Metabolic and ruck performance effects of a novel, light‐weight, energy‐dense ketogenic bar

Abstract Rucksack marches (‘rucks’) are strenuous, military‐relevant exercises that may benefit from pre‐event fuelling. The purpose of this investigation was to explore whether acute ingestion of carbohydrate‐ or lipid‐based nutritional bars before rucking can elicit unique advantages that augment exercise performance. Recreationally active and healthy males (n = 29) were randomized and counterbalanced to consume 1000 kcal derived from a novel, energy‐dense (percentage energy from carbohydrate/fat/protein: 5/83/12) ketogenic bar (KB), or isocaloric high‐carbohydrate bars (CB; 61/23/16) 3 h before a time‐to‐exhaustion (TTE) ruck. Conditions were separated by a 1‐week washout. The rucksack weight was standardized to 30% of bodyweight. Steady‐state treadmill pace was set at 3.2 km/h (0.89 m/s) and 14% grade. TTE was the primary outcome; respiratory exchange ratio (RER), capillary ketones (R‐β‐hydroxybutyrate), glucose and lactate, plus subjective thirst/hunger were the secondary outcomes. Mean TTE was similar between conditions (KB: 55 ± 25 vs. CB: 54 ± 22 min; P = 0.687). The RER and substrate oxidation rates revealed greater fat and carbohydrate oxidation after the KB and CB, respectively (all P < 0.0001). Capillary R‐βHB increased modestly after the KB ingestion (P < 0.0001). Neither bar influenced glycaemia. Lactate increased during the ruck independent of the condition (P < 0.0001). Thirst/fullness perceptions changed independent of the nutritional bar consumed. A novel KB nutritional bar produced equivalent TTE ruck results to the isocaloric CBs. The KB's energy density relative to CB (6.6 vs. 3.8 kcal/g) may provide a lightweight (–42% weight), pre‐event fuelling alternative that does not compromise ruck physical performance.


INTRODUCTION
Soldiers march with heavy rucksacks (rucksack marches; 'rucks') in training to simulate long-range infantry detachment.Rucks are energy intensive physical events that can expend 1000 kcal/h (Walsh et al., 2020), and can contribute significantly to the wide range of total daily energy expenditure observed in active soldiers (3000-7000 kcal/day) (Tassone & Baker, 2017).Energy expenditure monitored during field exercises increases non-linearly based on bodyweight, carry load, distance, speed and terrain conditions (Army, 2022;Looney et al., 2022;Margolis et al., 2014).Underfeeding for these events is common and is often associated with reduced performance (Jacobs et al., 1989), highlighting the need for operationalizing adequate pre-event fuelling.
Rations are portable and energy-dense food items that the military provides to sustain the soldier's nutritional requirements during long patrols or rucks (Hirsch et al., 2005;McClung et al., 2020).
However, ration components (main meal + discretionary items) are rarely consumed in their entirety by soldiers, thereby worsening their energy deficits in the field (Hirsch et al., 2005;Huang et al., 2014;Margolis et al., 2014).While exertion and field conditions, specifically environmental temperature, can involuntarily alter appetite and reduce energy intake, voluntary item removal can reduce exposure by up to 30% of total daily calories (approx.1000-1200 kcal), a detrimental choice for soldiers who are already prone to energetic deficits.(Ahmed et al., 2019).
A logical countermeasure to prevent performance deterioration is to include light and energy-dense discretionary items that are more widely accepted by soldiers (Hirsch et al., 2005;Huang et al., 2014;Institute of Medicine Committee on Military Nutrition, 1996).
Nutrition guidelines stipulate consuming ample carbohydrates (45-65% of total kilocalories) before exercise to elicit ergogenic benefits (American College of Sports et al., 2000;Army, 2022; Defense Logistics Agency, 2022), whereas dietary lipids and proteins have been less studied with respect to performance.In general, criticisms aimed at current field rations stem from containing too many simple carbohydrates (i.e., sugar) and inadequate protein; alternative formulations-with more complex carbohydrates and protein, and less sugar-have recently emerged as a feasible, nutrient-dense and energy-adequate option relative to NATO standards for military populations (Lenferna De La Motte et al., 2021).Given the rising interest in alternative nutrition research for the military (Karl et al., 2022;LaFountain et al., 2019), it remains to be determined how acute modifications in macronutrient quality and quantity influences military-relevant rucking performance.
Several studies have characterized the ∼60-65% maximal aerobic consumption ( VO 2 max ) range as the discrete interval where fatty acid (FA) oxidation peaks during submaximal exercise (Achten & Jeukendrup, 2003;Lambert et al., 1997).Rucking is characterized as a moderate-to-intense physical activity event (Army, 2022) that may benefit from dietary manipulations to sustain energy supply without the need for refuelling.A plausible mechanism to obviate refuelling is to restrict dietary carbohydrates to a threshold where

Highlights
• What is the central question of the study?
Can a novel, energy-dense and lightweight ketogenic bar (1000 kcal) consumed 3 h before exercise modulate steady-state incline rucksack march ('ruck') performance compared to isocaloric carbohydrate bars in recreationally active, college-aged men?
• What is the main finding and its importance?
Acute ingestion of either nutritional bar sustained fat oxidation supersedes carbohydrates for the main substrate utilized during exercise (Helge et al., 2001;Jacobs et al., 1989;Phinney et al., 1983;Volek et al., 2016).The primary expectation is for lipolysis to sustain ATP production, which may concomitantly delay glycogenolysis for intense portions of the ruck (>70% VO 2 max ), notably if ketones are also present in circulation (Cox et al., 2016;Lambert et al., 1997).While ketogenic diets have been demonstrated as a feasible alternative nutrition strategy to improve body composition and preserve strength and power in military reserve-officer training corps cadets (LaFountain et al., 2019), it remains to be determined how acute lipid or carbohydrate ingestion in the context of a mixed-diet influences exercise performance.
Collectively, using the proposed dietary manipulations and recommendations for alternative military nutrition, this study has been designed to explore how acute macronutrient modifications affect military-relevant rucking performance.To our knowledge, there is no study that has examined the differences between commercially

Ethical approval
This

Participants
This study planned to enrol healthy, recreationally active, college-aged men.Twenty-nine males applied and completed all details of the study (Table 1).Participants were included if they (1) currently participated in at least 150 min of moderate activity per week for at least 6 months based on the guidelines by American College of Sports Medicine (Pescatello et al., 2013); (2) were between 18 and 35 years old; and (3) were consuming a Standard American Diet (Shan et al., 2019).
Participants were excluded from the study if they (1) had low levels of aerobic fitness (defined as VO 2 max < 40 ml/kg/min); (2) had a history of smoking; (3) had any known metabolic (e.g., diabetes) or cardiovascular disease; (4) had orthopaedic, musculoskeletal, neurological or psychiatric disorders, and/or any medical conditions that prohibit exercise; (5) used any prescription medications; or (6) were following a low-carbohydrate or ketogenic diet.Participants were prohibited from using any ergogenic aids for 1 month preceding the study and were asked to refrain from taking any performance enhancing supplement(s) during the study.Participants were instructed to refrain from caffeine and alcohol consumption for 48 h and racing or training for 24 h, and food and drink for 8 h before each exercise test.Each participant reported to the laboratory between 06.00 and 09.00 h.Participants were asked to fast for at least 8 h prior to the start of each trial.

Study design
A randomized, single-blind, counterbalanced crossover design was used to assess the effects of consuming either a KB or an isocaloric CB on weighted incline treadmill walking to exhaustion performance.
During the first visit, each participant's VO 2 max was determined using a progressive multistage treadmill running protocol (Figure 1).

Pretrial preparation
Participants were instructed to maintain their usual training frequency during the study intervention without increasing or decreasing the training load.The participants were instructed to maintain a training log (mode, duration and intensity of each workout) for 2 weeks before the first experimental trial.They were provided with a copy of their pre-trial log and instructed to have the same training routine during the intervention period.In addition, participants were asked to record their training every week during the study (mode, duration and intensity of each workout).Furthermore, to quantify the subjects' training session intensity, participants were asked to record their session RPE (sRPE) after every training session (Lovell et al., 2013) (pre-trial and within a trial), using the OMNI Walk/Run 0-10 Perceived Exertion Scale (Robertson et al., 2004).The training load for each session was calculated by sRPE × duration of session (minutes) (Foster et al., 2001).(Shan et al., 2019) through the intervention timeline.
of their pre-trial log and instructed to have the same dietary intake, specifically during the 2 days before the experimental visit and during the remainder of the study.At the familiarization session participants were given precise oral and written instructions individually on how to accurately record amounts and types of food and beverages.
Participants were provided with a digital portable scale (Ozeri ZK 14-S Pronto, San Diego, CA, USA) and instructed to weigh all food items separately if possible or to estimate the amounts (Table 3).

Familiarization and anthropometric measurements
At the first laboratory visit, all the experimental procedures were explained to the participants.The participants underwent an orientation involving the practice of the TTE test, the various measurement instruments, equipment, affect measures and perceived exertion.Affect was measured using a validated 11-point Feeling Scale (Hardy, 1989), with participants informed that their responses should reflect the affective or emotional components of the exercise and not the physical sensation of effort or strain.The OMNI Walk/Run Perceived Exertion Scale (Robertson et al., 2004) was used to measure the physical perceptions of exertion for the overall body (RPE-O), legs (RPE-L) and chest (RPE-C).Following the orientation session, anthropometric measures were obtained including height (cm), weight (kg), fat free mass (kg) and fat mass (% and kg).Height (cm) was measured using a physician's scale (Detecto, Webb City, MO, USA).
Participants' body mass (kg) and body composition (fat and lean mass) were measured using a Tanita bioelectrical impedance analyser (MC-980Uplus, Tanita Corporation of America, Arlington Heights, IL, USA).
Finally, the participants performed a weighted ruck familiarization trial on a motorized treadmill (Trackmaster TMX425C treadmill, Newton, KS, USA).

Maximal aerobic capacity
On the second laboratory visit, participants performed an incremental test to exhaustion on a motorized treadmill (TMX425C treadmill).VO 2 and VCO 2 production were measured using an automated metabolic  (Bruce, 1981).In this protocol, speed and grade of the treadmill increases every  4. Participants were also provided with 500 ml of water to consume ad libitum.Each condition was separated by at least 1 week.
The crunchy peanut butter flavour of the CB was used because it most closely matched the KB for calories and contains a contrasting macronutrient composition.Testing was single-blinded as participants did not know the type of nutrition bar consumed.The blinding was achieved by removing the wrappers from the bars and cutting each bar into bite-size portions given the energy bars were similar in appearance (i.e., the same colour and consistency) (Figure 2).

Blood sampling
Fingertip (capillary) blood samples for blood R-βHB (Precision Xtra, Abbott Diabetes Care Inc., Almeda, CA, USA), glucose (Precision Xtra, Abbott Diabetes Care Inc.) and lactate (Lactate Plus, Nova Biomedical, Waltham, MA, USA) concentrations were measured at baseline, 3 h post energy bar ingestion, at 10-min increments during exercise, and immediately following the TTE test.Samples were collected using a lancet following cleaning of the fingertip with an alcohol swab and then dried.The first droplet was wiped away with a cotton swab to remove any alcohol and the subsequent droplets were used for analysis.Blood sampling during exercise lasted ∼30-60 s -at each 10 min increment of exercise, the participant straddled the treadmill for a 1 min period to allow a capillary blood sample to be taken for subsequent blood R-βHB, glucose and lactate analysis.

Perceptual measurements
Participants' RPE (RPE-Overall; RPE-Chest; RPE-Legs) and affect (Feeling Scale) were recorded at 10 min intervals during the TTE protocol.Ratings of perceived exertion and affect for the entire exercise session (session RPE and session affect) were obtained 5 min following the test.Thirst and gut fullness levels were measured at baseline, 3 h post energy bar ingestion and post-TTE trial on a scale 1-7 (1: 'not thirsty at all' , 7: 'very, very thirsty') and on a scale 0-10 (0: 'empty' , 10: 'extremely full') (Engell et al., 1987).exercise and immediately post exercise) repeated measures ANOVA was conducted to assess the effect of time, treatment and interaction between time and treatment, on plasma glucose, ketones and lactate.A 2 × 3 (baseline, 3 h post and immediately post-exercise) repeated measures ANOVA was conducted to assess the effect of time, treatment and interaction between time and treatment on subjective measures of thirst and fullness.A one-way repeated measures ANOVA was used to analyse differences over time for training load and nutrient intake before and during the intervention.Post-hoc analyses of significant main and interaction effects were conducted where appropriate using the Bonferroni adjustment to determine which conditions were significantly different.The assumption of sphericity was confirmed using Mauchly's test.Greenhouse-Geisser epsilon corrections were used when the sphericity assumption was violated.

Performance
All participants (n = 29) were included in the final analysis (Table 5).
Self-reported daily energy intake, macronutrient composition and exercise intensity were maintained between the experimental visits and wash-out.There were no order effects between visits, evidencing proper counterbalancing, randomization and wash-out duration.
When analysing the conditions individually, there were no significant mean differences (∆) between the mean TTE achieved on the KB and CB (∆: 1.2 ± 16.1 min; P = 0.687).Secondary performance parameters such as heart rate, fatigue, affect, mean VO 2 and session affect were also unaffected by condition.
When combining the results from both the KB and CB conditions, participants terminated the ruck exercise after ∼55 min (range: 21-115 min).Mean work capacity during the TTE was 53% ± 11% of VO 2 max .extra 137 kcal/h from carbohydrates to sustain equal workload (1:1.5 fat-to-carbohydrate ratio) (Figure 3).

Capillary blood parameters
There were no differences between participant metabolite concentrations while fasted and rested at baseline (Table 6).There were significant R-βHB changes detected within-KB, between conditions, and significant interaction effects (all P < 0.0001; Figure 4a).Capillary R-βHB concentrations increased marginally from baseline to pre-exercise (∆: 0.1 ± 0.02 mmol/l; P < 0.0001), an effect that was sustained thereafter throughout post-exercise measurements (mean R-βHB: ∼0.2 mmol/l; P < 0.0001).There were no significant R-βHB effects in the CB condition.
Neither the KB nor CB influenced glycaemia during the study.Participants demonstrated normal glycaemia at baseline (glucose < 100 mg/dl) (Figure 4b).Capillary glucose values remained generally stable throughout the KB and CB conditions (88 ± 0.9 vs. 87 ± 2.1 mg/dl; P = 0.635), recording a ∼2% coefficient of variation throughout all four time point measurements.
Lactate concentrations did not change significantly from the baseline resting phase to pre-exercise.Average lactate values increased significantly during exercise relative to baseline, independent of the condition (∆: 1.4 ± 1.7 mmol/l; P < 0.0001), an effect that was sustained beyond baseline at the post-exercise measurement (Figure 4c).

Perceptual responses
There were no significant differences between participant subjective thirst and fullness measures at baseline (Table 7).Surveys for both perceptual parameters demonstrated a significant main effect of time (P < 0.001), but no between-condition or interaction effects.

Key findings
Twenty-nine, recreationally active and military phenotype males were able to sustain ∼1 h of steady-state incline rucking under 30% of body weight load.Consuming isocaloric KB or CB 3 h before the ruck did not differentially modulate TTE.Athletes demonstrated good metabolic flexibility during submaximal workload as revealed by increased lipid or carbohydrate oxidation rates after KB or CB ingestion, respectively.Capillary R-βHB was augmented by the KB, likely attributed to the medium-chain triglycerides in the KB formulation and lower VCO 2 .Glycaemia was unaffected by condition.
Exercise increased lactate predictably during exercise and postexercise, and trended higher in the CB condition relative to KB.
Perceptual measures of thirst and fullness were similar between conditions.

Performance was comparable between the KB and CB
Participants spent on average 1 h rucking, or approximately 3 km, before reaching volitional exhaustion.Previous ruck studies have implemented longer ruck designs, flatter terrain, heavier rucks, nonsteady-state components (i.e., running, variable temperature, uneven terrain), or no pre-event nutrition (Army, 2022;Looney et al., 2022;Walsh et al., 2020), and therefore our simulation must be viewed with the understanding of precise laboratory conditions.
When accounting for all the physiological parameters and ruck grade, predictive ruck metabolic equations revealed that the average participant in this study expended 270 kcal/h (Looney et al., 2022).
Our original speculation was that rucking would induce an energy expenditure rate closer to 1000 kcal/h (Jacobs et al., 1989;Tassone & Baker, 2017;Walsh et al., 2020) and create an energy gap that would be filled by the nutritional bars (Hirsch et al., 2005;McClung et al., 2020).Although we observed significantly less energy expenditure during our simulated ruck, the nutritional KB and CB bars consumed pre-ruck were non-limiting to performance.Rucking over longer distances, with a lower percentage grade, greater speed and modifiable environmental temperature should be considered in the future for improving the ecological validity of modern military exercises.

Macronutrient ingestion determined substrate oxidation preference
The RER and substrate oxidation rates during exercise corroborated the main macronutrient ingested 3 h before the ruck.Mean relative oxygen consumption in our study (∼53% of VO 2 max ) was maintained between conditions; therefore, the KB to CB comparisons were interpreted within the context of similar ruck effort.While participants did not attain the 'fat-max' range that we originally expected (Achten & Jeukendrup, 2003;Lambert et al., 1997), the pre-determined speed and grade for this ruck were adequate for eliciting intensities often expected during military operations (Army, 2022).Acute KB ingestion increased fat oxidation during the ruck beyond the CB (Δ: ∼0.2 g/min), whereas the CB increased mean carbohydrate oxidation relative to the KB (Δ: ∼0.6 g/min).In other words, for every gram of lipid oxidized during the KB condition, 3 g of carbohydrate was oxidized during the CB condition to sustain equal ruck workload.

Blood analytes
Capillary R-βHB was elevated hours after the KB ingestion, revealing that the medium-chain triglycerides within the KB matrix predictably influenced ketonaemia (Décombaz et al., 1983).Whereas R-βHB effects (>0.5 mmol/l) have been previously tested for athletic performance using a ketogenic diet or acute ingestion of exogenous F I G U R E 4 Capillary blood results.Capillary ketones (R-βHB) (a), glucose (b), and lactate (c) were measured enzymatically in whole blood at baseline (BL), 3 h after KB/CB ingestion and pre-exercise (Pre-EX), during exercise (EX) and immediately post-exercise (Post-EX).There were no significant differences between-conditions at BL.A 2 (condition) × 4 (time) repeated measures ANOVA model revealed significant within-time, between-condition, and interaction effects for R-βHB (all P < 0.0001).There were no significant changes in glucose.Lactate increased significantly over time at EX and Post-EX relative to BL (P < 0.0001), independent of the condition.Data presented as means ± SD.CB, carbohydrate bars; KB, ketogenic bar.
ketone supplements (Cox et al., 2016;Evans et al., 2022;Kackley et al., 2020;LaFountain et al., 2019), this investigation modified preexercise macronutrient ingestion rather than providing a robust ketone supplement per se.The capillary R-βHB results must be viewed with the understanding that there are (1) unclear effects in the literature attributing power, work capacity, or speed to R-βHB directly (Evans et al., 2022;Valenzuela et al., 2020); and (2) the magnitude R-βHB change that we detected in this study was unlikely to have influenced ruck performance.The nutritional bars also did not exert any adverse effects on capillary glucose -despite large differences in total carbohydrates (Δ: 148 g) and sugar (Δ: 68 g) -although predictable given the 3 h gap between pre-and post-ingestion measurements.
Moreover, lactate was also unaffected by condition and increased predictably with ruck exertion independent of the bar consumed.These results collectively suggest that healthy, recreationally active athletes may consume either a lipid-or carbohydrate-dense nutritional bar before rucking without experiencing detrimental blood responses, thereby demonstrating elements of individualized nutrition (Karl et al., 2022).

Perceptions of thirst and fullness
Self-reported thirst perceptions were replicated between experimental visits.Each participant consumed a fixed amount of water (500 ml) before consuming the nutritional bar to minimize confounding responses.Both the KB and CB provided sodium equivalent of onethird of daily sodium requirements for US adults (mean: 835 mg; ∼2 g of table salt), and decreased thirst perception from rest to 3 h post-ingestion.This effect was surprising because sodium was expected to increase subjective thirst; however, it only increased after exercise as confirmed by the surveys, and is likely attributed to sweat loses during the ruck (Stachenfeld, 2008).Moreover, we predicted that the CB volume relative to the KB (Δ: 32%) and carbohydrate content, specifically fibre content (Δ: 12 g), should have increased fullness measures beyond the KB; however, this was not the case in our investigation.Second, we expected that fat and carbohydrate would differentially modulate fullness sensations through humoral signalling conferred by unique carbohydrate and fat digestion (Karhunen et al., 2008).Nevertheless, this was also not the case, as fullness increased significantly before exercise and independent of the bar consumed, followed promptly by a return to baseline values after exercise (∼4 h after ingestion).Measurements of circulating blood hormones, such as leptin, ghrelin and other hormones/peptides involved in fullness and satiety mechanisms (Christ et al., 2006), may provide greater insight into how these subjective perceptions are modulated by pre-ruck nutrition.

Limitations and future directions
This novel pre-ruck nutritional investigation produced many observations that have not been realized in other studies.Despite these observations, there were several limitations that we feel should be addressed.While a healthy population was used in this study, we did not assess active-duty service members, which could have led to differences in performance outcomes.The exercise protocol used was like military rucking events; however, lack of rucking experience, Participants completed three surveys: before consuming the KB/CB at baseline (BL), 3 h later and pre-exercise (Pre-EX), and immediately post-exercise (Post-EX).There were no differences in either thirst or fullness between conditions at BL.A 2 (condition) × 3 (time) repeated measures ANOVA revealed significant time effects, but no condition or interaction effects.Thirst measures decreased significantly from BL to Pre-EX (P < 0.05), whereas Post-EX thirst increased significantly relative to BL (P < 0.001).Fullness measures increased significantly from BL to Pre-EX (P < 0.001) with a return to BL values Post-EX.Data presented as means ± SD.CB, carbohydrate bars; KB, ketogenic bar.
activities should be explored in the future to address military-specific outcomes.
A methodological strength was standardizing all participants to consume the Standard American Diet during and between experimental periods to control for diet confounders (Shan et al., 2019).We are aware that military camp nutrition may not resemble this dietary strategy.Therefore, more work may be required to verify ecological validity of our snacking alternatives in the field.A closer examination into how the KB and CB can complement field rations, not replace them, may be prudent to focus on, as this information can advance military research on field nutrition alternatives.Additionally, future research should focus on assessing similar pre-exercise fuel ingestion using distances and time standards relevant to a military setting, plus soldier-specific performance parameters, including measures like cognitive function and marksmanship, to increase military performance relevance.

Conclusion
Energy-dense nutritional bars, containing complex carbohydrates or lipids, sustained ∼1 h of steady-state, graded rucking with a 30% of bodyweight rucksack.Athletes demonstrated good metabolic flexibility as reflected by the primary substrate oxidation shift during exercise.The KB elicited a modest increase in capillary ketones, whereas glycaemia remained stable in both conditions.While lactate increased predictably with exercise, more work is needed to evaluate how acute carbohydrate or lipid ingestion before exercise modulates lactate appearance during submaximal effort.Both bars were equally as filling and did not stimulate thirst differently.The weight and energy density advantage conferred by a portable and lipid-rich, pre-event nutritional bar merits further evaluation.
h of exhaustive rucking with a 30% of body weight rucksack.This proof-of-concept study is the first to demonstrate that carbohydrate bars and lipid bars are equally feasible for preserving ruck performance.Novel ketogenic nutrition bars may have military-relevant applications to lessen carry load without compromising exercise capacity.
study was approved by the Institutional Review Board of the Grove City College-Department of Exercise Science (IRB number 124-2020), in accordance with the latest version of the Declaration of Helsinki (2013), except for registration in a database.All participants were informed of the experimental procedures, potential risks and the purpose of the study prior to enrolment and before obtaining their written and informed consent.
The sum of each session's training load provides the quantification of the weekly training load.Training load was assessed each week to measure compliance (Table2).Participants' habitual pre-trial and within-trial dietary intake was assessed weekly by use of integrative mobile technology (MyFitnessPal, San Francisco, CA, USA).The use of a mobile app for quantifying food intake has been previously shown to be an effective monitoring tool(Turner-McGrievy et al., 2013).Subjects were asked to keep a detailed diary for 14 days prior to the start of the first experimental trial.Participants were provided with a copy F I G U R E 1 Study design.Healthy, recreationally trained men (n = 29) were randomized and counterbalanced to consume 1000 kcal of a ketogenic bar (KB) or isocaloric carbohydrate bars (CB) 3 h before a time-to-exhaustion (TTE) treadmill ruck.In-person sessions were conducted prior to the experimental visits to familiarize the participants with testing procedures and protocols.Experimental visits were separated by at least 7 days to ensure adequate recovery and to minimize carryover effects.BIA, bioelectrical impedance analysis; HR, heart rate; βHB, β-hydroxybutyrate; RPE, rating of perceived exertion; TTE, time to exhaustion.TA B L E 2Training load.

F
Experimental visit time line.Participants (n = 29) completed two (KB or CB) cross-over experimental visits in random order.Visits stipulated consuming a supplement bar (KB or CB) shortly after lab arrival, while fasted.Three hours post-ingestion, participants began the ruck time-to-exhaustion (TTE) trial until volitional termination.Performance, physiological, metabolic and perceptual measures were collected pre-, during and post-exercise.*Average TTE completion time was approximated to 1 h.BL, baseline; CB, carbohydrate bars; EX, exercise; KB, ketogenic bar; min, minutes elapsed; RPE, rate of perceived exertion.
including unfamiliarity with the load of the ruck, could have skewed the results in the studied population.Using a population of active-duty service men and women and who actively participate in rucking TA B L E 7 Thirst and fullness measures.means ± SD.Thirst scale (1: 'not thirsty at all' , 7: 'very, very thirsty'); Fullness Scale (0: 'empty' , 10: 'extremely full').All participants received 500 ml of water at BL to control for thirst confounders.BL, baseline; CB, carbohydrate bars; EX, exercise; KB, ketogenic bar.F I G U R E 5 Perceptual results.Subjective measurements of thirst and fullness were assessed via validated Likert-scale surveys.
Nutrition bar characteristics.
Statistical analyses were performed using SPSS Statistics version 26.0 (IBM Corp., Armonk, NY, USA).Statistical significance was set a priori at P < 0.05.Descriptive statistics were calculated for all TA B L E 4 CB represents four full servings (4 × 68 g).Total nutritional bar volume and physical density were determined using water displacement (water temperature: 20 • C).Medium chain triglycerides provided 70% C8 + 30% C10 bound to acacia fibre.Other nutritional values are reported from the nutrition bar label.Price (United States dollar; $USD) was calculated from the manufacturer's listed market value for single unit purchase of KB ($12.00) and CB ($1.89).
Blood metabolites (n = 29).SD.Finger capillary blood glucose, R-β-hydroxybutyrate and lactate were assessed across four time points.The data was collected at 10-min intervals during EX and are presented as the grand mean.Abbreviations: BL, baseline; CB, carbohydrate bars; EX, exercise; KB, ketogenic bar; RM, repeated measures.
TA B L E 6