Aerobic Capacity, Lactate Concentration, and Work Assessment During Maximum Exercise at Sea Level and High Altitude in Miners Exposed to Chronic Intermittent Hypobaric Hypoxia (3,800 m)

Abstract

We previously showed that arterial oxygen content during maximum exercise remains constant at high altitude (HA) in miners exposed to chronic intermittent hypobaric hypoxia (CIHH). Nevertheless, information about VO₂, lactate concentration [Lac], and work efficiency are absent in this CIHH miner population. Our aim was to determine aerobic capacity, [Lac], and work efficiency at sea level (SL) and HA during maximum exercise in miners acclimatized to CIHH at 3,800 m. Eight volunteer miners acclimatized to CIHH at HA (> 4 years) performed an exercise test at SL and HA. The test was performed on the 4th day at HA or SL and consisted of three phases: Rest (5 min); Exercise test, where the load was increased by 50 W every 3 min until exhaustion; and a Recovery period of 30 min. During the procedure VO₂, transcutaneous arterial saturation (SpO₂, %), and HR (bpm) were assessed at each step by a pulse oximeter and venous blood samples were taken to measure [Lac] and hemoglobin concentration. No differences in VO₂ and [Lac] in SL vs. HA were observed in this CIHH miner population. By contrast, a higher HR and lower SpO₂ were observed at SL compared with HA. During maximum exercise, a reduction in VO₂ and [Lac] was observed without differences in intensity (W) and HR. A decrease in [Lac] was observed at maximum effort (250 W) and recovery at HA vs. SL. These findings are related to an increased work efficiency assessment such as gross and net efficiency. This study is the first to show that miners exposed to CIHH maintain their work capacity (intensity) with a fall in oxygen consumption and a decrease in plasmatic lactate concentration at maximal effort at HA. These findings indicate that work efficiency at HA is enhanced.

Keywords: aerobic capacity; chronic hypobaric intermittent hypoxia; lactate concentration; miners workers; work assessment.

Figure 1

A model of chronic intermittent hypobaric hypoxia exposure. Arrows show day when the evaluations were performed during the shiftwork day at high altitude or sea level.

Figure 2

Average values of oxygen consumption (VO₂) as a function of intensity (in W) obtained on the fourth day at sea level and 3,800 m. * represents a significant difference between Sea level vs. 3,800 m (p < 0.05).

Figure 3

(A,B) show average values of calculated Net efficiency and Gross efficiency as a function of intensity (in W/kg) obtained on the fourth day at Sea level and 3,800 m. * represents a significant difference between Sea level vs. High altitude (p < 0.05).

Figure 4

Average values of plasmatic lactate concentration (mmol/L) as a function of intensity (in W) obtained on the fourth day at sea level and high altitude. In the inserted figure, red bars represent the average lactate concentration at Sea level; blue bars are the average lactate concentration (mmol/L) at 3,800 m. * represents a significant difference between sea level vs. high altitude and a cross represents a significant difference compared to rest (p < 0.05).