Returning astronauts have frequently been seen being carried from their re-entry capsules on stretchers. This was even evident last year with NASA astronauts Suni Williams and Butch Wilmore, who completed an unexpectedly extended nine-month mission aboard the International Space Station before their return.
Despite the rigorous health and fitness standards required for astronaut selection, and the dedicated exercise regimens maintained during missions, prolonged periods in space can leave some astronauts more frail. They may experience reduced mobility and a greater susceptibility to injury than many elderly individuals on Earth.
Essentially, the physical transformations an astronaut’s body undergoes in orbit are akin to an accelerated form of human aging. The effects of a space mission on the spine, muscle weakening, and the disruption of the balance system mirror, in a compressed timeframe, what many people experience after recovering from certain injuries, extended hospital stays, or simply from years of sedentary living.
This correlation implies that the methods astronauts employ to maintain their physical condition during missions, and subsequently regain it upon returning to Earth, offer vital insights for enhancing our own health and potentially mitigating back pain. It also underscores the significance of incorporating anti-gravity activities into our daily routines if we aim to counteract the constant downward pull of Earth’s gravity. Importantly, this does not solely rely on conventional gym workouts.
The Impact of a Gravity-Deficient Environment
Since humans first ventured into space in 1961 and began continuous occupation of the International Space Station (ISS) in 2000, substantial knowledge has been acquired regarding the detrimental effects of reduced gravity on the human body, particularly the musculoskeletal system. Bones can lose up to 2 percent of their mass monthly, with weight-bearing bones experiencing the most significant depletion, while arm bones remain largely unaffected. Similarly, muscle strength can decline by as much as 10 percent within a few weeks, escalating to 20 percent over three to six months.
To combat these effects, astronauts on the ISS now dedicate approximately two hours daily to exercise. They utilize specialized treadmills, stationary bikes, and resistance machines designed for low-gravity environments. However, for many, these efforts are insufficient to fully compensate for the lack of gravity. Studies involving astronauts over the years have provided further details on microgravity’s impact.
Unveiling the ‘Forgotten’ Core Muscles
A pivotal realization from space medicine centers on the critical role of our “forgotten” core muscles. These are the deep stabilizers, situated behind the more superficial “six-pack” abdominal muscles, which maintain the lumbar spine’s stability and support within the abdomen. This group includes the multifidus, a muscle that runs along each side of the spinal column and aids in vertebral movement, and the transversus abdominis, a muscular layer encircling the trunk horizontally, much like a corset.
Core Muscle Weakness in Space
In the low-gravity environment of space, many bodily muscles decrease in size and strength. This phenomenon is particularly pronounced in postural muscles, such as the multifidus and transversus abdominis, responsible for maintaining an upright posture. For example, a 2021 study led by Julie Hides at Griffith University in Brisbane, Australia, examined five astronauts who spent six months on the ISS. The research revealed a reduction in the cross-sectional area of the multifidus in their lower backs by approximately 10 percent, while their transversus abdominis diminished by a substantial 34 percent.
Furthermore, in microgravity, the brain’s signals that activate these core muscles become imprecisely timed. Consequently, specific muscle fiber groups may not engage when required for certain movements.
Muscle atrophy directly contributes to spinal elongation observed in low-gravity conditions. The torsos of crew members can lengthen by over 6 centimeters, more than double the change typically experienced during natural daily cycles on Earth.
The cumulative effect of these changes is widespread back pain among astronauts. A 2024 review indicated that over half of astronauts reported moderate to severe lower back pain during spaceflight, with some individuals experiencing persistent pain a year later.
Consequently, maintaining the health of deep core muscles is now a central aspect of space medicine and crucial for the rehabilitation of individuals suffering from chronic back pain. However, Kirsty Lindsay from Northumbria University’s Aerospace Medicine and Rehabilitation Laboratory notes that these postural muscles do not respond effectively to conventional weightlifting routines typically used to build mass in the limbs. This implies that even highly trained athletes may exhibit insufficient multifidus strength.
Restoring Spinal Support and Motor Control
These spinal support muscles necessitate a specific training pattern. They require sustained, low-level activation, a condition not replicated in space. Unlike the more superficial abdominal or bicep muscles, it can be challenging to perceive when these deep core muscles are actively engaged. Therefore, post-mission astronaut reconditioning programs, such as those at the European Astronaut Centre in Cologne, Germany, emphasize deliberate, controlled movements, a concept known in physiotherapy as motor control.
This approach involves subjects learning to activate muscles like the multifidus and transversus abdominis, often utilizing ultrasound for real-time biofeedback to confirm muscle contraction. Once these activation skills are refined, astronauts can progress to exercises like sit-to-stand transitions or step-ups and step-downs. These activities involve gradually increasing loads and intensity, with a constant focus on maintaining correct spinal posture.
Such exercises form an integral part of the post-flight reconditioning protocols for both NASA and the European Space Agency (ESA). Innovations like FRED (Functional Re-adaptive Exercise Device), developed at Northumbria University, exemplify this approach. FRED, a modified cross-training machine providing minimal resistance, is engineered to target core stabilizer muscles. It is suitable for patients in physiotherapy clinics experiencing frailty, as well as for deconditioned astronauts.
The necessity for novel exercise methods extends to maintaining back health during space missions. Researchers at Northumbria University are developing a method called low-intensity continuous activation (LICA) exercise, specifically for training deep core stabilizer muscles. The objective is to ensure these muscles function correctly both in space and upon re-entry to Earth. On the ground, LICA exercises involve slow, controlled movements while the user’s balance is challenged, such as standing on a stationary cycle-ergometer and performing unloaded cycling. A walking variation also exists, achievable with devices like FRED.
For space applications, however, specialized exercise equipment will be required. LICA movements inherently engage the core muscles, inducing low-level contraction. Unlike typical activities like walking or weightlifting, which involve intermittent muscle activation, LICA exercise maintains continuous engagement throughout the movement. This eliminates the need for the user to consciously control muscle activation.
This development holds potential benefits for individuals on Earth as well. Tests indicate that LICA exercise can aid in rehabilitation following bed rest, alleviate lower back pain, and address urinary stress incontinence post-childbirth.
Leveraging Gravity-Altering Technologies
Various “gravity-altering” systems are also available to clinicians. These technologies allow for precise adjustment of gravity levels to stimulate core engagement in patients. For instance, following an injury, body-weight-support or anti-gravity treadmills enable individuals to walk or run at 50 to 80 percent of their body weight while trunk control is progressively restored.
These technologies were initially conceived to allow astronauts to practice lunar walking and to re-acclimate to Earth’s gravity after extended periods in orbit. The Alter-G treadmill, developed at NASA, is a prime example. It employs a sealed chamber that encloses the lower body, using increased air pressure to support the runner. Studies demonstrate that such devices can reduce pain in patients recovering from spinal, hip, or knee surgery, and enhance walking confidence in older adults and individuals with neurological conditions.
Wearable technology also offers valuable support. The Gravity-Loading Countermeasure Skinsuit, a skintight elastic garment developed over five years at ESA, mimics the head-to-toe gravitational pull. Designed for space use, the suit has been shown to mitigate spinal elongation and back pain, while promoting proper postural alignment and engaging deep stabilizer muscles. This concept is now being adapted into apparel for ground-based use, offering support for posture and trunk endurance—the capacity of core muscles to sustain effort without fatigue—in individuals with weakened backs, chronic pain, or age-related stooping.
Simple Anti-Gravity Habits for Daily Life
Beyond high-tech solutions, numerous simple anti-gravity habits can be integrated into daily life. These include sitting without back support for ten minutes, opting to stand during phone calls, choosing stairs over elevators, and, a personal favorite, standing on a train while loosely holding a rail or strap, which compels the body to make continuous minor balance adjustments. Implementing these practices significantly improved my own lower back pain that developed after long workdays.
Additionally, some evidence suggests that exercise regimens with a strong emphasis on core strengthening, such as Pilates, can be beneficial.
Re-calibrating the Balance System
Extended periods in space not only affect the body’s physical structure but also disrupt the balance system. In microgravity, the vestibular structures in the inner ear no longer respond to head movements or gravitational pull in the typical manner. Similarly, the sensory receptors in muscles and joints, crucial for proprioception—the sense of limb position—are also affected. Over time, the brain reduces its reliance on these cues, increasingly depending on visual input.
Upon returning to Earth, astronauts often experience unsteadiness and a tendency to overcorrect or veer when walking as their balance system re-calibrates. NASA astronaut Tom Marshburn recounted an experience two hours after returning from a space shuttle mission, where he and his crewmate exaggerated their steps when walking up a ramp, lifting their feet unusually high. He also noted a tendency to misjudge corner turns, stumbling into walls. A practical consequence of this is that astronauts are prohibited from driving for one to two weeks post-landing.
To restore coordination, space agencies implement sensorimotor reconditioning. This involves balance exercises performed with eyes closed, employing wobble boards, or performing tasks that combine motion-tracking goggles with head movements to retrain the reflexes linking balance and vision.
The balance improvement strategies employed for astronauts have direct benefits for the general population. Enhancing and refining balance is achievable well into later life through progressively destabilizing tasks, such as standing on one leg while turning the head, walking heel-to-toe on a line, or using balance boards. For older adults, this form of “neural tuning” can reduce the risk of falls and sharpen spatial awareness. In essence, drills used for post-flight astronaut rehabilitation can help Earth-bound individuals maintain upright stability and independence.
Combating Bone Loss and Strengthening Foundation
Another significant consequence of time in space is bone loss and weakening. Healthy bones are maintained through a dynamic interplay of bone resorption and formation, a process that ensures constant renewal. Microgravity disrupts this balance, leading to increased bone fragility and a higher susceptibility to fractures. One potential countermeasure is vibration.
Initial research into vibration focused on protecting the bones and muscles of people on Earth, evolving into whole-body, low-intensity vibration (LIV) therapy. This technique is now extensively studied for its potential in preserving astronauts’ bone health. LIV involves an individual standing on a device resembling bathroom scales that transmits tiny vibrations through the feet into the legs, hips, and lower spine.
This stimulation can activate stem cells in the bone marrow, prompting their differentiation into cells responsible for bone formation. Short durations of LIV are currently undergoing clinical trials for treating osteoporosis and frailty, as well as for post-operative spinal or hip rehabilitation, though conclusive evidence is still pending.
Standing Up to Gravity: The Human Advantage
These findings may not be surprising, given that humans are bipedal beings highly adapted to spending much of their day upright against gravity’s pull. Without this inherent daily workout, the body quickly deteriorates. This is starkly illustrated in studies of prolonged bed rest. Although gravity still acts on the body when lying down, it does not exert its pull along the head-to-toe axis, leading to consequences similar to those experienced by astronauts. Studies consistently show that postural muscles become disproportionately weaker after extended bed rest. This is also why bed-rest studies, where volunteers remain recumbent for months, are utilized to research the body’s adaptation to weightlessness.
Ultimately, years of experience in space medicine have led to the understanding that gravity is not merely a constant force but a training partner. The principles that enable astronauts to maintain an upright posture after prolonged microgravity exposure can assist everyone in resisting the gradual decline associated with aging and inactivity. Gravity, it appears, serves as both the force that challenges us and the remedy that supports us.