In this episode of Longevity By Design, Dr. Rachele Pojednic describes the mechanism behind how exercise improves healthspan—discussing different modes of exercise and how each caters to a key health metric. Muscle integrity declines as we age, and Dr. Pojednic shares why preserving this tissue is critical for healthspan. She encourages listeners to choose the best physical activity type for themselves and quantifies how much exercise they should get per week. Finally, Dr. Pojednic discusses a passion of hers—how the scientific community can improve communication with the general public and vice versa.
About Dr. Rachele Pojednic
Dr. Rachele Pojednic is an Associate Professor & Program Director of Exercise Science in the Department of Health and Human Performance at Norwich University. She is also a research associate at the Institute of Lifestyle Medicine at Harvard Medical School. Dr. Pojednic holds a PhD in Biochemical and Molecular Nutrition from Tufts University and completed her postdoctoral training at Joslin Diabetes Center, Harvard Medical School. Dr. Pojednic is currently the Director of Scientific Research and Outreach at Restore Hyperwellness. Her current work examines nutrition and physical activity education for healthcare and fitness professionals as well as dietary, supplementation, and physical activity interventions on muscle physiology, performance, recovery, and chronic disease. Dr. Pojednic has a passion for scientific communications and has been an active member of the fitness community for over twenty years as an indoor cycling instructor and an ambassador for Specialized and Lululemon.
How are lifestyle medicine and traditional medicine similar?
It is no secret that nutrition, exercise, stress management, and sleep affect both physiology and healthspan. Lifestyle medicine asserts that it’s possible to age healthfully, reaching the age of 80, 90, and above while maintaining good health. Lifestyle medicine aims to create an education to show healthcare workers that pharmaceuticals and exercise actually act on the same biological pathways. During this episode, Dr. Pojednic provides interesting examples of how medication and lifestyle interventions use the same pathways to decrease disease risk.
Exercise and healthspan
If there is one major takeaway from the conversation with Dr. Pojednic, it's that exercise improves healthspan. She makes this clear by sharing insight on some physiological benefits of exercise as well as the importance of muscle integrity for healthy aging.
Health benefits of contracting your muscles during exercise
Contracting our muscles during physical activity confers many metabolic health benefits. Muscles use fuel from the bloodstream, namely carbohydrates, and fats, to promote contraction. This action benefits the metabolism because excess circulating carbohydrates and fats can be problematic for health in the case of no exercise or muscle contraction.
An example of how excess sugar in the bloodstream can be harmful is the accumulation of advanced glycation end products (AGEs). Under normal physiologic conditions, sugar molecules react with proteins in the blood to create AGEs. However, in the case of chronic high blood sugar, AGEs will accumulate, leading to inflammation in the body and an increased risk for multiple chronic diseases.
Similarly, excess fat in the bloodstream is problematic. Continuously consuming dietary fat above the body’s energy needs can cause triglycerides to stick to the outside of your arteries and veins, causing them to collapse and become smaller. Over time, this will lead to high cholesterol and increased blood pressure, both of which are risk factors for cardiovascular disease and stroke.
Key takeaway: Exercise promotes healthspan by clearing nutrients from the bloodstream that can be harmful in excess amounts.
Muscle tissue is a "master communicator" in the body
Another reason muscle tissue is vital for health is its role as a master communicator. Muscle tissue secretes small molecules called myokines, which communicate with the brain, pancreas, heart, and gut. Dr. Pojednic further explains this important role of muscle tissue, "When muscle tissue is not strong and robust, we see these communication pathways begin to break down. Dysfunction in these pathways can cause diseases including type 2 diabetes, cardiovascular disease, Alzheimer's, and dementia to start to progress." She closes by noting that continuously using your muscles throughout the day helps maintain their function.
Key takeaway: Robust, active muscle is critical for health and longevity. When you continuously use your muscle, e.g., moving throughout the day, the muscle can better communicate with other organs, resulting in better health metrics for the long haul.
Health outcomes of different exercise modalities
Before diving into the science behind different exercise modalities, Dr. Pojednic notes that the best exercise you can do is the one you love. Enjoying the exercise you participate in leads to more sustainable exercise habits than forcing an activity you dislike.
Dr. Pojednic describes how different forms of exercise can have different physiological effects on the body.
Aerobic exercise improves the cardiovascular system. Heart muscle gets stronger and blood volume increases. Aerobic activity increases the demand for oxygen to be delivered to working muscles, increasing capillarization. As a result, oxygen utilization increases. This is how you become a better runner, a better hiker, and a better biker—improving endurance over time.
What counts as aerobic exercise? Forms of aerobic exercise include running, swimming, and biking.
Resistance training increases muscle tissue, also known as hypertrophy, and can improve strength and power metrics. This type of training increases type-two muscle fibers, which are the fast twitch fibers. It also increases mitochondria in these fibers to ensure the muscle is producing the right amount of energy. As a result, resistance training enables heavier lifting, which is impactful for activities of daily living such as picking up children or groceries.
What counts as resistance training? Forms of resistance training include weight training with free weights, weight machines, or resistance bands.
Power training allows your body to move quickly with force—making it better able to perform with speed. Older individuals are at an increased risk of early death from falls. Monitoring vitamin D and calcium levels can help. Exercise keeps our bones strong; improving power metrics can help us catch ourselves before we hit the ground.
What counts as power training? Leg press, squat jump, barbell curl, and quickly lifting weights count as power training.
High intensity interval training (HIIT)
In the scientific space, HIIT is defined as pushing a body to about VO2 max or higher for short periods, followed by a rest period. Examples include sprinting for 30-60 seconds, followed by an active recovery or stopping until the body is completely recovered. During HIIT training, this cycle repeats for 15-30 minutes. When done properly, HIIT training greatly benefits health. Dr. Pojednic notes that solid data supports that short, intense pushes can result in physiologic benefits similar to participating in long, slow endurance runs.
What counts as HIIT? Running, biking, or swimming sprints followed by an active recovery count as HIIT.
Key takeaway: Find the exercise you love and do it for life. Whatever exercise keeps your body moving is the best for you.
How much physical activity should you get weekly?
According to the most recent revision to the Physical Activity Guidelines for Americans (2018), healthy adults should get 150 minutes of moderate-intensity activity or 75 minutes of vigorous activity per week.  The secondary recommendation is to get two days of resistance training per week.
Dr. Pojednic explains that the most benefit occurs within the first 60 minutes of exercise. So, if you cannot achieve 150 minutes of physical activity in a week, aiming for at least 60 minutes can still confer health benefits.
Key takeaway: All healthy adults should get at least 150 minutes of moderate-intensity physical activity or 75 minutes of vigorous physical activity per week, but some exercise is better than no exercise. 
Is it possible to overexercise?
The health benefits of exercise reach a maximum at around 300 minutes per week. After 300 minutes, there can be slight health risks compared to being sedentary. Dr. Pojednic discusses the two major risks of overtraining: injury and mental health implications.
“If there are other things in your life that are going poorly because you are exercising so much—for example, you are sleeping less, hindering relationships, or are disrupted during work—you are likely over the line. There is a fine line between making exercise a habit and then tipping into an unhealthy behavioral pattern where it affects your quality of life,” she notes.
Key takeaway: Overtraining can impact overall health outcomes. Of note, this does not account for training outcomes like endurance events.
Decoupling weight loss from exercise
The conversation around exercise and weight loss is nuanced in many ways. Interestingly, the data shows that exercise isn't always the best weight loss tool.
On the one hand, exercise helps you to burn more calories. Not only do you burn calories at the moment that you are exercising, but you are also increasing muscle strength and lean tissue mass, effectively increasing metabolic rate throughout the day.
On the other hand, increasing lean tissue stimulates your appetite. For example, marathon runners tend to gain weight compared to middle-distance runners because their drastic increase in running volume simultaneously increases their hunger and subsequent fueling.
Where the conversation becomes even more nuanced is, "What type of weight are you gaining from exercise?" As previously mentioned, robust muscle is critically important for long-term health and longevity. "If weight is increasing because exercise causes you to gain six pounds of muscle, you have just made your body a healthier, stronger, more efficient machine, even though the pounds on the scale went up," explains Dr. Pojednic. "This is why I roll my eyes with exercising for weight loss. I really don't understand why that needs to be the goal of exercise—what if the goal was to make our muscles really strong and prevent chronic diseases?"
Key takeaway: While historically marketed as a weight loss tool, the benefits of exercise stretch far beyond weight loss and into improving healthspan.
Identify the warning signs of scientific misinformation in the media
In a time where scientific information is broadly shared on social media platforms, it is critically important to be able to differentiate fact from fiction. Dr. Pojednic points out three red flags to pay be aware of while browsing the web.
- Outrageous new claims: Science is a process of consensus learning, meaning it takes a long time for data to become substantial enough to draw conclusions. If someone says, “This brand-new study contains new information, and you should act on it,” be skeptical.
- Questioning experts in the field: The saying, “Experts don't know about this,” or “The experts have been wrong about this forever,” tend to be incorrect. Dr. Pojednic firmly notes: Influencers on the internet can not become an expert in nutrition or exercise science by doing their own research.
- Sales involvement: Be wary of influencers or companies trying to sell you a quick health fix. Companies may make outrageous claims to promote their products are may not always share sound science.
Where to find accurate scientific information
For Longevity by Design listeners who are science enthusiasts and looking for credible resources, Dr. Pojednic highlights two trusted websites:
Top tip to improve healthspan
Dr. Pojednic’s top tip for health is to increase muscle integrity. She reiterates that strong muscles are critical for metabolic regulation and can help prevent injuries later in life.