Elevated plasma hydroxyproline. A possible risk factor associated with connective tissue injuries during overuse.

Basal plasma hydroxyproline was measured in 104 male Navy Seal candidates 1 week into their intense physical training program, which lasted 7 weeks, and correlated to the incidence of connective tissue injuries incurred later in the training program. Eleven subjects (10.6%) were diagnosed as having connective tissue injuries. Those subjects with connective tissue injuries had a significantly higher (P less than 0.05) mean plasma hydroxyproline value (4.02 micrograms/ml) than subjects without injury (3.10 micrograms/ml). The majority of graduates (75%) had plasma hydroxyproline values less than 3.3 micrograms/ml. These graduates represented the strongest and most enduring injury-free subjects. Of the subject pool who incurred connective tissue injuries, only 27% had plasma hydroxyproline values less than 3.3 micrograms/ml. The majority of the injured subjects (73%) had plasma hydroxyproline values greater than or equal to 3.3 micrograms/ml. In conclusion, there is a relationship between initial training basal plasma hydroxyproline levels and connective tissue injuries later incurred in an intense physical training program. These data suggest that elevated plasma hydroxyproline levels may represent a risk factor associated with connective tissue injuries.