To examine the effects of a 3-day high carbohydrate (H-CHO) and low carbohydrate (L-CHO) diet on 45 min of cycling exercise, 12 endurance-trained cyclists performed a 45-min cycling exercise at 82 ± 2% VO2peak following an overnight fast, after a 6-day diet and exercise control. The 7-day protocol was repeated under 2 randomly assigned dietary trials H-CHO and L-CHO. On days 1–3, subjects consumed a mixed diet for both trials and for days 4–6 consumed isocaloric diets that contained either 600 g or 100 g of carbohydrates, for the HCHO and the L-CHO trials, respectively. Muscle biopsy samples, taken from the vastus lateralis prior to the beginning of the 45-min cycling test, indicated that muscle glycogen levels were significantly higher (p < .05) for the H-CHO trial (104.5 ± 9.4 mmol/kg wet wt) when compared to the L-CHO trial (72.2 ± 5.6 mmol/kg wet wt). Heart rate, ratings of perceived exertion, oxygen uptake, and respiratory quotient during exercise were not significantly different between the 2 trials. Serum glucose during exercise for the H-CHO trial significantly increased (p < .05) from 4.5 ± 0.1 mmol · L−1 (pre) to 6.7 ± 0.6 mmol · L−1 (post), while no changes were found for the L-CHO trial. In addition, post-exercise serum glucose was significantly greater (p < .05) for the H-CHO trial when compared to the L-CHO trial (H-CHO, 6.7 ± 0.6 mmol · L−1; L-CHO, 5.2 ± 0.2 mmol · L−1). No significant changes were observed in serum free fatty acid, triglycerides, or insulin concentration in either trial. The findings suggest that L-CHO had no major effect on 45-min cycling exercise that was not observed with H-CHO when the total energy intake was adequate.
Stavros A. Kavouras, John P. Troup and Jacqueline R. Berning
Graeme I. Lancaster, Roy L.P.G. Jentjens, Luke Moseley, Asker E. Jeukendrup and Michael Gleeson
The purpose of the present study was to examine the effect of pre-exercise carbohydrate (CHO) ingestion on circulating leukocyte numbers, plasma interleukin (IL)-6, plasma cortisol, and lipopolysaccharide (LPS)-stimulated neutrophil degranulation responses in moderately trained male cyclists who completed approximately 1-h of high-intensity cycling. The influence of the timing of pre-exercise CHO ingestion was investigated in 8 subjects who consumed 75 g CHO as a glucose solution at either 15 (–15 trial), or 75 (–75 trial) min before the onset of exercise. The influence of the amount of pre-exercise CHO ingestion was investigated in a further 10 subjects who consumed either 25 g or 200 g CHO as a glucose solution or a placebo 45 min before the onset of exercise. At the onset of exercise in the timing experiment, the plasma glucose concentration was significantly (p < .05) lower on the –75 trial compared with pre-drink values, and the plasma cortisol concentration and neutrophil to lymphocyte (N/L) ratio were significantly (p < .05) elevated in the post-exercise period. In the –15 trial, plasma glucose concentration was well maintained, and the plasma cortisol concentration and N/L ratio were not significantly elevated above resting levels. However, LPS-stimulated neutrophil degranulation was similar in the –15 and –75 trials. The amount of CHO ingested had no effect on the magnitude of the rise in the N/L ratio compared with placebo when consumed 45 min pre-exercise. Finally, although an exercise-induced increase in the plasma IL-6 concentration was observed, this effect was independent of pre-exercise CHO ingestion.
Nicolette C. Bishop, Michael Gleeson, Ceri W. Nicholas and Ajmol Ali
Ingesting carbohydrate (CHO) beverages during prolonged, continuous heavy exercise results in smaller changes in the plasma concentrations of several cytokines and attenuates a decline in neutrophil function. In contrast, ingesting CHO during prolonged intermittent exercise appears to have negligible influence on these responses, probably due to the overall moderate intensity of these intermittent exercise protocols. Therefore, we examined the effect of CHO ingestion on plasma interIeukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and lipopolysaccharide (LPS)-stimuIated neutrophil degranulation responses to high-intensity intermittent running. Six trained male soccer players performed 2 exercise trials, 7 days apart, in a randomized, counterbalanced design. On each occasion, they completed six 15-min periods of intermittent running consisting of maximal sprinting interspersed with less intense periods of running and walking. Subjects consumed either CHO or artificially sweetened placebo(PLA) beverages immediately before and at 15-min intervals during the exercise. At 30 min post-exercise, CHO versus PLA was associated with a higher plasma glucose concentration (p< .01), a lower plasma cortisol and IL-6 concentration (p < .02), and fewer numbers of circulating neutrophils (p < .05). Following the exercise, LPS-stimulated elastase release per neutrophil fell 31 % below baseline values on the PLA trial (p = .06) compared with 11% on the CHO trial (p = .30). Plasma TNF-α concentration increased following the exercise (main effect of time, p < .001) but was not affected by CHO. These data indicate that CHO ingestion attenuates changes in plasma IL-6 concentration, neutrophil trafficking, and LPS-stimulated neutrophil degranulation in response to intermittent exercise that involves bouts of very high intensity exercise.
Matthew S. Ganio, Jennifer F. Klau, Elaine C. Lee, Susan W. Yeargin, Brendon P. McDermott, Maxime Buyckx, Carl M. Maresh and Lawrence E. Armstrong
The purpose of this study was to compare the effects of a carbohydrate-electrolyte plus caffeine, carnitine, taurine, and B vitamins solution (CE+) and a carbohydrate-electrolyte-only solution (CE) vs. a placebo solution (PLA) on cycling performance and maximal voluntary contraction (MVC). In a randomized, double-blind, crossover, repeated-measures design, 14 male cyclists (M ± SD age 27 ± 6 yr, VO2max 60.4 ± 6.8 ml · kg−1 · min−1) cycled for 120 min submaximally (alternating 61% ± 5% and 75% ± 5% VO2max) and then completed a 15-min performance trial (PT). Participants ingested CE+, CE, or PLA before (6 ml/kg) and every 15 min during exercise (3 ml/kg). MVC was measured as a single-leg isometric extension (70° knee flexion) before (pre) and after (post) exercise. Rating of perceived exertion (RPE) was measured throughout. Total work accumulated (KJ) during PT was greater (p < .05) in CE+ (233 ± 34) than PLA (205 ± 52) but not in CE (225 ± 39) vs. PLA. MVC (N) declined (p < .001) from pre to post in PLA (988 ± 213 to 851 ± 191) and CE (970 ± 172 to 870 ± 163) but not in CE+ (953 ± 171 to 904 ± 208). At Minutes 60, 90, 105, and 120 RPE was lower in CE+ (14 ± 2, 14 ± 2, 12 ± 1, 15 ± 2) than in PLA (14 ± 2, 15 ± 2, 14 ± 2, 16 ± 2; p < .001). CE+ resulted in greater total work than PLA. CE+, but not PLA or CE, attenuated pre-to-post MVC declines. Performance increases during CE+ may have been influenced by lower RPE and greater preservation of leg strength during exercise in part as a result of the hypothesized effects of CE+ on the central nervous system and skeletal muscle.
Alexander S.D. Gamble, Jessica L. Bigg, Tyler F. Vermeulen, Stephanie M. Boville, Greg S. Eskedjian, Sebastian Jannas-Vela, Jamie Whitfield, Matthew S. Palmer and Lawrence L. Spriet
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.
Al Haddad Hani, Paul B. Laursen, Ahmaidi Said and Buchheit Martin
To assess the effect of supramaximal intermittent exercise on long-term cardiac autonomic activity, inferred from heart rate variability (HRV).
Eleven healthy males performed a series of two consecutive intermittent 15-s runs at 95% VIFT (i.e., speed reached at the end of the 30-15 Intermittent Fitness Test) interspersed with 15 s of active recovery at 45% VIFT until exhaustion. Beat-to-beat intervals were recorded during two consecutive nights (habituation night and 1st night) before, 10 min before and immediately after exercise, as well as 12 h (2nd night) and 36 h (3rd night) after supramaximal intermittent exercise. The HRV indices were calculated from the last 5 min of resting and recovery periods, and the first 10 min of the first estimated slow wave sleep period.
Immediate post-supramaximal exercise vagal-related HRV indices were significantly lower than immediate pre-supramaximal exercise values (P < .001). Most vagal-related indices were lower during the 2nd night compared with the 1st night (eg, mean RR intervals, P = .03). Compared with the 2nd night, vagal-related HRV indices were significantly higher during the 3rd night. Variables were not different between the 1st and 3rd nights; however, we noted a tendency (adjusted effect size, aES) for an increased normalized high-frequency component (P = .06 and aES = 0.70) and a tendency toward a decreased low-frequency component (P = .06 and aES = 0.74).
Results confirm the strong influence of exercise intensity on short- and long-term post exercise heart rate variability recovery and might help explain the high efficiency of supramaximal training for enhancing indices of cardiorespiratory fitness.
Tyler T. Truxton and Kevin C. Miller
Exertional heat stroke (EHS) is a medical emergency which, if left untreated, can result in death. The standard of care for EHS patients includes confirmation of hyperthermia via rectal temperature (Trec) and then immediate cold-water immersion (CWI). While CWI is the fastest way to reduce Trec, it may be difficult to lower and maintain water bath temperature in the recommended ranges (1.7°C–15°C [35°F–59°F]) because of limited access to ice and/or the bath being exposed to high ambient temperatures for long periods of time. Determining if Trec cooling rates are acceptable (ie, >0.08°C/min) when significantly hyperthermic humans are immersed in temperate water (ie, ≥20°C [68°F]) has applications for how EHS patients are treated in the field.
Are Trec cooling rates acceptable (≥0.08°C/min) when significantly hyperthermic humans are immersed in temperate water?
Summary of Findings:
Trec cooling rates of hyperthermic humans immersed in temperate water (≥20°C [68°F]) ranged from 0.06°C/min to 0.19°C/min. The average Trec cooling rate for all examined studies was 0.11±0.06°C/min.
Clinical Bottom Line:
Temperature water immersion (TWI) provides acceptable (ie, >0.08°C/min) Trec cooling rates for hyperthermic humans post-exercise. However, CWI cooling rates are higher and should be used if feasible (eg, access to ice, shaded treatment areas).
Strength of Recommendation:
The majority of evidence (eg, Level 2 studies with PEDro scores ≥5) suggests TWI provides acceptable, though not ideal, Trec cooling. If possible, CWI should be used instead of TWI in EHS scenarios.
Nidia Rodriguez-Sanchez and Stuart D.R. Galloway
Dual energy x-ray absorptiometry (DXA) is a popular tool to determine body composition (BC) in athletes, and is used for analysis of fat-free soft tissue mass (FFST) or fat mass (FM) gain/loss in response to exercise or nutritional interventions. The aim of the current study was to assess the effect of exercise-heat stress induced hypohydration (HYP, >2% of body mass (BM) loss) vs. maintenance of euhydration (EUH) on DXA estimates of BC, sum of skinfolds (SF), and impedance (IMP) measurements in athletes. Competitive athletes (23 males and 15 females) recorded morning nude BM for 7 days before the first main trial. Measurements on the first trial day were conducted in a EUH condition, and again after exercise-heat stress induced HYP. On the second trial day, fluid and electrolyte losses were replaced during exercise using a sports drink. A reduction in total BM (1.6 ± 0.4 kg; 2.3 ± 0.4% HYP) and total FFST (1.3 ± 0.4 kg), mainly from trunk (1.1 ± 0.5 kg), was observed using DXA when participants were HYP, reflecting the sweat loss. Estimated fat percent increased (0.3 ± 0.3%), however, total FM did not change (0.1 ± 0.2 kg). SF and IMP declined with HYP (losses of 1.5 ± 2.9% and 1.6 ± 3% respectively) suggesting FM loss. When EUH was maintained there were no significant changes in BM, DXA estimates, or SF values pre to post exercise, but IMP still declined. We conclude that use of DXA for FFST assessment in athletes must ensure a EUH state, particularly when considering changes associated with nutritional or exercise interventions.
Dawn M. Maffucci and Robert G. McMurray
The purpose of this study was to compare the effect a 6-hr versus 3-hr prefeeding regimen on exercise performance. The subjects were 8 active women (21.4 ± 0.9 years, 60.4±2.4 kg, 19.9 ± 1.3% body fat. and 165.6±2.1 cm). All women completed 2 exercise trials (separated by 3—6d) on a treadmill where they ran at moderate intensity for 30 min with 30-s sprints at 5-min intervals, followed directly by increasing incrementally the grade until volitional fatigue was achieved. The exercise trials were performed 3 hr and 6 hr after consuming 40 ± 3 kJ/kg meal. Time to exhaustion was 0.75 min shorter (p = .0001) for the 6-H trials compared to the 3-H trials. There were no significant differences in submaximal or peak oxygen uptake, heart rate, or rating of perceived exertion (p > .05). The 6-H trials compared to the 3-H trials resulted in .05 lower RERs (p = .0002), and a 2 mmol lower blood lactate at exhaustion (p = .012). Blood glucose levels and cortisol responses to exercise were similar between trials (p > .05). However, both resting and post exercise insulin levels were lower during 6-H trials. It was concluded that performance of moderate- to high-intensity exercise lasting 35—40 min is improved by consuming a moderately-high carbohydrate. low fat, low protein meal 3-hr before exercise compared to a similar meal consumed 6 hr prior to exercise. Thus, athletes should not skip meals before competition or training sessions.
Kevin D. Tipton
Adaptations to exercise training are determined by the response of metabolic and molecular mechanisms that determine changes in proteins. The type, intensity, and duration of exercise, as well as nutrition, determine these responses. The importance of protein, in the form of intact proteins, hydrolysates, or free amino acids, for exercise adaptations is widely recognized. Exercise along with protein intake results in accumulation of proteins that influence training adaptations. The total amount of protein necessary to optimize adaptations is less important than the type of protein, timing of protein intake, and the other nutrients ingested concurrently with the protein. Acute metabolic studies offer an important tool to study the responses of protein balance to various exercise and nutritional interventions. Recent studies suggest that ingestion of free amino acids plus carbohydrates before exercise results in a superior anabolic response to exercise than if ingested after exercise. However, the difference between pre- and post exercise ingestion of intact proteins is not apparent. Thus, the anabolic response to exercise plus protein ingestion seems to be determined by the interaction of timing of nutrient intake in relation to exercise and the nutrients ingested. More research is necessary to delineate the optimal combination of nutrients and timing for various types of training adaptations. Protein and amino acid intake have long been deemed important for athletes and exercising individuals. Olympic athletes, from the legendary Milo to many in the 1936 Berlin games, reportedly consumed large amounts of protein. Modern athletes may consume slightly less than these historical figures, yet protein is deemed extremely important by most. Protein is important as a source of amino acids for recovery from exercise and repair of damaged tissues, as well as for adaptations to exercise training, such as muscle hypertrophy and mitochondrial biogenesis.