Foot forces during typical days on the international space station

Area of Science:

• Space physiology
• Biomechanics
• Bone health

Background:

• Spaceflight causes decreased bone mineral density (BMD) in astronauts.
• The mechanical loading environment contributing to bone loss is not well understood.

Purpose of the Study:

• Characterize the lower extremity (LE) loading environment for astronauts on the International Space Station (ISS).
• Relate mechanical loading dose to changes in BMD.
• Evaluate the effectiveness of current exercise protocols.

Main Methods:

• In-shoe force measurements were collected from four astronauts during daily activities on Earth and the ISS.
• Enhanced Daily Load Stimulus (EDLS) model was used to quantify mechanical dose.
• BMD was assessed using dual energy X-ray absorptiometry (DXA) pre- and post-flight.

Main Results:

• On-orbit LE forces during walking and running were reduced by 25% and 46% compared to Earth.
• Mean on-orbit LE loads ranged from 0.20 to 1.3 body weight (BW) during resistance exercise.
• EDLS showed a 25% decrease in daily LE load on the ISS.
• BMD decreased by 0.71% (femoral neck) and 0.83% (lumbar spine) per month.

Conclusions:

• Measured ISS exercise durations and loading are insufficient to prevent bone loss.
• Reduced mechanical loading on the ISS contributes to decreased BMD.
• Future exercise countermeasures should aim for Earth-equivalent loading levels.