Training-induced alterations in glucose metabolism during moderate-intensity exercise.

This research investigated the effects of exercise training on the glucose metabolism of horses during moderate intensity exercise. After six weeks of training, the horses showed reduced glucose flux during submaximal exercise at the same absolute workload. These changes may be partially due to altered levels of hormones that regulate glucose.

Objective and Methodology

• This study was designed to shed light on how exercise training affects plasma glucose kinetics in horses when they undertake submaximal exercise. Submaximal exercise refers to physical activity that is less intense than the maximum effort a horse can exert.
• The subjects of the research were 7 horses, including 5 thoroughbreds and 2 standardbreds, aged between 3 to 9 years, which had not undergone any significant physical activities for at least six months.
• The horses initially underwent a test to determine their maximum aerobic capacity (VO2max). Following this, the horses were made to run on a treadmill at 55% of their VO2max, for a duration of 60 minutes or until they reached fatigue. Then they were introduced to a program of moderate-intensity treadmill training five days per week, lasting for six weeks.
• After the training, a second VO2max test was conducted, and the horses underwent exercise trials at the same absolute (ABS) and relative (REL) workload, with a minimum of 3 days between each test.

Results

• After six weeks of exercise training, the horses’ VO2max, meaning their capacity for oxygen consumption during intense exercise, increased by an average of 14.9%.
• The average duration of exercise was longer in the ABS trial compared to both the untrained (UT) and REL trials.
• Plasma glucose concentration, which increased during exercise, was found to be lower in the ABS trial compared to the UT and REL trials by the end of the exercise.
• The mean glucose rate of appearance (Ra) and disappearance (Rd) were 22% and 21% lower, respectively, in the ABS trial compared to the UT trial. However, there was no significant difference between the UT and REL trials in terms of mean glucose Ra and Rd.
• The study also found that the exercise-induced changes in glucagon, epinephrine and norepinephrine – three key hormones that regulate glucose – were blunted when compared between ABS and UT, but not between REL and UT.

Conclusion

• The researchers concluded that moderate-intensity training over six weeks results in a decrease in glucose flux during submaximal exercise at the same absolute workload, but does not affect it at the same relative workload.
• The study also proposes that the decrease in glucose flux following exercise training could be linked to changes in the plasma concentrations of key glucoregulatory hormones like glucagon, epinephrine and norepinephrine.