What physical change occurs to muscles in the pugilistic posture?

In the context of the pugilistic posture, which refers to the specific position that a body may adopt during the intense heat of a fire, the physical change that takes place in the muscles is characterized by dehydration and shrinkage. This occurs because, when exposed to extreme heat, the body's tissues can lose moisture, leading to the muscle fibers contracting and becoming smaller.

The muscles often assume a contracted state due to the intense thermal environment, which can cause them to curl or pull inwards, resulting in a visibly altered position often interpreted as the pugilistic stance, where the arms may be bent in a defensive posture, similar to a boxer. This phenomenon is primarily the result of the heat causing tissue dehydration, which effectively reduces the muscle volume.

In contrast, other options describe different physiological responses that do not accurately represent what occurs in the scenario of extreme heat. For instance, spasms and contractions imply a different type of muscular reaction not solely tied to the mechanism of dehydration in this specific context. Hardening and rigidity would imply a different form of muscle response that does not specifically convey the same alterations seen with dehydration and shrinkage. Similarly, expansion and elongation contradict the observable effects of heat on muscle tissue in the pugilistic posture.