Energy Metabolism

Energy metabolism is a series of chemical reactions that result in the breakdown of foodstuffs (carbohydrate, fat, protein) by which energy is produced, used, and given off as heat. Roughly, the body is about 20% efficient at trapping energy released. About 80% is released as heat, which explains why your body heats up quickly when you exercise. A closer look at your muscle anatomy reveals that the mode of energy storage and energy systems used is related to your physical activity.

Physical activities can be classified into four basic groups, based on the energy systems that are used to support these activities.

• Strength-Power: Energy coming from immediate ATP stores. Shot put, power lift, high jump, golf swing, tennis serve, or a throw; lasting about 0 to 3 seconds of all out effort.

• Sustained-Power: Energy coming from immediate ATP and CP stores. Sprints, fast breaks, football lineman; lasting about 0 to 10 seconds of near maximum effort.

• Anaerobic Power-Endurance: Energy coming from ATP, CP, and lactic acid. 200- to 400-meter dash, 100-yard swim; lasting about 1 to 2 minutes.

• Aerobic-Endurance: Energy coming from the oxidative pathway. Events lasting over 2 minutes in duration.

In power events, which last a few seconds or less, the muscles depend on the immediate energy system, namely ATP and CP reserves. In speed events, the immediate and non-oxidative, or glycolytic energy sources are utilized. In endurance events, the immediate and non-oxidative energy sources are used, and the oxidative energy mechanisms become a more important source of energy. ATP and CP are replenished from energy derived from complete breakdown of glucose, fatty acids, and some proteins.

Figure 1-2: Homeostasis example