Effects of acute and sub-acute hypobaric hypoxia on oxidative stress: a field study in the Alps.

PURPOSE: High altitude results in lower barometric pressure and hence partial pressure of O2 decrease can lead to several molecular and cellular changes, such as generation of reactive oxygen species (ROS). Electron Paramagnetic Resonance technique was adopted in the field, to evaluate the effects of acute and sub-acute hypobaric hypoxia (HH) on ROS production by micro-invasive method. Biological biomarkers, indicators of oxidative stress, renal function and inflammation were investigated too. METHODS: Fourteen lowlander subjects (mean age 27.3 ± 5.9 years) were exposed to HH at 3269 m s.l. ROS production, related oxidative damage to cellular components, systemic inflammatory response and renal function were determined through blood and urine profile performed at 1st, 2nd, 4th, 7th, and 14th days during sojourn. RESULTS: Kinetics of changes during HH exposition showed out significant (range p < 0.05-0.0001) increases that at max corresponds to 38% for ROS production rate, 140% for protein carbonyl, 44% for lipid peroxidation, 42% for DNA damage, 200% for inflammatory cytokines and modifications in renal function (assessed by neopterin concentration: 48%). Conversely, antioxidant capacity significantly (p < 0.0001) decreased - 17% at max. CONCLUSION: This 14 days in-field study describes changes of oxidative-stress biomarkers during HH exposure in lowlanders. The results show an overproduction of ROS and consequent oxidative damage to protein, lipids and DNA with a decrease in antioxidant capacity and the involvement of inflammatory status and a transient renal dysfunction. Exposure at high altitude induces a hypoxic condition during acute and sub-acute phases accompanied by molecular adaptation mechanism indicating acclimatization.

Biomechanical and metabolic aspects of backward (and forward) running on uphill gradients: another clue towards an almost inelastic rebound.

PURPOSE: On level, the metabolic cost (C) of backward running is higher than forward running probably due to a lower elastic energy recoil. On positive gradient, the ability to store and release elastic energy is impaired in forward running. We studied running on level and on gradient to test the hypothesis that the higher metabolic cost and lower efficiency in backward than forward running was due to the impairment in the elastic energy utilisation. METHODS: Eight subjects ran forward and backward on a treadmill on level and on gradient (from 0 to + 25%, with 5% step). The mechanical work, computed from kinematic data, C and efficiency (the ratio between total mechanical work and C) were calculated in each condition. RESULTS: Backward running C was higher than forward running at each condition (on average + 35%) and increased linearly with gradient. Total mechanical work was higher in forward running only at the steepest gradients, thus efficiency was lower in backward running at each gradient. CONCLUSION: Efficiency decreased by increasing gradient in both running modalities highlighting the impairment in the elastic contribution on positive gradient. The lower efficiency values calculated in backward running in all conditions pointed out that backward running was performed with an almost inelastic rebound; thus, muscles performed most of the mechanical work with a high metabolic cost. These new backward running C data permit, by applying the recently introduced 'equivalent slope' concept for running acceleration, to obtain the predictive equation of metabolic power during level backward running acceleration.