Oral Rehydration Improved Exercise Performance and Decreased Core Temperature and Heartrate Compared With Intravenous Rehydration in Recreationally Active Men.

BACKGROUND

The purpose of this study was to examine the effect of oral versus intravenous (IV) rehydration during exercise in the heat on exercise performance and physiological responses.

HYPOTHESIS: Oral rehydration will lead to better performance and physiological outcomes.

STUDY

DESIGN

Cross-over study.

LEVEL OF EVIDENCE: Level 2.

METHODS

A total of recreational active men (age, 29 ± 12 years; peak oxygen consumption [VO2peak], 49.8 ± 6.6 ml kg-1 min-1) performed 90 minutes of cycling exercise at 55% watts at VO2peak (WVO2peak) followed by a 12-km time trial in the heat (34.9 ± 0.6°C; 30.3 ± 0.9%; wind speed, 3.4 m sec-1). Two experimental trials were performed in random order: (1) drank 25 ml of water every 5 minutes (ORAL) and (2) 25 ml of isotonic saline infused intravenously every 5 minutes (IV). Rectal temperature (Trec) and thirst sensation were measured every 5 minutes. Urine specific gravity (USG) and body mass loss were measured before and after trials. Changes (Δ) were calculated based on the resting value for each trial.

RESULTS

Participants started both trials euhydrated (USG < 1.020), and no differences were found in hydration status between ORAL and IV after trials (USG:ORAL, 1.012 ± 0.006; P = 0.14; IV, 1.013 ± 0.007; body mass loss: ORAL, 2.4 ± 0.8%; IV, 2.3 ± 0.5%, P = 0.68). Thirst levels were higher in IV than ORAL from 20 to 50 minutes (P = 0.03 to 0.05) and after 65 minutes throughout 90 minutes of cycling exercise and the 12-km time trial (P < 0.001 to 0.04). ΔTrec was also significantly higher in IV after 20 minutes throughout 90 minutes of cycling exercise and a 12-km time trial (P = 0.003 to 0.04). The time trial was significantly faster in ORAL (17.7 ± 4.6 minutes) compared with IV (19.6 ± 6.2 minutes, P = 0.05).

CONCLUSION

Oral rehydration enhances exercise performance and decreases Trec and heartrate compared with IV rehydration.

CLINICAL RELEVANCE: Oral rehydration might have more benefits than IV in exercise performance and physiological response.