What type of metabolism produces energy for strenuous exertion lasting more than 20 seconds?

The type of metabolism that produces energy for strenuous exertion lasting more than 20 seconds is anaerobic lactic metabolism. This process occurs when the body's demand for energy exceeds the supply of oxygen available to the muscles, making it necessary for the body to rely on energy production without oxygen.

During high-intensity activities, such as sprinting or heavy lifting, the muscles primarily use glucose for energy. In the absence of sufficient oxygen, glucose is broken down into pyruvate through glycolysis, and then converted into lactic acid. This pathway allows the muscles to generate ATP (adenosine triphosphate) rapidly but also leads to the accumulation of lactic acid, which can contribute to fatigue.

Anaerobic lactic metabolism is particularly important in activities that require short bursts of intense effort, lasting from around 20 seconds up to a couple of minutes, as it provides a quick energy source when aerobic metabolism (which requires oxygen and is more sustainable for longer periods) cannot meet the energy demand. Thus, for exercises of this duration and intensity, anaerobic lactic metabolism becomes the dominant energy-producing pathway.