Effects of heat exposure and 3% dehydration achieved via hot water immersion on repeated cycle sprint performance

Journal Title (Medline/Pubmed accepted abbreviation): J Strength Cond Res
Year: 2011
Volume: 25
Page numbers: 778-786
doi (if applicable):10.1519/JSC.0b013e3181c1f79d

Summary of Background and Research Design

Background:It is well established that hydration status is critical to work performance. Hypohydration of only 2% has been shown to impair endurance performance, and some studies indicate that hypohydration can likewise impair anaerobic work with dehydration ≥ 3%. However, data are lacking on the effects of dehydration on intermittent high-intensity bouts of work.

Hypothesis/purpose of study:Performance during intermittent cycle sprints would be impaired by 3% dehydration but not by simple heat immersion.

Subjects:Ten males were included in the study (mean age, 22.4 ± 3.0 yr; mean height, 182.0 ± 6.5 cm; mean body mass, 81.9 ± 6.8 kg; mean body fat, 11.8% ± 2.1%).

Experimental design:Crossover

Treatments and protocol:Subjects completed 3 separate trials of cycle sprints 1 week apart: 1) control (CT) trial; 2) heat exposure (HE) trials included heat immersion in a 39°C hot water bath with water replacement; 3) dehydration (DEHY) trials included similar heat immersion but were conducted after 3% of body weight dehydration with no fluid replacement. The study was designed to differentiate between heat exposure and dehydration. Thus, CT and HE comparisons distinguished effects of no treatment vs heat treatment; CT and DEHY comparisons differentiated between no treatment and heat immersion plus dehydration; and differences between HE and DEHY were attributed to dehydration. The cycle test consisted of a 3-minute warm-up followed by 6 maximal sprints of 15 seconds with 30 seconds of active recovery (total exercise time, 4.5 min). The test was completed with 3 minutes of active recovery. Analyses included urine output, weight, blood samples for hematocrit, mean power (MP), and peak power (PP). A survey determined perceived energy levels (1 to 10 points).

Summary of research findings:
  • Overall, the combination of heat plus dehydration impaired both MP and PP more than heat immersion alone.k
    - Notable impairment started in cycles 3 and 4, and was greatest in cycles 5 and 6.
  • MP for both HE and DEHY groups were lower than CT.
      --   HE (582 W) vs CT (596 W), P = .07
      --   DEHY (569 W) vs CT (596 W), P < .05
      --   No significant difference between HE and DEHY
  • PP for both HE and DEHY groups were lower than CT.
      --   HE (870 W) vs CT (900 W), P < .05
      --   DEHY (857 W) vs CT (900 W), P = .07
      --   No significant difference between HE and DEHY
  • Post-sprint ratings of perceived exertion were highest with DEHY (6.4), followed by HE (6.3) and CT (5.7).

Interpretation of findings/Key practice applications:

The authors stated that this was the first study to examine dehydration, specifically, on intermittent performance activity, even though this is one of the most common physical requirements between both sports and occupational exertions. All performance measures followed similar patterns and were similar across trials. These results can perhaps be explained by the increased contribution of aerobic energy with the later exercise bouts as research has shown that aerobic activity is impaired with dehydration. The authors speculate that this could have a specific effect on athletes who experience a decline in maximal performance at critical points of a competition. The results further indicate that passive dehydration could affect performance capability. Limitations of interpreting the comparison of HE and DEHY include using body weight to determine hydration status and having only water as fluid replacement.
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