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The TBone studies: Effects of microgravity on astronauts' bones

Health science

The Canadian TBone experiment used 3D imaging technology to study changes in astronauts' bone health caused by the time they spend in space. Its successor, TBone2, will continue this work


The TBone experiment confirmed that although astronauts on the International Space Station (ISS) follow daily exercise programs, bone loss progresses proportionally to the length of their missions. An astronaut's skeleton, floating in microgravity, appears to age at an accelerated rate during a six-month stay in space – the equivalent of almost 20 years of bone loss on Earth. The study's findings also suggest that increasing exercise during their mission as opposed to pre-flight is more likely to preserve bone strength while spending time away from Earth's gravity.

Data collected during the TBone study also allowed researchers from Canada, the United States and Germany to study the structure of the tibia in 14 astronauts for up to one year after their return from the ISS.

Results from their analysis showed that:

  • Even after a year on Earth following their missions, more than 50% of the astronauts who participated in TBone had not regained their pre-flight bone density.
  • Astronauts who spent less than six months in space recovered more bone than those who lived in space for over six months.
  • Bones age differently in space than they do on Earth! The researchers noticed differences between the bone loss caused by microgravity and bone loss that occurs naturally during aging. On Earth, the external part of the bone becomes fragile more quickly than the interior part of the bone as a person ages. But in space, the effect is the opposite: the internal part of the bone becomes weaker faster than its exterior.

These findings have important implications for future space travellers headed to distant destinations like Mars, and for patients on Earth who are immobilized or injured for long periods of time.


Our bones constantly undergo a reshaping process in response to everyday use. On Earth, bones are optimized for working in gravity, the force they must work against to support our body weight.

Due to weightlessness and reduced exercise, more bone is lost than replaced during extended space flight.

While adults past age 50 typically lose about 1% of their bone mass each year (a process that can eventually lead to osteoporosis), astronauts in space can lose up to 1.5% each month. Fortunately, much of this loss is reversed when astronauts return to Earth.

Researchers want to know whether bone loss might reach its highest levels during the first six months of space flight and continue afterward, as astronauts remain in space.

The objective of the TBone investigation was to determine how this cycle of loss and regain affects the long-term strength and quality of bones. TBone2 will continue to investigate the mechanisms of bone loss and regain in astronauts undertaking missions of up to one year on the ISS.

Studies like TBone and TBone2 could:

Effects of microgravity on bones with astronaut Tim Peake. (Credits: Canadian Space Agency, NASA, European Space Agency)

Human bones contain a honeycomb-like structure that helps give support and strength. When we walk, dance, play hockey, and enjoy other forms of exercise, the force required for us to work against gravity in order to carry our own body weight regenerates our bone tissue, and makes our skeletal system stronger. When we are less mobile, our bones lose density and strength.



Using high-resolution imagery, TBone's researchers:


Researchers will:

 Impacts on Earth

"What we can learn in six months of space flight would take us a decade on Earth," said Dr. Steven Boyd, TBone's Principal Investigator.

TBone offered researchers a better understanding of diseases like osteoporosis, a bone loss disorder that affects approximately 10% of the Canadian population aged 40 and over. According to Osteoporosis Canada, at least 1 in 3 women and 1 in 5 men will break a bone due to osteoporosis in their lifetime. Further research could help identify those who are prone to bone loss, and design individualized treatment strategies to predict and prevent fractures caused by low bone density.

How it works


Seventeen astronauts participated in this study.


Thirty astronauts will take part in this study.

As part of NASA's CIPHER program, TBone2 will examine subjects who take part in space flights of six weeks, six months, and one year – longer than the original TBone study. Comparing how astronauts' bodies react to different lengths of time exposed to microgravity will help researchers test a hypothesis: that bone loss happens most during the first six months of space flight and then stabilizes within one year in space.

TBone2 is one of two Canadian Space Agency studies that are part of NASA's CIPHER program. The other is Vascular Calcium.

CIPHER, which stands for Complement of Integrated Protocols for Human Exploration Research, brings together specially selected studies to be conducted on the ISS. CIPHER is designed to help better understand the impact of long-duration space flight by comparing the effects of different mission lengths: short stays, standard six-month missions, and long-duration (one-year) space flights.


Astronauts in space get about 2 hours of exercise each day

Astronauts in space get about two hours of exercise each day, which helps prevent some of the bone loss that occurs in microgravity. (Credit: NASA)

Research team

Dr. Steven Boyd of the University of Calgary is principal investigator for the TBone series.

His co-investigators for TBone were:

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