*2.4. Graded Exercise Test*

The participants performed a GXT until exhaustion to determine the exercise intensity (80% VO2max). The treadmill (pulsar; h/p/cosmos, Nussdorf, Germany) GXT protocol was based on a previous study [31], wherein the treadmill speed started at 2.0 m/s and increased by 0.5 m/s every 4 min for the first three stages, after which the intensity was further elevated in increments of 0.5 m/s every 2 min until the participant reached exhaustion. Expired gas, VO2, and VCO2 were analyzed using gas analysis (Vmax Spectra 29c; SensorMedics, Yorba Linda, CA, USA), and HR was monitored (Polar S610; Kempele, Finland) at the same time points. Individual VO2max was assumed to have been achieved when two of the following criteria were met: (1) respiratory exchange ratio greater than 1.1, (2) rating of perceived exertion greater than 18, and (3) HR within 15 beats/min of individual predicted HRmax.

### *2.5. Blood Sampling and Analysis*

Blood samples were drawn from the participants through antecubital vein suction into ethylenediaminetetraacetic acid tubes. A small portion of whole blood (400 μL) was then immediately analyzed for lymphocyte apoptosis and MTP decline in lymphocytes. Other blood samples were centrifuged at 2500× *g* for 20 min at 4 ◦C in an Eppendorf centrifuge 5804 R (Eppendorf AG, Hamburg, Germany). The supernatant was collected and stored at −20 ◦C before being analyzed for the concentrations of betaine, choline, thiobarbituric acid reactive substance (TBARS), and protein carbonyl (PC).
