Increased exogenous but unaltered endogenous carbohydrate oxidation with combined fructose-maltodextrin ingested at 120 g h-1 versus 90 g h-1 at different ratios

Highly branched cyclic dextrin supplementation and resistance training: A randomized double-blinded crossover trial examining mechanical, metabolic, and perceptual responses

BACKGROUND & AIMS

The aim of this study was to investigate the potential ergogenic effects of intra-session supplementation of highly branched cyclic dextrin (HBCD) on mechanical (number of repetitions completed and repetition velocity), metabolic (lactate concentration), and perceptual (gastrointestinal complaints and ratings of perceived exertion [RPE]) responses to resistance training.

METHODS

This study used a randomized, double-blinded, placebo-controlled crossover study design. Thirty physically active individuals (15 men and 15 women) completed two experimental sessions that only differed in the supplement condition (placebo or HBCD). In each experimental session, subjects were prescribed five sets of eight repetitions with the 12-repetition maximum load during the bench press, bench pull, and squat exercises. During the sessions, participants consumed a total of 750 mL of the beverage, which either contained diluted 45 g of cyclic dextrin (HBCD condition) or only 2.5 g of the calorie-free excipients (placebo condition). The supplement (placebo or HBCD) was ingested during the inter-set rest periods (50 mL before each set).

RESULTS

The main findings indicated that intra-session HBCD supplementation (i) was well-tolerated without causing gastrointestinal complaints, (ii) led to improved repetition velocity during RT in men but not in women, (iii) tended to generate comparable or higher lactate values, and (iv) did not significantly influence the perception of fatigue.

CONCLUSIONS

These results suggest that HBCD can be considered an ergogenic supplement, particularly for enhancing mechanical performance in men, without noticeably affecting the perception of fatigue or discomfort.

The race within a race: Together on the marathon starting line but miles apart in the experience

Every four years the world's best athletes come together to compete in the Olympic games, electrifying audiences with incredible feats of speed, strength, endurance and skill as personal best performances and new records are set. However, the exceptional talent that underpin such performances is incomprehensible to most casual observers who often cannot appreciate how unique these athletes are. In this regard, endurance running, specifically the marathon, a 42.195 km foot race, provides one of the few occasions in sport outside of Olympic, world and national competitions, that permits sport scientists and fans alike to directly compare differences in the physiology between recreational and elite competitors. While these individuals may all cover the same distance, on the same course, on the same day - their experience and the physiological and psychological demands placed upon them are vastly different. There is, in effect, a "race within a race". In the current review we highlight the superior physiology of the elite endurance athlete, emphasizing the gap between elite competitors and well-trained, but less genetically endowed athletes. We draw attention to a range of inconsistencies in how current sports science practices are understood, implemented, and communicated in terms of the elite and not-so-elite endurance athlete.

Substrate utilization and durability during prolonged intermittent exercise in elite road cyclists

PURPOSE

This study investigated the effects of prolonged intermittent cycling exercise on peak power output (PPO) and 6-min time-trial (6 min-TT) performance in elite and professional road cyclists. Moreover, the study aimed to determine whether changes in performance in the fatigued state could be predicted from substrate utilization during exercise and laboratory measures obtained in a fresh state.

METHODS

Twelve cyclists (age: 23 years [21;25]; body mass: 71.5 kg [66.7;76.8]; height: 181 cm [178;185]; V ˙ O2peak: 73.6 ml kg-1 min-1 [71.2;76.0]) completed a graded submaximal cycling test to determine lactate threshold (LT1), gross efficiency (GE), and maximal fat oxidation (MFO) as well as power output during a maximal 6 min-TT (MPO6 min) in a fresh condition. On a separate day, the cyclists completed a 4-h intermittent cycling protocol with a high CHO intake (100 g h-1). Substrate utilization and PPO was measured hourly during the protocol, which was followed by another 6 min-TT.

RESULTS

MPO6 min and PPO was reduced by 10% [4;15] and 6% [0;6], respectively, after the cycling protocol. These reductions were accompanied by reductions in the anaerobic energy contribution and V ˙ O2peak, whereas the average V ˙ O2 during the 6 min-TT was unchanged. Correlation analyses showed no strong associations between reductions in MPO6 min and PPO and laboratory measures (i.e., LT1, GE, MFO, V ˙ O2peak) obtained in the fresh condition. Additionally, fat oxidation rates during the cycling protocol were not related to changes in neither PPO nor MPO6 min.

CONCLUSION

PPO and MPO6 min were reduced following prolonged intermittent cycling, but the magnitude of these reductions could not be predicted from laboratory measures obtained in the fresh condition.

Dose-response effect of pre-exercise carbohydrates under muscle glycogen unavailability: Insights from McArdle disease

BACKGROUND

This study aimed to determine the effect of different carbohydrate (CHO) doses on exercise capacity in patients with McArdle disease-the paradigm of "exercise intolerance", characterized by complete muscle glycogen unavailability-and to determine whether higher exogenous glucose levels affect metabolic responses at the McArdle muscle cell (in vitro) level.

METHODS

Patients with McArdle disease (n = 8) and healthy controls (n = 9) underwent a 12-min submaximal cycling constant-load bout followed by a maximal ramp test 15 min after ingesting a non-caloric placebo. In a randomized, double-blinded, cross-over design, patients repeated the tests after consuming either 75 g or 150 g of CHO (glucose:fructose = 2:1). Cardiorespiratory, biochemical, perceptual, and electromyographic (EMG) variables were assessed. Additionally, glucose uptake and lactate appearance were studied in vitro in wild-type and McArdle mouse myotubes cultured with increasing glucose concentrations (0.35, 1.00, 4.50, and 10.00 g/L).

RESULTS

Compared with controls, patients showed the "classical" second-wind phenomenon (after prior disproportionate tachycardia, myalgia, and excess electromyographic activity during submaximal exercise, all p < 0.05) and an impaired endurance exercise capacity (-51% ventilatory threshold and -55% peak power output, both p < 0.001). Regardless of the CHO dose (p < 0.05 for both doses compared with the placebo), CHO intake increased blood glucose and lactate levels, decreased fat oxidation rates, and attenuated the second wind in the patients. However, only the higher dose increased ventilatory threshold (+27%, p = 0.010) and peak power output (+18%, p = 0.007). In vitro analyses revealed no differences in lactate levels across glucose concentrations in wild-type myotubes, whereas a dose-response effect was observed in McArdle myotubes.

CONCLUSION

CHO intake exerts beneficial effects on exercise capacity in McArdle disease, a condition associated with total muscle glycogen unavailability. Some of these benefits are dose dependent.

Assessing exogenous carbohydrate intake needed to optimize human endurance performance across sex: insights from modeling runners pursuing a sub-2-h marathon

Carbohydrate (CHO) availability sustains high metabolic demands during prolonged exercise. The adequacy of current CHO intake recommendations, 30-90 g·h-1 dependent on CHO mixture and tolerability, to support elite marathon performance is unclear. We sought to scrutinize the current upper limit recommendation for exogenous CHO intake to support modeled sub-2-h marathon (S2M) attempts across elite male and female runners. Male and female runners (n = 120 each) were modeled from published literature with reference characteristics necessary to complete a S2M (e.g., body mass and running economy). Completion of a S2M was considered across a range of respiratory exchange rates, with maximal starting skeletal muscle and liver glycogen content predicted for elite male and female runners. Modeled exogenous CHO bioavailability needed for male and female runners were 93 ± 26 and 108 ± 22 g·h-1, respectively (P < 0.0001, d = 0.61). Without exogenous CHO, males were modeled to deplete glycogen in 84 ± 7 min, females in 71 ± 5 min (P < 0.0001, d = 2.21) despite higher estimated CHO oxidation rates in males (5.1 ± 0.5 g·h-1) than females (4.4 ± 0.5 g·h-1; P < 0.0001, d = 1.47). Exogenous CHO intakes ≤ 90 g·h-1 are insufficient for 65% of modeled runners attempting a S2M. Current recommendations to support marathon performance appear inadequate for elite marathon runners but may be more suitable for male runners in pursuit of a S2M (56 of 120) than female runners (28 of 120).NEW & NOTEWORTHY This study scrutinizes the upper limit of exogenous carbohydrate (CHO) recommendations for elite male and female marathoners by modeling sex-specific needs across an extreme metabolic challenge lasting ∼2 h, a sub-2-h marathon. Contemporary nutritional guidelines to optimize marathon performance appear inadequate for most elite marathon runners but appear more appropriate for males over their female counterparts. Future research examining possible benefits of exogenous CHO intakes > 90 g·h-1 should prioritize female athlete study inclusion.

Mass Sportrometry: An annual look back at applications of mass spectrometry in sport and exercise science

Research in sport and exercise science (SES) is reliant on robust analyses of biomarker measurements to assist with the interpretation of physiological outcomes. Mass spectrometry (MS) is an analytical approach capable of highly sensitive, specific, precise, and accurate analyses of a range of biomolecules, many of which are of interest in SES including, but not limited to, endogenous metabolites, exogenously administered compounds (e.g. supplements), mineral ions, and circulating/tissue proteins. This annual review provides a summary of the applications of MS across studies investigating aspects related to sport or exercise in manuscripts published, or currently in press, in 2022. In total, 93 publications are included and categorized according to their methodologies including targeted analyses, metabolomics, lipidomics, proteomics, and isotope ratio/elemental MS. The advantageous analytical opportunities afforded by MS technologies are discussed across a selection of relevant articles. In addition, considerations for the future of MS in SES, including the need to improve the reporting of assay characteristics and validation data, are discussed, alongside the recommendation for selected current methods to be superseded by MS-based approaches where appropriate. The review identifies that a targeted, mostly quantitative, approach is the most commonly applied MS approach within SES, although there has also been a keen interest in the use of 'omics' to perform hypothesis-generating research studies. Nonetheless, MS is not commonplace in SES at this time, but its use to expand, and possibly improve, the analytical options should be continually considered to exploit the benefits of analytical chemistry in exercise/sports-based research. Overall, it is exciting to see the gradually increasing adoption of MS in SES and it is expected that the number, and quality, of MS-based assays in SES will increase over time, with the potential for 2023 to further establish this technique within the field.

New Horizons in Carbohydrate Research and Application for Endurance Athletes

The importance of carbohydrate as a fuel source for exercise and athletic performance is well established. Equally well developed are dietary carbohydrate intake guidelines for endurance athletes seeking to optimize their performance. This narrative review provides a contemporary perspective on research into the role of, and application of, carbohydrate in the diet of endurance athletes. The review discusses how recommendations could become increasingly refined and what future research would further our understanding of how to optimize dietary carbohydrate intake to positively impact endurance performance. High carbohydrate availability for prolonged intense exercise and competition performance remains a priority. Recent advances have been made on the recommended type and quantity of carbohydrates to be ingested before, during and after intense exercise bouts. Whilst reducing carbohydrate availability around selected exercise bouts to augment metabolic adaptations to training is now widely recommended, a contemporary view of the so-called train-low approach based on the totality of the current evidence suggests limited utility for enhancing performance benefits from training. Nonetheless, such studies have focused importance on periodizing carbohydrate intake based on, among other factors, the goal and demand of training or competition. This calls for a much more personalized approach to carbohydrate recommendations that could be further supported through future research and technological innovation (e.g., continuous glucose monitoring). Despite more than a century of investigations into carbohydrate nutrition, exercise metabolism and endurance performance, there are numerous new important discoveries, both from an applied and mechanistic perspective, on the horizon.