Display Settings:

Format

Send to:

Choose Destination
See comment in PubMed Commons below
J Athl Train. 2009 Mar-Apr;44(2):117-23. doi: 10.4085/1062-6050-44.2.117.

Sodium replacement and plasma sodium drop during exercise in the heat when fluid intake matches fluid loss.

Author information

  • 1Harokopio University, Athens, Greece.

Abstract

CONTEXT:

Sodium replacement during prolonged exercise in the heat may be critically important to maintaining fluid and electrolyte balance and muscle contractility.

OBJECTIVE:

To examine the effectiveness of sodium-containing sports drinks in preventing hyponatremia and muscle cramping during prolonged exercise in the heat.

DESIGN:

Randomized crossover study.

PATIENTS OR OTHER PARTICIPANTS:

Thirteen active men.

INTERVENTION(S):

Participants completed 4 trials of an exercise protocol in the heat (30 degrees C) consisting of 3 hours of exercise (alternating 30 minutes of walking and cycling at a heart rate of 130 and 140 beats per minute, respectively); a set of standing calf raises (8 sets of 30 repetitions); and 45 minutes of steep, brisk walking (5.5 km x h(-1) on a 12% grade). During exercise, participants consumed fluids to match body mass loss. A different drink was consumed for each trial: carbohydrate-electrolyte drink containing 36.2 mmol/L sodium (HNa), carbohydrate-electrolyte drink containing 19.9 mmol/L sodium (LNa), mineral water (W), and colored and flavored distilled water (PL).

MAIN OUTCOME MEASURE(S):

Serum sodium, plasma osmolality, plasma volume changes, and muscle cramping frequency.

RESULTS:

During both HNa and LNa trials, serum sodium remained relatively constant (serum sodium concentration at the end of the protocol was 137.3 mmol/L and 136.7 mmol/L, respectively). However, a clear decrease was observed in W (134.5 +/- 0.8 mmol/L) and PL (134.4 +/- 0.8 mmol/L) trials compared with HNa and LNa trials (P < .05). The same trends were observed for plasma osmolality (P < .05). Albeit not significant, plasma volume was preserved during the HNa and LNa trials, but a reduction of 2.5% was observed in the W and PL trials. None of the volunteers experienced cramping.

CONCLUSIONS:

The data suggest that sodium intake during prolonged exercise in the heat plays a significant role in preventing sodium losses that may lead to hyponatremia when fluid intake matches sweat losses.

KEYWORDS:

endurance; fluid replacement; hydration; hyponatremia; plasma volume; sports drinks

Comment in

PMID:
19295955
[PubMed - indexed for MEDLINE]
PMCID:
PMC2657026
Free PMC Article

Images from this publication.See all images (4)Free text

Figure 1
Figure 2
Figure 3
Figure 4
PubMed Commons home

PubMed Commons

0 comments
How to join PubMed Commons

    Supplemental Content

    Icon for PubMed Central
    Loading ...
    Write to the Help Desk