Does usefulness of potassium supplementation depend on speed?
BACKGROUND
Electrolyte mixtures given to counter sweat loss usually contain abundant potassium. However, increases in plasma [K+] occur with exercise and supplementation may further increase plasma levels, potentially increasing the risk of neuromuscular hyperexcitability and development of adverse clinical sequellae. This proposition requires study.


OBJECTIVE
To compare effects of a K-rich electrolyte supplement (EM+K) to a K-free one (EM-K) on plasma [K+], [Ca++] and acid-base status during an endurance incremental exercise test on the treadmill.


METHODS
The test consisted of 3 bouts (simulating loops in an endurance race) of 12 km performed at 6, then 7, then 8 m/sec with 25 min rest stops (S1, S2) between loops on 13 endurance trained Arabian horses (7 EM-K, 6 EM+K). Electrolytes were supplied orally 60 mins before exercise (Pre) and at each stop. Blood samples were taken before exercise and during exercise, each S and 120 mins of recovery (R). Blood was analysed for pH, PCO2, packed cell volume (PCV), plasma [Na+], [K+], [Cl-], [Ca++], glucose, and lactate [La-]; plasma [H+] and osmolality (osm) were calculated. The dietary cation anion difference (DCAD) was calculated to be -27 meq/dose EM-K and 109 meq in EM+K, respectively.


RESULTS
Plasma [H+] decreased during the 6 and 7 m/sec loops, increased during the 8 m/sec loop, and returned to Pre at S1, S2 and R. Plasma [K+] was higher at 8 m/sec and plasma [Ca++] was overall lower in the EM+K group compared to EM-K. Other findings included higher overall PCV, overall glucose, and [La-] during the 8 m/sec loop (P<0.040) in EM+K compared to EM-K horses.


CONCLUSIONS
EM+K supplementation leads to higher plasma [K+] increasing the risk of neuromuscular hyperexcitability during exercise. Acute effects of a lower DCAD in EM-K may have led to higher plasma [Ca++]. Potassium-rich electrolytes may have triggered the release of epinephrine, contributing to higher PCV, glucose release and increased lactate production.


CONCLUSIONS
Lower plasma [K+] and higher plasma [Ca++] with EM-K supplementation may help reduce the risk of conditions associated with neuromuscular hyperexcitability occurring especially during higher speeds in endurance races.
Hess
T M
TM
Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0306, USA.
Kronfeld
D S
DS
Carter
R A
RA
Treiber
K H
KH
Byrd
B M
BM
Staniar
W B
WB
Smith
L T
LT
Gay
L A
LA
Harris
P A
PA
D000136:Acid-Base Equilibrium / Q000187:drug effects / Q000502:physiology; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001774:Blood Chemical Analysis / Q000662:veterinary; D002118:Calcium / Q000097:blood*; D019587:Dietary Supplements; D005080:Exercise Test / Q000662:veterinary; D006736:Horses / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D009751:Nutritional Requirements; D009994:Osmolar Concentration; D010805:Physical Conditioning, Animal / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*; D011188:Potassium / Q000097:blood*; D017419:Potassium, Dietary / Q000008:administration & dosage* / Q000494:pharmacology; D013542:Sweat / Q000737:chemistry; D014882:Water-Electrolyte Balance / Q000187:drug effects / Q000502:physiology
D017419:Potassium, Dietary; D011188:Potassium; D002118:Calcium