Do Different Interval Durations of High-Intensity Interval Training Influence Blood Glucose and Lactate, and Cause Hepatic Damage in Rats?

Background: High-intensity interval training (HIIT) is an exercise modality that can induce reactive oxygen species (ROS) pro-duction in skeletal muscles, the extent of which depends on the intensity, duration, and volume of exercise, potentially leading to oxidative stress.Objective: To analyze the effects of a single session of two HIIT protocols with different intensity levels on the markers of blood sugar, lactate, and hepatic damage in rats.Methods: Overall, 24 male Wistar rats were included in the study and divided into three groups (n = 8/group): control group (CG); short-interval HIIT (H1): HIIT involving 14 swimming periods lasting 20 s each, with 10-s intervals between each period, totaling a duration of 7 min; long-interval HIIT (H2): HIIT involving 14 swimming periods lasting 35 s each, with 25-s intervals between each period, totaling a duration of 14 min.Results: Regarding blood sugar levels, there were no significant differences in the H1 (113.00 +/- 8.21 vs. 123.25 +/- 10.78; p = 0.3303) and H2 (112.25 +/- 12.55 vs. 114.25 +/- 8.77; p = 0.9545) groups, respectively. Regarding lactate levels, there was a significant difference in both the groups compared with the CG (H1: 2.75 +/- 0.55 vs. 10.06 +/- 1.93; p = 0.0003; H2: 2.65 +/- 1.07 vs. 9.99 +/- 1.30; p = 0.0001). However, there was no difference in lactate levels between the H1 and H2 groups (10.06 +/- 1.93 vs. 9.99 +/- 1.30; p = 0.9965). Regarding hepatic damage, only H1 demonstrated a reduction in aspartate aminotransferase (AST) and alanine transaminase (ALT) levels compared with CG (30% and 29.65%, respectively; p < 0.05). Conversely, there were no significant differences in the AST levels between both the groups and CG (16.40 +/- 1.91 [H2] vs. 13.98 +/- 1.06 [CG]; -14.75%; p = 0.0918; 11.48 +/- 1.59 [H1] vs. 13.98 +/- 1.06 [H2]; p = 0.0792). Additionally, there was no significant difference in the ALT levels between the HIIT groups (8.54 +/- 1.70 [H1] vs. 10.32 +/- 0.78 [H2]; p = 0.1756).Conclusions: A single session of HIIT training with different intensity levels does not induce changes in blood sugar and lactate markers. Furthermore, short-duration HIIT induced alterations in the hepatic markers (AST and ALT) compared with the control group. However, when comparing the HIIT groups, no significant alterations were observed following a single HIIT session.