Significant and serious dehydration does not affect skeletal muscle cramp threshold frequency
- 1Departments of Health, Nutrition, and Exercise Sciences, North Dakota State University, Fargo, North Dakota, USA
- 2Department of Health and Physical Education, Minnesota State University Moorhead, Moorhead, Minnesota, USA
- 3Healthy Weight Center, Helen DeVos Children's Hospital, Grand Rapids, Michigan, USA
- 4Human Development and Family Science, North Dakota State University, Fargo, North Dakota, USA
- Correspondence to Dr Kevin C Miller, Department of Health, Nutrition, and Exercise Sciences, North Dakota State University, NDSU Dept #2620, PO Box 6050, Fargo ND 58108-6050, USA;
- Received 26 June 2012
- Revised 8 October 2012
- Accepted 10 November 2012
- Published Online First 6 December 2012
Objective Many clinicians believe that exercise-associated muscle cramps (EAMC) occur because of dehydration. Experimental research supporting this theory is lacking. Mild hypohydration (3% body mass loss) does not alter threshold frequency (TF), a measure of cramp susceptibility, when fatigue and exercise intensity are controlled. No experimental research has examined TF following significant (3–5% body mass loss) or serious hypohydration (>5% body mass loss). Determine if significant or serious hypohydration, with moderate electrolyte losses, decreases TF.
Design A prepost experimental design was used. Dominant limb flexor hallucis brevis cramp TF, cramp electromyography (EMG) amplitude and cramp intensity were measured in 10 euhydrated, unacclimated men (age=24±4 years, height=184.2±4.8 cm, mass=84.8±11.4 kg). Subjects alternated exercising with their non-dominant limb or upper body on a cycle ergometer every 15 min at a moderate intensity until 5% body mass loss or volitional exhaustion (3.8±0.8 h; 39.1±1.5°C; humidity 18.4±3%). Cramp variables were reassessed posthypohydration.
Results Subjects were well hydrated at the study's onset (urine specific gravity=1.005±0.002). They lost 4.7±0.5% of their body mass (3.9±0.5 litres of fluid), 4.0±1.5 g of Na+ and 0.6±0.1 g K+ via exercise-induced sweating. Significant (n=5) or serious hypohydration (n=5) did not alter cramp TF (euhydrated=15±5 Hz, hypohydrated=13±6 Hz; F1,9=3.0, p=0.12), cramp intensity (euhydrated= 94.2±41%, hypohydrated=115.9±73%; F1,9=1.9, p=0.2) or cramp EMG amplitude (euhydrated=0.18±0.06 µV, hypohydrated= 0.18±0.09 µV; F1,9=0.1, p=0.79).
Conclusions Significant and serious hypohydration with moderate electrolyte losses does not alter cramp susceptibility when fatigue and exercise intensity are controlled. Neuromuscular control may be more important in the onset of muscle cramps than dehydration or electrolyte losses.