The Effects of Intermittent Hypoxic Exposure (IHE) on Haemorheology of Elite Middle Distance Runners

Field: Medicine (Health Sciences)

The present investigation posed the following questions; 1)What are the relative contributions of Plasma Viscosity (PV), Red Blood Cell Deformability Index (RBCDI) and Haematocrit (Hct) to Whole Blood Viscosity (WBV) in elite middle distance runners? 2)What is the relationship between WBV and performance in elite middle distance runners? 3)Is WBV modified by sleeping in a hypoxic environment? 4)Does sleeping in a hypoxic environment increase performance? Methodology. The present investigation was part of a larger study at the Australian Institute of Sport investigating the effect of Intermittent Hypoxic Exposure (IHE) on the performance of elite middle distance runners. IHE was regulated to simulate an altitude of 2650 metres by the use of nitrogen to generate a normobaric-hypoxia sleeping chamber (Oxygen 16.3 %, barometric pressure approximately 710 mmHg). Eleven elite middle distance runners volunteered to participate in the study. All runners were members of the Australian Institute of Sport Development Squad with a time of 232.3 ± 1.4 s for 1500 meters. There was (i) a 5 day testing block pre-IHE (at Altitude 600 m, the results of which were used to allocate runners into either the ALTITUDE or CONTROL group); (ii) 5 nights of IHE (2650 m), (iii) 3 days at home (all athletes resided in Canberra, Altitude 600 metres), (iv) 5 nights of IHE (2650 m), (v) 3 days home (600 m), (vi) 5 nights IHE (2650 m), (vii) a post-IHE 5 day testing block (600 m), (viii) 11 days out of the IHE chamber with no tests (600 m) and (ix) a post-IHE 5 day testing block (600 m). Three performance tests were completed each 5 day testing block. The performance tests included (i) long duration treadmill test (VO2max), (ii) short duration treadmill test (anaerobic capacity) and (iii) a 1500 m time trial on a synthetic 400 m track. Blood was collected from a superficial forearm vein on nine occasions. Of the nine occasions blood was collected, three were in the mornings immediately proceeding the 1500 m time trials, three were in the mornings following the first night of exposure in the IHE and the remaining three blood samples were collected in the mornings following the fifth night of exposure to the IHE. Blood was analysed for WBV, PV, Hct, Hb, Red Blood Deformability Index (RBCDI), Red Blood Cell Count (RBCC), White Blood Cell Count (WBCC), red blood cell Mean Cell Volume (MCV), percent Reticulocytes (% retics), Platelet Count (PC) and Mean Cell Volume of the Reticulocyte (MCVr). Results. 1.) 1500 m time trial results for the ALTITUDE and CONTROL groups over the three 5 day testing blocks were 241.3 ± 3.0 s vs 241.7 ± 1.9 s , 243.3 ± 1.4 s vs 238.6 ± 1.8 s and 236.6 ± 2.0 s vs 236.2 ± 0.8 s respectively. Long duration treadmill test (VO2max) time to exhaustion results for the ALTITUDE and CONTROL groups over the three 5 day testing blocks were 612 ± 18.4 s vs 588 ± 24.1 s, 645 ± 6.9 s vs 606 ± 24.1 s and 654 ± 10.2 s vs 645 ± 25.5 respectively. Short duration treadmill test to exhaustion results for the ALTITUDE and CONTROL groups over the three 5 day testing blocks were 120 ± 8.6 s vs 129 ± 12.5 s, 113 ± 2.9 s vs 126 ± 7.2 s and 146 ± 7.8 s vs 145 ± 10.7 s respectively. 2.) A significant (p=0.0004) and positive relationship was found between PV and WBV, Hct and WBV (p=0.0001), Hb and WBV (p=0.0001), RBCC and WBV (p=0.04), WBCC and WBV (p=0.04) and PC and WBV (p=0.01). A significant (p=0.05) and negative relationship was found between RBCDI and WBV. No significant relationship was found to exist between WBV and MCV, WBV and Percent Reticulocytes or WBV and MCVr. 3.) A significant (p=0.002) and positive relationship was found to exist between 1500 m time trial time and WBV and a significant (p=0.001) but negative relationship between 1500m time trial-time and Hct. No significant relationship was found to exist between the long duration treadmill test run time to exhaustion (aerobic capacity) and WBV. A significant (p=0.01) and positive relationship was found to exist between Hct and the long duration treadmill test run time to exhaustion. No significant relationship was found to exist between the short duration treadmill test time to exhaustion (anaerobic capacity) and WBV. A significant (p=0.02) and positive relationship was found to exist between short duration treadmill test time to exhaustion and Hct. 4.) Intermittent Hypoxic Exposure resulted in a significant elevation of WBV (p=0.001) in the ALTITUDE group compared to the CONTROL group over the course of the study. 5.) In elite middle distance runners, 15 nights of sleeping in IHE did not significantly improve anaerobic (short duration treadmill test), aerobic (long duration treadmill test) performance, or 1500 m time, any more than sleeping in normoxic (600 m) conditions. Conclusions. i) PV, RBCDI and Hct do significantly and positively contribute to WBV. ii) A significant and positive relationship exists between WBV and WBCC and WBV and PC. iii) There was a paradoxical situation in elite middle distance runners between WBV and 1500 m time trial time and Hct and 1500m time trial time. Increased WBV leads to slower 1500 m time trial times and a shorter time to exhaustion. Increased Hct leads to faster 1500 m time trial times and a longer time to exhaustion. We conclude; (1) that there exists an optimal combination of Hct and WBV to produce optimal performance in elite middle distance runners. (2) Whole blood is significantly more viscous as the result of IHE. (3) Intermittent hypoxic exposure did not improve 1500 m time trial performance, aerobic or anaerobic capacity in an elite middle distance runners.