Journal Title (Medline/Pubmed accepted abbreviation): Med Sci Sports Exerc
Page numbers: 2056-2063
Summary of Background and Research Design
Background: Dehydration during exercise may be associated with muscle cramps. Research into the mechanism of exercise-associated muscle cramping (EAMC) is often observational, and factors such as fatigue or electrolyte loss are rarely controlled. Inducing cramps with electrical stimulation, rather than from exercise, minimizes potential confounding factors (eg, fatigue, metabolites), allowing a more accurate assessment of the role of hypohydration in EAMC.
Hypothesis: The authors hypothesized that: 1) mild dehydration decreases the electrical stimuli required to elicit cramping (termed "threshold frequency") by 8 Hz ± 6 Hz; and 2) mild (3%) hypohydration will increase cramp intensity and duration in this model of EAMC.
Subjects: Ten healthy, college-aged males (mean ± standard error [SE], age = 23.5 ± 1.0 yr, height = 177.8 ± 1.8 cm, mass = 73.9 ± 2.8 kg) completed the study.
Experimental design: N/A
Treatments and protocol: Hypohydration was induced by 30-min bouts of cycling with the non?dominant leg at 41°C and 15% humidity until subjects lost ~3% of total body mass (~2 hours). Before and after hypohydration, muscle cramps were electrically induced in the dominant leg and the cramp threshold frequency was recorded.
Summary of research findings:
- Subjects were hypohydrated after exercise (pre-exercise plasma osmolality [OSMp] = 282.5 ± 0.7 mOsm/kg H2O, postexercise OSMp = 295.1 ± 1 mOsm/kg H2O, P < .001)
- Subjects lost 3.0% ± 0.1% of body mass, 144.9 ± 9.8 mmol of Na+, 11.2 ± 0.4 mmol of K+, 3.3 ± 0.3 mmol of Mg2+, and 3.1 ± 0.1 mmol of Ca2+
- Mild hypohydration with minimal neuromuscular fatigue did not affect the cramp threshold frequency (euhydrated = 23.7 ± 1.5 Hz, hypohydrated = 21.3 ± 1.4 Hz; F1,9 = 2.81, P = .12)
- Analysis of covariance (ANCOVA) calculations found no interaction between hydration status and experimental day for percent changes in body weight, plasma volume (PV), hematocrit (Hct), hemoglobin concentration ([Hb]), OSMp, [Na+], [K+], [Mg2+], or [Ca2+]
Interpretation of findings/Key practice applications:
In contrast with observations from the literature, mild hypohydration and electrolyte losses with minimal neuromuscular fatigue do not seem to predispose individuals to EAMC. Thus, cramps may be more associated with neuromuscular fatigue than dehydration/electrolyte losses. Health care professionals may have more success preventing EAMC by focusing on strategies that minimize neuromuscular fatigue rather than dehydration. However, the effect of fluid losses that are > 3% of body mass on cramp threshold frequency is unknown and merits further research.