title: Effects of unaccustomed downhill running on muscle damage, oxidative stress, and leukocyte apoptosis.
abstract: OBJECTIVE
  The purpose of this study was to investigate the effect of unaccustomed downhill running on muscle damage, oxidative stress, and leukocyte apoptosis.
  
  
  METHODS
  Thirteen moderately trained male subjects performed three 40 min treadmill runs at ~70% VO2max on separate days: a level run (L) followed by two downhill runs (DH1 and DH2). Blood samples were taken at rest (PRE) and immediately (POST), 2 h, 24 h, and 48 h after each run. Data were analyzed using 2-way repeated measures ANOVA with post hoc Tukey tests.
  
  
  RESULTS
  Creatine kinase (CK) activity and oxidative stress level were significantly elevated at 24 h and 48 h following DH1 (P < 0.05). The level of oxidative stress at the POST measurement following DH1 and DH2 was greater than PRE. The rate of leukocyte apoptosis was significantly increased at the POST measurement following all three runs, and remained elevated for up to 48 h following DH1 (P < 0.01).
  
  
  CONCLUSIONS
  CK activity and oxidative stress were elevated following an acute bout of moderate intensity downhill running, resulting in a greater apoptotic response at 24 h and 48 h post-exercise in comparison with level grade running or a second downhill run. These elevations were blunted following DH2. Although the link between exercise-induced muscle damage and leukocyte apoptosis is currently unknown, the differential response to DH1 vs. L and DH2 indicates that it may be mediated by the elevation of oxidative stress.
authors.affiliation: Kinesiology program Texas A&M International University, Laredo, TX, USA.
authors.forename: Kyung-Shin
authors.initials: KS
authors.lastname: Park
authors.affiliation: Graduate School of Physical Education, Kyung Hee University, Gyeonggi-do, Republic of Korea.
authors.forename: Man-Gyoon
authors.initials: MG
authors.lastname: Lee
keywords: Muscle damage; apoptosis; eccentric exercise; oxidative stress