David’s body temperature rises above normal during the surgery (hyperthermia).
How does skeletal muscle tissue contribute to body temperature?
Skeletal muscle produces heat when it contracts, which is an essential function in
maintaining normal core body temperature.

through generation of heat energy during contraction

Generally the large mass of skeletal muscles makes it to contribute to Thermogenesis in mammals. when skeletal muscles contract, they pull on the tendon. Remember muscles are  attached to bones by tendons. Therefore  the contraction  shorten   muscles's length , shifting the  bone  and hence causing movement of the body.  This movement generate heat energy. It is a process which involve the expenditure of ATPs, and abundant mitochondria.

The higher the rate of contraction of the muscles , the higher is the heat generated.

It  is the lysis of ATPs bonds  that  liberates heat energy during muscles contraction. Although this process raises the  body temperature, it does not favour the body physiological  process; because it causes loss of large amount of heat energy from the core body temperature,  to  the external environment through  vasodilated capillaries  under the skin. Thus affecting  body temperature set points.

in some case  the rate of muscle contraction is too high,  due to  high diffusion of Calcium ions into  the muscles  this  generate too  much heat causing Hypothermia, from sustained contraction of skeletal muscles.

is in the form atp or adenosine triphosphate