How do astronauts exercise on the ISS?
Astronauts on the International Space Station exercise every day to counter the effects of microgravity on the human body.
The routine is highly structured, using specialized equipment to protect muscle mass, bone density, and cardiovascular health in orbit.
In space, the body adapts quickly to weightlessness in ways that can make returning to Earth difficult.
That is why the ISS exercise program is one of the most important parts of astronaut health, combining resistance training, cycling, and treadmill work in a compact orbital gym.
Why exercise is essential in microgravity
On Earth, gravity constantly loads the skeleton and muscles.
In low Earth orbit, that constant load disappears, and the body begins to decondition in surprising ways.
- Muscles weaken, especially in the legs, back, and core.
- Bones lose minerals, increasing the risk of fractures after landing.
- Cardiovascular fitness declines, because the heart does not work against gravity in the same way.
- Fluid shifts move toward the head, affecting balance and circulation.
The goal of ISS exercise is to mimic the stresses of Earth as closely as possible.
NASA, ESA, JAXA, and Roscosmos all rely on exercise protocols to keep astronauts functional during missions lasting months.
What equipment is used on the ISS?
The ISS does not have a traditional gym, but it does have three core exercise systems designed for spaceflight.
Advanced Resistive Exercise Device (ARED)
The ARED is the primary resistance machine on the station.
It uses vacuum cylinders and flywheel-like resistance to simulate weightlifting without relying on gravity.
Astronauts use the ARED to perform exercises such as squats, deadlifts, heel raises, rows, and bench press variations.
This helps maintain the major muscle groups and supports bone loading, which is critical in preventing bone loss in microgravity.
Combined Operational Load Bearing External Resistance Treadmill (COLBERT)
The treadmill, often referred to as COLBERT, allows astronauts to run or walk while tethered by a harness.
Because they would otherwise float away, the harness presses them down onto the treadmill surface.
This setup helps preserve aerobic fitness and leg strength.
The harness load can be adjusted to simulate body weight, making the workout more Earth-like than simple floating movement.
Cycle Ergometer with Vibration Isolation and Stabilization System (CEVIS)
The CEVIS is a stationary bike used for cardiovascular training.
Astronauts secure themselves with straps and pedals, then cycle for endurance work, interval sessions, or warm-ups.
Cycling is especially useful because it is low-impact, efficient, and easier to perform in a confined space.
It also provides a reliable way to monitor heart rate and workload.
How often do astronauts work out?
ISS crew members typically exercise about two hours per day, six days a week.
The exact schedule depends on mission demands, maintenance tasks, science experiments, and crew time allocation.
A common routine includes a mix of resistance training and cardio.
Astronauts may split the session between ARED, treadmill running, and cycling to target different systems in one day.
- Resistance training: usually several times per week
- Cardio sessions: often daily or near-daily
- Recovery and stretching: built into warm-up and cool-down periods
This consistency matters because physical decline in space begins early.
Without regular exercise, astronauts would lose strength and endurance rapidly, making reentry, landing, and post-mission rehabilitation much harder.
What does a typical ISS workout look like?
A standard session on the ISS is highly organized and monitored.
Astronauts often follow individualized exercise prescriptions created by flight surgeons, exercise specialists, and rehabilitation teams on the ground.
A typical workout may include:
- A short warm-up on the bike or treadmill
- Resistance exercises on ARED targeting lower body, upper body, and core
- Interval training or steady-state cycling
- Cool-down stretches and mobility work
Data such as heart rate, power output, and exercise duration are tracked closely.
This allows medical teams to adjust the plan over time and ensure each astronaut is meeting performance goals.
How do astronauts stay secured while exercising?
Securing the body is one of the most unique parts of exercising in orbit.
Since there is no gravity to hold an astronaut in place, nearly every piece of equipment uses restraints, straps, or harnesses.
On the treadmill, the harness provides downward force so the runner can maintain contact with the belt.
On the bike, straps keep the feet attached to the pedals.
On ARED, the astronaut braces against foot plates and handles to create stable force during lifts.
These stabilization systems are essential because they let astronauts generate the correct mechanical load without drifting away from the machine.
How does ISS exercise protect long-term health?
Exercise helps preserve the physical capacity needed for both spaceflight and return to Earth.
It reduces the severity of muscle atrophy and bone demineralization, two of the most studied health risks in human spaceflight.
It also supports:
- Balance and coordination after landing
- Circulatory adaptation during long missions
- Joint mobility and range of motion
- Mental health, because structured exercise can improve mood and sleep
NASA research has shown that exercise is one of the most effective countermeasures for microgravity-induced changes.
Even with a strong regimen, however, astronauts still need rehab after returning to Earth gravity.
What challenges make ISS exercise difficult?
Working out in orbit is not just a smaller version of Earth fitness.
Microgravity changes the mechanics, the equipment design, and even the way the body responds to training.
Some of the biggest challenges include:
- Limited space: exercise hardware must fit into a crowded station module
- Noise and vibration: equipment must not disturb experiments or the structure of the ISS
- Maintenance: hardware has to function reliably in a remote environment
- Scheduling: workouts must fit around scientific operations and station duties
There is also the challenge of motivation.
Astronauts must train consistently for months, often in a windowless environment where daily routines can become repetitive.
How is ISS exercise different from Earth workouts?
ISS exercise is similar to Earth training in purpose, but very different in execution.
On Earth, a runner relies on gravity and ground reaction force; on the ISS, a treadmill user must be strapped down to recreate that loading.
Likewise, a weightlifter on Earth lifts against gravity, while an astronaut uses resistance created by the machine itself.
The focus is not athletic performance in the usual sense, but preservation of the body for mission readiness and safe return.
That difference explains why the ISS exercise program is so carefully engineered.
It is not about fitness trends or general wellness; it is about maintaining human function in an environment the body was not designed to inhabit.
Why does this matter for future Moon and Mars missions?
The question of how do astronauts exercise on the ISS is especially important because it informs future exploration missions.
Longer voyages to the Moon, Mars, and beyond will require even more effective strategies to protect the human body.
Research from the ISS helps engineers and physicians improve exercise hardware, optimize training volume, and develop better countermeasures for deep-space travel.
The station remains a living laboratory for understanding what humans need to stay healthy far from Earth.
As space agencies plan for Artemis missions and eventual Mars expeditions, the lessons learned from ISS exercise routines will continue shaping spacecraft design, mission planning, and astronaut medical care.