ALTITUDE – EXERCISE PERFORMANCE

Issues:Ergonomics:

Sport and recreation:mountain climbersmany other competitions affected at lower levels

Health and medical concerns: - Acute Mountain Sickness (AMS)

symptoms appear in 6 to 72 hours; head ache, nausea, vomiting, fatigue, weakness, dizziness and lightheadedness

- High Altitude Pulmonary Edema HAPE

- High Altitude Cerebral Edema HACE

Physiological Challenges:

barometric pressure declines above sea level: gas laws (Boyle’s, Charles, Dalton’s Laws) influence gas volumes atmospheric air expands

- composition of air is the same - partial pressure of each gas declines in proportion to the altitude gain- fewer molecules of per breath

environmental (ambient) temperature declines 1 degree C (1.8 degrees F) for every 150m (490 ft) of ascent summit of Everest is minus 9 C in summer and minus 40 C in winter cold issues also complicate exercise wind-chill often greater low humidity: dehydration via ventilation at rest and in exercise (fluid loss via lungs recorded at 200ml per hour

during moderate exercise at moderate altitudes (5,500m or 18,000 ft) UV exposure higher

Some general acute responses to altitude:

mostly due hypoxia – (lack of O2 availability to tissues) - considerable variability

1500m - night vision begins to decline

2000m - heart rate and ventilation begin to increase

3000m - at rest - few signs of any stress- performance of novel tasks begins to decline, reaction time slows, and skilled task performance

begins to be impaired- physical exercise capacity declines significantly- Acute Mountain Sickness and sometimes HAPE begins to occur

4500m - signs of significant hypoxia apparent even at rest- tingling fingers and mouth- neuromuscular impairment (loss of orientation- judgment decreases- variable emotional changes: (euphoria, - pupilary responses vary- skin (lips, fingers) slightly cyanoticHAPE, HACE more likely

6000m - Rapid onset of severe signs and symptoms- comprehension and performance decline

dramatically and rapidly

Exercise performance and related responses to acute hypoxia: At rest and in exercise:- Cardiac output (Q) increases- HR may be up 50% at rest; maximum HR may be lower- SV drops- Plasma volume drops quickly via diuresis (increased urine production and natriuresis (increased sodium

excretion by kidneys – mediated by CNS hypoxia)- Ventilation increases: hyperventilation causes CO2 drop in blood; less need for blood buffer – HCO3

is excreted in urine- reliance on anaerobic metabolism increases from rest through all submaximal exercise intensities (aerobic

capacity (AT) decreased)- maximal LA levels reduced due to loss of buffering capacity- rate of glycolysis slows (mechanisms not clear)

Aerobic Performance - declines begin at 1200m (3%)- linear decline of 10 - 11 % for every 1000m (3300 ft)- top of Everest VO2 max drops to 5 from 50 ml/kg/min at sea level- (5 ml/kg/min is barely life-sustaining)

- VO2max (MAP) declines (effects variable) - highly trained athletes seem to be affected more than UT people

Anaerobic Performance - Power records and overall power performances improve

- mechanism(s): less air resistance (drag) in thin air- 3-9 % of running energy cost at sea level - >90% in cycling- no benefit in swimming

- Sports involving repeated anaerobic lactic bursts - performance declines with acute exposure due to loss of buffering capacity & slower recovery Chronic Exposure and Acclimatization:

Physiological adaptations begin almost immediately:

- Ventilation increases quickly then less rapidly- Pulmonary diffusion rate increases 15-20% over 7-10 weeks- Resting and submaximal Q (CO): return to sea level values over several months (due to an increase in HR and ongoing lower SV

- Erythropoietin (EPO) increases to max in 24 -48 hours then returns to baseline over 3-4 weeks;- 20-25% increase in RBCs which continues even after EPO returns to baseline- Hb per RBC increases in relation to the altitude (probably due to long term diuresis and less fluid in each RBC)- blood viscosity increases (a potential danger)

- At moderate altitudes- oxidative enzymes in muscle increase- glycolytic enzymes unchanged

- At high altitudes (>6000m):- oxidative enzymes decrease with long exposure (21 – 50%)- glycolytic enzymes increase (shift form aerobic to anaerobic reliance? - a controversy)

- capillary density in muscle and heart increase- muscle atrophy occurs in Type 1 and 2 at very high altitudes (survival based? – more capillaries per unit mass of tissue?)- at lower elevations – not seen and lowland and highland endurance athletes are similar in muscle mass

- declines in CNS drive:- maximal performances reduced - training intensities and volumes drop

Training at Altitude:

Mexico Olympics (at 2250m (7400 ft)):

Lots of questions: How to best prepare athletes for peak performances at these altitudes. Should we train only at altitude? At what

altitudes and for how long? Should we alternate between sea level and altitudes? are there ways to simulate altitude?

Early research;

Explored living and training at various altitudes problems of diminished maximal intensity in training on sea level performance 2200m narrow band worked best further researchlive high / train lowlive / sleep in hypobaric chambers