Authors: Reginald B. O’Hara1 and Brenda Moore2

1Chief, Biochemistry Services Division, Department of Clinical Investigation, William Beaumont Army Medical Center, For Bliss, TX, USA.

2 Moore Enterprises, LLC., Independent Research Contractor, Yellow Springs, OH, USA

Correspondence:

Reginald B. O’Hara, PhD, ACSM-EP
William Beaumont Army Medical Center
Department of Clinical Investigation
Building 18509 Highlander Medics Street
El Paso, TX 79918
reginald.b.ohara.civ@health.mil
210-792-1048

Reginald B. O’Hara, Ph.D., is the Chief of the Biochemistry Services Division at William Beaumont Army Medical Center, Department of Clinical Investigation, Fort Bliss, TX. His research interests focus on the clinical pathology of the disease process, human performance, exertional heat stress, and physiological fatigue and recovery in military personnel.

Brenda Moore, Ph.D., nutrition microbiologist, is retired but continues to support her own research contracting business in Yellow Springs Ohio. Dr. Moore worked as a research nutrition microbiologist under an ORISE contract from 2016-2019 in the United States Air Force School of Aerospace Medicine, WPAFB, OH where she conducted research on thermal stress and dehydration in military personnel.

Sports Performance: A Comparison of Oral Rehydration Solutions on Hydration Biomarkers in Military Personnel

ABSTRACT

Purpose: Exertional heat stress is a serious condition, especially for military personnel working in high-heat and humid climates, such as flight maintainers, flight crew, loadmasters, and Special Operations Forces Operators. Hence, this study assessed the effects of military-approved oral rehydration solutions (ORS) in highly fit military personnel while performing a 10-mile run. The ORS tested were Gatorade (G) and CeraSport (CS), with water (W) as the control. Methods: Fifteen “well-trained” participants (13 male, 2 female) (mean± SD: age, height, weight, % body fat, and VO2 max = 28.07 ± 5.0 yrs., 69.79 ± 4.2 in, 174.4 ± 21.53 lbs., 13.7 ± 6.7%, and 52.9 ± 5.0 mL/kg/min, respectively) completed three separate 10-mile treadmill runs, separated by a one-week recovery period. Hydration biomarkers were measured at baseline, post, and 20-minute run pause increments during each 10-mile testing trial run. Study investigators measured the following hydration biomarkers 1) Body weight change (BWC), 2) hematocrit (Hc), 3) exercise heart rate (HR), 4) blood glucose (BG), 5) blood lactate concentration ([BLa¯] b), 6) hemoglobin (Hb), and 7) total urinary output (UO). Results: No statistical difference occurred in the hydration biomarkers, likely due to the large volume (1500 mL) of fluid consumed. While no significant differences in BG were detected between G and CS, both CS and G values were significantly higher than water (p< 0.05) throughout the study. Additionally, blood lactate concentrations ([BLa¯] b) were lower during the last 40 minutes of the study when CS was consumed in comparison to G, approaching significance (p= 0.09) at Time 7 (T7).Conclusions: Outcomes from the present study provide preliminary evidence that consumption of CS in the same volume and time as G results in the preservation of BG values with lower sugar and carbohydrate consumption and without a concurrent rise in blood lactate. The present study showed that although there were no statistical differences in hydration biomarkers, potential differences may be more clearly extricated in future studies conducted in varying environmental conditions, such as higher temperatures and humidity, with a larger sample size, or a more prolonged exercise period.

Keywords: rehydration solutions, biomarkers, physical exertion, sports, military personnel

INTRODUCTION

The Defense Medical Surveillance System records and tracks ambulatory and hospitalization visits of active duty serving in all military branches. The report noted that an estimated 720 incidents of heat-related injuries of personnel serving in Afghanistan and Iraq, and 6.9% of these diagnoses were for heat-related injuries (1). In addition, an estimated 1,953 cases of “other heat-related injuries” were cited in 2015 for all Service members (1). Of particular concern for military operating in tropical climates is to microhydrate during activity. Microhydrating during activity can prevent a >2% bodyweight loss, which may result in dehydration, ultimately impeding physical performance (2).

The physical performance and neuromuscular function of military personnel working in hot and humid climates during training evolutions or on the battlefield can impede mission success. Exertional Heat Illness (EHI) continues to be prevalent. It can arise through exercise-induced metabolic heat production, environmental conditions (heat, humidity), and wearing Personal Protective Equipment (PPE) that impairs evaporative heat transfer. Specifically, wearing PPE by military personnel during training and arduous deployments may result in a reduced vapor gradient between the skin and the environment, reducing the rate of evaporative heat dissipation (3).For example, PPE is often needed in specific Military Occupational Specialties (MOS), such as fighter pilots, flight maintainers, and Special Operations Forces. For example, subjects’ sweat typically drips from the body. It becomes trapped within the fabric fibers of the overlying PPE, resulting in significant reductions in the capacity to remove heat storage that builds up while operating in hot and humid climates.

From a physiological and neuromuscular perspective, impairment in physical performance due to working in high-heat environments may result in systemic insufficiency of the oxidative energy system. Additionally, the competition for blood flow to active skeletal muscles and skin for conductive heat exchange, coupled with a significant loss of plasma volume through sweating, results in significant dehydration. Concurrently, the smooth muscle within skin blood vessels dilates, increasing blood flow to the skin. Hence, exertional heat illness (EHI) may occur even when military personnel perform simple tasks in hot and humid climates. For instance, the contraction of skeletal muscles alone while performing routine tasks (e.g., flight maintainers, loadmasters) may increase heat production up to 20 times that produced at rest and in wet bulb globe temperatures (WBGT) as low as 65° Fahrenheit (F) (4).

Exertional heat illness (EHI) is still elusive to detect or prevent, especially in active-duty personnel who may have to work in tropical climates. Therefore, supporting energy, performance, and hydration is critical. For example, when a Service member suffers from a heat-related illness, estimated four-unit members must carry that member any distance. Therefore, using an effective ORS could help reduce heat illness among military troops, thereby reducing EHI and sustaining work performance in the field (5).

Although consistent water consumption may aid in preventing exertional heat illness (EHI), it may not be sufficient to prevent EHI. For example, heavy consumption of water over a short period may cause a condition known as hyponatremia, which is marked by reductions in serum sodium concentrations from normative values of 135 to 145mmoL·L to levels below 130 mmoL·L (6). Various ORSs or sports drinks containing electrolytes, such as sodium and chloride ions and varying sources of carbohydrates (CHO), are frequently recommended to increase water absorption and retention and prevent dangerous drops in serum sodium levels. A weak link in any level of the warfighter’s chain of operational fitness, including >2% body weight loss from water deficit, could significantly affect performance during patrol evolutions and sustained operations missions (7,8). 

Specialized groups such as Special Operations Forces (SOF) operators must train routinely and vigorously to prepare for missions and deployments in hot and humid environments, which may include special reconnaissance, counterterrorism operations, and counter-proliferation (7).Although it is common for certain military personnel to perform training evolutions in hot and humid climates, dehydration can also occur in normothermic environments. Both acclimatization and physical fitness help prevent dehydration. For example, physical training increases blood plasma volume, which helps support central blood volume during dehydration. Furthermore, physical training also causes more dilute sweat by reducing its electrolyte content (9). Humans are stimulated to drink fluids by osmoreceptors in the hypothalamus. The hypothalamus regulates body temperature and is analogous to a thermostat. Thus, the hypothalamus increases the rate of heat production when the body temperature falls and increases the heat dissipation rate when the body temperature rises (9). Functions of these mechanisms often require alterations in hydration. Unfortunately, the thirst mechanism does not keep up with the body’s fluid requirements, so military personnel or anyone performing in a hot climate can easily experience fluid deficits of >2% of body weight, resulting in physical and cognitive performance declines (2,9).

The primary purpose of this study was to examine the physiological effects of military-approved oral rehydration solutions (ORS) on hydration biomarkers in healthy, well-trained military personnel while performing a 10-mile run in a normothermic environment. The ORS tested were Gatorade® (G) and CeraSport® (CS), with water as the control. The null hypothesis was that there would be no statistically significant differences in the hydration markers measured during a 10-mile run in “well-trained” military personnel.

METHODS

Participants

This study utilized data from fifteen active-duty military service members (13 male, 2 female) (age = 28.0 ±5.0 yr., 177.0 ± 4.2 cm, body mass= 79.2 ± 21.5 kg, BMI 25.1 ± 1.4 kg·m-2, estimated VO2 max 52.9 ± 5.0 mL/kg/min, and body fat 13.1 ± 6.7%). All study participants were defined as “well-trained” as defined by the American College of Sports Medicine (ACSM) guidelines for exercise testing and prescription (10). This study was approved by the Air Force Research Laboratory (AFRL) Institutional Review Board at Wright Patterson Air Force Base, OH.

Inclusion and Exclusion Criteria

Study participants were screened for inclusion and exclusion criteria. Subjects had to show an aerobic capacity at or above the 80th percentile according to the ACSM values of VO2 max >46 mL/kg/min for men and >34 mL/kg/min for women to qualify for the study (10). Additionally, for each of the three separate run trials, all participants had to be physically able to jog on a treadmill at five mph (12min/mile) for 10 miles at a zero percent grade.

Study participants were excluded if presenting with any one of the following limitations 1) Soft-tissue/musculoskeletal injury to the upper thigh or lower leg in the past 2 months, 2) uncontrolled hypertension or diabetes mellitus, 3) heart dysrhythmia diagnoses in the past 2 months, 4) on medical restrictions in any one of the following domains a) mobility deployment/assignment limitation code; b) on a fitness testing or military medical waiver; and c) duty.  

Design

A repeated measure within the group counterbalance design was applied for this investigation. Three different fluids (treatments) were administered during three separate running trials: Water (control), Cerasport® (CS), and Gatorade® (G) in a normothermic laboratory environment (See Table 1). For this investigation, we operationally defined a run trial as one testing session consisting of a 10-mile distance (testing baseline-post and every 20 minutes for data collection) and entailing the consumption of one ORS (e.g., Water, CS, or G) for a total of 1500 mL in 250 aliquots (e.g., time zero and every 20 minutes after that).

At the first meeting with potential study participants, the investigators determined if the participant qualified for study entry based on the established inclusion criteria. If the participant met all inclusion criteria, the principal investigator verbally reviewed the medical history of the study participant and then signed by the participant. After the study participants were provided explanations of all testing procedures, potential participants reviewed and signed an informed consent document. Participants were then scheduled for their first pre-inclusion submaximal aerobic testing session to determine their eligibility for participation in the study.

 This study’s independent variable(s) were the ORS (Water, CS, G). The dependent variables included 1) Heart rate (HR), 2) ratings of perceived exertion (RPE), 3) hematocrit (Hc), 4) hemoglobin (Hb), 5) blood glucose (BG), 6) blood lactate (BLa), 7) total urinary output (TUO), and 8) body weight change (BWC).

Procedures

Pre-inclusion testing session one consisted of no ORS consumption. Participants’ height, body weight, and body mass index were measured using a stadiometer (Tanita Digital Physicians scale, Tanita Corp. of America, Inc. Arlington Heights, VA; to 0.1 cm and 0.02 kg). Further, participant’s percent body fat was measured in triplicate with Lange skinfold calipers (Beta Technology, Ann Arbor, MI; to ± 1 mm) at three sites on the right half of the body (chest, abdomen, and thigh for men; triceps, supra-iliac, and upper thigh for women) (10). The Ebbeling submaximal walking protocol was administered to determine initial eligibility for participant inclusion (11). Prior to administering the Ebbeling submaximal walking protocol, each study participant received detailed instructions on the submaximal walking test procedures as outlined in the Ebbeling single-stage submaximal treadmill walking protocol (11), followed by an explanation of how to use Borg’s subjective ratings of perceived exertion scale according to the American College of Sports Medicine (ACSM) guidelines for exercise testing (10).

Before the pre-inclusion testing and the remaining three separate run trials, participants were instructed to refrain from caffeine consumption for at least four hours before the test, with only a light, easily digestible meal at least two hours before the start time. Additionally, participants were instructed to consume the same foods prior to the start of each run and to approximate the same exercise pattern the day before each run trial.

Apart from the pre-inclusion submaximal test session, participants engaged in three separate run trial sessions, with a minimum of one-week recovery between each run trial. The total time for each testing trial was an estimated three hours. Further, three different beverages (Water, CS, or G) were randomly administered to study participants during the three separate run trials.

For each run trial, the distance consisted of 10 miles at a speed of 5 mph (12 min/mile) and zero grade, pausing every 20-minutes (as well as prior to the start of the run) for parameter measurements and consumption of 250 milliliters (mL) of beverage (water, CS, G), at the start (time zero) and every 20-minutes thereafter, with a total consumption of 1500 mL over the 10-mile run. During each 20-minute data collection pause, a bathroom break and static stretching were permitted if requested by the study participant. Lastly, participants were required to void their bladders before the start of each run trial (pre-bodyweight obtained at this time), and total urine output was collected throughout each run trial (post-bodyweight obtained after final bladder void).

Blood Sample Measurements

All blood samples were obtained by fingerstick, using Safe-t-Lance (Smiths Medical ASD, Inc. Keene, NH) disposable lancets. Participants’ fingers were disinfected with an alcohol wipe, and finger sticks were performed. The lancets and strips were adequately disposed of in a biohazard sharps container. The meters were calibrated before each run trial with proper standards and following recommended manufacturer protocols.

Blood lactate (mmol/L) levels were measured with Nova Biomedical Lactate Plus (Nova Biomedical, Waltham MA, USA) meter. The Lactate Plus analyzer requires 0.7 microliters (µL) of whole blood to analyze the amount of lactate in the blood. Blood glucose values were obtained via a finger stick using the FreeStyle Freedom Lite glucose meter (Abbot Diabetes Care, Alameda, CA, USA). Blood lactate and glucose levels were measured at the start, end, and every 20 minutes throughout each trial.

Blood hematocrit (Hc) and Hemoglobin (Hb) were measured before and after each 10-mile run trial using the HemoPoint H2 photometer and Hemopoint H2 nxt Microcuvettes (Stanbio Laboratory, and EKF Diagnostics Company, Boerne, TX).

Fluid Volume Measurements

Drink volume was measured by pouring them into a 500 mL measuring cup (Anchor Hocking Co., Lancaster, OH), filling to the 250 mL mark at eye level. CeraSport® and Gatorade® were shaken six times vigorously before the first measurement to ensure homogenization of the fluid. Once measured, all drinks were transferred into a sports drink bottle for consumption by the study participant.

Physiological Measures

The Subjective Ratings of Perceived Exertion (RPE) scale, range 6 (Very, Very Light) to 20 (Very, Very Hard), were measured at the start and completion of each run and every 20-minute pause. A Polar Heart Rate H1 System (Polar Electro Inc., USA) was used to measure resting heart rate before the start of each run trial and during the last minute of each 20-minute segment of the run.

Total Urinary Output and Bodyweight Measures

Participants were required to void their bladders before starting each 10-mile run trial, and total urine output was collected throughout each run trial. Additionally, each study participant’s body weight was measured prior to the start of the run trial, and post bodyweight was obtained after the final bladder void.

Data Analyses

The data were entered in Microsoft Excel, with the alpha established a priori at the 0.05 level. Data were analyzed by an independent third party, using Bonferroni-corrected linear mixed model and Student’s paired t-tests. The Independent variable(s) for this study were the ORS. The dependent variables included (1) Exercise Heart Rate (HR);(2) Ratings of Perceived Exertion (RPE); (3) Hematocrit (Hc); (4) Hemoglobin (Hg) (5) Blood Glucose (BG); (6) Blood Lactate (BLa); and (7) total urinary output and (8) body weight change. Data was recorded before, after, and every 20 minutes throughout the 10-mile run trial.

RESULTS

No significant differences were found (p >0.05) in the temperature and humidity levels observed between each of the running trials (Table 1) or in the demographics for any of the runners (See Table 2). No differences (p >0.05) were observed for any of the initial values (Time T1) for any of the parameters measured (See Table 2). Blood glucose values were significantly higher (p <0.05) for all T2-T7 when CS was compared to water and for all periods except T4 and T5 (approached significance) when water was compared to G (See Table 3). Blood glucose levels remained relatively more stable across the trial periods for CS in comparison to water and G (Figure 1). Although BLa levels were not significantly different between treatments, differences between CS and G approached significance (p= 0.09) during the last 20 minutes of the run (Time T7, Table 3). Figure 2 illustrates these differences. Hydration status was based on changes in body mass, urine output, Hc, and Hb, with plasma volume calculated from these numbers.

Figure 1
Figure 2

Lastly, there were no differences in Hc, Hb, or plasma volumes (calculated from Hc and Hb) observed during the trial for any treatment (data not shown) (12). Likewise, there were no differences in body weight change (See Tables 4 and 5) or urinary output (Table 6) for any treatments.

DISCUSSION

As noted previously, there were no significant differences (environmental conditions were normothermic) in the temperature and humidity levels observed during each of the runs (See Table 1) or in the demographics for any of the runners (Table 2). No differences (p >0.05) were observed for any of the initial values (Time 1) for any of the parameters measured, indicating that all subjects started exercising with similar biomarker values for every treatment. Blood glucose values were significantly higher (p< 0.05) for all periods (T2-7) when CS was compared to water and for all periods except T4 and T5 (approaches significance, p <0.09) when water was compared to G, which confirms that consumption of an ORS maintains blood glucose values much better for endurance related activities than the consumption of water with the same volume.

No significant differences between CS and G for BG were observed despite the total consumption of 86 g of sugar in 1500 mL of G and only 12 g of sugar in 1500 mL of CS ( Table 7). The carbohydrate (CHO) content was 91 g for G (mainly consisting of sugars) compared to 60 g in CS, mostly from the medium chain CHO, maltodextrin (MD), with an energy consumption of 240 calories with CS compared to 364 calories for G. The CHO of G was comprised of 95% sugar. In contrast, the CHO of CS was comprised of 20% sugar, ultimately resulting in 2 grams (g) of sugar intake every 20 minutes in 250 mL of CS versus an estimated 14 g every 20 minutes in 250 mL of G. Glucose is primarily absorbed in the duodenum and jejunum by the sodium /glucose (gluc) (SGLT 1) cotransporters (5,13).

Researchers have recently identified two additional gluc transporters in the ileum, which may indicate that gluc can be absorbed farther down the gastrointestinal tract than initially thought (14). OSR drinks containing more complex CHOs may be absorbed farther down the gastrointestinal tract than initially understood. Hence, compared to other sports drinks containing sugars (mostly absorbed from the duodenum), the longer CHO chains present in CS may decrease digestion in the duodenum/jejunum and allow more of the CHO to reach the ileum, which may result in a slower and more sustained release of glucose. Alternatively, digestion and absorption of MD may occur in the duodenum/jejunum. Although the mechanism is undecided, the data from this investigation provide clear evidence that CS supports blood glucose levels just effectively as G during an endurance event, but with a much lower sugar/CHO intake. Additionally, the data derived from this study suggests that the molecular structure of nutrient components may play a significant role in preserving exercise performance.

The differences in the structural CHO content between CS and G may impact the physiological function of other factors, not just BG. For instance, one of the most exciting findings from this study is the progressive rise in BLa with G compared to CS (See Table 3 and Figure 1). Despite no differences in BG levels, BLa values were lower (approaching significance at p=0.09) for the last twenty minutes of the ten-mile run trial (See Table 3, blood lactate T7) when CS was consumed, in comparison to G. Blood lactate levels also remained stable for the last 40 minutes of the CS run in comparison to G (See Table 3 and Figure 1). Based on this evidence, we hypothesized that future replication of this study and the data derived from the replicated study might provide additional evidence that more lactate is generated when G is consumed compared to CS during endurance events.

It is widely accepted that the end product of glycolysis under oxygenic conditions is pyruvate (which is transported into the mitochondrion for further oxidation via the Krebs Cycle and Electron Transport Chain), while under non-oxidative conditions, it is lactate. However, several studies have indicated that the end product of glycolysis is lactate and not pyruvate under both low oxygen (non-oxidative) and high oxygen (oxidative) intracellular environments. Lactate is a product of the catalysis of pyruvate to lactate, as follows: Pyruvate– + NADH + H+ <-> Lactate–+ NAD+

This reaction is catalyzed by the enzyme lactate dehydrogenase (LDH). With an equilibrium constant of 1.62 x 11 M-L, this reaction strongly favors lactate formation, as does a considerable free energy (standard DG0’) change of -25.1 kJ/mol (19-20). The energy states shown by these values heavily favor lactate production, which further provides evidence that the end product of glycolysis is undoubtedly lactate, not pyruvate.

Previous researchers have observed and reported the efflux of lactate from exercising muscle while under oxygenated cellular conditions (16-18, 21). Several factors may play a role in increasing BLa, including metabolic rate, mitochondrial activity, and O2 tension (22). These factors may explain the significance of the higher BLa levels observed in runners consuming G versus CS (See Table 3, T7). The higher sugar content of G may suggest that cellular glucose uptake is greater (while still maintaining BG) than when CS is consumed, increasing the lactate (lac) to the point where more significant cellular efflux occurs, thus increasing the [lac] in blood.

Scientists who conducted research in the early 19th century concluded lactate was a waste product of metabolism (23). More recent research studies have associated increased [lactate] to be the cause of increased pain and decreased contractile force (24). Several additional authors provide evidence that lactate in exercising skeletal muscle and blood has a much more significant role in metabolism and may still play a vital role in exercise exhaustion, pain, and recovery time. However, the precise mechanism of action is yet to be determined (25).

CONCLUSIONS

The data obtained from this study suggests that the consumption of CS in the same volume and time as G results in the maintenance of blood glucose values with lower sugar and CHO consumption and without a concomitant rise in BLa. While there were no statistical differences in the hydration biomarkers, potential differences may be more clearly differentiated in future studies performed in different environmental conditions (e.g., higher temperatures and humidity), with a larger sample size, or with a more prolonged exercise period.

APPLICATION TO SPORT

Well-trained athletes routinely suffer from exertional heat illness, which can impede athletic performance on the field. Therefore, coaches and athletes should consider the importance of micro hydrating throughout the athletic event and avoid large water boluses over a given period due to the potential risk of hyponatremia. Hyponatremia is considered a severe condition that can dilute the percentage of sodium in the blood and result in electrolyte imbalances. Hence, athletes and trainers should consider ORSs comprised of electrolytes, such as sodium and chloride ions, and an array of carbohydrate sources to enhance water absorption and retention to avert unsafe drops in serum sodium levels.

Disclaimer: “The views expressed in this publication are those of the author(s) and do not reflect the official policy or position of William Beaumont Army Medical Center, Department of the Army, Defense Health Agency, or the US Government.”

Acknowledgements: This research project was intramurally funded by the United States School of Aerospace Medicine (USAFSAM), Research Science and Advisory Committee (RSAAC) under project number DHP 8, RSAAC 18-121

References

  1. Armed Forces Health Surveillance Branch.(2012).Update: Heat injuries, Active component, U.S. Army, Navy, Air Force, and Marine Corps, Medical Surveillance Monthly Report, (23),16- 19.
  2. Sawka, N.S., Cheuvont, S.N., & Kenficke, R.W. (2015). Hypohydration and Human Performance: Impact of Environment and Physiological Mechanisms. Sports Medicine, (45) (Supp.1), 51-60.
  3. Nunneley, S.A.(1989).Heat Stress in protective clothing: interactions among physical and physiological factors. Scandinavian Journal of Work and Environmental Health, (15) (Suppl. 1), 52-57.
  4. Gerold, K.B., and Greenough, W.B. (2013). Rice-based electrolyte drinks more effective than water in replacing sweat losses during hot weather training and operations. Journal of Special Operations Medicine, (13),12-14.
  5. Moore, B., and O’Hara, R.B. (2016).Mitigating Exertional Heat Illness in Military Personnel: The Science Behind a Rice-Based Electrolyte and Rehydration Drink. Journal of Special Operations Medicine, (16), 49- 53.
  6. Williams, M.H. (2007).Nutrition for Health, Fitness, and Sport. 8th ed. New York, NY: McGraw-Hill.
  7. O’Hara, R.B., Henry, A., Serres, J., Russel, D., & Locke, R. (2014). Operational stressors on physical performance in special operators and countermeasures to improve performance: a review of the literature. Journal of Special Operations Medicine, 14 (1), 67-78.
  8. Cheung, S. (2010).  Advanced Environmental Exercise Physiology. Human Kinetics.
  9. Sawka, S.M. and K.B. Pandolf. (1993). Perspectives in Exercise: Effects of Body Water Loss on Physiological Function and Exercise Performance. National Academies Press (US), Washington, DC.
  10. American College of Sports Medicine.ACSM’s Guidelines for Exercise Testing and Prescription (2014). 9th ed. Baltimore, MD: Lippincott Williams & Wilkins (6).
  11. Ebbeling, C.B., Ward, A., Puleo, E.M., Wildreck, J., & Rippe, J.M. (1991). Development of a single-stage submaximal treadmill walking test. Medicine & Science in Sports & Exercise, 23 (8), 966-973.
  12. Van Beaumont, W. (1972). Evaluation of hemoconcentration from hematocrit measurements. Journal of Applied Physiology, 32 (5),712-713.
  13. Hediger, M.A. and Rhoads, D.R. (1994). Molecular physiology of sodium-glucose cotransporters. Physiological Review, (74), 993-1026.
  14. Yin, L., Vijaygopal, P., & MacGregor G.G. (2104). Glucose stimulates calcium-activated chloride secretion in small intestinal cells. American Journal of Physiology Cell Physiology, (306), C687-C696.
  15. Stainsby, W.N. and Welch, H.G. (1966). Lactate metabolism of contracting dog skeletal muscle in situ. American Journal of Physiology, (211), 177-183.
  16. Jobsis, F.W. and Stainsby, W. (1968). Oxidation of NADH during contraction of circulated Mammalian skeletal muscle. Respiratory Physiology,(4),292-300.
  17. Connett, R.J., Gayeski, T., & Honig, C. (1986). Lactate efflux is unrelated to intracellular PO2 in a working red muscle in situ. Journal of Applied Physiology, (61),402-408.
  18. Brooks, G.A. (2000). Intra- and extra-cellular lactate shuttles. Medicine & Science in Sports & Exercise, (32), 790-799.
  19. Lambeth, M.J. and Kushmerick, M.A. (2002). Computational model for glycogenolysis in skeletal muscle. Annals Biology England, (30), 808-827.
  20. Nelson, D.L., and M.M., Cox. (2003) [In]: Lehninger Principles of Biochemistry. 8th edition. W.H. Freeman and Co., NY. p. 452.
  21. Richardson, R.S., et al. (1998). Lactate efflux from exercising human skeletal muscle: role of intracellular PO2. Journal Applied Physiology, (85), 627-634.
  22. Rogatski, MJ, et al., (2015). Lactate is always the end product of glycolysis. Frontiers Neuroscience.9 (22),1-7.
  23. Philip A., A.l., Macdonald & P.W., Watt. (2005). Lactate- A signal coordinating cell and systemic function. Journal Experimental Biology.  (208), 4561-4575.
  24. Brooks G.A., Fahey T.D., & Baldwin K.M. (2004). Exercise Physiology: Human Bioenergetics and its Application, 4thed. Mountain View (CA): McGraw-Hill Education.
  25. Noakes, J.D., St. Clair Gibson, A. (2004). From catastrophic to complexity: A novel model of integration in CN regulation of effort and fatigue during exercise in human. British Journal Sports Medicine (38), 511-524.
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