A 32-year-old male construction worker is found dead in his apartment in Delhi during summer. The body is discovered 18 hours after death by his roommate. On examination at the mortuary, the pathologist notes that rigor mortis is fully developed in the jaw, neck, and upper limbs, but is absent in the lower limbs and trunk. The ambient temperature in the room is 38°C. The body shows signs of early decomposition with skin discoloration. Which of the following factors is most likely responsible for the uneven distribution of rigor mortis in this case?