• Cold → Skin and core temperature drop
• The brain's control center, the hypothalamus, springs into action.

What Happens Next? 🤔

• Vasoconstriction! Blood vessels in the skin and skeletal muscles narrow down.
  • Decreases blood flow.
  • Less heat transfer from the body’s core to the outer shell (skin, fat, and muscle).

Real-world example: Imagine water flowing through a narrow straw vs. a wide hose. The straw allows less water to flow, just like vasoconstriction reduces blood flow.

• Shivering: It's like your body's mini-workout to produce heat.
  • Starts either immediately or after a few minutes in the cold.
  • Minimal movement, but very effective!
  • Starts in the torso, then to limbs.
  • More shivering = more muscles used = more heat.
  • Intense shivering can be a real workout for your body, using over 1 liter of oxygen every minute!

• If exercising doesn’t produce enough heat, shivering steps in to help.
  • This means more oxygen is taken up due to shivering muscles.
• Heart reacts differently in the cold
  • Lower heart rates but higher stroke volume (amount of blood pumped out with each beat).
  • This helps maintain overall cardiac output (blood flow).
  • Why? Vasoconstriction leads to more blood in the center of the body.

Fashion Tip: Dress in layers when exercising in the cold. As you exercise and heat up, shed a layer to avoid overheating.

• Cold + exercise = faster carbohydrate (like bread or pasta) depletion.
• Shivering's main energy source? Fats! But it also uses blood glucose, muscle glycogen, and even protein.
• Factors determining the fuel mix
  • Current glycogen levels
  • Intensity of shivering
  • Severity of cold
• Think of increasing carbohydrate intake if you’re exposed to the cold for longer durations.