Strenuous exercises greatly increase oxygen consumption in the whole body, especially in skeletal muscles. Large part of oxygen consumption is reduced to H2O and ATP, but smaller part (2-5%) results in an increased leakage of electrons from the mitochondrial respiratory chain, forming various reactive oxygen species-ROS (02, H2O,iOH). These free ra- dicals are capable of triggering a chain of damaging biochemical and physiological reactions (oxidative stress, lipid peroxi- dation), as a base for skeletal muscles damage after exercise. MDA (malondialdehyde) is a marker of exercise induced lipid peroxidation process. L-ascorbic acid is a major aqueous-phase antioxidant. To estimate antioxidant role of ascorbic acid we use rate between dehydroascorbate and ascorbate. In this paper those markers of lipid peroxidation (MDA, MDA ind, % ind MDA), and ascorbic acid status (ascorbic acid Asc, ascorbat A, dehidroascorbat DHA, DHA/A) were determinated in 30 stu- dents, in rest and after treadmill running protocol (Bruce Treadmill Protocol). It was found that after the treadmill test, plas- ma MDA level had increased from 3,04 to 4,39 M/L (p<0,0001) and % ind MDA decreased significantly from 35% to 24,7% (p=0,0003). Plasma ascorbic acid was also found to be higher after the treadmill test comparing to rest level (from 55,4 to 67,6 μM/L). DHA/A level in rest was 1,62 and after treadmill test it increased to 2,05 (p=0,0014). These results suggests that strenuous exercise increased process of lipid peroxidation (MDA †, % ind MDA), but in the same time incre- ased ascorbic acid level in plasma and DHA/A rate indicates stronger activation of nonenzymatic antioxidant defense system.