INTRODUCTION

Skeletal muscle cramps are a common affliction in sports. Highly fit athletes must

sometimes succumb to debilitating cramping episodes, and some often compete with

concern, knowing that these painful, involuntary muscle contractions can appear seemingly

without warning or apparent cause.

TWO PERSPECTIVES: FATIGUE VERSUS ELECTROLYTE DEFICIT

Muscle Overload and Fatigue

During sports competition and training repeated or extended loading on muscles can lead to

muscle or tendon strain and local fatigue. The neural mechanisms designed to inhibit muscle

contraction, in response to muscle tension detected by the Golgi tendon organ, are disrupted

or depressed. At the same time, enhanced excitatory activity from the muscle triggers an

intense and sustained involuntary muscle contraction that is unopposed by Golgi tendon

organ control. Notably, shortened muscles with sustained contraction may be particularly

vulnerable to such cramping.

Predisposing risk factors associated with overload and fatigue-related muscle cramping

might include

- older age

- poor stretching habits

- insufficient conditioning

- cramping history

- excessive exercise intensity and duration

- related metabolic disturbances.

Electrolyte Deficit

With exertional heat cramps, an athlete typically has been sweating extensively with

appreciable sweat electrolyte losses as well, particularly sodium and chloride. Whether

during a single long race, match, game, or training session or consequent to multiple sameor

repeated-day exercise bouts, a sizeable whole-body exchangeable sodium deficit

develops when sweat sodium and chloride losses measurably exceed salt intake (6,7,57).

The deficit threshold required to prompt muscle cramping is not well described; however, an

estimated sweat-induced loss of 20%-30% of the exchangeable Na+ pool has been noted

with severe muscle cramping (6,29).

How readily this occurs depends upon

- sweating rate (10)

- sweat sodium concentration (typically 20-80 mmol·L-1) (7,12,28),

- dietary intake (27).

- continuous physical activity over an extended period of time (e.g., 3-4 h or more).

A high sweat sodium concentration generally stays high, even as whole-body water and

sodium deficits progressively increase. This is possible because sweating rate remains fairly

consistent during such long-term activity and serum sodium concentration is typically

maintained or elevated, along with potential changes in sweat gland function or sympathetic

nervous system activity that would tend to increase sweat sodium concentration (33).

Other electrolytes also are lost in sweat to a much lesser degree, and several of these

(namely calcium, magnesium, and potassium) have been implicated falsely as the cause of

muscle cramping during or after exercise when purported deficiencies are suspected

(3,15,23,24,31,56,62,63). However, exertional heat cramp-prone athletes characteristically

develop a sodium deficit because their sweat sodium and chloride losses are not offset

promptly and sufficiently by dietary intake (6,7,57).

RECOVERY AND PREVENTION

Muscle Overload and Fatigue

Overload and fatigue-related muscle cramps remain localized to the overworked muscle(s),

and these cramps often can be resolved readily by passive stretching, massage, active

contraction of the antagonist muscle group, or icing of the affected muscles. Lowering

overall exercise intensity and altering the load on the distressed muscle(s) can be effective

as well. Preventive measures include reducing training and competition intensity and

duration, as well as improving conditioning and range of motion through appropriate and

regular individualized progressive fitness and stretching programs. Adjustments to

equipment configuration and selection (e.g., bicycle seat and handle position, shoes),

biomechanics, and relaxation techniques may also help to avert or delay fatigue-induced

muscle cramping (4,23,30,42,50,54,56).

Electrolyte Deficit

At the first sign of muscle twitches or mild exertional heat cramps, a prompt oral bolus of a

high-salt solution (e.g., 0.5 L of a carbohydrate-electrolyte drink, with 3.0 g of salt added

and thoroughly mixed, consumed all at once or over 5-10 min) has been a proven effective

field strategy in relieving cramping or preventing muscle fasciculations from developing

into a more severe and debilitating condition (6).

Massaging and applying ice to the affected area can assist in relaxing the muscles and

relieving some of the discomfort while waiting for the ingested fluid and salt to be absorbed

adequately into circulation, although the effects of an oral salt solution often can be seen in

just a few minutes (6), as the ingested beverage is rapidly absorbed (14) and plasma sodium

levels quickly begin to change (21).

After such a high-salt solution bolus, athletes can often promptly continue and immediately

resume training or competition effectively without muscle cramping or twitching symptoms

for an hour or more (6), while additional lower-sodium fluid is consumed appropriately at

subsequent regular intervals. Continuation of activity at the same intensity likely would not

be possible if muscle overload or fatigue was the sole or primary contributing factor to the

muscle cramping.

After the training or competition session, any remaining body water and electrolyte deficits

need to be replaced with a particular emphasis on salt intake, in order to help retain (52) and

distribute the ingested fluid, so that all fluid compartments are restored sufficiently (32).

References

1. Appel, L.J., T.J. Moore, E. Obarzanek, et al. A clinical trial of the effects of dietary

patterns on blood pressure. DASH Collaborative Research Group. N. Engl. J. Med.

336:1117-1124, 1997. [Context Link]

2. Barber, B., J. Cummings, B. Farley, et al. Friend at Court: The USTA Handbook of Tennis

Rules and Regulations. White Plains, NY: United States Tennis Association Inc., 2008.

[Context Link]

3. Benda, C. Outwitting muscle cramps – is it possible? Physician Sportsmed. 17:173-178,

1989. Library Holdings [Context Link]

4. Bentley, S. Exercise-induced muscle cramp: proposed mechanisms and management.

Sports Med. 21:409-420, 1996. Bibliographic Links Library Holdings [Context Link]

5. Bergeron, M.F. Exertional heat cramps: recovery and return to play. J. Sport Rehabil.

16:190-196, 2007. Bibliographic Links Library Holdings [Context Link]

6. Bergeron, M.F. Heat cramps during tennis: a case report. Int. J. Sport Nutr. 6:62-68,

1996. Bibliographic Links Library Holdings [Context Link]

7. Bergeron, M.F. Heat cramps: fluid and electrolyte challenges during tennis in the heat. J.

Sci. Med. Sport. 6:19-27, 2003. Bibliographic Links Library Holdings [Context Link]

8. Bergeron, M.F. Sodium: the forgotten nutrient. Sports Sci. Exch. 13:1-4, 2000. [Context

Link]

9. Bergeron, M.F., C.M. Maresh, L.E. Armstrong, et al. Fluid-electrolyte balance associated

with tennis match play in a hot environment. Int. J. Sport Nutr. 5:180-193, 1995.

Bibliographic Links Library Holdings [Context Link]

10. Buono, M.J., K.D. Ball, and F.W. Kolkhorst. Sodium ion concentration vs. sweat rate

relationship in humans. J. Appl. Physiol. 103:990-994, 2007. Bibliographic Links Library

Holdings [Context Link]

11. Cleary, M., D. Ruiz, L. Eberman, I. Mitchell, and H. Binkley. Dehydration, cramping,

and exertional rhabdomyolysis: a case report with suggestions for recovery. J. Sport

Rehabil. 16:244-259, 2007. Bibliographic Links Library Holdings [Context Link]

12. Costill, D.L. Sweating: its composition and effects on body fluids. Ann. N.Y. Acad. Sci.

301:160-174, 1977. Bibliographic Links Library Holdings [Context Link]

13. Costill, D.L., R. Cote, and W. Fink. Muscle water and electrolytes following varied

levels of dehydration in man. J. Appl. Physiol. 40:6-11, 1976. [Context Link]

14. Davis, J.M., D.R. Lamb, W.A. Burgess, and W.P. Bartoli. Accumulation of deuterium

oxide in body fluids after ingestion of D2O-labeled beverages. J. Appl. Physiol.

63:2060-2066, 1987. Bibliographic Links Library Holdings [Context Link]

15. Eaton, J.M. Is this really a muscle cramp? Postgrad. Med. 86:227-232, 1989.

Bibliographic Links Library Holdings [Context Link]

16. Eichner, E.R. The role of sodium in ‘heat cramping.’ Sports Med. 37:368-370, 2007.

Bibliographic Links Library Holdings [Context Link]

17. Fortney, S.M., E.R. Nadel, C.B. Wenger, and J.R. Bove. Effect of blood volume on

sweating rate and body fluids in exercising humans. J. Appl. Physiol. 51:1594-1600, 1981.

Bibliographic Links Library Holdings [Context Link]

18. Hubbard, R.W., and L.E. Armstrong. The heat illnesses: biochemical, ultrastructural, and

fluid-electrolyte considerations. In: Human Performance Physiology and Environmental

Medicine at Terrestrial Extremes, K.B. Pandolf, M.N. Sawka, and R.R. Gonzalez (Eds.).

Indianapolis, IN: Benchmark Press, 1988, pp. 305-359. [Context Link]

19. Hutton, R.S., and D.L. Nelson. Stretch sensitivity of Golgi tendon organs in fatigued

gastrocnemius muscle. Med. Sci. Sports Exerc. 18:69-74, 1986. Ovid Full Text

Bibliographic Links Library Holdings [Context Link]

20. Jung, A.P., P.A. Bishop, A. Al-Nawwas, and R.B. Dale. Influence of hydration and

electrolyte supplementation on incidence and time to onset of exercise-associated muscle

cramps. J. Athl. Training. 40:71-75, 2005. [Context Link]

21. Kenefick, R.W., C.M. Maresh, L.E. Armstrong, et al. Plasma vasopressin and

aldosterone responses to oral and intravenous saline rehydration. J. Appl. Physiol.

89:2117-2122, 2000. [Context Link]

22. Layzer, R.B. The origin of muscle fasciculations and cramps. Muscle Nerve.

17:1243-1249, 1994. Bibliographic Links Library Holdings [Context Link]

23. Levin, S. Investigating the cause of muscle cramps. Phys. Sportsmed. 21:111-113, 1993.

Bibliographic Links Library Holdings [Context Link]

24. Liu, L., G. Borowski, and L.I. Rose. Hypomagnesemia in a tennis player. Phys.

Sportsmed. 11:79-80, 1983. Library Holdings [Context Link]

25. Maddali, S., S.A. Rodeo, R. Barnes, et al. Postexercise increase in nitric oxide in

football players with muscle cramps. Am. J. Sports Med. 26:820-824, 1998. Bibliographic

Links Library Holdings [Context Link]

26. Maughan, R.J., and J.B. Leiper. Sodium intake and post-exercise rehydration in man.

Eur. J. Appl. Physiol. Occup. Physiol. 71:311-319, 1995. Bibliographic Links Library

Holdings [Context Link]

27. Maughan, R.J., J.B. Leiper, and S.M. Shirreffs. Restoration of fluid balance after

exercise-induced dehydration: effects of food and fluid intake. Eur. J. Appl. Physiol. Occup.

Physiol. 73:317-325, 1996. [Context Link]

28. Maughan, R.J., S.J. Merson, N.P. Broad, and S.M. Shirreffs. Fluid and electrolyte intake

and loss in elite soccer players during training. Int. J. Sport Nutr. Exerc. Metab. 14:333-346,

2004. Bibliographic Links Library Holdings [Context Link]

29. McCance, R.A. Proceedings of the Royal Society of London. Series B-Biological

Sciences, Volume 119, 1935-1936: Experimental sodium chloride deficiency in man. Nutr.

Rev. 48:145-147, 1990. Bibliographic Links Library Holdings [Context Link]

30. McGee, S.R. Muscle cramps. Arch. Intern. Med. 150:511-518, 1990. Bibliographic

Links Library Holdings [Context Link]

31. Miles, M.P., and P.M. Clarkson. Exercise-induced muscle pain, soreness, and cramps. J.

Sports Med. Phys. Fitness. 34:203-216, 1994. [Context Link]

32. Mitchell, J.B., M.D. Phillips, S.P. Mercer, et al. Postexercise rehydration: effect of Na+

and volume on restoration of fluid spaces and cardiovascular function. J. Appl. Physiol.

89:1302-1309, 2000. Bibliographic Links Library Holdings [Context Link]

33. Morgan, R.M., M.J. Patterson, and M.A. Nimmo. Acute effects of dehydration on sweat

composition in men during prolonged exercise in the heat. Acta Physiol. Scand. 182:37-43,

2004. Bibliographic Links Library Holdings [Context Link]

34. Nelson, D.L., and R.S. Hutton. Dynamic and static stretch responses in muscle spindle

receptors in fatigued muscle. Med. Sci. Sports Exerc. 17:445-450, 1985. Ovid Full Text

Bibliographic Links Library Holdings [Context Link]

35. Nguyen, M.K., and I. Kurtz. Quantitative interrelationship between Gibbs-Donnan

equilibrium, osmolality of body fluid compartments, and plasma water sodium

concentration. J. Appl. Physiol. 100:1293-1300, 2006. Bibliographic Links Library Holdings

[Context Link]

36. Nguyen, M.K., and I. Kurtz. Whole-body electrolyte-free water clearance: derivation

and clinical utility in analyzing the pathogenesis of the dysnatremias. Clin. Exp. Nephrol.

10:19-24, 2006. Bibliographic Links Library Holdings [Context Link]

37. Noakes, T.D. Postexercise increase in nitric oxide in football players with muscle

cramps. Am. J. Sports Med. 27:688-689, 1999. Bibliographic Links Library Holdings

[Context Link]

38. Nose, H., G.W. Mack, X.R. Shi, and E.R. Nadel. Role of osmolality and plasma volume

during rehydration in humans. J. Appl. Physiol. 65:325-331, 1988. Bibliographic Links

Library Holdings [Context Link]

39. Nose, H., G.W. Mack, X.R. Shi, and E.R. Nadel. Shift in body fluid compartments after

dehydration in humans. J. Appl. Physiol. 65:318-324, 1988. Bibliographic Links Library

Holdings [Context Link]

40. Nygren, A.T., and L. Kaijser. Water exchange induced by unilateral exercise in active

and inactive skeletal muscles. J. Appl. Physiol. 93:1716-1722, 2002. Bibliographic Links

Library Holdings [Context Link]

41. Pyne, S. Intravenous fluids post marathon: when and why? Sports Med. 37:434-436,

2007. Bibliographic Links Library Holdings [Context Link]

42. Riley, J.D., and S.J. Antony. Leg cramps: differential diagnosis and management. Am.

Fam. Physician. 52:1794-1798, 1995. Bibliographic Links Library Holdings [Context Link]

43. Roeleveld, K., B.G. van Engelen, and D.F. Stegeman. Possible mechanisms of muscle

cramp from temporal and spatial surface EMG characteristics. J. Appl. Physiol.

88:1698-1706, 2000. Bibliographic Links Library Holdings [Context Link]

44. Ross, B.H., and C.K. Thomas. Human motor unit activity during induced muscle cramp.

Brain. 118:983-993, 1995. Bibliographic Links Library Holdings [Context Link]

45. Ruff, R.L. Effects of length changes on Na+ current amplitude and excitability near and

far from the end-plate. Muscle Nerve. 19:1084-1092, 1996. Bibliographic Links Library

Holdings [Context Link]

46. Sacks, F.M., L.P. Svetkey, W.M. Vollmer, et al. Effects on blood pressure of reduced

dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) diet. DASHSodium

Collaborative Research Group. N. Engl. J. Med. 344:3-10, 2001. [Context Link]

47. Sanders, B., T.D. Noakes, and S.C. Dennis. Sodium replacement and fluid shifts during

prolonged exercise in humans. Eur. J. Appl. Physiol. 84:419-425, 2001. Bibliographic Links

Library Holdings [Context Link]

48. Sanders, B., T.D. Noakes, and S.C. Dennis. Water and electrolyte shifts with partial fluid

replacement during exercise. Eur. J. Appl. Physiol. Occup. Physiol. 80:318-323, 1999.

Bibliographic Links Library Holdings [Context Link]

49. Schwellnus, M.P. Muscle cramping in the marathon: aetiology and risk factors. Sports

Med. 37:364-367, 2007. [Context Link]

50. Schwellnus, M.P., E.W. Derman, and T.D. Noakes. Aetiology of skeletal muscle ‘cramps’

during exercise: a novel hypothesis. J. Sport Sci. 15:277-285, 1997. Library Holdings

[Context Link]

51. Schwellnus, M.P., J. Nicol, R. Laubscher, and T.D. Noakes. Serum electrolyte

concentrations and hydration status are not associated with exercise associated muscle

cramping (EAMC) in distance runners. Br. J. Sports Med. 38:488-492, 2004. Bibliographic

Links Library Holdings [Context Link]

52. Shirreffs, S.M., and R.J. Maughan. Volume repletion after exercise-induced volume

depletion in humans: replacement of water and sodium losses. Am. J. Physiol. 274:F868-

F875, 1998. Bibliographic Links Library Holdings [Context Link]

53. Siegel, A.J. Hypertonic (3%) sodium chloride for emergent treatment of exerciseassociated

hypotonic encephalopathy. Sports Med. 37:459-462, 2007. Bibliographic Links

Library Holdings [Context Link]

54. Simchak, A.C., and R.M. Pascuzzi. Muscle cramps. Semin. Neurol. 11:281-287, 1991.

Bibliographic Links Library Holdings [Context Link]

55. Sjogaard, G., R.P. Adams, and B. Saltin. Water and ion shifts in skeletal muscle of

humans with intense dynamic knee extension. Am. J. Physiol. 248:R190-R196, 1985.

Bibliographic Links Library Holdings [Context Link]

56. Stamford, B. Muscle cramps: untying the knots. Phys. Sportsmed. 21:115-116, 1993.

Bibliographic Links Library Holdings [Context Link]

57. Stofan, J.R., J.J. Zachwieja, C.A. Horswill, et al. Sweat and sodium losses in NCAA

football players: a precursor to heat cramps? Int. J. Sport Nutr. Exerc. Metab. 15:641-652,

2005. Bibliographic Links Library Holdings [Context Link]

58. Sulzer, N.U., M.P. Schwellnus, and T.D. Noakes. Serum electrolytes in Ironman

triathletes with exercise-associated muscle cramping. Med. Sci. Sport Exer. 37:1081-1085,

2005. Ovid Full Text Bibliographic Links Library Holdings [Context Link]

59. Taylor, H.L., A. Henschel, O. Mickelsen, and A. Keys. The effect of sodium chloride

intake on the work performance of man during exposure to dry heat and experimental heat

exhaustion. Am. J. Physiol. 140:439-451, 1943. [Context Link]

60. Vaamonde, C.A. Sodium depletion. In: Sodium: Its Biological Significance, S. Papper

(Ed.). Boca Raton: CRC Press, 1982, pp. 207-234. [Context Link]

61. Valentine, V. The importance of salt in the athlete’s diet. Curr. Sports Med. Rep.

6:237-240, 2007. Ovid Full Text Bibliographic Links Library Holdings [Context Link]

62. Weller, E., P. Bachert, H.M. Meinck, et al. Lack of effect of oral Mg-supplementation on

Mg in serum, blood cells, and calf muscle. Med. Sci. Sport Exer. 30:1584-1591, 1998. Ovid

Full Text Bibliographic Links Library Holdings [Context Link]

63. Williamson, S.L., R.W. Johnson, P.G. Hudkins, and S.M. Strate. Exertion cramps: a

prospective study of biochemical and anthropometric variables in bicycle riders. Cycling

Sci. 5:15-20, 1993. [Context Link]