I am a 47-year-old man in good health. I started walking as a first step to a regular exercise schedule and a potential to start running. In the first few days I have noticed two consistencies and I am curious if they mean anything.
1. During the walk (total about 2 miles through wooded areas) I found that about 1.1 miles I started to sweat.
2. At 1.5 miles I start feeling fatigue in my legs.
Since you are just beginning this regimen, it is likely an issue of acclimation…an outcome of dehydration; dormant muscle activation; ramped up cardiopulmonary demand; or even the change-up of adding 30 to 60 minutes of movement to your day. Consider trying compression tights, compression socks or compression calf sleeves to give your vessels some support and better recovery odds while you push your fitness envelope. Bearing in mind the detrimental health impacts of excessive sitting*…which many of our work lives exacerbate…starting a workout program if you normally sit more than three hours a day is bound to have a shakedown period. So hydrate, begin your walk with dynamic stretching, practice deep diaphragmatic breathing, massage fatigued areas, elevate your feet after you walk, reduce stress, check your medications for related side effects, and ease back on the caffeine and/or alcohol if those are integral to your life.
That said and considering your observation regarding the fatigue setting in shortly after you start to sweat, I would suggest visiting your doctor if these symptoms continue or get worse over two weeks’ time. When bodies perspire, the sympathetic nervous system gets busy. The vessels of our circulatory system, respiratory system, and even our pupils dilate. Vasodilation of the circulatory and respiratory systems increases blood flow to our skeletal muscles and lungs allowing more oxygen and nutrients to be delivered throughout our bodies and more oxygen to be exchanged in our lungs. Increased oxygen, glucose and nutrient flow helps our bodies to keep up with the increased demands of our chosen activity…at least until we exceed our current level of cardiopulmonary health. Your current cardiopulmonary health level is the level of exertion at which your body’s ramped up efforts to meet resource demand is outstripped by the demands of continued activity. Good news is, with more exercise, your cardiopulmonary health will rise.
The fatigue you mention could merely be a sign that your cardiopulmonary health needs to catch up to your current activity challenge. If that is the case, the fatigue should resolve itself quickly with continued exercise. But fatigue could also be a sign of something amiss in one of the systems you are taxing, a failing in a metabolic process, or possibly an indication of infection. Vessels opening wide while the heart muscle constricts to pump larger volumes of blood, is akin to pressure testing a plumbing system. Small issues do not become obvious until the pressure rises.
By the way, a great second step to building a healthy lifestyle could be to switch from a seated to a standing desk if your work demands a desk. Decreasing sitting cannot only add years to your life, it is helpful in toning the muscles of the body, maintaining better posture and increasing cardiovascular health.