*3.2. Antioxidant Parameters*

Table 2 shows the outcomes of CAT, SOD, GSSG, GSH, %GSSG/GSH and GSSG+GSH, which were measured at baseline before the incremental tests. Higher levels in CAT (30.0%, *p* < 0.001), GSSG (63.2%, *p* < 0.001) and %GSSG/GSH (70.1%, *p* < 0.001), and lower levels in SOD (−16.2%, *p* = 0.009) were found in PRO compared to AMA. However, no differences in GSH (−4.3%, *p* = 0.216) and GSSG+GSH (−3.5%, *p* = 0.317) values were observed between PRO and AMA.


**Table 1.** Baseline general characteristics and hemogram variables of professional and amateur cyclists.

Values are expressed as mean (SD). Abbreviations: RBC = red blood cell; Hb = hemoglobin; HCT = hematocrit; MCV = mean corpuscular volume; MCH = mean corpuscular hemoglobin; MCHC = mean corpuscular hemoglobin concentration and SD = standard deviation.

**Table 2.** Endogenous antioxidant enzymes from professional and amateur cyclists.


Values are expressed as mean (SD). Abbreviations: CAT = catalase; SOD = superoxide dismutase; GSH = reduced glutathione; GSSG = oxidized glutathione; % GSSG/GSH = oxidized/reduced glutathione ratio and SD = standard deviation.

#### *3.3. Physiological and Metabolic Parameters at VT1*

VO2, W, WR, %VO2MAX, HR and RER values at VT1 are shown in Table 3. Significant group differences in VO2 (76.0%, *p* < 0.001), W (90.4%, *p* < 0.001), WR (92.5%, *p* < 0.001), %VO2MAX (53.3%, *p* < 0.001) and HR (12.9%, *p* = 0.004), but not for RER (0.78%, *p* = 0.707) were observed.

**Table 3.** Metabolic and performance variables of professional and amateur cyclists.



**Table 3.** *Cont.*

Values are expressed as mean (SD). Abbreviations: VO2 = oxygen uptake; VO2max = maximum oxygen consumption; VO2/R = maximum oxygen consumption relative to weight; W = power output; WR = power output relative to weight; %VO2max = percentage of VO2max; HR = heart rate (beats·min−1); RER = respiratory exchange ratio; VT1 = ventilatory threshold 1; VT2 = ventilatory threshold 2 and SD = standard deviation.

GSSG/GSH was significantly correlated with WVT1 and VO2VT1(r = −0.657 and r = −0.651; *p* < 0.05, respectively) in PRO (Table 4) (Figure 1).

**Table 4.** Correlation between endogenous antioxidant enzymes and performance-metabolic variables from professional and amateur cyclists.



**Table 4.** *Cont.*

Values are expressed as mean (SD). Abbreviations: CAT = catalase (U/g Hb); SOD = superoxide dismutase (U/g Hb); GSH = reduced glutathione (nmol/mg protein); GSSG = oxidized glutathione (nmol/mg protein); % GSSG/GSH = oxidized/reduced glutathione ratio; VO2 = oxygen uptake; VO2MAX = maximum oxygen consumption; VT1 = ventilatory threshold 1; VT2 = ventilatory threshold 2 and W = power output.

**Figure 1.** Correlations between the power generated at the ventilation threshold 1 and 2 between the GSSS/GSH ratio in PRO and AMA.

#### *3.4. Physiological and Metabolic Parameters at VT2*

Table 3 demonstrates the VT2 results of VO2, W, WR, %VO2MAX, HR and RER. Significant group differences in VO2VT2 (25.6%, *p* = <0.001), WVT2 (32.5%, *p* = <0.001), WRVT2 (34.1%, *p* < 0.001) and %VO2MAXVT2 (6.6%, *p* = 0.005) were observed.

GSSG/GSH was significantly correlated with WVT2 and VO2VT2(r = −0.635 and r = −0.622; *p* < 0.05, respectively) in PRO (Figure 1). GSSG tended to correlate with WVT2 (r = −0.575; *p* = 0.06) in PRO (Table 4).
