The Environment and Metabolism

The outside environment also influences metabolic rate. When you are exposed to a progressively colder climate, your body will increase its metabolic rate to keep the body temperature constant and to prevent shivering. Shivering is invoked when the core temperature of the body begins to drop from being in the cold. Shivering is actually a series of involuntary muscle contractions that are triggered to create heat in the body, like turning on a furnace. When exposed to higher than average cold conditions for a few days, your body actually increases its basal metabolic rate to run hotter than average to compensate for being in a colder climate. When things begin to warm up, even a 60 degree F day can seem extremely hot, because your metabolic rate is running at a fast rate. After several days of acclimation to the hot climate, your metabolic rate will decrease, and 80 degree F will feel as hot as the 60 degree F day did a few months earlier.

Exercise and Metabolic Responses

Exercise will stimulate a series of metabolic responses that affect the body’s anatomy, physiology, and biochemical makeup.

Here are some of the changes that are stimulated by endurance exercise:

• Increased muscle glycogen storage capacity

• Increased muscle mitochondria density

• Increased resting ATP content in muscles

• Increased resting CP content in muscles

• Increased resting creatine in muscles

• Increased aerobic enzymes

• Increased slow twitch muscle fiber %

• Decreased fast twitch muscle fiber %

• Decreased muscle size, when compared to strength training

• Increased cardiac output

• Decreased resting heart rate

• Decreased body fat

• Increased Krebs cycle enzymes

• Increased capillaries

The magnitude of these changes is driven primarily by whether the exercise is anaerobic or aerobic. The type and duration of exercise will physically stimulate muscles to develop more fast or slow twitch muscle fibers, and in turn dictate the primary energy mix used. High intensity exercise stimulates fast twitch muscle fiber development, while low intensity exercise results in slow twitch muscle fiber development. There are also a series of hormonal changes that occur on an overall basis during exercise and non-exercising periods. These changes also are benefited and facilitated with a nutrient profile that matches the type of metabolic flux.

Aerobic System Changes

Aerobic training greatly increases the body’s functional capacity to transport and use oxygen and to burn fatty acids during exercise. Some of the major changes measured as a result of aerobic exercise include:

• Increased mitochondria density in slow twitch muscle fiber, which results in higher energy production from fatty acids. Maximum oxidative capacity develops in all fiber types.

• Higher aerobic capacity.

• Increase in trained muscle capacity to utilize and mobilize fat, resulting from higher amounts of fat metabolizing enzymes, and increased blood flow.

• Greater development of slow twitch muscle fibers, increased myoglobin content, which is an iron-protein compound in muscle, which acts to store and transport oxygen in the muscles.

Anaerobic System Changes

Anaerobic training greatly increases the body’s functional capacity for development of explosive strength and maximization of short-term energy systems. Some of the major changes measured as a result of anaerobic exercise include:

• Increased size and number of fast twitch muscle fibers.

• Increased tolerance to higher levels of blood lactate.

• Increases in enzymes involved in the anaerobic phase of glucose breakdown (glycolysis).

• Increased muscle resting levels of ATP, CP, creatine, and glycogen content.

• Increased growth hormone and testosterone levels after short bouts (45 to 75 minutes) of high intensity weight training.