Fluid and electrolyte supplementation after prolonged moderate-intensity exercise enhances muscle glycogen resynthesis in Standardbred horses

Abstract

Waller AP, Heigenhauser GJ, Geor RJ, Spriet LL, Lindinger MI. Fluid and electrolyte supplementation after prolonged moderateintensity exercise enhances muscle glycogen resynthesis in Standardbred horses. J Appl Physiol 106: 91-100, 2009. First published October 23, 2008 doi:10.1152/japplphysiol.90783.2008.-We hypothesized that postexercise rehydration using a hypotonic electrolyte solution will increase the rate of recovery of whole body hydration, and that this is associated with increased muscle glycogen and electrolyte recovery in horses. Gluteus medius biopsies and jugular venous blood were sampled from six exercise-conditioned Standardbreds on two separate occasions, at rest and for 24 h following a competitive exercise test (CET) designed to simulate the speed and endurance test of a 3-day event. After the CETs, horses were given water ad libitum, and either a hypotonic commercial electrolyte solution (electrolyte) via nasogastric tube, followed by a typical hay/grain meal, or a hay/grain meal alone (control). The CET resulted in decreased total body water and muscle glycogen concentration of 8.4 Ϯ 0.3 liters and 22.6%, respectively, in the control treatment, and 8.2 Ϯ 0.4 liters and 21.9% in the electrolyte treatment. Electrolyte resulted in an enhanced rate of muscle glycogen resynthesis and faster restoration of hydration (as evidenced by faster recovery of plasma protein concentration, maintenance of plasma osmolality, and greater muscle intracellular fluid volume) during the recovery period compared with control. There were no differences in muscle Na, K, Cl, or Mg contents between the two treatments. It is concluded that oral administration of a hypotonic electrolyte solution after prolonged moderate-intensity exercise enhanced the rate of muscle glycogen resynthesis during the recovery period compared with control. It is speculated that postexercise dehydration may be one key contributor to the slow muscle glycogen replenishment in horses. skeletal muscle; rehydration; exercise; instrumental neutron activation analysis IN THE HORSE, BOTH short-term, high-intensity, and prolonged submaximal exercise result in dehydration, loss of water and electrolytes, and depletion of skeletal muscle glycogen (23,30,31,52,53,56). Resynthesis of muscle glycogen stores requires 48 -72 h in horses, compared with 2.5 h in rats (16) and Ͻ24 h in humans (12). Previous studies in horses have altered postexercise nutrition strategies in attempts to enhance muscle glycogen resynthesis. Despite demonstrations that intravenous infusion of large amounts of glucose (3-6 g/kg) modestly accelerated muscle glycogen replenishment (14, 17), conventional feeding strategies have not been successful (23,(53)(54)(55). Initial glycogen resynthesis rates in horses after ingestion of meals with varying soluble carbohydrate (CHO) contents ranged from ϳ8 to ϳ12 mmol⅐kg dry wt Ϫ1 ⅐h Ϫ1 for mixed and high-soluble CHO diets, respectively. In contrast, in humans, initial glycogen storage rates are ϳ40 mmol⅐kg dry wt Ϫ1 ⅐h Ϫ1when at least 5 g/kg...

Do hematologic constituents really increase due to endurance exercise in horses?

“…Splenic contraction due to an adrenergic stimulus (Snow et al 1992) and sweating leading to extense body ϐluid losses, in more prolonged exercises. As thermoregulation leads to intense sweating with evident body ϐluids losses and haemoconcentration (Waller et al 2009). He, Hb and HT values showed the relationship with haemoconcentration during rides while its values increased right at the ϐirst timepoint of rides and returned to basal values 24 hours after the exercise was completed.…”

“…Horses can suffer from dehydration and heat stress (Waller et al 2009), leading to a large number of clinical disorders indicating that the equine athlete is not prepared for the task. The exercising horse produces a tremendous amount of metabolic heat and, like humans, cools primarily by the evaporation of sweat leading to ϐluids and electrolytes losses that, if uncompensated for, can lead to cardiovascular and thermoregulatory instability (McKeever 2008).…”

Nutritional aspects of post exercise skeletal muscle glycogen synthesis in horses: A comparative review

“…This led us to hypothesise that rehydration with electrolyte solution with provision of a CHO source should have an even greater positive effect. We demonstrated that administration of a balanced hypotonic commercial electrolyte solution post exercise, followed by a typical hay and grain meal, resulted in enhanced muscle glycogen synthesis during the recovery period, compared to a typical hay/grain meal alone (Waller et al. 2009b).…”

“…Water alone is also not effective in restoring hydration and there is a requirement for electrolytes to osmotically retain water in the appropriate extracellular and intracellular fluid compartments (Maughan et al. 1994; Maughan and Lindinger 1995; Jansson and Dahlborn 1999; Waller et al. 2009b).…”

“…Therefore the importance of replacing the electrolytes lost in sweat as a means to recovering fluid balance horses is clear. Water alone is also not effective in restoring hydration and there is a requirement for electrolytes to osmotically retain water in the appropriate extracellular and intracellular fluid compartments (Maughan et al 1994;Maughan and Lindinger 1995;Jansson and Dahlborn 1999;Waller et al 2009b). In addition, it is well accepted that dehydration, from loss of total body water, and alterations in blood/muscle electrolyte and consequently acid-base state, can impair health, well-being, and physical and cognitive performance (Carlson et al 1976;Guthrie and Lund 1998;McKeever 1998;Hoffman et al 2002).…”