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What to Expect When You Start Getting Fit: A Timeline of Your Body’s Changes

 Written by 

Julien Raby

 Last updated on 


Leading a more active lifestyle is on the minds of many Americans, and for good reason. 

Whether you’re looking to boost your fitness, build muscle, or simply move more, regular exercise brings numerous benefits. 

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However, changes won’t happen overnight. Here’s a detailed look at what to expect as you begin your fitness journey, from the first workout to one year in.

The First Workout: Immediate Changes and Challenges

Starting a new workout routine can be both exhilarating and exhausting. During that initial session, your heart rate spikes, pumping more blood and oxygen to your brain, which can leave you feeling more alert and energized.

However, don’t be surprised if you wake up sore the next day. This soreness, known as delayed onset muscle soreness (DOMS), typically kicks in about 24 to 48 hours after exercise and can last up to 72 hours. 

It’s a normal response to muscle fibers being stretched and stressed in new ways. The good news? As you continue to work those muscles regularly, your body adapts, and DOMS will become less frequent.

First Few Weeks: Boosting Your Energy at the Cellular Level

In the first few weeks of consistent exercise, your body starts ramping up the production of mitochondria, often called the “powerhouses” of your cells. 

This process, known as mitochondrial biogenesis, enhances your cells’ ability to turn carbohydrates, fats, and proteins into energy that fuels your muscles.

Studies show that within six to eight weeks of regular exercise, you can increase your mitochondria by up to 50%. 

With more mitochondria, your stamina and overall fitness improve, making activities that once felt challenging, like running a few miles, significantly easier.

Six Months In: Seeing Muscle Definition and Sticking to the Routine

By the six-month mark, noticeable changes start to occur, especially if your workouts include strength training. 

You’ll likely see increased muscle definition and improved muscle tone. This period is crucial because exercise programs often report a 50% dropout rate within the first six months. 

However, if you’ve made it this far, you’re more likely to stick with your routine long-term, making exercise a lasting habit.

Nine Months: Cardio Gains and Improved Endurance

If your focus has been on cardio, expect significant improvements in your cardiovascular fitness around the nine-month mark. 

Research indicates that consistent aerobic exercise can boost your VO2 max—a measure of how efficiently your body uses oxygen—by approximately 25%.

A higher VO2 max means you can run faster and further. 

For example, a 25% increase in VO2 max allows you to run about 20% further in the same time, making those once-daunting distances much more manageable.

One Year: Stronger Bones and Long-Term Health Benefits

After a year of regular exercise, the benefits extend beyond muscle tone and endurance. One major change is in your bone density. 

Weight-bearing exercises, such as resistance training combined with aerobic activity, can significantly improve bone strength, helping to combat and even reverse the effects of osteoporosis.

Moreover, regular exercise lowers your risk of several chronic conditions, including arthritis, type 2 diabetes, dementia, and certain cancers like breast and colon cancer. 

The financial perks are notable too. Studies have shown that older adults who exercise regularly can save an average of $2,500 per year in healthcare costs related to heart disease alone.

Mental Health Boost: Less Stress, Better Mood

The physical changes are impressive, but exercise also brings substantial mental health benefits. 

Regular physical activity helps reduce stress hormones like cortisol and adrenaline, decreasing the risk of anxiety and depression. 

As a result, you’re likely to feel more balanced and fulfilled in your everyday life.

Finding the Right Balance: Exercise Recommendations

The U.S. Department of Health and Human Services recommends at least 150 minutes of moderate-intensity exercise, such as brisk walking or cycling, or 75 minutes of vigorous activity, like running or swimming, per week. 

In addition, aim for muscle-strengthening activities, like weightlifting, on two or more days each week.

Pacing yourself is key—don’t rush into intense workouts too soon. Gradually increase your activity levels to avoid injury and burnout. 

As your fitness improves, you’ll find that you can handle more challenging workouts with ease.

Conclusion: Stay Consistent for Lifelong Benefits

Committing to regular exercise offers a wealth of physical, mental, and financial benefits. From stronger muscles and bones to a reduced risk of chronic diseases and improved mental health, staying active can transform your life. 

Start at your own pace, stay consistent, and watch as each workout brings you closer to a healthier, happier you.

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