 600 ml of W or a combination of salt and CES solutions. Following this practice will minimize the incidence of starting a practice or competition hypohydrated.