Downhill Running: An Effective Countermeasure To Limitations Of Exercise In Acute Hypoxia?

Abstract

Exercise stress that results in increased expression of heat shock protein 72 (Hsp72) is linked to physiologic adaptations. Adaptations to one environmental stressor, such as heat, increase Hsp72 and induce cross adaptations to other stressors (i.e. hypoxia). Previously, two bouts of downhill running (DHR) conferred classic markers of heat acclimation (lower Tc, earlier onset of sweating). We sought to increase Hsp72 through repeated DHR to potentially expedite the acclimation process. PURPOSE: To analyze the effect of DHR on exercise performance in normobaric hypoxia. METHODS: 8 males (23.8 ± 5.8 years, VO2max 54.1 ± 5.1 ml kg-1 min-1, 13.6 ± 5.2% body fat) performed two 45-minute DHR bouts (-12.5% grade) separated by 5-7 days in the speed that elicited VT while running downhill. Pre and post blood samples were collected to quantify monocyte Hsp72. Muscle soreness (DOMS) was assessed 24 and 48 hours after each downhill bout using a Likert scale. Two normobaric hypoxic (16% FiO2) 5 km time trials (TT) were performed: one before any DHR and one 5-7 days after the last bout. Hydration was assessed before the TT while blood lactate was measured pre and post TT. During the TT, heart rate, RPE and O2 saturation (SaO2) were recorded every 1 km. RESULTS: Monocyte Hsp72 showed no change across time (p=0.53). Specifically, basal concentration from DHR I to DHR II were not different (3.5 ± 2.3 to 2.9 ± 1.5 AU). TT performance was similar between conditions (1377 ± 192 ; 1364 ± 174 sec). Hydration (1.018 ± 0.007; 1.013 ± 0.009 urine specific gravity), RPE (14.9 ± 1.1; 14.6 ± 1.3), HR (178 ± 8;178 ± 8), and blood lactate (post TT1 11.6 ± 1.8; post TT2 12.0 ± 3.1 mM) were similar in both TTs. However, SaO2 significantly increased from TT1 to TT2 (84.5 ± 4.0; 87.2 ± 2.3%, p<0.05). DOMS was significantly lowered 24 (5.1 ± 0.8 to 3.5 ± 1.4, p = 0.00) and 48 (4.6 ± 1.0 to 2.6 ± 1.5, p = 0.00) hours following the second DHR trial when compared to the first trial. CONCLUSIONS: While no change in Hsp72 or TT time were observed, this could be due to large variations found in the data with these variables. The increase in SaO2 after DHR may improve exercise capacity at elevation during moderate exercise intensities.