How quickly do retired soldiers typically lose their operational fitness and capabilities?

 Three months after the Kosovo War concluded, I participated in a combat mission with a small guerrilla group operating in southern Serbia known as the Liberation Army of Preševo, Medveđa, and Bujanovac (UCPMB).  

The mission involved a nighttime march to a Serbian checkpoint, where the team launched a few RPGs before retreating to base. The total distance of the operation was no more than thirty kilometers, and I carried only a rifle and some ammunition.  

Despite my prior experience as an endurance athlete, including running a 51k ultramarathon, I found myself completely sore the next morning. My legs were especially painful, but the discomfort extended to every muscle in my body. The mission itself was not particularly demanding—the underlying issue was that I was out of condition.  

In the three months following the end of the war, I had maintained only minimal physical activity: occasional 5k runs and a few sets of push-ups in my office. Most of my time was spent celebrating, often late into the night. Victory felt like a reason to indulge, and I did.  

Combat, particularly in a guerrilla context, places extreme physical demands that result in unparalleled fitness levels. Before the war, I was already a marathon runner and triathlete in the German Army, yet the intensity of the final months of the Kosovo conflict surpassed anything I had previously experienced.  

We were constantly on the move, day and night, traversing challenging terrain while carrying heavy loads. This relentless pace over weeks resulted in the highest level of physical conditioning I had ever achieved.  

Maintaining such a level of fitness in civilian life, however, is unrealistic. Even with dedicated exercise, the continuous physical strain and discipline required during warfare are not replicable in a non-combat environment.  

Some combat skills, in contrast, decline more gradually. Although it has been years since my last mission, I remain proficient in handling firearms and maintaining accuracy. Situational awareness and other cognitive skills honed in combat persist in a dormant state. I am confident that, under the right circumstances, they would quickly resurface.  

Nevertheless, the exceptional physical fitness achieved during the war is something I can never fully regain.