1 Exercise and Altitude Moderate altitude 1500m (5000ft) –Dec max O2 consumption Extreme altitude 6000m(20000ft) –Progressive deterioration - death Fig 23-1 less O2 available –As barometric pressure decreases –Less O2 per volume - same % as sea level Table 23-1 Acute exposure –Still see dec in O2 tx capacity at higher and higher altitudes Fig 23-3 effect of altitude on VO2 max –3% decline / 300m (1000ft) –O2 cost is similar - perception of effort is greater - higher % of max

2 Human Responses With proper acclimatization humans can tolerate high altitudes Table ability to adapt Slow ascent to 5500m (18000ft) can be accomplished with few symptoms If ascent is rapid -AMS -acute mountain sickness - within a few hours –Headache, nausea, irritability, weakness, poor appetite, vomiting, tachycardia, disturbed breathing Above 3000m AMS common –Blunted breathing response more susceptible –Slow ascent can reduce AMS –Acclimation hikes important

3 Pulmonary Function Ventilation inc further for 2 weeks –Hypoxia is driving force (fig 23-4) –Bicarb is excreted - inc central and peripheral sensitivity HVR - hypoxic ventilatory response –Important to maintain Alv and Art O2 –Determines Max O2 consumption –Elite athletes - often blunted HVR Observe dec in PaO2 with intense ex –May be pulmonary gas exchange Diffusion limitation at altitude –Partial P of O2 determines driving force O2 cascade(fig 23-5) –Fig same transit time - dec driving force (slope)

4 Cardiovascular Adjustments Acute - submax HR inc - SV ~ same Chronic –SV dec, CO dec 20-25% (1-2 weeks) –Fig 23-7 MAP - mean arterial BP - gradually inc with exposure –Due to inc systemic resistance and vascular resistance in ms –Due to inc bld viscosity and catecholamines Above 3000m EPO stimulates Hb and Hct - requires ~ 3 months –Time reduced with adequate energy, protein and iron

5 Acclimatization Rate Pressure Product - work load on heart (HR * Systolic BP) Inc 100% above 3000m (exercise) Significant challenge to heart Lungs - PAP - pulmonary Arterial P Inc with altitude - symp stimulation Inc size of sm ms in pulmonary arterioles –Implicated in HAPE (pulmonary edema) Brain - hypoxemia - vasodilation –Implicated in HACE (cerebral edema) Hypocapnea - vasoconstriction –Counteracats vasodilation

6 Muscle Acclimatization Dec submax bld flow (20-25%) Due to inc Nep and dec CO O2 delivery maintained - through inc O2 content in blood Inc myoglobin, buffering capacity, aerobic enzymes (small change) Oxidative capacity –Altitude native - low mito volume –Activity limited by pulmonary vent –Even unfit have sufficient Ox capacity at altitude –Endurance capacity inc with acclimatization (no change in VO2 max)

7 Nutrition and Energetics Weight loss and ms atrophy common – g/day - dehydration, energy deficit, inc activity level, inc BMR –High carb diet can help > 60% Exercise Energetics Lactate paradox - fig 23-8 –Bld lactate higher at given power output with acute exposure –Acclim - dec bld lactate but no change in max O2 consumption Fig 23-9 –With acclimatization –Dec Ep, Nor Ep stays high –Working ms oxidizes more of its own lactate - inc dependence on bld glucose

8 Metabolism Carbohydrates - thought to be preferred fuel - higher yield of ATP/O2 Limited storage –Hypoglycemia and liver glycogen depletion –Reduced with high carbohydrate diet Fat and Protein –Inc fat catabolism if diet is inadequate - glucose preferred

9 Athletics at Altitude Table Improvements in short duration, high intensity activities –Reduced gravity and wind resistance Decreased endurance performance - longer than 800m Athletes benefit from 1-12 weeks of acclimatization Problem - reduced absolute training intensity at altitude - even if same % –Can not train as hard - detraining effect –Further - do not see improvements in sea level performance (reduction) –Reduced bld volume, buffering capacity, inc ventilation (more work)

10 Live High - Train Low Combine benefits of sedentary adaptations to altitude With maximal training stimulus at sea level Either live m and drive down every day to train Or sleep in hypoxic tent - reduced oxygen tension –Stimulates adaptation

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