Reducing gravity takes the bounce out of running

Area of Science:

• Biomechanics
• Human Physiology
• Gravitational Biology

Background:

• Reduced gravity environments, such as those experienced in spaceflight or simulated conditions, are expected to alter human locomotion.
• Previous assumptions suggested that lower gravity would enable higher leaps during running due to reduced gravitational force.

Purpose of the Study:

• To investigate human running biomechanics in simulated reduced gravity.
• To determine the factors influencing ballistic height and gait adaptations during running in altered gravitational conditions.

Main Methods:

• Ten subjects ran on a treadmill under five simulated reduced gravity levels.
• Optoelectronic motion capture was used to track center-of-mass kinematics.
• Vertical take-off velocity and other kinematic parameters were analyzed.

Main Results:

• Subjects consistently exhibited reduced ballistic height in reduced gravity compared to normal gravity.
• Vertical take-off velocity scaled with the square root of gravitational acceleration.
• Gait adaptations were explained by energetic optimality, balancing collision costs and leg swing work.

Conclusions:

• Reduced gravity running leads to lower ballistic height due to a decrease in vertical take-off velocity.
• Human gait adaptation in reduced gravity is driven by energetic cost optimization, not solely by stance phase unloading.
• The motor control system prioritizes energy efficiency by reducing vertical momentum in the stance phase, leading to less 'bouncy' gaits.