JohnEric W. Smith

Fuel selection and cycling endurance performance with ingestion of [13C]glucose: evidence for a carbohydrate dose response

Endurance performance and fuel selection while ingesting glucose (15, 30, and 60 g/h) was studied in 12 cyclists during a 2-h constant-load ride [approximately 77% peak O2 uptake] followed by a 20-km time trial. Total fat and carbohydrate (CHO) oxidation and oxidation of exogenous glucose, plasma glucose, glucose released from the liver, and muscle glycogen were computed using indirect respiratory calorimetry and tracer techniques. Relative to placebo (210+/-36 W), glucose ingestion increased the time trial mean power output (%improvement, 90% confidence limits: 7.4, 1.4 to 13.4 for 15 g/h; 8.3, 1.4 to 15.2 for 30 g/h; and 10.7, 1.8 to 19.6 for 60 g/h glucose ingested; effect size=0.46). With 60 g/h glucose, mean power was 2.3, 0.4 to 4.2% higher, and 3.1, 0.5 to 5.7% higher than with 30 and 15 g/h, respectively, suggesting a relationship between the dose of glucose ingested and improvements in endurance performance. Exogenous glucose oxidation increased with ingestion rate (0.17+/-0.04, 0.33+/-0.04, and 0.52+/-0.09 g/min for 15, 30, and 60 g/h glucose), but endogenous CHO oxidation was reduced only with 30 and 60 g/h due to the progressive inhibition of glucose released from the liver (probably related to higher plasma insulin concentration) with increasing ingestion rate without evidence for muscle glycogen sparing. Thus ingestion of glucose at low rates improved cycling time trial performance in a dose-dependent manner. This was associated with a small increase in CHO oxidation without any reduction in muscle glycogen utilization.

Carbohydrate and carbohydrate + protein for cycling time-trial performance.

Abstract Carbohydrate intake during endurance exercise delays the onset of fatigue and improves performance. Two recent cycling studies have reported increased time to exhaustion when protein is ingested together with carbohydrate. The purpose of the present study was to test the hypothesis that ingestion of a carbohydrate + protein beverage will lead to significant improvements in cycling time-trial performance relative to placebo and carbohydrate alone. Thirteen cyclists completed 120 min of constant-load ergometer cycling. Thereafter, participants performed a time-trial in which they completed a set amount of work (7 kJ · kg−1) as quickly as possible. Participants completed four experimental trials, the first for familiarization and then three randomized, double-blind treatments consisting of a placebo, carbohydrate, and carbohydrate + protein. Participants received 250 ml of beverage every 15 min during the constant-load ride. Time-trial performance for carbohydrate (37.1 min, s = 3.8) was significantly (P < 0.05) faster than placebo (39.7 min, s = 4.6). Time-trial performance for carbohydrate + protein (38.8 min, s = 5.5) was not significantly different from either placebo or carbohydrate. Ingestion of a carbohydrate beverage during two hours of constant-load cycling significantly enhanced subsequent time-trial performance compared with placebo. The carbohydrate + protein beverage provided no additional performance benefit.

Curvilinear dose-response relationship of carbohydrate (0-120 g·h(-1)) and performance.

BACKGROUND There is a lack of consensus regarding the optimal range of carbohydrate (CHO) ingestion rates recommended for endurance athletes. PURPOSE This study investigated the relationship between CHO dose and cycling time trial performance to identify an optimal range of CHO ingestion rates for endurance performance. METHODS Fifty-one cyclists and triathletes (28 ± 7 yr, mean ± SD) across four research sites completed four trials. Each trial consisted of a 2-h constant load ride at 95% of the workload that elicited a 4-mmol·L(-1) blood lactate concentration immediately followed by a computer-simulated 20-km time trial, which subjects were asked to complete as quickly as possible. Twelve CHO electrolyte (18 mmol·L(-1) Na, 3 mmol·L(-1) K, and 11 mmol·L(-1) Cl) beverages (three at each site) were tested in a double-blind manner, providing subjects 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, and 120 g CHO (1:1:1 glucose-fructose-maltodextrin) per hour during the 2-h constant load ride at a fluid intake rate of 1 L·h(-1). All subjects also consumed a noncaloric placebo on one counterbalanced test occasion. Data were natural log transformed, subjected to a mixed-model analysis, and are reported as adjusted treatment means. RESULTS We estimate incremental performance improvements of 1.0%, 2.0%, 3.0%, 4.0%, and 4.7% at 9, 19, 31, 48, and 78 g·h, respectively, with diminishing performance enhancement seen at CHO levels >78 g·h(-1). CONCLUSIONS CHO beverage ingestion and endurance (∼160 min) performance appear to be related in a curvilinear dose-response manner, with the best performance occurring with a CHO (1:1:1 glucose-fructose-maltodextrin) ingestion rate of 78 g·h(-1).

Effects of Carbohydrate Ingestion and Carbohydrate Mouth Rinse on Repeat Sprint Performance

The purpose of this investigation was to examine to the influence of carbohydrate ingestion (CHOI) and carbohydrate mouth rinse (CHOR) on acute repeat maximal sprint performance. Fourteen healthy males (age: 21.7 ± 1.8 years, mass: 82.3 ± 12.3 kg) completed a total of five 15-s maximal repeat sprints on a cycle ergometer against 0.075 kg ・ kg-1 body mass each separated by 4 min of active recovery. Subjects completed four experimental trials and were randomly assigned one of four treatments: (1) CHOI, (2) CHOR, (3) placebo mouth rinse (PLAR), (4) placebo ingestion (PLAI). Subjects rinsed or ingested six 50 mL 10% CHO solutions throughout each trial. Performance variables measured included rating of perceived exertion, peak heart rate, peak and mean power output, fatigue index, and total work. Significant treatment main effects were observed for mean power output (p = 0.026), total work (p = 0.020), fatigue index (p = 0.004), and heart rate (p = 0.013). Overall mean power output and total work were significantly greater with CHOI (659.3 ± 103.0 watts, 9849.8 ± 1598.8 joules) compared with CHOR (645.8 ± 99.7 watts, 9447.5 ± 1684.9 joules, p < .05). CHOI (15.3 ± 8.6 watts/s) significantly attenuated fatigue index compared with CHOR (17.7 ± 10.4 watts/s, p < .05). Based on our findings, CHOI was more likely to provide a beneficial performance effect compared with CHOR, PLAI, and PLAR. Athletes required to complete repeat bouts of high intensity exercise may benefit from CHOI.

Nutritional Considerations for Performance in Young Athletes.

Nutrition is an integral component to any athletes training and performance program. In adults the balance between energy intake and energy demands is crucial in training, recovery, and performance. In young athletes the demands for training and performance remain but should be a secondary focus behind the demands associated with maintaining the proper growth and maturation. Research interventions imposing significant physiological loads and diet manipulation are limited in youth due to the ethical considerations related to potential negative impacts on the growth and maturation processes associated with younger individuals. This necessary limitation results in practitioners providing nutritional guidance to young athletes to rely on exercise nutrition recommendations intended for adults. While many of the recommendations can appropriately be repurposed for the younger athlete attention needs to be taken towards the differences in metabolic needs and physiological differences.

Superhero Physiology: The Case for Captain America.

Using pop icons in the science classroom represents a creative way to engage often-distracted students in a relevant and, perhaps more importantly, fun way. When the pop icon is as universally known as Captain America, the pedagogical stage is set. However, when the movies can also be employed to link dramatic references to the science concepts at hand, we may have a very powerful tool by which linkages between fiction and science can be forged. In this regard, Captain Americas performances in several movies to date can be used to explain actual science. Granted, script writers and movie directors may or may not be interested in whether the physical performances they depict can be explained, but that is irrelevant. The point is to make a connection using science to explain how the superhero can run faster, jump higher, or lift more than is humanly possible. If a teachable moment has occurred and an important concept has been communicated, the educator has accomplished his or her job well.

Ingestion of an Amino Acid Electrolyte Beverage during Resistance Exercise Does Not Impact Fluid Shifts into Muscle or Performance

The purpose of this study was to investigate the impact of ingesting an amino acid-electrolyte (AAE) beverage during upper body resistance exercise on transient muscle hypertrophy, exercise performance, markers of muscle damage, and recovery. Participants (n = 15) performed three sets of six repetitions—bench press, lat pull down, incline press, and seated row—followed by three sets of eight repetitions at 75% of the estimated 1 repetition maximum—triceps kickback, hammer curl, triceps push down, and preacher curl—with 90 s of rest between sets. The final set of the push down/preacher curl was performed to failure. Prior to and immediately post-exercise, as well as 24, 48, and 72 h post exercise, cross-sectional muscle thickness was measured. Blood samples were collected prior to exercise, as well as 24, 48, and 72 h post-exercise for serum creatine kinase (CK) analysis. No treatment effect was found for muscle cross-sectional area, repetitions to failure, or serum CK. A main effect (p < 0.001) was observed in the change in serum CK levels in the days following the resistance exercise session. The findings of this study suggest that the acute ingestion of a AAE beverage does not alter acute muscle thickness, performance, perceived soreness and weakness, or markers of muscle damage.

Effects of psychological stress during exercise on markers of oxidative stress in young healthy, trained men

PURPOSE Those engaged in high stress occupations such as firefighters and military personnel are exposed to a variety of psychological and physiological stressors. The combination of mental and physical stress [i.e., dual stress challenges (DSC)] results in significant increases in stress hormones, which causes oxidative stress (OS) and contributes to elevated risk for cardiovascular disease. However, data are needed to determine the impact of DSC on markers of OS in exercise-trained individuals. METHOD Fourteen healthy trained men aged 21-30 yrs. participated in a randomized, cross-over design to investigate the impact of DSC on blood markers of OS. The exercise alone condition (EA) consisted of 35 min of cycling at 60% V̇O2 peak. The DSC involved 20 min of mental stress challenges during exercise. Blood was sampled before exercise, as well as immediately, and 30 and 60 min after exercise and analyzed for glutathione (GSH), superoxide dismutase (SOD), hydrogen peroxide (H2O2) and advanced oxidation protein products (AOPP). RESULT No significant treatment × time interactions were found. No time effects were noted for SOD, or H2O2; however, AOPP were reduced at 30 (p = .034) and 60 min post exercise (p = .006). GSH was reduced at 30 (p = .009) and 60 min post exercise (p = .031). CONCLUSION These results indicate the OS response from DSC is not greater than that produced from EA in exercise trained men. Future work should investigate the impact of chronic resistance and endurance exercise training on OS resulting from DSC.

A shift toward a high-fat diet in the current metabolic paradigm: A new perspective

OBJECTIVE Investigations into the relationship between dietary carbohydrate restriction and health are mixed. Current guidelines for nutrition promote low-fat foods and higher carbohydrate consumption for optimal health and weight loss. However, high-fat, low-carbohydrate diets are revealing both intra- and extracellular adaptations that have been shown to elicit favorable cardiometabolic changes associated with obesity. Moreover, dietary fat is associated with higher satiety levels from the hormones adiponectin, leptin, and cholecystokinin. Additionally, insulin responses from high-glycemic carbohydrates are known to alter these pathways, potentially leading to an increase in energy consumption and a possible mechanism for obesity. CONCLUSION There is convincing evidence of beneficial effects of controlled trials implementing high-fat, low-carbohydrate diets in both sedentary and obese individuals, but longer duration clinical trials are required to confirm this hypothesis.

Impact of occupational footwear during simulated workloads on energy expenditure

Limited research exists on the physiological demands of occupational footwear. Therefore, the purpose of this investigation was to examine the impact of tactical boots (TB) (0.5 kg) and steel-toed work boots (WB) (0.9 kg) on oxygen consumption (V̇O2) and cardiorespiratory responses during simulated walking protocols. Seventeen healthy male (age: 21.9 ± 2.0 years; height: 177.6 ± 4.8 cm; mass: 80.0 ± 9.4 kg) participants completed a total of four 20-min experimental walking trials: (1) WB horizontal protocol, (2) WB graded protocol, (3) TB horizontal protocol, and (4) TB graded protocol, following a randomized repeated measures design. On average, across each protocol, the larger mass of the WB increased absolute V̇O2 by 6.2% and 7.1% for the horizontal and graded protocols, respectively. The WB also caused a significant increase in absolute V̇O2 compared to TB during the horizontal protocol while walking at speeds of 4.0, 5.2, and 6.4 km/h (p < 0.05). No significant differences were observed for heart rate, breathing rate, or ratings of perceived exertion (p > 0.05). The results of this study indicate that wearing occupational footwear with a larger mass can significantly increase energy expenditure compared to footwear of lighter mass. However, energy expenditure increased without changes in physiological measures of energy expenditure. Footwear manufacturers may want to improve footwear design characteristics to maintain required safety guidelines while minimizing footwear mass.