CHO Feeding Research Articles

A Comparison Of Protein And Carbohydrate-fed Sprint Interval Training On Skeletal Muscle And Performance Adaptations

Sprint interval training (SIT) has emerged as a potent metabolic stimulus inducing beneficial musculoskeletal adaptations. However, nutritional support to optimise the adaptive response to SIT remains poorly characterised. Carbohydrate (CHO) has previously been shown to blunt metabolic adaptations to training while there is increased interest in the role of protein in regulating training adaptations. PURPOSE: The aim of this study was to determine the effects of whey protein concentrate (WPC) compared with CHO feeding on the acute regulation of skeletal muscle mitochondrial gene expression, enzyme activity and performance following a 3 week SIT intervention. METHODS: This study was ethically approved and conducted in line with the Declaration of Helsinki. Healthy, recreationally active (VO2 max <50 ml.kg-1.min-1) males (n = 17) were randomised to complete SIT under CHO or WPC conditions. Participants attended the lab after an overnight fast (≥10 h) and ingested 0.33 g.kg-1 body mass (BM) of WPC, or 0.91 g.kg-1 BM maltodextrin (CHO) 45 min prior to SIT consisting of four 30 s sprints at a resistance of 7.5 % BM, interspersed with 4 min recovery. Muscle biopsies were obtained under local anaesthetic from m. vastus lateralis at rest and 3 h post-exercise. RNA extracted from skeletal muscle underwent multiplex PCR to determine mRNA expression relative to reference gene UBE2D2. Independent t-tests determined between-group differences in changes from baseline. RESULTS: Acute changes in PGC-1α, NMRK2, NNMNAT1/3 were not differentially regulated by condition (p > 0.05). Fold-change in PDK4, SIRT4, NAMPT and NNMT were differentially regulated by nutrient condition following an acute bout of SIT (WPC vs CHO: 6.6. vs 2.6; 0.62 vs 0.86; 1.73 vs 1.14; 6.0 vs 2.8, respectively, p < 0.05). Citrate synthase and β-3-Hydroxyacyl-CoA dehydrogenase (HAD) enzyme activity increased to a greater extent in response to SIT with WPC (Fold change WPC vs CHO: 1.3 vs 1.1; 1.23 vs 1.02, respectively, p < 0.05). Post-SIT Wingate performance changes were not different between conditions (% change WPC vs CHO: 6.3 vs 4.1%, p > 0.05). CONCLUSION: Pre-exercise nutrients result in divergent regulation of mitochondrial enzyme activity and some genes in response to SIT, however this is not associated with differential performance adaptations.

Prolonged effects of DPP-4 inhibitors on steato-hepatitic changes in Sprague-Dawley rats fed a high-cholesterol diet.

Sitagliptin and other dipeptidyl peptidase (DPP)-4 inhibitors/gliptins are antidiabetic drugs known to improve lipid profile, and confer anti-inflammatory and anti-fibrotic effects, which are independent of their hypoglycemic effects. However, in our previous short-term (35days) studies, we showed that sitagliptin accentuates the hepato-inflammatory effects of high dietary cholesterol (Cho) in male Sprague-Dawley rats. Since most type 2 diabetics also present with lipid abnormalities and use DPP-4 inhibitors for glucose management, the present study was conducted to assess the impact of sitagliptin during long-term (98days) feeding of a high Cho diet. An additional component of the present investigation was the inclusion of other gliptins to determine if hepatic steatosis, necro-inflammation, and fibrosis were specific to sitagliptin or are class effects. Adult male Sprague-Dawley rats were fed control or high Cho (2.0%) diets, and gavaged daily (from day 30 through 98) with vehicle or DPP-4 inhibitors (sitagliptin or alogliptin or saxagliptin). On day 99 after a 4h fast, rats were euthanized. Blood and liver samples were collected to measure lipids and cytokines, and for histopathological evaluation, determination of hepatic lesions (steatosis, necrosis, inflammation, and fibrosis) using specific staining and immunohistochemical methods. Compared to controls, the high Cho diet produced a robust increase in NASH like phenotype that included increased expression of hepatic (Tnfa, Il1b, and Mcp1) and circulatory (TNFα and IL-1β) markers of inflammation, steatosis, necrosis, fibrosis, and mononuclear cell infiltration. These mononuclear cells were identified as macrophages and T cells, and their recruitment in the liver was facilitated by marked increases in endothelium-expressed cell adhesion molecules. Importantly, treatment with DPP-4 inhibitors (3 tested) neither alleviated the pathologic responses induced by high Cho diet nor improved lipid profile. The potential lipid lowering effects of DPP-4 inhibitors were diminished by high Cho (a significant risk factor for inducing liver damage). The robust inflammatory responses induced by high Cho feeding in long-term experiment were not exacerbated by DPP-4 inhibitors and a consistent hepatic inflammatory environment persisted, implying a prospective physiological adaptation.

Carbohydrate improves exercise capacity but does not affect subcellular lipid droplet morphology, AMPK and p53 signalling in human skeletal muscle.

Muscle glycogen and intramuscular triglycerides (IMTG, stored in lipid droplets) are important energy substrates during prolonged exercise. Exercise-induced changes in lipid droplet (LD) morphology (i.e. LD size and number) have not yet been studied under nutritional conditions typically adopted by elite endurance athletes, that is, after carbohydrate (CHO) loading and CHO feeding during exercise. We report for the first time that exercise reduces IMTG content in both central and peripheral regions of type I and IIa fibres, reflective of decreased LD number in both fibre types whereas reductions in LD size were exclusive to type I fibres. Additionally, CHO feeding does not alter subcellular IMTG utilisation, LD morphology or muscle glycogen utilisation in type I or IIa/II fibres. In the absence of alterations to muscle fuel selection, CHO feeding does not attenuate cell signalling pathways with regulatory roles in mitochondrial biogenesis. We examined the effects of carbohydrate (CHO) feeding on lipid droplet (LD) morphology, muscle glycogen utilisation and exercise-induced skeletal muscle cell signalling. After a 36h CHO loading protocol and pre-exercise meal (12 and 2gkg-1 , respectively), eight trained males ingested 0, 45 or 90gCHOh-1 during 180min cycling at lactate threshold followed by an exercise capacity test (150% lactate threshold). Muscle biopsies were obtained pre- and post-completion of submaximal exercise. Exercise decreased (P<0.01) glycogen concentration to comparable levels (∼700 to 250mmolkg-1 DW), though utilisation was greater in type I (∼40%) versus type II fibres (∼10%) (P<0.01). LD content decreased in type I (∼50%) and type IIa fibres (∼30%) (P<0.01), with greater utilisation in type I fibres (P<0.01). CHO feeding did not affect glycogen or IMTG utilisation in type I or II fibres (all P>0.05). Exercise decreased LD number within central and peripheral regions of both type I and IIa fibres, though reduced LD size was exclusive to type I fibres. Exercise induced (all P<0.05) comparable AMPKThr172 (∼4-fold), p53Ser15 (∼2-fold) and CaMKIIThr268 phosphorylation (∼2-fold) with no effects of CHO feeding (all P>0.05). CHO increased exercise capacity where 90gh-1 (233±133s)>45gh-1 (156±66s; P=0.06)>0gh-1 (108±54s; P=0.03). In conditions of high pre-exercise CHO availability, we conclude CHO feeding does not influence exercise-induced changes in LD morphology, glycogen utilisation or cell signalling pathways with regulatory roles in mitochondrial biogenesis.

682-P: Carbohydrate Needs for Prolonged Fasted Exercise with and without Basal Rate Reductions in CSII

The amount of oral carbohydrate (CHO) needed to prevent hypoglycemia during prolonged fasted exercise in CSII is unclear. We assessed CHO intake needs during 3 different basal rate strategies during prolonged fasted exercise in active patients with T1D. Individuals with T1D on CSII (n=15) completed three 120-min treadmill exercise (∼45% of VO2peak) visits in a randomized crossover design. Strategies included: A) no basal rate reduction (BRR) and a dextrose intake of 0.3 g/kg/hr when BG was &amp;lt;10mmol/L (CHO only); B) a 50% BRR set 90 min pre-exercise, with dextrose as needed to treat hypoglycemia (50% BRR); and C) a 50% BRR set at exercise start plus dextrose intake of 0.3 g/kg/hr when BG was &amp;lt;10 mmol/L (Combo). Glycemia was higher in C compared to A or B by 105 min of exercise (P &amp;lt; 0.05). The drop in blood glucose during exercise was greater in A (-2.7 ± 3.4 mmol/L) than in B (-1.9 ± 2.5 mmol/L) or C (0.3 ± 2.6 mmol/L). Total CHO intake was 38.0 ± 18.8 g, 0.8 ± 3.1 g, and 29.5 ± 16.2 g, for A, B and C, respectively. Compared to A, B had lower RER (0.83 ± 0.04 vs. 0.79 ± 0.04), higher ketones (0.1 ± 0.1 vs. 0.4 ± 0.3 mmol/L), greater net loss of calories (709.2 ± 217.4 vs. 859.7 ± 239.6 kcal) and greater fat oxidation rate (0.39 ± 0.1 vs. 0.51 ± 0.2 g/min) (all P &amp;lt; 0.05). A BRR, set 90 min prior to exercise is associated with good glycemic control and an increased rate of lipid oxidation compared to CHO feeding alone or combined BRR and CHO feeding approach at exercise onset. Disclosure S.M. McGaugh: None. R. Pooni: None. D. Zaharieva: Speaker’s Bureau; Self; Ascensia Diabetes Care, Insulet Corporation, Medtronic. N.C. D’Souza: None. T. Vienneau: Employee; Self; Insulet Corporation. Stock/Shareholder; Self; Insulet Corporation. T.T. Ly: Employee; Self; Insulet Corporation. M. Riddell: Advisory Panel; Self; Zucara Therapeutics Inc. Consultant; Self; Lilly Diabetes. Research Support; Self; Dexcom, Inc., Insulet Corporation. Speaker’s Bureau; Self; Medtronic, Novo Nordisk A/S. Funding Insulet Corporation

A Short-Term Ketogenic Diet Impairs Markers of Bone Health in Response to Exercise.

Objectives: To investigate diet-exercise interactions related to bone markers in elite endurance athletes after a 3.5-week ketogenic low-carbohydrate, high-fat (LCHF) diet and subsequent restoration of carbohydrate (CHO) feeding.Methods: World-class race walkers (25 male, 5 female) completed 3.5-weeks of energy-matched (220 kJ·kg·d−1) high CHO (HCHO; 8.6 g·kg·d−1 CHO, 2.1 g·kg·d−1 protein, 1.2 g·kg·d−1 fat) or LCHF (0.5 g·kg·d−1 CHO, 2.1 g·kg·d−1 protein, 75–80% of energy from fat) diet followed by acute CHO restoration. Serum markers of bone breakdown (cross-linked C-terminal telopeptide of type I collagen, CTX), formation (procollagen 1 N-terminal propeptide, P1NP) and metabolism (osteocalcin, OC) were assessed at rest (fasting and 2 h post meal) and after exercise (0 and 3 h) at Baseline, after the 3.5-week intervention (Adaptation) and after acute CHO feeding (Restoration).Results: After Adaptation, LCHF increased fasting CTX concentrations above Baseline (p = 0.007, Cohen's d = 0.69), while P1NP (p < 0.001, d = 0.99) and OC (p < 0.001, d = 1.39) levels decreased. Post-exercise, LCHF increased CTX concentrations above Baseline (p = 0.001, d = 1.67) and above HCHO (p < 0.001, d = 0.62), while P1NP (p < 0.001, d = 0.85) and OC concentrations decreased (p < 0.001, d = 0.99) during exercise. Exercise-related area under curve (AUC) for CTX was increased by LCHF after Adaptation (p = 0.001, d = 1.52), with decreases in P1NP (p < 0.001, d = 1.27) and OC (p < 0.001, d = 2.0). CHO restoration recovered post-exercise CTX and CTX exercise-related AUC, while concentrations and exercise-related AUC for P1NP and OC remained suppressed for LCHF (p = 1.000 compared to Adaptation).Conclusion: Markers of bone modeling/remodeling were impaired after short-term LCHF diet, and only a marker of resorption recovered after acute CHO restoration. Long-term studies of the effects of LCHF on bone health are warranted.

Muscle Glycogen Utilization During an Australian Rules Football Game.

To better understand the carbohydrate (CHO) requirement of Australian Football (AF) match play by quantifying muscle glycogen utilization during an in-season AF match. After a 24-h CHO-loading protocol of 8 and 2g/kg in the prematch meal, 2 elite male forward players had biopsies sampled from m. vastus lateralis before and after participation in a South Australian Football League game. Player A (87.2kg) consumed water only during match play, whereas player B (87.6kg) consumed 88g CHO via CHO gels. External load was quantified using global positioning system technology. Player A completed more minutes on the ground (115 vs 98min) and covered greater total distance (12.2 vs 11.2km) than player B, although with similar high-speed running (837 vs 1070m) and sprinting (135 vs 138m). Muscle glycogen decreased by 66% in player A (pre: 656mmol/kg dry weight [dw], post: 223mmol/kg dw) and 24% in player B (pre: 544mmol/kg dw, post: 416mmol/kg dw). Prematch CHO loading elevated muscle glycogen concentrations (ie,>500mmol/kg dw), the magnitude of which appears sufficient to meet the metabolic demands of elite AF match play. The glycogen cost of AF match play may be greater than in soccer and rugby, and CHO feeding may also spare muscle glycogen use. Further studies using larger sample sizes are now required to quantify the interindividual variability of glycogen cost of match play (including muscle and fiber-type-specific responses), as well examining potential metabolic and ergogenic effects of CHO feeding.

Metabolic Responses to Carbohydrate Ingestion during Exercise: Associations between Carbohydrate Dose and Endurance Performance.

Carbohydrate (CHO) ingestion during exercise lasting less than three hours improves endurance exercise performance but there is still debate about the optimal dose. We utilised stable isotopes and blood metabolite profiles to further examine metabolic responses to CHO (glucose only) ingestion in the 20–64 g·h−1 range, and to determine the association with performance outcome. In a double-blind, randomized cross-over design, male cyclists (n = 20, mean ± SD, age 34 ± 10 years, mass 75.8 ± 9 kg, peak power output 394 ± 36 W, VO2max 62 ± 9 mL·kg−1·min−1) completed four main experimental trials. Each trial involved a two-hour constant load ride (185 ± 25 W) followed by a time trial, where one of three CHO beverages, or a control (water), were administered every 15 min, providing 0, 20, 39 or 64 g CHO·h−1. Dual glucose tracer techniques, indirect calorimetry and blood analyses were used to determine glucose kinetics, exogenous CHO oxidation (EXO), endogenous CHO and fat oxidation; and metabolite responses. Regression analysis revealed that total exogenous CHO oxidised in the second hour of exercise, and suppression of serum NEFA concentration provided the best prediction model of performance outcome. However, the model could only explain ~19% of the variance in performance outcome. The present data demonstrate that consuming ~40 g·h−1 of CHO appears to be the minimum ingestion rate required to induce metabolic effects that are sufficient to impact upon performance outcome. These data highlight a lack of performance benefit and few changes in metabolic outcomes beyond an ingestion rate of 39 g·h−1. Further work is required to explore dose-response effects of CHO feeding and associations between multiple metabolic parameters and subsequent performance outcome.

Influence Of Carbohydrate Intake On Pacing Changes During Prolonged Cycling

PURPOSE: The effects of carbohydrate intake on temporal changes in power output during cycling were examined. METHODS: Eight male cyclists (VO2max: 62 ± 6 mL[BULLET OPERATOR]kg-1[BULLET OPERATOR]min-1) completed two trials consisting of 120 min of constant load cycling at 55% Wmax, followed by a simulated 30 km time trial (TT). Subjects consumed 150 ml of a glucose-fructose solution (CHO) or a non-caloric placebo (PL) every 15 minutes during the constant-load portion of the trial, and at 7.5 km intervals during the TT. Average power output during the TT was compared between treatments, and changes in power output within trials were examined across four segments of the TT (S1 = 0-7.5 km, S2 = 7.5-15 km, S3 = 15-22.5 km, and S4 = 22.5-30 km). Power output was also averaged for three minutes immediately before and after each feeding, to determine if changes in pacing between treatments were influenced by the proximity to CHO feedings. Magnitude-based qualitative inferences were used to evaluate differences between treatments and/or time-points. RESULTS: Average TT power output during the CHO trial (242 ± 30 W) was ‘likely’ greater than PL (217 ± 40 W). In the PL trial, cycling power ‘almost certainly’ decreased between S1 (235 ± 41 W) and S2 (223 ± 38 W), and ‘likely’ decreased further during S3 (201 ± 41 W). Subsequently, cycling power ‘very likely’ increased between S3 and S4 (219 ± 43 W), but remained lower than S1 levels. By contrast, power output during the CHO trial showed no clear changes from S1 (246 ± 41 W) to S2 (242 ± 28 W). Thereafter, power output ‘possibly’ decreased during S3 (232 ± 27 W), followed by a ‘likely’ increase in power during S4 (249 ± 32 W), resulting in power levels during S4 that were similar to S1. Power output during the period immediately following each PL ingestion (210 ± 40 W) was not clearly different from the period prior to PL ingestion (213 ± 39 W); whereas power output immediately following CHO ingestion (244 ± 27 W) was ‘possibly’ increased versus pre-ingestion (236 ± 31 W). CONCLUSIONS: CHO ingestion increased average power output during a cycling TT and attenuated declines in power output over the duration of the trial, compared to PL. In addition, improvements in power output with CHO were possibly greater in the periods immediately following each feeding, potentially due to effects of CHO on the central nervous system.

Effect of carbohydrate feeding on the bone metabolic response to running.

Bone resorption is increased after running, with no change in bone formation. Feeding during exercise might attenuate this increase, preventing associated problems for bone. This study investigated the immediate and short-term bone metabolic responses to carbohydrate (CHO) feeding during treadmill running. Ten men completed two 7-day trials, once being fed CHO (8% glucose immediately before, every 20 min during, and immediately after exercise at a rate of 0.7 g CHO·kg body mass−1·h−1) and once being fed placebo (PBO). On day 4 of each trial, participants completed a 120-min treadmill run at 70% of maximal oxygen consumption (V̇o2 max). Blood was taken at baseline (BASE), immediately after exercise (EE), after 60 (R1) and 120 (R2) min of recovery, and on three follow-up days (FU1-FU3). Markers of bone resorption [COOH-terminal telopeptide region of collagen type 1 (β-CTX)] and formation [NH2-terminal propeptides of procollagen type 1 (P1NP)] were measured, along with osteocalcin (OC), parathyroid hormone (PTH), albumin-adjusted calcium (ACa), phosphate, glucagon-like peptide-2 (GLP-2), interleukin-6 (IL-6), insulin, cortisol, leptin, and osteoprotogerin (OPG). Area under the curve was calculated in terms of the immediate (BASE, EE, R1, and R2) and short-term (BASE, FU1, FU2, and FU3) responses to exercise. β-CTX, P1NP, and IL-6 responses to exercise were significantly lower in the immediate postexercise period with CHO feeding compared with PBO (β-CTX: P = 0.028; P1NP: P = 0.021; IL-6: P = 0.036), although there was no difference in the short-term response (β-CTX: P = 0.856; P1NP: P = 0.721; IL-6: P = 0.327). No other variable was significantly affected by CHO feeding during exercise. We conclude that CHO feeding during exercise attenuated the β-CTX and P1NP responses in the hours but not days following exercise, indicating an acute effect of CHO feeding on bone turnover.

The Effect of Adding Caffeine to Postexercise Carbohydrate Feeding on Subsequent High-Intensity Interval-Running Capacity Compared With Carbohydrate Alone

The aim of this study was to test the hypothesis that adding caffeine to postexercise carbohydrate (CHO) feedings improves subsequent high-intensity interval-running capacity compared with CHO alone. In a repeated-measures design, 6 men performed a glycogen-depleting exercise protocol until volitional exhaustion in the morning. Immediately after and at 1, 2, and 3 hr postexercise, participants consumed 1.2 g/kg body mass CHO of a 15% CHO solution, a similar CHO solution but with addition of 8 mg/kg body mass of caffeine (CHO+CAFF), or an equivalent volume of flavored water only (WAT). After the 4-hr recovery period, participants performed the Loughborough Intermittent Shuttle Test (LIST) to volitional exhaustion as a measure of high-intensity interval-running capacity. Average blood glucose values during the 4-hr recovery period were higher in the CHO conditions (p < .005) than in the WAT trial (4.6 ± 0.3 mmol/L), although there was no difference (p = .46) between CHO (6.2 ± 0.8 mmol/L) and CHO+CAFF (6.7 ± 1.0 mmol/L). Exercise capacity during the LIST was significantly longer in the CHO+CAFF trial (48 ± 15 min) than in the CHO (32 ± 15 min, p = .04) and WAT conditions (19 ± 6 min, p = .001). All 6 participants improved performance in CHO+CAFF compared with CHO (95% CI for mean difference = 1-32 min). The study provides novel data by demonstrating that adding caffeine to postexercise CHO feeding improves subsequent high-intensity interval-running capacity, a finding that may be related to higher rates of postexercise muscle glycogen resynthesis previously observed under similar feeding conditions.

Should Protein Be Included in CHO-Based Sports Supplements?

Should Protein Be Included in CHO-Based Sports Supplements?

The Effect of Energy Supplementation on Markers of Muscle Stress During Indoor Rock Climbing

The effect of nutritional supplementation on exercise induced markers of muscle stress has been extensively researched. However, no research exists on the influence of carbohydrate (CHO) or a carbohydrate-protein sports gel (GEL) supplementation on indices of muscle stress during rock climbing (RC). RC is an intermittent activity characterized by a high percentage of isometric muscle contractions combined with a moderate level of total energy expenditure. Climbers are limited to how much fluid they can carry, thus, liquid energy supplementation may also be limited. Ingesting an energy GEL may provide a viable alternative to carrying a large fluid volume. PURPOSE: To determine whether CHO and GEL feedings have a significant effect upon plasma creatine kinase (CK) levels, post exercise blood lactate levels (LA), RPE, and exercise HR after 60 minutes of RC. METHODS: Eight experienced subjects (3 males, 5 females; Mean ± SD: 24 ± 2 yrs) performed three bouts of climbing with a week between each bout. Each bout consisted of four 15 min intervals with a five minute rest between each interval. Subjects received one of three treatments during each RC session: a non-caloric placebo drink (PL); CHO drink; or GEL. The experimental treatments were isocaloric (1130 kJ or 270 kcal) and isovolumetric (600 mL). The liquid treatments were administered in a double blind crossover design. Heart rate and RPE's were collected after each RC interval. Blood samples were collected before, directly after, and 24 hrs after each RC bout for LA and CK analysis. Data were analyzed by ANOVA and t-tests. RESULTS: 24 h change in CK was significantly different (p<.05) between all treatments (GEL: 24.5 + 29.7; CHO: 56.8 + 36.5; PL: 119.0 + 126.5 U). No statistical differences between treatments were observed for HR, LA, and change in RPE CONCLUSIONS: Energy supplementation during RC significantly lowered muscle stress, as assessed by CK, when compared to PL. Additionally, the combining of protein and CHO provided an added benefit in minimizing muscle stress when compared to a CHO only drink. These findings indicate that GEL ingestion provided a viable option to energy supplementation when compared to a CHO only fluid.

Elevating skeletal muscle total carnitine content increases the expression of genes regulating fat metabolism in humans

Insulin mediated augmentation of muscle carnitine transport acutely increases skeletal muscle total carnitine (TC) content and diverts carbohydrate (CHO) from oxidation towards storage in humans, most likely by increasing muscle fat oxidation (Stephens et al. 2006). Here we aimed to determine the influence of prolonged L-carnitine and CHO feeding on genes known to encode proteins regulating fuel metabolism in human skeletal muscle. mRNA expression levels of 188 genes involved in fat and CHO metabolism and mitochondrial ATP production was determined in muscle biopsy samples obtained before and after 12 and 24 weeks of twice daily feeding of 80 g CHO (Control) or 2 g L-carnitine + 80 g CHO (Carnitine) in 14 healthy male volunteers (age 26 ± 2 y), using low density, real-time quantitative PCR arrays (Applied Biosystems 7900HT). Muscle TC content did not change over 24 weeks in Control, but increased in Carnitine by 20% (22.0 ± 1.1 to 26.7 ± 2.4 mmol/kg dry muscle; P<0.05). Significance Analysis for Microarrays revealed 66 genes were significantly upregulated in Carnitine compared to Control (FDR <1%) at 12 and 24 weeks. Of these, gene enrichment and cluster analysis highlighted PPARα and associated genes involved in fatty acid liberation (LPL, ATGL), transport (FABP3), mitochondrial translocation (ACC, CPT1, CACT, CPT2), and oxidation (HAD). This study had local Ethics Committee approval and was supported by QinetiQ.

Supplemental Feedings Increase Self-Selected Work Output during Wildfire Suppression

The purpose of this study was to determine the impact of supplemental feeding strategies on self-selected activity during wildland fire suppression. Seventy-six wildland firefighters were studied in three experiments for three fire seasons. During the first two seasons, subjects consumed, in addition to their sack lunch, 1) liquid carbohydrate (CHO) (200 mL.h, 20% CHO (40 g.h, 160 kcal.h)) or placebo (PLA) every hour, or 2) liquid CHO (200 mL.h, 20% CHO (40 g.h, 160 kcal.h) every even hour and solid CHO (25 g of CHO, 10 g of protein, 2 g of fat, and 160 kcal.h) every odd hour, or PLA, using counterbalanced crossover designs. During the third season, subjects consumed their sack lunch halfway through their workday, or shift food items of approximately 150-400 kcal at 90-min intervals after breakfast in a randomized crossover design (isocaloric intake, 1534+/-265 kcal per workday). Work output was monitored using CSA and MiniMitter actigraphy units. During the liquid CHO trials, subjects consuming CHO demonstrated significantly higher average activity counts throughout the day compared with PLA (50,262+/-36,560 and 40,159+/-35,969 counts per hour for 12 h for the CHO and PLA trials, respectively; P<0.05). For the liquid+solid CHO trials, subjects consuming CHO demonstrated higher average activity counts per minute 2 h before lunch and the last 4 h of the workday compared with PLA (P<0.05). For the sack lunch and shift food trials, subjects consuming shift foods demonstrated higher average counts per minute during the final 2 h compared with those consuming sack lunch (521+/-421 vs 366+/-249 counts per minute during 2 h; P<0.05). Liquid and/or solid supplemental CHO and regular feedings increased self-selected work rates during wildland fire suppression, particularly during the latter hours of the workday.

Effects Of Caffeinated Sports Drinks On Physical/Mental Function During Team Sports Exercise

The ergogenic effects of caffeine ingestion (240–840 mg) on exercise performance is well established, albeit in some cases with negative side effects. However, recent evidence shows that much smaller doses can have beneficial effect on endurance performance as well as on mental function. Less is known about the possible synergistic effects of low dose of caffeine (CAF) and carbohydrate (CHO) feedings, especially as related to team sports performance. PURPOSE: To determine the effects of low dose (100 mg) CAF ingestion along with typically recommended CHO on physical and mental function during intermittent high intensity exercise that mimics the demands of competitive team sports. METHODS: Physically active male (N=6) and female (N=4) low to moderate caffeine users participated in this study. Experimental trials consisted of four ∼22-minute quarters (QTR) of shuttle running. Physical and mental function tests were administered throughout the experimental trial including (20-m sprint, vertical jump, gross motor skill test, force sensation, rating of perceived exertion, profile of mood states and psychomotor vigilance test).On four separate occasions, subjects received 20-oz of flavored water placebo (PLA), CHO, PLA+CAF and CHO+CAF prior to exercise. During exercise, subjects ingest PLA, CHO, PLA and CHO respectively (3.5 ml·kg-1). RESULTS: No difference was found in 20-m sprint time, vertical jump and gross motor skills performance between any treatments. However, both caffeine treatments (PLA+CAF and CHO+CAF) significantly improved psychomotor vigilance and reduced force sensation at HALFTIME (p<0.05). CHO+CAF also improved self-reported perception of fatigue, vigor and overall mood compared to PLA+CAF (p<0.05). Systolic blood pressure was increased with CHO+CAF compare to other three treatments. However, no difference was found in heart rate, core body temperature, plasma volume change, or hydration status between any treatments. CONCLUSION: The data suggest that ingestion of a low dose of caffeine prior to exercise did not add to the expected benefits of CHO feedings alone on physical tasks. However, all of the mental function tasks were significantly enhanced with the combination of CHO plus CAF, with little or no adverse side effects. Funded by Gatorade Sports Science Institute.

Does Carbohydrate Ingestion Affect Cycling Economy and Efficiency during 8 H of Prolonged Exercise?

Ingesting a carbohydrate (CHO) solution during prolonged submaximal exercise appears to delay the onset of fatigue and enhance endurance performance, especially in exercise lasting more than 2 hours. However, whether CHO feeding affects cycling economy and efficiency during extended-duration exercise remains to be elucidated. PURPOSE: The purpose of this study was to determine the effects of CHO ingestion (10%CHO solution: 60 g·h−1) on cycling economy and gross efficiency during 8 h of prolonged exercise. METHODS: Seven moderately trained individuals [cycling %VO2peak at ventilatory threshold (Tvent); 63.8±7.1] served as subjects. All subjects randomly completed a placebo-controlled, double-blind, cross over-design. Each subject performed a total of 8 h of exercise including 25 min of leg cycling (freely chosen crank rate; average from 72 to 85 rpm) and 25 min of treadmill walking with 5 min of transition between modes each hour and a 30 min lunch rest period. Each exercise session consisted of a variety of intensities (min 0–6=70%Tvent, min 7–8=110%Tvent, min 9=70%Tvent, min 10–11=100%Tvent, min 12=70%Tvent, min 13–14=90%Tvent, min 15–25=70%Tvent). Cycling economy (w·l−1min−1) and gross efficiency (%) were determined during 70% Tvent from min 18 to 25 during hours 1,4, 5, and 8. RESULTS: With a two-way repeated measures ANOVA, the main effect for trial for economy and gross efficiency and interaction (trial x time) were not statistically significant. However, the main effect for time demonstrated significant decreases at hour 8 compared to hour 4 in both economy (p < 0.01) and gross efficiency (p < 0.05). CONCLUSION: Carbohydrate ingestion during 8 h of endurance exercise appears to have no influence on cycling economy and gross efficiency at relatively moderate intensity with freely chosen crank rate.

Effects Of Carbohydrate Feeding On Muscle Glycogen And Substrate Oxidation During Extended Exercise In Females

There has been limited research on carbohydrate (CHO) feeding during long duration exercise in females. Although previous research has reported rates of muscle glycogen use and fuel selection in females during exercise up to 2 hours in length, we are unaware of any data for exercise durations exceeding 2 hours. PURPOSE To determine the effects of CHO feeding during 10-hours of moderate exercise on muscle glycogen and substrate utilization in females. METHODS Six moderately trained females (age 23+/−3 yr, eumenorrheic and not taking oral contraceptives) served as subjects. Subjects performed a GXT on a treadmill (TM) and on an electronically braked cycle ergometer (C) to determine ventilatory threshold (VT) and VO2peak. In a double blind, random crossover design, subjects ingested either a CHO (0.6g CHO/kg fat free mass (FFM) of a 20% maltodextrin solution) or placebo (PLA) drink each hour. Subjects completed ten, 60 minute bouts of exercise at 70% VT (46+/−6 and 45+/−7% VO2peak for the C and TM, respectively). Each 60 minute bout consisted of 9 minutes of a self-selected intensity on the arm ergometer (double poling), 19 minutes on the C, 20 minutes on the TM, followed by a 10-minute rest and feeding period. A standardized lunch was provided (5.46 g/kg FFM CHO, and 1.31 g/kg FFM protein) during both trials after the fifth hour. Muscle biopsies were taken pre- and post-exercise on the vastus lateralis, and metabolic gases were collected every other hour on the TM. Blood glucose was continuously measured throughout the day with an indwelling glucose sensor, and total urine void was collected. RESULTS Whole body CHO oxidation on the TM was significantly higher during the CHO trial (269.1+/−64.1g) compared to PLA (209.6+/−45.8g, p=0.0012). Rates of muscle glycogenolysis were also significantly lower during the CHO trial (2.5 +/−1.8 and 5.4+/−2.2 g/kg wet wt.thr, for CHO and PLA respectively, p=0.048). Blood glucose and RPE were similar for both trials. Total urinary nitrogen was also similar for both trials (525.2 +/−455.3 and 617.7+/−508.2 mg/dl, for CHO and PLA respectively, p= 0.1417). CONCLUSION: These data indicate regular CHO feedings during long duration exercise increase overall CHO oxidation while lowering rates of muscle glycogenolysis during 10 hours of moderate intensity intermittent exercise in females.

Carbohydrate Feedings during Team Sport Exercise Preserve Physical and CNS Function

This study was designed to examine the effect of carbohydrate (CHO) feedings on physical and central nervous system (CNS) function during intermittent high-intensity exercise with physical demands similar to those of team sports such as basketball. Twenty active men (N = 10) and women (N = 10), with experience competing in team sports, performed three practice sessions before two experimental trials during which they were fed either a 6% CHO solution or a flavored placebo (PBO). Experimental trials consisted of four 15-min quarters of shuttle running with variable intensities ranging from walking (30% VO(2max)), to running (120% VO(2max)), to maximal sprinting, and 40 jumps at a target hanging at 80% of their maximum vertical jump height. Subjects received 5 mL.kg(-1) of fluid before exercise and 3 mL.kg(-1) after exercise, in addition to 3 mL.kg(-1) over a 5-min span after the first and third quarters, and 8 mL.kg(-1) during a 20-min halftime. During each break, the subjects performed a battery of tests measuring peripheral and CNS function, including 20-m sprints, a 60-s maximal jumping test, internal and external mood evaluation, cognitive function, force sensation, tests of motor skills, and target-jumping accuracy. Compared with PBO, CHO feedings during exercise resulted in faster 20-m sprint times and higher average jump height in the fourth quarter (P < 0.05). CHO feedings also reduced force sensation, enhanced motor skills, and improved mood late in exercise versus PBO (P < 0.05). These results suggest that CHO feedings during intermittent high-intensity exercise similar to that of team sports benefited both peripheral and CNS function late in exercise compared with a flavored placebo.

Failure of Repeated Carbohydrate Loading to Supercompensate Muscle Glycogen Stores

0155 A number of different dietary/training interventions have been used to supercompensate muscle glycogen stores and enhance prolonged aerobic exercise performance. These studies have all evaluated the efficacy of such regimens on a single exercise bout. At present it is not known whether it is possible to repeatedly supercompensate muscle glycogen stores within several days. PURPOSE: To evaluate the effect of repeated carbohydrate (CHO) loading on muscle glycogen resynthesis and exercise performance. METHODS: Six well trained subjects completed a high-intensity intermittent exhaustive exercise protocol (EX) on four occasions, with the first trial serving as a familiarization trial. During a 5 d intervention period, subjects repeated EX on three occasions separated by 48 h (i.e. DAY 1, 3 and 5). Before the familiarisation trial and DAY 1, subjects consumed a moderate (6 g·kg−1) CHO diet. Throughout the 5 d intervention period, subjects consumed a high (12 g·kg·d−1) CHO diet. Subjects consumed 4 g·kg−1 CHO immediately after completing the EX. Muscle biopsies were taken before, immediately upon completing the EX, and after 3 h of recovery and analysed for glycogen and intramuscular triacylglycerol (IMTG) concentration. RESULTS: Compared to a moderate CHO diet, high CHO feeding resulted in elevated pre-exercise glycogen on DAY 3 (435 ± 57 vs 713 ± 60 mmol·kg−1 dw, P <0.001) but not DAY 5 (409 ± 40 mmol·kg−1 dw). Muscle glycogen utilization was higher on DAY 3 compared to both DAY 1 and 5 (600 ± 86 vs 340 ± 84 and 350 ± 51 mmol·kg−1 dw respectively, P <0.001). Neither pre-exercise IMTG concentration nor utilization was altered during the 5 d intervention period. Compared to DAY 1, performance was increased on DAY 3 and 5, (22 ± 1 vs 31 ± 2 and 35 ± 4 kJ·kg−1 respectively, P <0.05). CONCLUSIONS: Repeated muscle glycogen supercompensation is not possible, even when subjects consume a high CHO diet and maintain only light training. However, performance enhancement is maintained. Supported by a research grant from GlaxoSmithKline (United Kingdom)

LIQUID CARBOHYDRATE FEEDING IMPROVES SELF-SELECTED EXERCISE PERFORMANCE DURING A 24K HIKE

During prolonged exercise, when muscle glycogen stores are depleted, blood glucose can assume 100% of the total carbohydrate (CHO) oxidation. The effectiveness of exogenous CHO during endurance exercise has been widely documented. However, CHO ingestion during extended exercise at lower intensities has received little attention. PURPOSE To determine the effects of carbohydrate feeding on blood glucose and self-selected hiking speed during a prolonged submaximal exercise bout. METHODS Subjects (n=12) completed two extended hikes (24K) in a single-blind double-crossover design 7 days apart. Blood glucose concentration was measured pre, post, and hourly during the hike using an automated glucometer. Concurrently, subjects consumed 200mL of a CHO (40g.hour-1, 20% maltodextrin) or placebo (PLA) drink hourly. Rating of perceived exertion (RPE) was also recorded hourly using the Borg 6–20 scale. Data were analyzed using apriori planned comparisons across trials. RESULTS Blood glucose was similar prior to exercise and for the first 8K of the hike. Thereafter blood glucose remained significantly higher (p < 0.05) during the CHO trial (12K: CHO=6.1 ± 0.9, PLA=5.2 ± 0.6; 16K: CHO=6.3 ± 1.0, PLA=5.4 ± 1.1; 20K: CHO=7.8 ± 1.0, PLA=5.8 ± 1.2; 24K: CHO=7.4 ± 0.9, PLA=5.7 ± 1.0 mM). Subjects self-selected a faster hiking speed during the CHO trial as demonstrated by the significant difference in return time (124 ± 15 vs. 136 ± 12 minutes for the CHO and PLA trials, respectively, p < 0.05) despite no differences in RPE values (11.92 ± 3.00 vs. 11.75 ± 2.30, p < 0.05). CONCLUSION These data demonstrate that supplemental CHO feedings can improve self-selected exercise performance during low to moderate extended hiking regardless of the subject's rating of perceived exertion.