Brown JJ et al 1998 published a 1 year survey of over 1000 Royal Canadian Mounted Police officers. Officers throughout the country doing a variety of tasks were randomly selected from the RCMP database.
Of those selected, 80% completed the survey. 55% complained of chronic or recurrent back pain since joining the RCMP, 8.5% reported having back pain prior to joining, 76% had a problem within the last year. It was determined that approximately 42% of RCMP officers would miss some duty due to back pain each year. However, this excuses the wearing of the duty belt and hours spent driving since the incidence of back pain in the general population of Canada is at 40%.
Nabeel et al 2007 published a similar study on the Minneapolis police department. Their study not only looked at back pain and injury rates but also self-reported fitness levels and BMI. Officers reporting high fitness had 33% fewer incidence of back pain and half the chronic pain than their more sedentary counter-parts. Officers with a BMI over 35 were 3x more likely to experience an injury that year than those with a BMI 20-25.
Clearly fitness levels matter and even among police officers, levels of fitness differ to the point where it can have radically differing outcomes on their health and injury rates.