Dehydration is not the cause of Cramping!

Dehydration is not the cause of Cramping!
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Take Home Points
  1. Significant hypohydration does not increase cramp risk.
  2. Cramps are likely induced by neuromuscular control changes. 
  3. Attempts should be made to improve these neuromuscular impairments during fatigue. 

Many are convinced cramping is the result of dehydration or electrolyte deficiency. Unfortunately, if you believe this, you’ve been duped into flawed thinking! Although cramping is highly common during exercise you will see, the research does not support this notion.

Braulick had thirteen men (~24.4 years) without previous leg

injury in the last twelve months, who did experience leg cramps within the past twelve months first undergo a familiarization session. This session consisted of using surface electrodes on the FHB (flexor hallucis brevis), then performed twenty repetitions of 2 second isometric contractions of the FHB with the foot being angled at 120 degrees. EMG was also measured of the FHB, to ensure activity was greater than 8 mV. A muscle cramp was defined as an involuntary contraction of the FHB immediately following the end of the electrical stimuli. EMG amplitude needed to be greater than 50% and the subject needed to verify a cramp.


The subjects then reported the procedure again, on a separate day, after they exercised in heat until they lost 5% of their body mass [note this is a lot of body mass!]or were too exhausted to continue. After these, they repeated the same cramping procedure to the FHB, as described above.

The average exercise duration to become hypohydrated was 3.9 hours! Five subjects experienced volitional exhaustion before reaching the 5% body mass reduction.

Significant hypohydration did not alter threshold frequency (TF), cramp intensity, or cramp EMG amplitude. In fact, maximal voluntary isometric contraction EMG amplitude was higher when euhydrated (the cramp was worse when euhydrated).
Cramp TF is often used as an indicator of cramp susceptibility.  This study disputes the notion that dehydration and electrolyte losses cause cramping. In fact, sodium and postasium in plasma is similar in crampers and non-crampers. Also, stretching often relieves cramps, despite no improvement in hydration, impairing the cramp notion.

Instead, cramps appear to be the result of neuromuscular changes. Some have proposed cramping is the combination of increased excitation from the Ia and decreased inhibition from Ib afferents altering the alpha-motor neuron activity. 

Next, a study must look at exercise induced (not electronically induced) cramping.


Reference

  1. Braulick KW, Miller KC, Albrecht JM, Tucker JM, Deal JE. Significant and serious dehydration does not affect skeletal muscle cramp threshold frequency. Br J Sports Med. 2013 Jul;47(11):710-4. doi: 10.1136/bjsports-2012-091501. Epub 2012 Dec 6.
 Dr. G. John Mullen, DPT, CSCS