What group of substances consists of amino acids that maintain and build muscle and are used as an energy source during times of stress?

The group of substances that consists of amino acids which are essential in maintaining and building muscle, as well as serving as an energy source during times of stress, is indeed proteins. Proteins are made up of long chains of amino acids that are linked together, and they play vital roles in various bodily functions. They are crucial for muscle growth and repair, serving as the building blocks for muscle tissue.

In situations of stress, the body can utilize protein as an energy source after carbohydrates and fats. The body breaks down proteins into their constituent amino acids, which can then be used to fuel bodily functions or synthesized into new proteins to support recovery or muscle building.

While amino acids are the components of proteins and are essential for these processes, referring to proteins encompasses the entirety of their role in muscle maintenance and energy supply. Supplements, on the other hand, may contain amino acids or proteins but are not defined by a single nutrient group. Therefore, proteins are the more accurate and comprehensive answer to the question asked.