Emerging Research

84 Pages·2016·17.74 MB·English

ETIOLOGY AND TREATMENT OF
EXERCISE-ASSOCIATED MUSCLE CRAMPS:
EMERGING RESEARCH
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SYMPOSIUM AGENDA
▪ Bob Murray, PhD, FACSM - Challenges of EAMC Research
▪ Kevin Miller, PhD, AT, ATC - EAMCs: Characteristics & Cures
▪ Bruce Bean, PhD - Activating Sensory Neurons to Affect Muscle Cramps
▪ Tom Wessel, MD, PhD - Neurology of Muscle Cramps
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• Bob Murray - consultant
• Kevin Miller - research funding, 2014
• Bruce Bean - company co-founder
• Tom Wessel - chief medical officer
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CASE STUDY: EAMCs IN
AN EXPERIENCED CYCLIST
▪ 40-yr-old male cyclist,

racing since age 15
▪ Leg cramps began in 2009
▪ Progressively more frequent
▪ Occur at high power outputs
▪ No impact of bike position, 

time of year, weather
▪ Has tried variations 

of hydration, sports drinks,
electrolytes, pickle juice,
beet juice, training
adjustments, nifedipine,
albuterol, nitroglycerin 

[during angiogram]
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DIFFERENTIATING
MUSCLE CRAMPS
• Neurogenic muscle cramps - EAMCs, nocturnal
• Myopathic muscle cramps - electrically silent
• Myotonia - delayed relaxation
• Myokymia - irregular twitching/rippling
• Neuromyotonia - stiffness and twitching
• Hypertonia - stiffness with upper motor neuron signs
• Dystonia - co-contractions of agonists and antagonists
• Stiff limb syndrome - painful muscle spasms
Katzberg HD. Neurogenic muscle cramps. J Neurol 262:1814-1821, 2015.
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DIFFERENTIATING
MUSCLE CRAMPS
✓
• Neurogenic muscle cramps - EAMCs, nocturnal
• Myopathic muscle cramps - electrically silent
• Myotonia - delayed relaxation
• Myokymia - irregular twitching/rippling
• Neuromyotonia - stiffness and twitching
• Hypertonia - stiffness with upper motor neuron signs
• Dystonia - co-contractions of agonists and antagonists
• Stiff limb syndrome - painful muscle spasms
Katzberg HD. Neurogenic muscle cramps. J Neurol 262:1814-1821, 2015.
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WHAT IS
A MUSCLE CRAMP?
Def. “… a sudden, involuntary, painful contraction of a muscle
or part of it, self-extinguishing within seconds to minutes and is
often accompanied by a palpable knotting of the muscle.”
Minetto MA et al. (2013) Origin and development of muscle cramps. Exerc Sports Sci Rev 41(1):3-10.
EXTENT
▪ Fasciculations / twitches
▪ One muscle or part of it
▪ A muscle group
▪ Whole-body
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CRAMP
INCIDENCE
• 68% of triathletes (lifetime)
• 30-50% of marathon runners (lifetime)
• 95% of PE students (lifetime)
• 50% of endurance athletes report nocturnal leg
cramps at least 1/wk; 50% of those athletes
suffer them nightly
• 50% of those over age 65 report nocturnal
cramps at least 1/wk
• 44-80% in neuro- and myopathic disorders
• 55-75% in diabetics
Katzberg HD. Neurogenic muscle cramps. J Neurol 262:1814-1821, 2015.
Minetto MA et al. Origin and development of muscle cramps. Exerc Sports Sci Rev 41(1):3-10, 2013.
Norris FH et al. An electromyographic study of induced and spontaneous muscle cramps. Electroencephalogr Clin Neurophysiol 9(1):139-147, 1957.
Schwellnus MP et al. Muscle cramping in athletes - risk factors, clinical assessment, and management. Clin Sports Med 27(1):183-194, 2008.
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WHAT DO WE KNOW 

ABOUT EAMCs?
▪ Occurs in active muscles
▪ Premonitory twitching (fasciculations)
▪ Triggers seem many and varied
▪ Happen in some athletes, 

not in others
▪ Range widely in severity, duration, 

and location
▪ Some “cures” seem to work for some
people some of the time
▪ Neurogenic origin
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3 THEORIES OF
EAMC ETIOLOGY
Fatigue, hyperthermia, dehydration, and/or other factors ...
produce volume/ECF changes that alter
sensitivity of the motor nerve and/or NMJ.
reduce inhibition from GTOs and increase
activation of muscle spindles.
increase persistent inward currents (PICs)
that eventually exceed the excitation
threshold of motor nerves, resulting in
fasciculations or full-blown cramps.
Katzberg HD. (2015) Neurogenic muscle cramps. J Neurol 262:1814-1821.
Miller KC. (2015). Rethinking the cause of exercise-associated muscle cramping: moving beyond dehydration and electrolyte loss.
Curr Sports Med Rep 14(5):353-354.
Minetto MA et al. (2013) Origin and development of muscle cramps. Exerc Sports Sci Rev 41(1):3-10.
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