Many crime scene workers have
mentioned that when "discovering the deceased that their face might have taken on what looks to be a grimace". That stage of rigor would potentially stay intact up to 7 days following death, so IMO, the "leaping" or "frozen" aspect of his condition doesn't sound that far-fetched.
Rigor &decomposition can be affected by exterior ambient temperatures. Rigor is accelerated in warmer temperatures and the return to flaccidity is equally accelerated. Rigor initially appears in the smallest muscles first, the eyelids, neck muscles, facial muscles, etc. moving through the body then ending with extremities. When rigor leaves the body, it leaves the same way it came. A town very close to Big Cypress Reserve called Immokalee had the following temperature and humidity during the the preceding days of HM's discovery:
July 20, 2017 Temp:29 degrees C Humidity 88%
July 21, 2017 Temp: 30 degrees C Humidity 83%
July 22, 2017 Temp: 31 degrees C Humidity 82%
July 23, 2017 Temp: 31 degrees C Humidity 80%
31 degrees C = 88 degrees F
I don't believe that rigor could last up to 7 days in those circumstances. As a matter of fact I've never heard of rigor lasting that long. There is a phenomena that can occur called cadaveric spasm that is usually the result of an extreme neurogenic response. An example of a neurogenic response is a convulsion or perhaps a seizure. Extremely high body tempertures can cause a neurogenic response as well. The neurological illness ALS can also cause spasmodic freezing of muscles.
The last example may be one of the terminal illnesses that people have suggested HM may have been referring to when he spoke about hiking the trail while he still could. It is very sad if that happened since he would have been incapable of helping himself to do anything.