Noakes et al. 10.1073/pnas.0509096102. |
Fig. 4. It has been suggested that the acute hyponatremia of exercise can occur for either of two reasons. One reason is that athletes overconsume fluids, failing to excrete the excess (1). As a result they retain fluid in the extracellular fluid (ECF), causing a dilutional hyponatremia to which the obligatory Na+ deficit induced by sweat and urine losses during exercise, plays an essential ancillary role (left side of the diagram). Alternatively, athletes may fail to replace both their obligatory Na+ and fluid losses during very prolonged exercise. As a result, they develop hyponatremia due to a combination of both dehydration and a Na+ deficit, so-called "hypovolemic hyponatremia" (2,3). If these latter two mechanisms exist, then the line describing changes in serum [Na+] with changes in body weight during prolonged exercise will take the form of an inverted U, as depicted here. In contrast, if hyponatremia results exclusively from an abnormal regulation of the total body water (TBW) and ECF volume, such that clinically significant exercise-associated hyponatremic encephalopathy (EAHE) results from gross fluid overload (4,5), whereas significant dehydration causes hypernatremia (to neither of which the obligatory Na+ deficit incurred during exercise plays a significant role), the relationship will be linear, rising from left to right (line not shown).
Fig. 5. Percent distribution of different serum [Na+] in athletes whose weight change during exercise exceeds +0.0% body weight (BW) and who therefore finish in an overhydrated state having shown a positive weight gain (a); athletes who finished these races in a euhydrated state (weight loss of 0.01–2.99% BW) (b); athletes who finished these races in a dehydrated state (weight loss greater than –3.0% BW) (c); and the total group (d).
Fig. 6. Risk of hyponatremia and severe hyponatremia according to weight changes during exercise. The total height of the bar represents the percentage of runners in the different weight change groups with postrace serum [Na+] below 135 mmol/liter. The dark colored part of the bar represents the percentage of athletes in each weight change group who finished races with serum [Na+] between 130–135 mmol/liter; the lightly colored part of the bar represents the percentage of athletes who finished races with serum [Na+] below 130 mmol/liter but without symptoms of exercise-associated hyponatremic (EAH) encephalopathy (EAHE). The clear part of the bar represents the percentage of athletes in each weight change group who finished races with a diagnosis of EAHE. Note that the risk of EAH and EAHE rises with increasing levels of weight gain during exercise.
1. Noakes, T. D. (2003) Br. Med. J. 327, 113–114.
2. Armstrong, L. E. (2000) in Performing in Extreme Environments, ed. Armstrong, L. E. (Human Kinetics, Champaign, IL), pp. 103–135.
3. Murray, B. & Eichner, E. R. (2004) Curr. Sports Med. Rep. 3, 117–118.
4. Noakes, T. (2002) Curr. Sports Med. Rep. 1, 197–207.
5. Noakes, T. D. (2003) Clin. J. Sport Med. 13, 309–318.
Table 2. Calculated whole-body fluid and Na+ balance during exercise in 18 subjects with exercise-associated hyponatremia (EAH) studied during recovery
Athlete | Weight before race, kg | TBW1, liters | Δ TBW, liters | Δ E, mmol | [Na+1p], mmol | [Na+2p], mmol | [Na+2p] – [Na+1p], mmol | Na+ inactivated or activated during exercise*, mmol | Ref. (subject) |
1 | 73 | 43.8 | 4.1 | –201 | 113 | 121.7 | –8.7 | –368 | 1 (1) |
2 | 84 | 50.4 | 5.9 | –245 | 113 | 118.4 | –5.4 | –262 | 1 (3) |
3 | 58 | 34.8 | 3.8 | –122 | 119 | 120.6 | –1.6 | –55 | 2 (2) |
4 | 80 | 48.0 | 3.3 | –307 | 122 | 123.3 | –1.3 | –61 | 1 (2) |
5 | 75 | 45.0 | 1.5 | –198 | 124 | 130.3 | –6.3 | –277 | 1 (4) |
6 | 55 | 33.0 | 2.7 | –72 | 124 | 125.5 | –1.5 | –49 | 1 (6) |
7 | 64 | 38.4 | 2.2* | –100 | 124 | 128.6 | –4.6 | –171 | 2 (3) |
8 | 59 | 35.4 | 1.4 | –98 | 127 | 131.0 | –4.0 | –138 | 1 (5) |
9 | 82 | 49.0 | 4.6 | –74 | 127 | 124.5 | + 2.5 | + 118 | 3 (1) |
10 | 50 | 30.0 | 3.3 | –24 | 128 | 123.0 | + 5.0 | + 145 | 1 (7) |
11 | 50 | 30.0 | 1.2 | –78 | 128 | 131.1 | –3.1 | –91 | 1 (8) |
12 | 69 | 41.1 | 0.4 | –119 | 128 | 135.5 | –7.5 | –298 | 2 (4) |
13 | 54 | 32.4 | 2.1 | –44 | 128 | 128.7 | –0.7 | –23 | 2 (5) |
14 | 63 | 37.5 | 1.3 | –132 | 129 | 131.0 | –2.0 | –73 | 2 (7) |
15 | 59 | 35.4 | 1.5 | 20 | 130 | 129.7 | + 0.3 | + 9 | 4 (2) |
16 | 54 | 32.4 | 3.7 | 0 | 130 | 123.2 | + 6.8 | + 214 | 2 (1) |
17 | 58 | 34.5 | 1.5 | –24 | 131 | 132.5 | –1.5 | –50 | 4 (1) |
18 | 70 | 42.0 | 0.8 | –58 | 134 | 135.5 | –1.5 | –63 | 2 (6) |
Mean (SD) | 64.3 (10.9) | 38.5 (6.6) | 2.5 (1.5) | –104.2 (86.8) | 125.5 (5.7) | 127.5 (5.1) | –1.95 (4.0) | –82.9 (154.3) |
TBW1, total body water (TBW) before racing; ΔTBW, change in TBW from before to after racing; ΔE, Na+ balance during exercise; [Na+1p], measured serum [Na+] after the race; [Na+2p], serum [Na+] predicted for after the race; [Na+2p] – [Na+1p], measured minus predicted [Na+] after the race.
*Note that positive values indicate appearance of Na+ in the serum that could not be accounted for by a positive whole-body Na+ balance during the race; hence osmotic activation of osmotically inactive Na+ stores. Negative values indicate the reverse process.
1. Irving, R. A., Noakes, T. D., Buck, R., van Zyl, S. R., Raine, E., Godlonton, J. & Norman, R. J. (1991) J. Appl. Physiol. 70, 342–348.
2. Speedy, D. B., Rogers, I. R., Noakes, T. D., Wright, S., Thompson, J. M., Campbell, R., Hellemans, I., Kimber, N. E., Boswell, D. R., Kuttner, J. A., et al. (2000) Clin. J. Sport Med. 10, 272–278.
3. Noakes, T. D., Sharwood, K., Collins, M. & Perkins, D. R. (2004) Br. J. Sports Med. 38, E16.
4. Speedy, D. B., Noakes, T. D., Rogers, I. R., Hellemans, I., Kimber, N. E., Boswell, D. R., Campbell, R. & Kuttner, J. A. (2000) Clin. J. Sport Med. 10, 136–141.
Table 3. Calculated Na+ balances during recovery and for the entire study period in 18 athletes with exercise-associated hyponatremia (EAH)
Athlete | Weight before race, kg | Measured serum [Na+] after the race, mmol | [Na+1p], mmol | [Na+2p], mmol | [Na+2p] – [Na+1p], mmol | Na activated or inactivated during recovery,*mmol | Na+ infused or ingested during recovery, mmol | Total Na+ balance before the race to after recovery,* mmol |
Activated osmotically inactive Na+ | ||||||||
1 | 73 | 113 | 138† | 130.5 | 7.7 | 357 | 780 | –11 |
2 | 84 | 113 | 138† | 134.0 | 4.2 | 228 | 390 | –34 |
5 | 75 | 124 | 138† | 133.5 | 4.7 | 214 | 260 | –63 |
8 | 59 | 127 | 138† | 135.8 | 2.4 | 85 | 260 | –53 |
11 | 50 | 128 | 138† | 136.8 | 1.4 | 44 | 130 | –47 |
15 | 59 | 130 | 141 | 140.3 | 0.7 | 27 | 26 | +36 |
16 | 54 | 130 | 138 | 147.8 | 9.8 | 214 | 0 | +223 |
17 | 58 | 131 | 140 | 138.4 | 1.6 | 54 | 37 | +4 |
Mean (SD) | 64 (11) | 124.5 (6.9) | 138.6‡ (1.1) | 137.1 (4.9) | 4.1§ (3.0) | 152.9§ (110.0) | 235.4 (242.8) | 8.1‡ (86.7) |
Inactivated osmotically active Na+ | ||||||||
3 | 58 | 119 | 128 | 138.2 | –10.2 | –382 | 5 | –437 |
4 | 80 | 122 | 138† | 138.6 | –0.4 | –20 | 630 | –81 |
6 | 55 | 124 | 138† | 138.3 | –0.1 | –5 | 130 | –54 |
7 | 64 | 124 | 131 | 135.2 | –4.2 | –164 | 450 | –335 |
9 | 82 | 127 | 136 | 142.7 | –4.5 | –235 | 0 | –117 |
10 | 50 | 128 | 138† | 145.5 | –7.3 | –237 | 130 | –82 |
12 | 69 | 128 | 130 | 132.5 | –2.5 | –99 | 148 | –397 |
13 | 54 | 128 | 135 | 139.2 | –4.2 | –142 | 0 | –165 |
14 | 63 | 129 | 128 | 137.9 | –9.9 | –374 | 2 | –447 |
18 | 70 | 134 | 135 | 138.4 | –3.4 | –142 | 5 | –205 |
Mean (SD) | 6.4 (11.0) | 126.3 (4.2) | 133.7 (4.1) | 138.7 (3.6) | –4.7 (3.5) | –180.0 (129.4) | 150.0 (218.6) | –232.0 (148.8) |
[Na+1p], measured serum [Na+] after recovery; [Na+2p], serum [Na+] predicted for after recovery; [Na+2p] – [Na+1p], measured minus predicted [Na+] after the race. Note that athletes in the upper group activated osmotically inactive exchangeable sodium during recovery whereas athletes in the lower group did the reverse.
*Note that positive values indicate appearance of Na+ in the serum that could not be accounted for by a positive whole body Na+ balance during the period of post-exercise recovery; hence osmotic-activation of osmotically-inactive sodium stores. Negative values indicate the reverse process.
†
Mean post-recovery [Na+] for all 8 subjects studied by Irving et al. (1)‡
P < 0.005 upper versus lower group§
P < 0.0001 upper versus lower group1. Irving, R. A., Noakes, T. D., Buck, R., van Zyl, S. R., Raine, E., Godlonton, J. & Norman, R. J. (1991) J. Appl. Physiol. 70, 342-348.