Economy of locomotion in high‐altitude Tibetan migrants exposed to normoxia

Abstract

High-altitude Tibetans undergo a pattern of adaptations to chronic hypoxia characterized, among others, by a more efficient aerobic performance compared with acclimatized lowlanders.To test whether such changes may persist upon descent to moderate altitude, oxygen uptake of 17 male Tibetan natives lifelong residents at 3500-4500 m was assessed within 1 month upon migration to 1300 m. Exercise protocols were: 5 min treadmill walking at 6 km h −1 on increasing inclines from +5 to +15% and 5 min running at 10 km h −1 on a +5% grade. The data (mean ± S.E.M.) were compared with those obtained on Nepali lowlanders. When walking on +10, +12.5 and +15% inclines, netV O 2 of Tibetans was 25.2 ± 0.7, 29.1 ± 1.1 and 31.3 ± 0.9 ml kg −1 min −1 , respectively, i.e. 8, 10 and 13% less (P < 0.05) than that of Nepali. At the end of the heaviest load, blood lactate concentration was lower in Tibetans than in Nepali (6.0 ± 0.9 versus 8.9 ± 0.6 mM; P < 0.05). During running,V O 2 of Tibetans was 35.1 ± 0.8 versus 39.3 ± 0.7 ml kg −1 min −1 (i.e. 11% less; P < 0.01). In conclusion, during submaximal walking and running at 1300 m, Tibetans are still characterized by lower aerobic energy expenditure than control subjects that is not accounted for by differences in mechanical power output and/or compensated for by anaerobic glycolysis. These findings indicate that chronic hypoxia induces metabolic adaptations whose underlying mechanisms still need to be elucidated, that persist for at least 1 month upon descent to moderate altitude. It has been long recognized that, with increasing altitude, acclimatized Caucasian lowlanders lose progressively greater fractions of their sea level maximal aerobic power (V O 2 peak ). By contrast, Tibetans, whose ancestors might have been living and thriving at altitudes between 3000 and 4500 m for more than 25 000 years (Dennell et al. 1988), are characterized by a peculiar pattern of adaptations to chronic hypoxia. In fact, compared with acclimatized lowlanders, Tibetan highlanders feature at peak exercise higher arterial O 2 saturation (S aO 2 ), higher aerobic power (V O 2 peak ) and heart rate (HR peak ), the values of the two latter variables being at altitude in the range of those found at sea level in age-, gender-and fitness-matched individuals (Sun et al. 1990;Niu et al. 1995;Zhuang et al. 1996;Chen et al. 1997). In addition, compared with acclimatized Han Chinese long-time residents of 4700 m, Tibetans performing an incremental cycle ergometer exercise are characterized by lower O 2 consumption for given submaximal exercise loads, i.e. a better economy of locomotion, and can develop greater peaks of mechanical power output despite lowerV O 2 peak levels (Ge et al. 1994). Interestingly, the same features were found at 3658 m in lifelong Tibetan residents of 4400 m compared with 3658 m (Curran et al. 1998). On the other hand, second generation Tibetan lowland natives born at 1300 m, never before exposed to high altitude, acclimatize to 5050 m more quickly than Caucasians and within 1 month reco...

High Altitude Adaptation in Tibetans

“…In any case, there are no reports of aerobic capacities getting near the values reported for elite endurance athletes (80 to 90 mL/kg Ϫ1 / min Ϫ1 ). But what seems to distinguish the Tibetans from other populations is that they are less penalized when working in hypoxia compared to normoxia by being able to reach a higher fraction of low-altitude aerobic capacity when exposed to hypoxia than lowlanders (Niu et al, 1995;Marconi et al, 2005). This characteristic is also present in Tibetans born at low altitude exposed for the first time to high altitude, a finding that supports the contention of an inborn quality for altitude adaptation in the Tibetans (Marconi et al, 2005).…”

Why Are High-Altitude Natives So Strong at Altitude? Maximal Oxygen Transport to the Muscle Cell in Altitude Natives

“…This is in contrast to recent work performed by Marconi and co-workers [ 42 ]. They reported that Tibet an migrants born and living between 3500 and 4500 m had a better treadmill assessed locomotor economy (assessed at 1300 m) as compared to Nepali born and living in the Kathmandu valley [ 42 ]. It was concluded that the increased economy in Tibetans was due to chronic hypoxia induced metabolic adaptations, although these still need to be elucidated.…”

“…Also when analyzing multiple data obtained from independent investigations no trend was observed toward higher work effi ciencies in high-altitude natives from around the world [ 7 ]. This is in contrast to recent work performed by Marconi and co-workers [ 42 ]. They reported that Tibet an migrants born and living between 3500 and 4500 m had a better treadmill assessed locomotor economy (assessed at 1300 m) as compared to Nepali born and living in the Kathmandu valley [ 42 ].…”

Gross cycling efficiency is not altered with and without toe-clips

“…Overall, these results do not support the original and previously untested suggestion of Sutton and colleagues (1988) that ''racing'' style toe clip pedals may reduce _ V O 2 by 8 -18% compared with cycling with flat pedals. Therefore, the significant reduction in _ V O 2 observed by Sutton and colleagues (1988) during their simulated ascent of Mount Everest is more likely to be a consequence of some other variable, such as an altitude-induced adaptation at the muscular level similar to that observed in native highlanders (Hochachka et al, 1991;Marconi, Marzorati, Sciuto, Ferri, & Cerretelli, 2005). Sutton and colleagues (1988) claimed that the addition of toe-clips and straps to flat pedals was the likely cause of a significant reduction (8 -18%) in submaximal _ V O 2 after 2 weeks spent at a simulated altitude of *4600 m. In the present study, however, the mean _ V O 2 was 2.1% higher for toe-clip pedals than flat pedals and there was a 99.9% probability that submaximal _ V O 2 was not at least 8% lower with toe-clip pedals.…”