What may cause muscle spasms in a patient who has run a long distance on a hot day?

Loss of salt due to sweating can indeed cause muscle spasms, particularly in situations where a person has been exerting themselves physically in hot conditions. During prolonged exercise, especially in the heat, the body loses not only water through perspiration but also important electrolytes, including sodium and potassium. These electrolytes are crucial for proper muscle function, and their depletion can disrupt the electrical signals that muscles rely on to contract and relax. When this balance is altered due to significant sweating, it can lead to muscle cramps or spasms.

In the context of a long-distance run on a hot day, the likelihood of losing a substantial amount of salt is high. This is particularly relevant for individuals who might not be compensating for their losses with adequate fluid and electrolyte intake. Thus, the loss of salt through sweating becomes a direct contributor to the occurrence of muscle spasms in this scenario.