Heinrich W. Nolte

Changes in total body water content during running races of 21.1 km and 56 km in athletes drinking ad libitum.

Objective:To measure changes in body mass (BM), total body water (TBW), fluid intake, and blood biochemistry in athletes during 21.1-km and 56-km foot races. Design:Observational study. Setting:2009 Two Oceans Marathon, South Africa. Participants:Twenty-one (21.1 km) and 12 (56 km) participants were advised to drink according to thirst or their own race drink plan (ad libitum). Main Outcome Measures:Body mass, TBW, plasma osmolality, plasma sodium (p[Na+]), and plasma total protein ([TP]) concentrations were measured before and after race. Fluid intake was recorded from recall after race. Results:Significant BM loss occurred in both races (21.1 km; −1.4 ± 0.6 kg; P < 0.000 and 56 km; −2.5 ± 1.1 kg; P < 0.000). Total body water was reduced in the 56-km race (−1.4 ± 1.1 kg; P < 0.001). A negative linear relationship was found between percentage change (%Δ) in TBW and %Δ in BM in the 56-km runners (r = 0.6; P < 0.01). Plasma osmolality and [TP] increased significantly in the 56-km runners (6.8 ± 8.2 mOsm/kg H2O; P < 0.05 and 5.4 ± 4.4 g/L; P < 0.01, respectively), but all other biochemical measures were within the normal range. Conclusions:Although TBW decreased in the 56-km race and was maintained in the 21.1-km race, the change in TBW over both races was less than the BM, suggesting that not all BM lost during endurance exercise is a result purely of an equivalent reduction in TBW. These findings support the interpretation that the body primarily defends p[Na+] and not BM during exercise and that a reduction in BM can occur without an equivalent reduction in TBW during prolonged exercise. Furthermore, these data support that drinking without controlling for BM loss may allow athletes to complete these events.

Protection of total body water content and absence of hyperthermia despite 2% body mass loss (‘voluntary dehydration’) in soldiers drinking ad libitum during prolonged exercise in cool environmental conditions

The extent to which humans need to replace fluid losses during exercise remains contentious despite years of focused research. The primary objective was to evaluate ad libitum drinking on hydration status to determine whether body mass loss can be used as an accurate surrogate for changes in total body water (TBW) during exercise. Data were collected during a 14.6-km route march (wet bulb globe temperature of 14.1°C ). 18 subjects with an average age of 26±2.5 (SD) years participated. Their mean ad libitum total fluid intake was 2.1±1.4 litres during the exercise. Predicted sweat rate was 1.289±0.530 l/h. There were no significant changes (p>0.05) in TBW, urine specific gravity or urine osmolality despite an average body mass loss (p<0.05) of 1.3±0.45 kg during the march. Core temperature rose as a function of marching speed and was unrelated to the % change in body mass. This suggests that changes in mass do not accurately predict changes in TBW (r=−0.16) because either the body mass loss during exercise includes losses other than water or there is an endogenous body water source that is released during exercise not requiring replacement during exercise, or both. Ad libitum water replacement between 65% and 70% of sweat losses maintained safe levels of hydration during the experiment. The finding that TBW was protected by ad libitum drinking despite ∼2% body mass loss suggests that the concept of ‘voluntary dehydration’ may require revision.

Ad Libitum Fluid Replacement in Military Personnel during a 4-h Route March

INTRODUCTION Opportunities to determine optimal rates of fluid ingestion could reduce the mass soldiers might need to carry on military missions. PURPOSE The first objective was to evaluate the effects of an ad libitum fluid replacement strategy on total body water (TBW), core temperature, serum sodium concentrations [Na+], and plasma osmolality (POsm). The second objective was to determine if an ad libitum water intake was sufficient to maintain these variables during exercise. A third objective was to determine if changes in body mass are an accurate measure of changes in TBW. METHODS A field study was conducted with 15 soldiers performing a 16.4-km route march. The average age of 15 subjects was 27 yr (SD = 4.6 yr). RESULTS Their mean hourly ad libitum fluid intake was 383 mL (SD = 150 mL). Predicted sweat rate was 626 +/-122 mL.h-1. Despite an average body mass loss of 1.0 kg (SD = 0.50 kg) TBW, POsm and serum [Na+] did not change significantly during exercise. There was a significant (P < 0.05) linear relationship with a negative slope between postexercise serum [Na+] and changes in both body mass and percentage of TBW. Postexercise POsm and serum [Na+] were significantly related (P < 0.05). Higher postexercise percentage of TBW was associated with lower postexercise POsm and serum [Na+] levels. There was no relation between percent body mass loss and postexercise core temperature (38.1 degrees C +/- 0.6 degrees C). CONCLUSIONS A mean ad libitum water intake of 383 mL.h-1, replacing approximately 61% of body mass losses during 4 h of exercise, maintained TBW, core temperature, POsm, and serum [Na+] despite a 1.4% body mass loss. A reduction in body mass of 1.4% (1.0 kg) was not associated with a reduction in TBW.

Trained humans can exercise safely in extreme dry heat when drinking water ad libitum

Abstract Guidelines to establish safe environmental exercise conditions are partly based on thermal prescriptive zones. Yet there are reports of self-paced human athletic performances in extreme heat. Eighteen participants undertook a 25-km route march in a dry bulb temperature reaching 44.3°C. The mean (± s) age of the participants was 26.0 ± 3.7 years. Their mean ad libitum water intake was 1264 ± 229 mL · h−1. Predicted sweat rate was 1789 ± 267 mL · h−1. Despite an average body mass loss of 2.73 ± 0.98 kg, plasma osmolality and serum sodium concentration did not change significantly during exercise. Total body water fell 1.47 kg during exercise. However, change in body mass did not accurately predict changes in total body water as a 1:1 ratio. There was a significant relationship (negative slope) between post-exercise serum sodium concentration and changes in both body mass and percent total body water. There was no relationship between percent body mass loss and peak exercise core temperature (39 ± 0.9°C) or exercise time. We conclude that participants maintained plasma osmolality, serum sodium concentration, and safe core temperatures by (1) adopting a pacing strategy, (2) high rates of ad libitum water intake, and (3) by a small reduction in total body water to maintain serum sodium concentration. Our findings support the hypothesis that humans are the mammals with the greatest capacity for exercising in extreme heat.

Exercise-associated hyponatremic encephalopathy and exertional heatstroke in a soldier: High rates of fluid intake during exercise caused rather than prevented a fatal outcome

Abstract Athletes are often advised to drink in order to “fully replace bodyweight losses” in order to prevent exertional heatstroke (EHS) during exercise in the heat. There is little evidence that “dehydration” in the range experienced by athletes adversely affects thermoregulation or is the exclusive cause of EHS. In contrast it is established that excess fluid intake can cause exercise-associated hyponatremia (EAH) sometimes associated with encephalopathy (EAHE). As part of a series of experiments to determine optimal fluid replacement during exercise in the heat, we studied a group of exceptionally well-conditioned and heat-adapted members of the South African National Defence Force. A 20 year old male started a time restricted 50 km route-march in a dry bulb temperature that reached 37.5°C (WBGT of 33.6°C, relative humidity of 85%). Pre-march plasma osmolality, serum [Na+] and total body water measures indicated euhydration. Fluid was available ad libitum and isotonic sports drinks at 5 km intervals. Fluid intake and core body temperature (Tc) were recorded throughout while he was tracked by a global positioning system measuring distance travelled, position and speed. Comparing the total fluid intake of the soldier (12930 mL) to the rest of the participants (mean intake of 9 038 mL) up to 40 km, it is evident that his intake was 3892 mL (approximately 300 mL h-1) more than the mean for group. At approximately 17h14 the soldier was found lying by himself at the side of the route, 2.24 km from the finish point. He passed away the next day in a medical care facility. This tragic event provides the valuable opportunity to present data on the pacing, temperature regulation and fluid consumption of an exceptional athlete during the development of a fatal case of combined EAHE and EHS. Pacing, fluid intake, Tc and environmental condition data are presented for 5km intervals throughout the march. We propose a novel hypothesis on the possible contribution of EAHE to the development of EHS.

Three dimensional musculoskeletal modelling of the abdominal crunch resistance training exercise

Abstract The aim of this study was to evaluate the benefits and limitations of using three dimensional (3D) musculoskeletal modelling (LifeModelerTM) in assessing the safety and efficacy of exercising on an abdominal crunch resistance training machine. Three anthropometric cases were studied, representing a 5th percentile female, and 50th percentile and 95th percentile male. Results indicated that the LifeModelerTM default model was capable of solving the forward dynamics simulations without adjustments. The modelling was able to indicate high risk for back injury when performing the abdominal crunch exercise as a result of the unacceptable intervertebral joint loading that occurs during the exercise. Individuals with small anthropometric dimensions such as some females and children cannot be accommodated suitably on the abdominal crunch machine which negatively impacts exercise posture and technique. Hip flexor muscle contribution in the execution of the exercise for the 5th percentile female was substantial thus reducing the efficacy of the exercise in isolating the abdominal muscles.

Ad libitum vs. restricted fluid replacement on hydration and performance of military tasks.

INTRODUCTION The primary objective was to evaluate the effect of ad libitum vs. restricted fluid replacement protocol on hydration markers and performance in selected military tasks. The secondary objective was to determine if 300 ml x h(-1) could be considered a safe minimum fluid intake under the experimental conditions. METHODS Data were collected simulating a route march over 16 km. There were 57 subjects who participated in the study. RESULTS The mean pre-exercise body mass of the ad libitum group was 70.4 +/- 13.3 (SD) kg compared to 69.3 +/- 8.9 kg in the restricted group. The mean total fluid intake of the ad libitum group was 2.1 +/- 0.9 L compared to 1.2 +/- 0.0 L in the restricted group. The ad libitum and restricted intake groups, respectively, lost a mean of 1.05 kg +/- 0.77 (1.5%) and 1.34 kg +/- 0.37 (1.9%). Calculated sweat rate was 608 +/- 93 ml x h(-1) compared to 762 +/- 162 ml x h(-1) in the ad libitum group. DISCUSSION There were no significant differences for either urine specific gravity (USG) or urine osmolality (UOsm) before or after the exercise. It is not clear whether fluid intake and calculated sweat rates are causally related or explained by their codependence on a third variable; for example, the exercising metabolic rate. Thus, 300 ml x h(-1) intake could be considered a current safe minimum water intake for soldiers of similar mass under similar experimental conditions, namely similar exercise durations at equivalent exercise intensities in a moderate, dry climate.

Total body water, electrolyte, and thermoregulatory responses to ad libitum water replacement using two different water delivery systems during a 19-km route march

Abstract Nolte, HW, Nolte, K, and van der Meulen, J. Total body water, electrolyte, and thermoregulatory responses to ad libitum water replacement using two different water delivery systems during a 19-km route march. J Strength Cond Res 29(11S): S88–S93, 2015—Hands-free hydration systems are often advocated for improved hydration and performance in military populations. The aim was to assess whether such systems indeed result in improved hydration in exercising soldiers. Subjects were required to complete a route march while consuming water ad libitum from either a hydration bladder (BG) or traditional canteen (CG). Water intakes of 538 ml·h−1 (BG) and 533 ml·h−1 (CG) resulted in no differences for changes in body mass, serum [Na+], plasma osmolality, total body water, or time required to complete the march. There were no differences between peak exercise core temperature of the BG (38.9° C) and CG (38.7° C) groups. There were no differences between the groups for fluid balance, thermoregulation, or performance. This is a not a surprising finding because the amount of fluid consumed ad libitum is determined by changes in serum osmolality and not the fluid delivery system as often proposed.

Reply on Baker’s comments to Nolte and Noakes: “change in body mass accurately and reliably predicts change in body water after endurance exercise”

The title of the original article by Dr Baker and her colleagues was: ‘‘Change in body mass accurately and reliably predicts change in body water after endurance exercise’’. In her response to our letter Dr Baker reduces her certainty. She now concludes only that the change in body mass is a ‘‘reasonable method to estimate hydration status’’. This is a more reasonable conclusion that better reflects the published literature. But the focus of our letter was not to show that change in body mass (DBM) is an unreliable method for estimating hydration status. Why would we try to disprove a relationship that we believe exists (Nolte et al. 2010a, b; Tam et al. 2009)? There were two reasons for our letter. First, we concluded that the methods used by Baker et al. (2009) to measure total body water (TBW) may have been relatively imprecise since their study found a significant relationship between DBM and the change in TBW (DTBW) in a total of 62 measurements only when those data were analysed in a manner that, for the reasons we described in detail, we consider inappropriate. The potential methodological errors we identified might explain why their data did not show a relationship between DBM and DTBW when their four experiments were analysed separately. Instead the real focus of our letter was to contest an apparent 1:1 relationship between the DBM (in grams) and DTBW (in mllilitres) that the authors were able to extract from their data. We have not been able to show this relationship (Nolte et al. 2010a, b; Tam et al. 2009). Instead all our studies show an offset of at least 500 g in this relationship so that a DBM of up to 1,000 g was required before it was possible to detect any DTBW. In our letter, we explained why it is logical to assume that some of the DBM during exercise is from sources other than water and which do not require replacement if the TBW is to be preserved. We are particularly interested in the hypothesis that a fluid reserve of up to 2 l, perhaps existing in the form of unabsorbed fluid in the intestine, may be retrieved as a fluid reserve when the rate of fluid loss from the body exceeds the immediate rate of fluid ingestion. There was substantial interest in this theory during the Second World War (Ladell 1947, 1955, 1965) but the issue was never resolved so that this possibility remains untested. This unresolved questions is not without practical importance. After 1996, the idea took root that athletes should drink to stay ahead of thirst during exercise (Convertino et al. 1996; Armstrong et al. 1996). This was based on the theory that any DBM during exercise is detrimental to both health and performance. Yet, when athletes drink to prevent any mass loss during exercise they usually develop a progressive hyponatremia as clearly shown in two separate studies by Dr Baker and her colleagues (Baker et al. 2005, 2008). We interpret this to mean that some body mass loss is essential during exercise if the serum sodium concentration is to be protected and exercise-associated hyponatremia is to be avoided (Noakes et al. 2005). Indeed changes in body mass alone explain almost all of the variance in the serum sodium concentrations during prolonged exercise (Noakes 2010). That is why it is important to Communicated by Susan Ward.