Negative energy balance could regulate leptin levels during a 4-hour treadmill test

It has been shown that serum Leptin concentrations (Lep) are directly correlated with energy balance. It has also been shown that exercise induces an increase in body energy expenditure (EE). In previous studies, we found that prolonged exercise, differing in intensity and duration, induce a decrease in Lep levels. Thus, we hypothesize a decrease in Lep levels is related to varying EE. PURPOSE: To evaluate the relationship between levels of Lep and metabolic responses during prolonged, strenuous exercise. METHODS: Seven male athletes (age 27±4.2 y, mean±SD) performed a four-hour treadmill exercise, with speed and gradient were modified to maintain Lactate (Lac) levels between 1.5-2.0 mM/L and with a steady Energy Expenditure of 60% of VO2 max. A 10-minute sample of Expiratory gas exchanges and blood samples for Lac, Lep, Blood Glucose (BG), Insulin (I), Free Fatty Acid (FFA), and Glicerol (GL) were collected at the beginning of exercise; and each hour during exercise. Results are expressed as mean±SE. RESULTS: Hourly EE ranged between 823±26 and 879±34, and average four hours EE was 3364±96 kcal. BG didn’t significantly change, while I decreased from 20.0±5.3 to 4.71±0.3 mU/mL, (p<.05). However, GL and FFA progressively increased during the test, (from 118.4±16.8 to 501.7±68.7 mg/L, p<.001, and from 166.4±20.1 to 1465.4±185.3 mM/L, p<.0005, respectively). Lep remained unchanged until 180 min and than showed a slight decrease (from 1,103±0.388, basally, to 0.846±0.246 mg/L at 240 min, p<.005) of about 19% at the end of the exercise. Moreover, it was significantly inversely correlated with EE during the time from 180 to 240 min (r=.557. p<.01) and with FFA during the overall test (r=.481 p<.01), but no relationship was found with insulin. CONCLUSION: these data support the hypothesis that during prolonged exercise Lep levels decrease related to intensity and respective EE. It still remains to be seen a Lep decrease may be due to EE per se, or related to hormonal changes occurring during exercise.