The Impact of a Short-Term Ketogenic Low-Carbohydrate High-Fat Diet on Biomarkers of Intestinal Epithelial Integrity and Gastrointestinal Symptoms.

Endurance exercise can disturb intestinal epithelial integrity, leading to increased systemic indicators of cell injury, hyperpermeability, and pathogenic translocation. However, the interaction between exercise, diet, and gastrointestinal disturbance still warrants exploration. This study examined whether a 6-day dietary intervention influenced perturbations to intestinal epithelial disruption in response to a 25-km race walk. Twenty-eight male race walkers adhered to a high carbohydrate (CHO)/energy diet (65% CHO, energy availability = 40 kcal·kg FFM-1·day-1) for 6 days prior to a Baseline 25-km race walk. Athletes were then split into three subgroups: high CHO/energy diet (n = 10); low-CHO, high-fat diet (LCHF: n = 8; <50 g/day CHO, energy availability = 40 kcal·kg FFM-1·day-1); and low energy availability (n = 10; 65% CHO, energy availability = 15 kcal·kg FFM-1·day-1) for a further 6-day dietary intervention period prior to a second 25-km race walk (Adaptation). During both trials, venous blood was collected pre-, post-, and 1 hr postexercise and analyzed for markers of intestinal epithelial disruption. Intestinal fatty acid-binding protein concentration was significantly higher (twofold increase) in response to exercise during Adaptation compared to Baseline in the LCHF group (p = .001). Similar findings were observed for soluble CD14 (p < .001) and lipopolysaccharide-binding protein (p = .003), where postexercise concentrations were higher (53% and 36%, respectively) during Adaptation than Baseline in LCHF. No differences in high CHO/energy diet or low energy availability were apparent for any blood markers assessed (p > .05). A short-term LCHF diet increased intestinal epithelial cell injury in response to a 25-km race walk. No effect of low energy availability on gastrointestinal injury or symptoms was observed.

Adaptation to a low carbohydrate high fat diet is rapid but impairs endurance exercise metabolism and performance despite enhanced glycogen availability.

KEY POINTS: Brief (5-6 days) adaptation to a low carbohydrate high fat diet in elite athletes increased exercise fat oxidation to rates previously observed with medium (3-4 weeks) or chronic (>12 months) adherence to this diet, with metabolic changes being washed out in a similar time frame. Increased fat utilisation during exercise was associated with a 5-8% increase in oxygen cost at speeds related to Olympic Programme races. Acute restoration of endogenous carbohydrate (CHO) availability (24 h high CHO diet, pre-race CHO) only partially restored substrate utilisation during a race warm-up. Fat oxidation continued to be elevated above baseline values although it was lower than achieved by 5-6 days' keto adaptation; CHO oxidation only reached 61% and 78% of values previously seen at exercise intensities related to race events. Acute restoration of CHO availability failed to overturn the impairment of high-intensity endurance performance previously associated with low carbohydrate high fat adaptation, potentially due to the blunted capacity for CHO oxidation. ABSTRACT: We investigated substrate utilisation during exercise after brief (5-6 days) adaptation to a ketogenic low-carbohydrate (CHO), high-fat (LCHF) diet and similar washout period. Thirteen world-class male race walkers completed economy testing, 25 km training and a 10,000 m race (Baseline), with high CHO availability (HCHO), repeating this (Adaptation) after 5-6 days' LCHF (n = 7; CHO: <50 g day-1 , protein: 2.2 g kg-1 day-1 ; 80% fat) or HCHO (n = 6; CHO: 9.7 g kg-1 day-1 ; protein: 2.2 g kg-1 day-1 ) diet. An Adaptation race was undertaken after 24 h HCHO and pre-race CHO (2 g kg-1 ) diet, identical to the Baseline race. Substantial (>200%) increases in exercise fat oxidation occurred in the LCHF Adaptation economy and 25 km tests, reaching mean rates of ∼1.43 g min-1 . However, relative V̇O2 (ml min-1  kg-1 ) was higher (P < 0.0001), by ∼8% and 5% at speeds related to 50 km and 20 km events. During Adaptation race warm-up in the LCHF group, rates of fat and CHO oxidation at these speeds were decreased and increased, respectively (P < 0.001), compared with the previous day, but were not restored to Baseline values. Performance changes differed between groups (P = 0.009), with all HCHO athletes improving in the Adaptation race (5.7 (5.6)%), while 6/7 LCHF athletes were slower (2.2 (3.4)%). Substrate utilisation returned to Baseline values after 5-6 days of HCHO diet. In summary, robust changes in exercise substrate use occurred in 5-6 days of extreme changes in CHO intake. However, adaptation to a LCHF diet plus acute restoration of endogenous CHO availability failed to restore high-intensity endurance performance, with CHO oxidation rates remaining blunted.

Sustained Exposure to High Carbohydrate Availability Does Not Influence Iron-Regulatory Responses in Elite Endurance Athletes.

This study implemented a 2-week high carbohydrate (CHO) diet intended to maximize CHO oxidation rates and examined the iron-regulatory response to a 26-km race walking effort. Twenty international-level, male race walkers were assigned to either a novel high CHO diet (MAX = 10 g/kg body mass CHO daily) inclusive of gut-training strategies, or a moderate CHO control diet (CON = 6 g/kg body mass CHO daily) for a 2-week training period. The athletes completed a 26-km race walking test protocol before and after the dietary intervention. Venous blood samples were collected pre-, post-, and 3 hr postexercise and measured for serum ferritin, interleukin-6, and hepcidin-25 concentrations. Similar decreases in serum ferritin (17-23%) occurred postintervention in MAX and CON. At the baseline, CON had a greater postexercise increase in interleukin-6 levels after 26 km of walking (20.1-fold, 95% CI [9.2, 35.7]) compared with MAX (10.2-fold, 95% CI [3.7, 18.7]). A similar finding was evident for hepcidin levels 3 hr postexercise (CON = 10.8-fold, 95% CI [4.8, 21.2]; MAX = 8.8-fold, 95% CI [3.9, 16.4]). Postintervention, there were no substantial differences in the interleukin-6 response (CON = 13.6-fold, 95% CI [9.2, 20.5]; MAX = 11.2-fold, 95% CI [6.5, 21.3]) or hepcidin levels (CON = 7.1-fold, 95% CI [2.1, 15.4]; MAX = 6.3-fold, 95% CI [1.8, 14.6]) between the dietary groups. Higher resting serum ferritin (p = .004) and hotter trial ambient temperatures (p = .014) were associated with greater hepcidin levels 3 hr postexercise. Very high CHO diets employed by endurance athletes to increase CHO oxidation have little impact on iron regulation in elite athletes. It appears that variations in serum ferritin concentration and ambient temperature, rather than dietary CHO, are associated with increased hepcidin concentrations 3 hr postexercise.

The impact of chronic carbohydrate manipulation on mucosal immunity in elite endurance athletes.

Carbohydrate (CHO) availability could alter mucosal immune responses to exercise. This study compared the effect of three dietary approaches to CHO availability on resting and post-exercise s-IgA levels. Elite race walkers (n = 26) adhered to a high CHO diet (HCHO), periodised CHO availability (PCHO) or a low CHO/high fat diet (LCHF) for 3 weeks while completing an intensified training program. HCHO and PCHO groups consumed 8.0-8.5 g.kg-1 CHO daily, with timing of ingestion manipulated to alter CHO availability around key training sessions. The LCHF diet comprised 80% fat and restricted CHO to < 50 g.day-1. A race walk test protocol (19 km females, 25 km males) was completed at baseline, after adaptation, and following CHO restoration. On each occasion, saliva samples were obtained pre- and post-exercise to quantify s-IgA levels. Resting s-IgA secretion rate substantially increased ~ two-fold post-intervention in all groups (HCHO: 2.2 ± 2.2, PCHO: 2.8 ± 3.2, LCHF: 1.6 ± 1.6; fold-change± 95% confidence limits), however, no substantial differences between dietary treatments were evident. Post-exercise, substantial 20-130% increases in s-IgA concentration and 43-64% reductions in flow rate occurred in all dietary treatments, with trivial differences evident between groups. It appears that high volume training overrides any effect of manipulating CHO availability on mucosal immunity in elite athletes.

Training Quantification and Periodization during Live High Train High at 2100 M in Elite Runners: An Observational Cohort Case Study.

The questionable efficacy of Live High Train High altitude training (LHTH) is compounded by minimal training quantification in many studies. We sought to quantify the training load (TL) periodization in a cohort of elite runners completing LHTH immediately prior to competition. Eight elite runners (6 males, 2 females) with a V̇O2peak of 70 ± 4 mL·kg-1·min-1 were monitored during 4 weeks of sea-level training, then 3-4 weeks LHTH in preparation for sea-level races following descent to sea-level. TL was calculated using the session rating of perceived exertion (sRPE) method, whereby duration of each training session was multiplied by its sRPE, then summated to give weekly TL. Performance was assessed in competition at sea-level before, and within 8 days of completing LHTH, with runners competing in 800 m (n = 1, 1500 m/mile (n = 6) and half-marathon (n = 1). Haemoglobin mass (Hbmass) via CO rebreathing and running economy (RE) were assessed pre and post LHTH. Weekly TL during the first 2 weeks at altitude increased by 75% from preceding sea-level training (p = 0.0004, d = 1.65). During the final week at altitude, TL was reduced by 43% compared to the previous weeks (p = 0.002; d = 1.85). The ratio of weekly TL to weekly training volume increased by 17% at altitude (p = 0.009; d = 0.91) compared to prior sea-level training. Hbmass increased by 5% from pre- to post-LHTH (p = 0.006, d = 0.20). Seven athletes achieved lifetime personal best performances within 8 days post-altitude (overall improvement 1.1 ± 0.7%, p = 0.2, d = 0.05). Specific periodization of training, including large increases in training load upon arrival to altitude (due to increased training volume and greater stress of training in hypoxia) and tapering, were observed during LHTH in elite runners prior to personal best performances. Periodization should be individualized and align with timing of competition post-altitude.

Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers.

KEY POINTS: Three weeks of intensified training and mild energy deficit in elite race walkers increases peak aerobic capacity independent of dietary support. Adaptation to a ketogenic low carbohydrate, high fat (LCHF) diet markedly increases rates of whole-body fat oxidation during exercise in race walkers over a range of exercise intensities. The increased rates of fat oxidation result in reduced economy (increased oxygen demand for a given speed) at velocities that translate to real-life race performance in elite race walkers. In contrast to training with diets providing chronic or periodised high carbohydrate availability, adaptation to an LCHF diet impairs performance in elite endurance athletes despite a significant improvement in peak aerobic capacity. ABSTRACT: We investigated the effects of adaptation to a ketogenic low carbohydrate (CHO), high fat diet (LCHF) during 3 weeks of intensified training on metabolism and performance of world-class endurance athletes. We controlled three isoenergetic diets in elite race walkers: high CHO availability (g kg-1  day-1 : 8.6 CHO, 2.1 protein, 1.2 fat) consumed before, during and after training (HCHO, n = 9); identical macronutrient intake, periodised within or between days to alternate between low and high CHO availability (PCHO, n = 10); LCHF (< 50 g day-1 CHO; 78% energy as fat; 2.1 g kg-1  day-1 protein; LCHF, n = 10). Post-intervention, V̇O2 peak during race walking increased in all groups (P < 0.001, 90% CI: 2.55, 5.20%). LCHF was associated with markedly increased rates of whole-body fat oxidation, attaining peak rates of 1.57 ± 0.32 g min-1 during 2 h of walking at ∼80% V̇O2 peak . However, LCHF also increased the oxygen (O2 ) cost of race walking at velocities relevant to real-life race performance: O2 uptake (expressed as a percentage of new V̇O2 peak ) at a speed approximating 20 km race pace was reduced in HCHO and PCHO (90% CI: -7.047, -2.55 and -5.18, -0.86, respectively), but was maintained at pre-intervention levels in LCHF. HCHO and PCHO groups improved times for 10 km race walk: 6.6% (90% CI: 4.1, 9.1%) and 5.3% (3.4, 7.2%), with no improvement (-1.6% (-8.5, 5.3%)) for the LCHF group. In contrast to training with diets providing chronic or periodised high-CHO availability, and despite a significant improvement in V̇O2 peak , adaptation to the topical LCHF diet negated performance benefits in elite endurance athletes, in part due to reduced exercise economy.

Factors influencing the post-exercise hepcidin-25 response in elite athletes.

PURPOSE: The extent to which hepcidin regulation after acute bouts of exercise is influenced by baseline (resting) concentrations of key iron parameters remains uncertain. This investigation explored the influence of selected iron parameters and 25-km race walk time on 3-h post-exercise hepcidin-25 levels in international-level race walkers. METHODS: Twenty-four male race walkers completed a graded exercise test and a 25-km race-walk trial. Throughout the 25-km race-walk, venous blood samples were collected pre-exercise, immediately post-exercise, and at 3-h post-exercise. Blood was analysed for serum ferritin, serum iron, Interleukin-6 (IL-6), and hepcidin-25 concentration. RESULTS: IL-6 and hepcidin-25 increased (7.6- and 7.5-fold, respectively) in response to the 25-km race-walk trial (both p < 0.01). Significant individual relationships were evident between 3-h post-exercise hepcidin-25, baseline serum ferritin and serum iron (r > 0.62; p < 0.05). Multiple regression analysis showed that these two iron parameters, in addition to post-exercise IL-6 concentration and 25-km race-walk time, accounted for ~77% of the variance in 3-h post-exercise hepcidin-25 (p < 0.01). A median split by the cohort's baseline serum ferritin concentration (LOW: 58.0 vs. HIGH: 101.8 µg/L; p < 0.01) showed a significant between group difference in the 3-h post-exercise hepcidin-25 (LOW: 6.0 ± 3.6 vs. 11.3 ± 5.4 nM; p = 0.01), despite no differences in baseline serum iron, post-exercise IL-6, or 25-km race-walk time (all p > 0.05). CONCLUSION: Despite exercise activating numerous hepcidin regulators, baseline iron status appears to play a dominant role in the regulation of hepcidin-25 in elite-level athletes subsequent to endurance exercise.

Four Weeks of Classical Altitude Training Increases Resting Metabolic Rate in Highly Trained Middle-Distance Runners.

High altitude exposure can increase resting metabolic rate (RMR) and induce weight loss in obese populations, but there is a lack of research regarding RMR in athletes at moderate elevations common to endurance training camps. The present study aimed to determine whether 4 weeks of classical altitude training affects RMR in middle-distance runners. Ten highly trained athletes were recruited for 4 weeks of endurance training undertaking identical programs at either 2200m in Flagstaff, Arizona (ALT, n = 5) or 600m in Canberra, Australia (CON, n = 5). RMR, anthropometry, energy intake, and hemoglobin mass (Hbmass) were assessed pre- and posttraining. Weekly run distance during the training block was: ALT 96.8 ± 18.3km; CON 103.1 ± 5.6km. A significant interaction for Time*Group was observed for absolute (kJ.day-1) (F-statistic, p-value: F(1,8)=13.890, p = .01) and relative RMR (F(1,8)=653.453, p = .003) POST-training. No significant changes in anthropometry were observed in either group. Energy intake was unchanged (mean ± SD of difference, ALT: 195 ± 3921kJ, p = .25; CON: 836 ± 7535kJ, p = .75). A significant main effect for time was demonstrated for total Hbmass (g) (F(1,8)=13.380, p = .01), but no significant interactions were observed for either variable [Total Hbmass (g): F(1,8)=1.706, p = .23; Relative Hbmass (g.kg-1): F(1,8)=0.609, p = .46]. These novel findings have important practical application to endurance athletes routinely training at moderate altitude, and those seeking to optimize energy management without compromising training adaptation. Altitude exposure may increase RMR and enhance training adaptation,. During training camps at moderate altitude, an increased energy intake is likely required to support an increased RMR and provide sufficient energy for training and performance.

Adherence to a Ketogenic Low-Carbohydrate, High-Fat Diet Is Associated With Diminished Training Quality in Elite Racewalkers.

PURPOSE: To examine the effects of a high-carbohydrate diet (HCHO), periodized-carbohydrate (CHO) diet (PCHO), and ketogenic low-CHO high-fat diet (LCHF) on training capacity. METHODS: Elite male racewalkers completed 3 weeks of periodic training while adhering to their dietary intervention. Twenty-nine data sets were collected from 21 athletes. Each week, 6 mandatory training sessions were completed, with additional sessions performed at the athlete's discretion. Mandatory sessions included an interval session (10 × 1-km efforts on a 6-min cycle), tempo session (14 km with a 450-m elevation gain), 2 long walks (25-40 km), and 2 easy walks (8-12 km) where "sleep-low" and "train-low" dietary strategies were employed for PCHO. Racewalking speed, heart rate, rating of perceived exhaustion, and blood metabolites were collected around key sessions. RESULTS: LCHF covered less total distance than HCHO and PCHO (P < .001); however, no differences in training load between groups were evident (P = .285). During the interval sessions, walking speed was slower in LCHF (P = .001), equating to a 2.8% and 5.6% faster speed in HCHO and PCHO, respectively. LCHF was also 3.2% slower in completing the tempo session than HCHO and PCHO (P = .001). Heart rate was higher (P = .002) and lactate concentrations were lower (P < .001) in LCHF compared to other groups, despite slower walking speeds during the interval session. No between-groups differences in rating of perceived exhaustion were evident (P = .077). CONCLUSION: Athletes adhering to an LCHF diet showed impaired training capacity relative to their high-CHO-supported counterparts, completing lower training volumes at slower speeds, with higher heart rates.

Short Severe Energy Restriction with Refueling Reduces Body Mass without Altering Training-Associated Performance Improvement.

PURPOSE: We investigated short-term (9 d) exposure to low energy availability (LEA) in elite endurance athletes during a block of intensified training on self-reported well-being, body composition, and performance. METHODS: Twenty-three highly trained race walkers undertook an ~3-wk research-embedded training camp during which they undertook baseline testing and 6 d of high energy/carbohydrate (HCHO) availability (40 kcal·kg FFM -1 ·d -1 ) before being allocated to 9 d continuation of this diet ( n = 10 M, 2 F) or a significant decrease in energy availability to 15 kcal·kg FFM -1 ·d -1 (LEA: n = 10 M, 1 F). A real-world 10,000-m race walking event was undertaken before (baseline) and after (adaptation) these phases, with races being preceded by standardized carbohydrate fueling (8 g·kg body mass [BM] -1 for 24 h and 2 g·kg BM -1 prerace meal). RESULTS: Dual-energy x-ray absorptiometry-assessed body composition showed BM loss (2.0 kg, P < 0.001), primarily due to a 1.6-kg fat mass reduction ( P < 0.001) in LEA, with smaller losses (BM = 0.9 kg, P = 0.008; fat mass = 0.9 kg, P < 0.001) in HCHO. The 76-item Recovery-Stress Questionnaire for Athletes, undertaken at the end of each dietary phase, showed significant diet-trial effects for overall stress ( P = 0.021), overall recovery ( P = 0.024), sport-specific stress ( P = 0.003), and sport-specific recovery ( P = 0.012). However, improvements in race performance were similar: 4.5% ± 4.1% and 3.5% ± 1.8% for HCHO and LEA, respectively ( P < 0.001). The relationship between changes in performance and prerace BM was not significant ( r = -0.08 [-0.49 to 0.35], P = 0.717). CONCLUSIONS: A series of strategically timed but brief phases of substantially restricted energy availability might achieve ideal race weight as part of a long-term periodization of physique by high-performance athletes, but the relationship between BM, training quality, and performance in weight-dependent endurance sports is complicated.

Effect of Acetaminophen on Endurance Cycling Performance in Trained Triathletes in Hot and Humid Conditions.

PURPOSE: The effect of acetaminophen (ACT, also known as paracetamol) on endurance performance in hot and humid conditions has been shown previously in recreationally active populations. The aim of this study was to determine the effect of ACT on physiological and perceptual variables during steady-state and time-trial cycling performance of trained triathletes in hot and humid conditions. METHODS: In a randomized, double-blind crossover design, 11 triathletes completed ∼60 minutes steady-state cycling at 63% peak power output followed by a time trial (7 kJ·kg body mass-1, ∼30 min) in hot and humid conditions (∼30°C, ∼69% relative humidity) 60 minutes after consuming either 20 mg·kg body mass-1 ACT or a color-matched placebo. Time-trial completion time, gastrointestinal temperature, skin temperature, thermal sensation, thermal comfort, rating of perceived exertion, and fluid balance were recorded throughout each session. RESULTS: There was no difference in performance in the ACT trial compared with placebo (P = .086, d = 0.57), nor were there differences in gastrointestinal and skin temperature, thermal sensation and comfort, or fluid balance between trials. CONCLUSION: In conclusion, there was no effect of ACT (20 mg·kg body mass-1) ingestion on physiology, perception, and performance of trained triathletes in hot and humid conditions, and existing precooling and percooling strategies appear to be more appropriate for endurance cycling performance in the heat.

Six Days of Low Carbohydrate, Not Energy Availability, Alters the Iron and Immune Response to Exercise in Elite Athletes.

PURPOSE: To quantify the effects of a short-term (6-d) low carbohydrate (CHO) high fat (LCHF), and low energy availability (LEA) diet on immune, inflammatory, and iron-regulatory responses to exercise in endurance athletes. METHODS: Twenty-eight elite male race walkers completed two 6-d diet/training phases. During phase 1 (Baseline), all athletes consumed a high CHO/energy availability (CON) diet (65% CHO and ~40 kcal·kg-1 fat-free mass (FFM)·d-1). In phase 2 (Adaptation), athletes were allocated to either a CON (n = 10), LCHF (n = 8; <50 g·d-1 CHO and ~40 kcal·kg-1·FFM-1·d-1), or LEA diet (n = 10; 60% CHO and 15 kcal·kg-1·FFM-1·d-1). At the end of each phase, athletes completed a 25-km race walk protocol at ~75% V˙O2max. On each occasion, venous blood was collected before and after exercise for interleukin-6, hepcidin, cortisol, and glucose concentrations, as well as white blood cell counts. RESULTS: The LCHF athletes displayed a greater IL-6 (P = 0.019) and hepcidin (P = 0.011) response to exercise after Adaptation, compared with Baseline. Similarly, postexercise increases in total white blood cell counts (P = 0.026) and cortisol levels (P < 0.001) were larger compared with Baseline after LCHF Adaptation. Decreases in blood glucose concentrations were evident postexercise during Adaptation in LCHF (P = 0.049), whereas no change occurred in CON or LEA (P > 0.05). No differences between CON and LEA were evident for any of the measured biological markers (all P > 0.05). CONCLUSIONS: Short-term adherence to a LCHF diet elicited small yet unfavorable iron, immune, and stress responses to exercise. In contrast, no substantial alterations to athlete health were observed when athletes restricted energy availability compared with athletes with adequate energy availability. Therefore, short-term restriction of CHO, rather than energy, may have greater negative impacts on athlete health.

Short-Term Very High Carbohydrate Diet and Gut-Training Have Minor Effects on Gastrointestinal Status and Performance in Highly Trained Endurance Athletes.

We implemented a multi-pronged strategy (MAX) involving chronic (2 weeks high carbohydrate [CHO] diet + gut-training) and acute (CHO loading + 90 g·h−1 CHO during exercise) strategies to promote endogenous and exogenous CHO availability, compared with strategies reflecting lower ranges of current guidelines (CON) in two groups of athletes. Nineteen elite male race walkers (MAX: 9; CON:10) undertook a 26 km race-walking session before and after the respective interventions to investigate gastrointestinal function (absorption capacity), integrity (epithelial injury), and symptoms (GIS). We observed considerable individual variability in responses, resulting in a statistically significant (p < 0.001) yet likely clinically insignificant increase (Δ 736 pg·mL−1) in I-FABP after exercise across all trials, with no significant differences in breath H2 across exercise (p = 0.970). MAX was associated with increased GIS in the second half of the exercise, especially in upper GIS (p < 0.01). Eighteen highly trained male and female distance runners (MAX: 10; CON: 8) then completed a 35 km run (28 km steady-state + 7 km time-trial) supported by either a slightly modified MAX or CON strategy. Inter-individual variability was observed, without major differences in epithelial cell intestinal fatty acid binding protein (I-FABP) or GIS, due to exercise, trial, or group, despite the 3-fold increase in exercise CHO intake in MAX post-intervention. The tight-junction (claudin-3) response decreased in both groups from pre- to post-intervention. Groups achieved a similar performance improvement from pre- to post-intervention (CON = 39 s [95 CI 15−63 s]; MAX = 36 s [13−59 s]; p = 0.002). Although this suggests that further increases in CHO availability above current guidelines do not confer additional advantages, limitations in our study execution (e.g., confounding loss of BM in several individuals despite a live-in training camp environment and significant increases in aerobic capacity due to intensified training) may have masked small differences. Therefore, athletes should meet the minimum CHO guidelines for training and competition goals, noting that, with practice, increased CHO intake can be tolerated, and may contribute to performance outcomes.

Acute Ketogenic Diet and Ketone Ester Supplementation Impairs Race Walk Performance.

PURPOSE: This study aimed to determine if LCHF and ketone ester (KE) supplementation can synergistically alter exercise metabolism and improve performance. METHODS: Elite race walkers (n = 18, 15 males and 3 females; V˙O2peak, 62 ± 6 mL·min-1·kg-1) undertook a four-stage exercise economy test and real-life 10,000-m race before and after a 5-d isoenergetic high-CHO (HCHO, ~60%-65% fat; CHO, 20% fat; n = 9) or LCHF (75%-80% fat, <50 g·d-1 CHO, n = 9) diet. The LCHF group performed additional economy tests before and after diet after supplementation with 573 mg·kg-1 body mass KE (HVMN; HVMN Inc., San Francisco, CA), which was also consumed for race 2. RESULTS: The oxygen cost of exercise (relative V˙O2, mL·min-1·kg-1) increased across all four stages after LCHF (P < 0.005). This occurred in association with increased fat oxidation rates, with a reciprocal decrease in CHO oxidation (P < 0.001). Substrate utilization in the HCHO group remained unaltered. The consumption of KE before the LCHF diet increased circulating KB (P < 0.05), peaking at 3.2 ± 0.6 mM, but did not alter V˙O2 or RER. LCHF diet elevated resting circulating KB (0.3 ± 0.1 vs 0.1 ± 0.1 mM), but concentrations after supplementation did not differ from the earlier ketone trial. Critically, race performance was impaired by ~6% (P < 0.0001) relative to baseline in the LCHF group but was unaltered in HCHO. CONCLUSION: Despite elevating endogenous KB production, an LCHF diet does not augment the metabolic responses to KE supplementation and negatively affects race performance.

Neither Beetroot Juice Supplementation nor Increased Carbohydrate Oxidation Enhance Economy of Prolonged Exercise in Elite Race Walkers.

Given the importance of exercise economy to endurance performance, we implemented two strategies purported to reduce the oxygen cost of exercise within a 4 week training camp in 21 elite male race walkers. Fourteen athletes undertook a crossover investigation with beetroot juice (BRJ) or placebo (PLA) [2 d preload, 2 h pre-exercise + 35 min during exercise] during a 26 km race walking at speeds simulating competitive events. Separately, 19 athletes undertook a parallel group investigation of a multi-pronged strategy (MAX; n = 9) involving chronic (2 w high carbohydrate [CHO] diet + gut training) and acute (CHO loading + 90 g/h CHO during exercise) strategies to promote endogenous and exogenous CHO availability, compared with strategies reflecting lower ranges of current guidelines (CON; n = 10). There were no differences between BRJ and PLA trials for rates of CHO (p = 0.203) or fat (p = 0.818) oxidation or oxygen consumption (p = 0.090). Compared with CON, MAX was associated with higher rates of CHO oxidation during exercise, with increased exogenous CHO use (CON; peak = ~0.45 g/min; MAX: peak = ~1.45 g/min, p < 0.001). High rates of exogenous CHO use were achieved prior to gut training, without further improvement, suggesting that elite athletes already optimise intestinal CHO absorption via habitual practices. No differences in exercise economy were detected despite small differences in substrate use. Future studies should investigate the impact of these strategies on sub-elite athletes' economy as well as the performance effects in elite groups.

A Contemporary Variable-Power Cycling Protocol to Discriminate Race-Specific Performance Ability.

PURPOSE: Traditional physiological testing and monitoring tools have restricted our ability to capture parameters that best relate to cycling performance under variable-intensity race demands. This study examined the validity of a 1-h variable cycling test (VCT) to discriminate between different-performance-level cyclists. METHODS: Ten male national- and 13 club-level cyclists (body mass, 67 [9] and 79 [6] kg; peak power output, 359 [43] and 362 [21] W, respectively) completed a VO2max test and two 1-h VCT protocols on 3 separate occasions. The VCT consisted of 10 × 6-min segments containing prescribed (3.5 W·kg-1) and open-ended phases. The open-ended phases consisted of 4 × 30-40 s of "recovery," 3 × 10 s at "hard" intensity, and 3 × 6-s "sprint" with a final 10-s "all-out" effort. RESULTS: Power output for the 6- and 10-s phases was moderately higher for the national- compared with club-level cyclists (mean [SD] 10.4 [2.0] vs 8.6 [1.6] W·kg-1, effect size; ±90% confidence limits = -0.87; ±0.65 and mean [SD] 7.5 [0.7] vs 6.2 [1.0] W·kg-1, effect size; ±90% confidence limits = -1.24; ±0.66, respectively). Power output for the final 10-s "all-out" sprint was 15.4 (1.5) for the national- versus 13.2 (1.9) W·kg-1 for club-level cyclists. CONCLUSION: The 1-h VCT can successfully differentiate repeat high-intensity effort performance between higher-caliber cyclists and their lower-performing counterparts.

Altitude exposure as a training & iron overload management strategy post leukemia.

OBJECTIVES: To examine iron stores, hemoglobin mass, and performance before, during and after intermittent altitude exposure in a professional male rugby player experiencing iron overload following blood transfusions for treatment for acute myeloid leukemia. DESIGN: Longitudinal, repeated measures, single case-study. METHODS: The player was followed prior to (control), and during (study), an in-season block of altitude training. During the control period two venesections were performed for a total of 750mL of blood removal. Internal and external training load, match statistics, blood volume, plasma volume, haemoglobin mass, serum ferritin and reticulocyte count were monitored throughout. RESULTS: During the control period serum ferritin declined following the two venesections (∼51%) as did haemoglobin mass (∼2%), reticulocyte count remained stable. During the study period serum ferritin further declined (∼30%), however haemoglobin mass and reticulocyte count increased (∼4% and ∼14% respectively). Internal training load for the control and study period was similar, however external training load was lower in the study period. Match statistics were not favourable for the player during the control period, however they improved during the study period. CONCLUSIONS: This case supports the theory that individuals with elevated iron availability are well placed to achieve increases in haemoglobin mass. Furthermore, although therapeutic venesections may still be required to manage iron overload, the addition of altitude exposure may be a method to assist in reducing total body iron by means of mobilising available (excessive) iron to incorporate into haemoglobin. Altitude exposure did not hinder the players' performance. Further research is encouraged.

Crisis of confidence averted: Impairment of exercise economy and performance in elite race walkers by ketogenic low carbohydrate, high fat (LCHF) diet is reproducible.

INTRODUCTION: We repeated our study of intensified training on a ketogenic low-carbohydrate (CHO), high-fat diet (LCHF) in world-class endurance athletes, with further investigation of a "carryover" effect on performance after restoring CHO availability in comparison to high or periodised CHO diets. METHODS: After Baseline testing (10,000 m IAAF-sanctioned race, aerobic capacity and submaximal walking economy) elite male and female race walkers undertook 25 d supervised training and repeat testing (Adapt) on energy-matched diets: High CHO availability (8.6 g∙kg-1∙d-1 CHO, 2.1 g∙kg-1∙d-1 protein; 1.2 g∙kg-1∙d-1 fat) including CHO before/during/after workouts (HCHO, n = 8): similar macronutrient intake periodised within/between days to manipulate low and high CHO availability at various workouts (PCHO, n = 8); and LCHF (<50 g∙d-1 CHO; 78% energy as fat; 2.1 g∙kg-1∙d-1 protein; n = 10). After Adapt, all athletes resumed HCHO for 2.5 wk before a cohort (n = 19) completed a 20 km race. RESULTS: All groups increased VO2peak (ml∙kg-1∙min-1) at Adapt (p = 0.02, 95%CI: [0.35-2.74]). LCHF markedly increased whole-body fat oxidation (from 0.6 g∙min-1 to 1.3 g∙min-1), but also the oxygen cost of walking at race-relevant velocities. Differences in 10,000 m performance were clear and meaningful: HCHO improved by 4.8% or 134 s (95% CI: [207 to 62 s]; p < 0.001), with a trend for a faster time (2.2%, 61 s [-18 to +144 s]; p = 0.09) in PCHO. LCHF were slower by 2.3%, -86 s ([-18 to -144 s]; p < 0.001), with no evidence of superior "rebound" performance over 20 km after 2.5 wk of HCHO restoration and taper. CONCLUSION: Our previous findings of impaired exercise economy and performance of sustained high-intensity race walking following keto-adaptation in elite competitors were repeated. Furthermore, there was no detectable benefit from undertaking an LCHF intervention as a periodised strategy before a 2.5-wk race preparation/taper with high CHO availability. TRIAL REGISTRATION: Australia New Zealand Clinical Trial Registry: ACTRN12619000794101.

Correction: Crisis of confidence averted: Impairment of exercise economy and performance in elite race walkers by ketogenic low carbohydrate, high fat (LCHF) diet is reproducible.

[This corrects the article DOI: 10.1371/journal.pone.0234027.].

Contemporary Periodization of Altitude Training for Elite Endurance Athletes: A Narrative Review.

Since the 1960s there has been an escalation in the purposeful utilization of altitude to enhance endurance athletic performance. This has been mirrored by a parallel intensification in research pursuits to elucidate hypoxia-induced adaptive mechanisms and substantiate optimal altitude protocols (e.g., hypoxic dose, duration, timing, and confounding factors such as training load periodization, health status, individual response, and nutritional considerations). The majority of the research and the field-based rationale for altitude has focused on hematological outcomes, where hypoxia causes an increased erythropoietic response resulting in augmented hemoglobin mass. Hypoxia-induced non-hematological adaptations, such as mitochondrial gene expression and enhanced muscle buffering capacity may also impact athletic performance, but research in elite endurance athletes is limited. However, despite significant scientific progress in our understanding of hypobaric hypoxia (natural altitude) and normobaric hypoxia (simulated altitude), elite endurance athletes and coaches still tend to be trailblazers at the coal face of cutting-edge altitude application to optimize individual performance, and they already implement novel altitude training interventions and progressive periodization and monitoring approaches. Published and field-based data strongly suggest that altitude training in elite endurance athletes should follow a long- and short-term periodized approach, integrating exercise training and recovery manipulation, performance peaking, adaptation monitoring, nutritional approaches, and the use of normobaric hypoxia in conjunction with terrestrial altitude. Future research should focus on the long-term effects of accumulated altitude training through repeated exposures, the interactions between altitude and other components of a periodized approach to elite athletic preparation, and the time course of non-hematological hypoxic adaptation and de-adaptation, and the potential differences in exercise-induced altitude adaptations between different modes of exercise.