Physiological Impact of a Single Serving Slow Absorption Carbohydrate on Metabolic, Hemodynamic, and Performance Markers in Endurance Athletes During a Bout of Exercise.

ABSTRACT: Davitt, PM, Saenz, C, Hartman, T, Barone, P, and Estremera, S. Physiological impact of a single serving slow absorption carbohydrate on metabolic, hemodynamic, and performance markers in endurance athletes during a bout of exercise. J Strength Cond Res 35(5): 1262-1272, 2021-The purpose of this study was to determine how a slow-absorbing carbohydrate affected markers of metabolism, hemodynamics, and performance in well-trained endurance athletes. We examined total and exogenous carbohydrate oxidation (CHO ox), glucose, and performance after consuming different glucose beverages, before a treadmill run. Ten male runners (32.4 years; V̇o2max, 55.9 ml·kg-1·min-1) participated on 3 occasions: slow digestion CHO (S), fast digestion CHO (F), and water (W). Subjects consumed a 50 g dose of either S or F before a 3-hour treadmill run at 57% V̇o2max. Variables were assessed at -15, 0, 30, 60, 90, 135, and 180 minutes. Immediately postrun, subjects completed a time-to-fatigue test at 110% V̇o2max. There was a significant difference in CHO ox for W vs. F and S (C,1.14; S,1.52; F,1.66 ± 0.2 g·min-1, p < 0.05). Fat ox was significantly higher in S vs. F (S,0.54; F,0.47 ± 0.08 g·min-1, p < 0.05). Exogenous CHO ox was significantly higher in F vs. S (F,0.26; S,0.19 + 0.04 g·min-1, p < 0.05). There was a significant difference in average blood glucose for trial (F,94.5; S,97.1 vs. W,88.4 + 2.1 mg·dl-1) and time × trial for F vs. S (0 minutes, p < 0.05). There were no significant performance differences. Consumption of a single bolus of CHO beverage before a 3-hour run elicits significant alterations in energy metabolism compared with just water, with S CHO oxidizing significantly more fat than a rapidly digested carbohydrate. These findings suggest that slow-digesting modified starch provides a consistent blood glucose level and sustained exogenous energy supply during a sustained, 3-hour endurance run. Significance was set at p < 0.05.

The effects of over-the-counter jaw-repositioning mouthguards on aerobic performance.

BACKGROUND: Though jaw-repositioning devices have been found to increase size of upper respiratory airways in individuals, the effects of jaw-repositioning mouthguards on respiratory function during exercise have not been fully explored. The purpose of this study is to determine the effects of over-the-counter (OTC) jaw-repositioning mouthguards on respiratory function and aerobic performance in male athletes. METHODS: College-aged, male athletes (N.=20) participated in this randomized, crossover, controlled study. Each subject completed one testing session per condition: a no mouthguard control (CON), a placebo mouthguard (PLA), an OTC self-adapted jaw-repositioning mouthguard (SA), and an OTC custom-fitted jaw-repositioning mouthguard (CF). Each testing session consisted of respiratory flow dynamic tests at rest. Ventilation and gas exchange were assessed during a graded maximal treadmill test. Peak blood lactate values were obtained from 0-10 min post-exercise. RESULTS: At rest, the CON had significantly higher peak expiratory flow rate values than the other conditions (P<0.03). Maximum voluntary ventilation values for PLA and SA were significantly lower compared to CON (P<0.02) at rest. No significant differences were observed between conditions for ventilation, oxygen consumption, or carbon dioxide production during any submaximal stage (P=0.81) nor at maximal aerobic capacity (P=0.35). Peak lactate and adjusted peak lactate values were not significantly different between conditions (P=0.30 and P=0.63, respectively). CONCLUSIONS: The OTC jaw-repositioning mouthguards in this study did not enhance aerobic performance. It is important to acknowledge that negative effects on aerobic performance were not observed, thus providing additional support for encouraging the use of this safety device in sports.

Metabolic characteristics of keto-adapted ultra-endurance runners.

BACKGROUND: Many successful ultra-endurance athletes have switched from a high-carbohydrate to a low-carbohydrate diet, but they have not previously been studied to determine the extent of metabolic adaptations. METHODS: Twenty elite ultra-marathoners and ironman distance triathletes performed a maximal graded exercise test and a 180 min submaximal run at 64% VO2max on a treadmill to determine metabolic responses. One group habitually consumed a traditional high-carbohydrate (HC: n=10, %carbohydrate:protein:fat=59:14:25) diet, and the other a low-carbohydrate (LC; n=10, 10:19:70) diet for an average of 20 months (range 9 to 36 months). RESULTS: Peak fat oxidation was 2.3-fold higher in the LC group (1.54±0.18 vs 0.67±0.14 g/min; P=0.000) and it occurred at a higher percentage of VO2max (70.3±6.3 vs 54.9±7.8%; P=0.000). Mean fat oxidation during submaximal exercise was 59% higher in the LC group (1.21±0.02 vs 0.76±0.11 g/min; P=0.000) corresponding to a greater relative contribution of fat (88±2 vs 56±8%; P=0.000). Despite these marked differences in fuel use between LC and HC athletes, there were no significant differences in resting muscle glycogen and the level of depletion after 180 min of running (-64% from pre-exercise) and 120 min of recovery (-36% from pre-exercise). CONCLUSION: Compared to highly trained ultra-endurance athletes consuming an HC diet, long-term keto-adaptation results in extraordinarily high rates of fat oxidation, whereas muscle glycogen utilization and repletion patterns during and after a 3 hour run are similar.

Influence of HMB supplementation and resistance training on cytokine responses to resistance exercise.

PURPOSE: The purpose of this study was to determine the effects of a multinutritional supplement including amino acids, ß-hydroxy-ß-methylbutyrate (HMB), and carbohydrates on cytokine responses to resistance exercise and training. METHODS: Seventeen healthy, college-aged men were randomly assigned to a Muscle Armor™ (MA; Abbott Nutrition, Columbus, OH) or placebo supplement group and 12 weeks of resistance training. An acute resistance exercise protocol was administered at 0, 6, and 12 weeks of training. Venous blood samples at pre-, immediately post-, and 30-minutes postexercise were analyzed via bead multiplex immunoassay for 17 cytokines. RESULTS: After 12 weeks of training, the MA group exhibited decreased interferon-gamma (IFN-γ) and interleukin (IL)-10. IL-1ß differed by group at various times. Granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-6, IL-7, IL-8, IL-12p70, IL-13, IL-17, monocyte chemoattractant protein-1 (MCP-1), and macrophage inflammatory protein-1 beta (MIP-1ß) changed over the 12-week training period but did not differ by group. CONCLUSIONS: Twelve weeks of resistance training alters the cytokine response to acute resistance exercise, and supplementation with HMB and amino acids appears to further augment this result.

The effects of a combined resistance training and endurance exercise program in inactive college female subjects: does order matter?

Although both endurance (E) and resistance (R) exercise improve various health and fitness variables, there is still debate regarding the optimal ordering of these modes of exercise within a concurrent bout. The purpose of this study was to determine the effects of performing E before R (E-R) or R before E (R-E) on strength, VO2max, and body composition over the course of an 8-week exercise program. Inactive college female subjects (N = 23; 19.8 ± 0.22 years; 61.0 ± 2.5 kg) were randomly assigned to either an E-R (n = 13) or an R-E (n = 10) group. Subjects trained 4 d·wk over the 8-week study. The E portion consisted of 30 minutes of aerobic exercise at 70-80% heart rate reserve (HRR). The R portion used a 3-way split routine with subjects performing 3 sets of 8-12 repetitions for 5-6 different exercises using a load equal to 90-100% 10 repetition maximum. There were 2 days of testing before and after 8 weeks of training to determine performance and body composition. There were significant improvements in chest press (p < 0.001), leg press (p < 0.001), VO2max (p < 0.001), and lean body mass (LBM) (p = 0.005) across both groups. Weight significantly increased (p = 0.038), but percent body fat did not change (p = 0.46). There were no differences as a function of group (p > 0.267). There were significant improvements in performance and LBM over an 8-week concurrent training program in inactive college female subjects, regardless of the order in which R and E were performed. It seems that fitness markers improve similarly regardless of the order of R or E in a 4 d·wk-1 program in inactive female subjects. Therefore, the order of these modalities for beginning exercisers should be based on personal preference and to facilitate adherence.

Postprandial triglyceride and free fatty acid metabolism in obese women after either endurance or resistance exercise.

We investigated the effects of two exercise modalities on postprandial triglyceride (TG) and free fatty acid (FFA) metabolism. Sedentary, obese women were studied on three occasions in randomized order: endurance exercise for 60 min at 60-65% aerobic capacity (E), ~60 min high-intensity resistance exercise (R), and a sedentary control trial (C). After exercise, a liquid-mixed meal containing [U-(13)C]palmitate was consumed, and subjects were studied over 7 h. Isotopic enrichment (IE) of plasma TG, plasma FFA, and breath carbon dioxide compared with meal IE indicated the contribution of dietary fat to each pool. Total and endogenously derived plasma TG content was reduced significantly in both E and R compared with C (P < 0.05), with no effect of exercise on circulating exogenous (meal-derived) TG content. Exogenous plasma FFA content was increased significantly following both E and R compared with C (P < 0.05), whereas total and endogenous FFA concentrations were elevated only in E (P < 0.05) compared with C. Fatty acid (FA) oxidation rates were increased significantly after E and R compared with C (P < 0.05), with no difference between exercise modalities. The present results indicate that E and R may be equally effective in reducing postprandial plasma TG concentration and enhancing lipid oxidation when the exercise sessions are matched for duration rather than for energy expenditure. Importantly, tracer results indicated that the reduction in postprandial lipemia after E and R exercise bouts is not achieved by enhanced clearance of dietary fat but rather, is achieved by reduced abundance of endogenous FA in plasma TG.