Introduction: Taking Your Sport to New Heights
Welcome! In this chapter, we are heading up into the mountains to look at Exercise at Altitude. This is a fascinating part of the "Environmental effects on body systems" section. We’ll explore why performing at high altitudes feels so much harder, how your heart and lungs react instantly, and how athletes "acclimatise" to get an edge over their competition. Don't worry if the science seems a bit "thin" at first—we'll break it down step-by-step!
1. The Science of "Thin Air"
One of the biggest myths in sport is that there is "less oxygen" at the top of a mountain. Actually, the percentage of oxygen in the air is the same as at sea level (about 21%). The real problem is Pressure.
What is Partial Pressure?
At high altitudes, the Atmospheric Pressure is much lower. This means the molecules of oxygen are spread further apart. Scientists measure this using Partial Pressure of Oxygen (\(PO_2\)).
Prerequisite Concept: Think of oxygen molecules like people in a lift. At sea level, the lift is crowded, and people are pushed out easily when the doors open. At altitude, the lift is nearly empty; there’s no pressure pushing the people out. In your body, this means there is less pressure pushing oxygen from your lungs into your blood.
Key Term: Reduced Arterial \(PO_2\)
Because the pressure in the air is lower, the pressure of oxygen in your arteries (the blood leaving your heart) also drops. This is the root cause of all the physiological struggles at altitude.
Quick Review:
• Oxygen % stays the same.
• Atmospheric pressure drops.
• Partial pressure of oxygen (\(PO_2\)) drops.
• This makes it harder for oxygen to enter the bloodstream.
2. Immediate Effects on the Body
When you first arrive at a high-altitude location (usually defined as anything above 2400m), your cardiovascular and respiratory systems have to work overtime to make up for the lack of oxygen pressure.
A. Elevated Ventilation (Breathing)
Your body detects the drop in oxygen and immediately tells you to breathe faster and deeper. This is called elevated ventilation. You are trying to bring in as much of that "thin air" as possible to find more oxygen molecules.
B. Elevated Heart Rate
Since each liter of blood is now carrying less oxygen than usual, the heart has to pump much faster to deliver the same amount of fuel to your muscles. Even at rest, your Heart Rate (HR) will be higher than it is at sea level.
C. Impaired Muscle Oxygen Delivery
This is the "bad news" for performance. Because of the reduced arterial \(PO_2\), there is a smaller pressure gradient between the blood and the muscles. Oxygen doesn't "jump" into the muscle cells as easily, leading to a decrease in VO2 Max and aerobic performance.
Did you know? An athlete's VO2 Max can drop by about 1% for every 100 metres they climb above 1500m!
Key Takeaway: When you first get to altitude, your heart and lungs work much harder (High HR and Breathing) just to do basic tasks because oxygen delivery to the muscles is impaired.
3. Acclimatisation: Adapting to the Height
If an athlete stays at altitude for several days or weeks, their body begins to adapt. This process is called Acclimatisation. The goal is to make the body more efficient at carrying oxygen.
The Process of Adaptation
1. Release of EPO: The kidneys detect low oxygen and release a hormone called Erythropoietin (EPO).
2. Red Blood Cell Production: EPO tells the bone marrow to produce more Red Blood Cells (and more Haemoglobin).
3. Increased Oxygen Carrying Capacity: More red blood cells mean the blood can eventually carry more oxygen, even if the pressure is low.
The Importance of Timing
Athletes must be very careful about when they arrive at altitude for a competition. There are generally two strategies:
• Arrive very early: Arrive 2–4 weeks before a race to allow full acclimatisation to take place.
• Arrive very late: Arrive right before the event (within 24 hours). This "beats" the onset of altitude sickness and the extreme fatigue that happens in the first few days of arrival.
Common Mistake to Avoid: Don't confuse acclimatisation (natural adjustment) with blood doping (illegal injection). They have the same result (more red blood cells), but acclimatisation is a natural response to the environment.
Memory Aid: The "A" Rule
Altitude = Above 2400m.
Arrive early or Arrive late.
Acclimatise to Adapt.
4. Impact on Performance
How altitude affects an athlete depends entirely on the type of event they are doing.
Aerobic Events (e.g., Marathon)
Performance is negatively affected. Because the aerobic system relies on oxygen, the reduced \(PO_2\) means athletes cannot maintain their usual pace. They will fatigue much faster.
Anaerobic Events (e.g., 100m Sprint)
Performance is often improved or unaffected. Short, powerful bursts don't rely on atmospheric oxygen. Furthermore, the lower air resistance (because the air is thinner/less dense) allows sprinters or throwers to move through the air faster!
Quick Review Box:
• Location: Effects become significant above 2400m.
• Respiratory: Ventilation (breathing) increases.
• Cardiovascular: Heart Rate increases.
• Blood: Eventually, Red Blood Cell count increases (Acclimatisation).
• The "Why": Low Partial Pressure of Oxygen (\(PO_2\)).
Summary: Key Takeaways
1. Pressure is the Key: Performance drops because lower atmospheric pressure leads to a reduced arterial \(PO_2\), making it harder for muscles to get oxygen.
2. Immediate Stress: The body compensates for low oxygen by elevating heart rate and ventilation.
3. Long-term Gains: Staying at altitude (over 2400m) triggers acclimatisation, increasing red blood cell count.
4. Timing Matters: Athletes must time their arrival carefully to ensure they are either fully adapted or haven't yet felt the negative "crash" of altitude fatigue.