The Effects on Your Body of Jogging for 21 Days

Jogging's renowned popularity as a form of cardiovascular exercise makes perfect sense. It burns as much as 1,000 calories an hour, tones the lower extremities and can turn a lackadaisical cardiovascular engine into the cardiac equivalent of a Ferrari. Most of the changes jogging induces, however, take time to manifest themselves. But not that much -- jogging for even 21 days produces noticeable effects.

  1. What Jogging Does

    • When you undertake a jogging program, your body undergoes a number of largely coordinated physiological changes. Depending on how much jogging you're doing, you can expect to start losing weight immediately, as jogging burns about 100 calories per mile. Your blood pressure at rest will trend toward a lower value thanks to improved arterial elasticity. Your heart muscle begins to grow stronger, allowing the heart to pump more blood with each beat both while jogging and at rest and therefore nudging your resting heart rate lower. You will likely also experience a degree of euphoria that accompanies the heavy endorphin release characteristic of people new to aerobic exercise.

    Immediate Effects on Muscle

    • If you go from no activity to some amount of jogging -- even 10 or 15 minutes a day -- you're likely to experience some soreness starting about 24 hours after your first jog. When muscles unaccustomed to both activity and impact stresses are suddenly subjected to both, the result is the breakdown of muscle cells accompanied by inflammatory processes and pain. This kind of soreness is called delayed-onset muscle soreness, or DOMS. According to Competitor Running, being careful to increase the duration and intensity of your workouts slowly can minimize, if not eliminate, this early-training effect. By the time 21 days are up, DOMS should be greatly diminished, if not vanquished altogether.

    Effects on Metabolism

    • When you start a jogging routine, certain changes in the ways you metabolize key substances involved in aerobic exercise start to occur virtually immediately. A study published in the February 1992 issue of the "Journal of Applied Physiology" demonstrated that previously sedentary subjects who rode an exercise bike for two hours a day at moderate intensity were already showing less fuel utilization at the same workload within a week, and producing less lactic acid. Given the overlap between jogging and cycling, you can expect that once your three weeks of jogging are up, you will already be much more efficient at using muscle glycogen and will generate significantly less lactate at the same intensity level.

    Cellular Changes

    • A lot of what happens when you start jogging, you can see -- weight loss and firmer muscles, for example. But improved fitness occurs at the cellular level. Within your muscle cells are mitochondria, which is where processes such as fatty-acid oxidation and carbohydrate metabolism take place. When you start a jogging program, the density of mitochondria in your muscle cells immediately starts to increase. According to the Gatorade Science and Sports Institute, this density reaches its maximum after about 28 to 35 days of training. Therefore, after you've been jogging for 21 days, the mitochondrial density in your muscle cells has already increased by about 60 to 75 percent of the amount that it will ultimately increase.