Increase Your Gravity: Strength, Health, and SpaceBed rest and sedentariness are like microgravity and should be avoided as much as possible. Instead, create your own gravity, and slowly increase it for as long as you possibly can.
Increase Your Gravity
By: Nick Soleyn, Editor in Chief
Bioastronautics, the study of life in space, may show some connections between gravity, aging, and strength training.
Strength and health tend to show up together in persons as they age. Stronger adults are not free from disease and disability, but they tend to have better outcomes. And healthier adults also tend to be strong, complementing a healthy and active lifestyle:
“Health and longevity seem to find a meeting place in functional assessments. Maintaining self-care, independence, and the ability to live and thrive in the presence of aging, disease, or disability is grounds for a positive, healthy outcome when life’s slings and arrows inevitably catch you. Their opposites tend to signal a declining quality of life, frailty, and the expectation of poor health markers.” (The Picture of Health Starts with Strength)
These are observations, however, not necessarily correlations.
There are some possible reasons why health and strength tend to go together. One theory from the American Heart Association is that the amount of sedentariness, not exercise, is more closely related to cardiovascular disease, driving the idea that “you can’t undo sitting.” It could be that health comes from a generally active lifestyle, and active people tend to be stronger than couch potatoes. But, how could a study parse out the difference between activity and training? The problem, wrote James Hamblin in an article called The Futility of the Workout-Sit Cycle, is that “testing the effectiveness of a complex intervention like decades of a physically active lifestyle is not well suited to randomized, controlled trials.”
Our position has always been that an active, healthy lifestyle is better than nothing but that an active, healthy lifestyle built on a foundation of strength leads to a better quality of life, generally. Strength is compatible (even complementary) with independence, performance, sports, longevity, and general health.
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But what does aging have to do with space?
Space is like a laboratory for artificial aging. One study, known as the NASA Twins Study, compared identical twins, Scott and Mark Kelly, before, during, and after Scott’s 340-day stay on the International Space Station. Predictably, the high-flying twin lost about 7% of his body mass, while his earth-bound brother gained about 4% during the mission. Some of this loss was structural (losses in bone mass, muscle, and tissue). Generally, astronauts are said to lose between 1% and 2% of bone mass per month in microgravity environments. Compare that to the 3% to 4% of bone loss per decade in the average fifty-year-old. The Twins Study may lead to insights not only for sustained spaceflight but for studying aging on earth:
“The health effects associated with spaceflight have several similarities to aging-related disorders, such as cancer and osteoporosis. While spaceflight’s parallels to aging are a concern for long-term crewed missions—such as those that would be required on a voyage to Mars—the unique space environment also presents a unique opportunity to study the physiology of aging.”
Notably, bone formation during the spaceflight mission was higher during periods with the astronaut brother exercised more vigorously. Of course, artificial aging in microgravity is not the same as aging on earth, but there are enough parallels for us to draw interesting conclusions.
Take bone loss, for example. Bones are constantly being formed through ossification and broken down in a process called resorption. As we age, resorption starts to outpace formation. Osteoporosis is greater than normal bone loss from a variety of causes. Similarly, “The lack of gravitation and the resulting decreased mechanical load on the weight-bearing bones induced during spaceflight results in an increase in bone resorption and a decrease in bone formation.” Similar amounts of increased resorption have been observed in spaceflight as those from conditions requiring long-term bed rest. Bone loss from the lack of normal weight-bearing activities in space is seen first in weight-bearing bones. These losses are due to the “gravitational unloading in a microgravity environment. The result is a condition that is suggested to be similar to disuse osteoporosis or secondary osteoporosis, which result from a decrease in weight-being activity.”
Bones get denser in response to compressive mechanical forces. Force is a somewhat amorphous concept. The best way we can describe it is that if the conditions are right, it is the thing that causes movement. A compressive force will tend to shorten objects if the force is great enough or if the object is sufficiently malleable.
There are two ways bones experience direct compressive forces. The first is by intercepting gravity. When you stand tall at the top of a squat, you are exerting only enough force with your muscles to “stack” the skeleton under the load of the barbell, holding it up through architecture rather than muscular force. As we grow, mature, and age, gravity provides a constant, squishing compressive force, whether we are carrying a barbell or just moving ourselves around the house. Bed rest can be so dramatically harmful because your skeleton is no longer supporting your weight against gravity, and the balance of bone formation and resorption can get skewed even more significantly toward bone loss, something many elderly adults cannot afford.
A second way to induce compression on your bones is through movement. When muscles pull on bones, they use leverage to create movement. Moving a lever can be thought of as a combination of compression and tension on the lever arm—your bones. So, taking the same example of the squat, as you descend into the bottom of the movement and stand up, your bones may not be directly resisting the downward force of gravity, but when your muscles pull on your bones to create movement, some of that pulling force is absorbed by the bone as compression.
During long-term stays in space, astronauts can mitigate slightly the amount of bone mass they lose through vigorous exercise. This should be expected since increase movement will increase some of the compressive force on the skeletal system, signaling some need to hold onto bone mass.
We can, perhaps, think of the relationship between strength and gravity in a more holistic way. Your body is efficient and will adapt to the needs of its environment. Like water filling a glass, your body takes the shape that fits whatever is required of it. Unfortunately for space travelers, some of our more basic functions are adapted to earth’s gravity, making long-term space missions hard on the body. For us on earth, however, we can take the “use it or lose it” approach to our bodies, and the lessons of gravity to help us target some functional necessities as we age.
Bed rest and sedentariness are like microgravity and should be avoided as much as possible. Instead, create your own gravity, and slowly increase it for as long as you possibly can, interspersed with periods of recovery. Lifting weights is not the answer to every health issue, but the simple mechanics of loaded human movement, combined with an active lifestyle, are the best ways to stay adapted to this environment. We may not be able to identify exactly the benefits of long-term, ingrained training habits versus other outcomes, but we can say with certainty, if you are getting stronger, you are not getting weaker. And that’s something.
 Deborah Rohm Young et al., “Sedentary Behavior and Cardiovascular Morbidity and Mortality: A Science Advisory From the American Heart Association,” Circulation 134, no. 13 (Sept. 2016). https://doi.org/10.1086/691233.
 James Hamblin, “The Futility of the Workout-Sit Cycle,” The Atlantic, August 16, 2016, https://www.theatlantic.com/health/archive/2016/08/the-new-exercise-mantra/495908/.
 Id. (emphasis original)
 Shi En Kim, “To Study Aging, Scientists are Looking to Outer Space,” Science, December 2, 2020.
 Daniela Grimm et al., “The Impact of Microgravity on Bone in Humans,” Bone 87: 44-56 (June 2016) 2016. https://doi.org/10.1016/j.bone.2015.12.057