**3. Results**

### *3.1. Cardiopulmonary Fitness and Hematological and Blood Gas Parameters*

There were no differences in anthropometric characteristics, hematological parameters, blood pH, lactate concentration or exercise performance among the groups at baseline (Table 1). Following 6 weeks of training, both the CCT and ECT groups demonstrated increases in work rate, VE, and VO2 at the ventilation threshold (VT). Moreover, CCT was superior to ECT for enhancing the work rate and VO2 at VT. At the peak performance, only CCT enhanced the VEmax and VO2 max, while ECT only resulted in an improvement in the work rate (Table 1). However, 6 weeks of the CTL did not influence hematological parameters or cardiopulmonary responses to a GXT (Table 1).

**Table 1.** Anthropometric data and ventilatory responses to graded exercise test in concentric and eccentric training groups.


Values were mean ± SEM. **Hb**, hemoglobin; **VE**, minute ventilation; **VO2**, oxygen consumption; **OUES**, oxygen uptake efficiency slope; **CCT**, concentric cycling training; **ECT**, eccentric cycling training; **CTL**, control group. **Pre**, pre-intervention; **Post**, post-intervention; **Rest,** at rest; **Ex,** immediately after the GXT; # *p* < 0.05, Rest vs. Ex; \* *p* < 0.05, Pre vs. Post; † *p* < 0.05, CCT vs. ECT.

#### *3.2. Pain Scale Scores, Heart Rate and Systolic Blood Pressure during the Training Period*

The CCT group had significantly higher levels of pain, H, and SBP than the ECT group throughout the 6 week training period (Figure 2). Concerning the assessment of pain or soreness, the specific pain scale score was close to zero in both groups before each training session (Figure 2A).

**Figure 2.** The physiological responses in each week during the training period. (**A**) pain scale score, (**B**) heart rate, and (**C**) systolic blood pressure. Whites— eccentric cycling training (ECT); Blacks concentric cycling training (CCT); Dots—before training; Triangles—after training. Values were mean ± SEM.

#### *3.3. Erythrocyte Senescence-Related Markers and Antioxidation Capacity*

The ratios of Ex to Rt in CD147 and CD47 cells were less than 1 before training, indicating enhanced senescence in erythrocytes due to an acute GXT. After the interventions, these ratios significantly increased to nearly 1 in response to a GXT (Figure 3A,B). Intracellular ROS levels were significantly increased after an acute GXT among the three groups; however, both training groups had lower ROS production related to the GXT after training (Figure 3C). Furthermore, as Figure 3D,F shows, a higher TBHP concentration induced greater ROS generation. Nevertheless, the two exercise regimens significantly diminished the extent of ROS generation under 50 and 100 mM TBHP conditions (Figure 3D,E). No alteration was observed in the CTL group (Figure 3F).

**Figure 3.** Effects of various ECT and CCT on the erythrocyte senescence-related biomarkers, intracellular reactive oxygen species (ROS) level and the ROS dose-response. (**A**) the ratio of post-graded exercise test (GXT) to pre-GXT in CD47, (**B**) the ratio of post-GXT to pre-GXT in CD147, (**C**) the intracellular ROS level among three groups; the ratio of Ex to Rt ROS response in erythrocytes treated with different concentrations of tert-butyl hydroperoxide (tb): (**D**) the CCT group, (**E**) the ECT group, and (**F**) the control (CTL) group. **Pre**, pre-intervention; Post, post-intervention; M or Ex, immediately after a GXT; R or Rt, at rest. \* *p* < 0.05, R vs. M; † *p* < 0.05, Pre vs. Post. Values were mean ± SEM.
