Adrenal Medulla Responsiveness to the Sympathetic Nervous Activity in Sprinters and Untrained Subjects During a Supramaximal Exercise

The purpose of this study was to compare the adrenal medullar responsiveness to the sympathetic nervous activity between sprinters and untrained subjects after a supramaximal exercise (Wingate-test). Thirteen subjects took part in this study: 7 male athletes (20.3 + 1.8 years) competing in sprint running (S) and 6 untrained men (UT) (21 + 1.3 years). They performed an incremental treadmill test to determine the maximal oxygen uptake (VO₂max), a force-velocity test and a Wingate-test on 3 different days, separated by a maximal interval of 15 days. The maximal power (Wmax) and the mean power (W) were determined from the Wingate-test on a cycle ergometer. Plasma lactate, adrenaline and noradrenaline concentrations were determined at rest (La₀, A₀, NA₀), immediately after the Wingate- test (Amax, NAmax) and after 5 minutes recovery (La-max, A₅ and NA₅). S exhibited higher performances than UT during the Wingate-test as shown by their significantly higher values of W_max (1111 ± 38 w in S vs 886 ± 148 w in UT), W (822 ± 37 w in S vs 646 ± 69 w in UT) and Lamax (16.8 ± 1.8 mmol · l^-1 in S vs 12.2 ± 2.5 mmol · l^-1 in UT). At the end of the test the NAmax values were similar in both groups whereas the Amax were significantly higher in S (7.6 + 1.4 nmol · l^-1 in S vs 3.6 ± 3.2 nmol · l^-1 in UT). This leads to a higher Amax/NAmax ratio for sprinters compared to untrained subjects (0.7 ± 0.2 in S vs 0.3 ± 0.2 in UT, p < 0.05). As the disappearance of A (estimated by the Amax-A₅ difference) was not lower in S (6.4 ± 1.5 nmol · l^-1 in S vs 1.8 ± 4 nmol · l^-1 in UT), the higher Amax values in S might be explained by a greater secretion level of A. Conversely the identical NAmax values in both groups suggested that this kind of exercise induced the same sympathetic input in S and UT. Consequently the higher Amax/NAmax ratio in S argued in favor of a higher responsiveness of the adrenal medulla of sprinters to the same sympathetic input.

Key words

Exercise - catecholamine - lactate - training