Ground Reaction Forces generated by a Lower Body Negative Pressure Exercise Device for Space Flight

Abstract

Loss of bone and muscle are leading concerns among astronauts during prolonged space flight. Lower body negative pressure (LBNP) chambers generate gravitational and cardiovascular stresses to maintain musculoskeletal strength and fitness by means of suction pressure. Ground reaction forces (GRFs) generated underneath the user’s feet are directly proportional to the level of negative pressure applied. However, the exact mechanism of GRF generation remains unresolved. We hypothesize that increasing the cross‐sectional area (CSA) of the user’s waist in contact with a flexible waist seal will increase the GRFs generated at a given vacuum pressure. To test our hypothesis, we collected GRFs generated by 6 healthy subjects under two conditions: original (unchanged) CSA of their waist and a greater waist CSA using expanded cushioning around waist of the same subjects. GRFs were measured with LBNP levels ranging from 0 (ambient pressure) to 50 mmHg with subjects lying in supine position to simulate microgravity. The original CSA of 467.7 cm2 ± 69.0 cm2 generated 118 % ± 31 % body weight at −50 mmHg. However, the larger CSA of 1,451.0 cm2 ± 331.0 cm2 generated a mean GRF of 146 % ± 31% body weight at −50 mmHg. A one‐way ANOVA test resulted in p‐values < 0.05 for all pressures, denoting statistically significant increases in larger compared with original CSA GRF. The GRF generated with larger CSA followed this equation GRF = −1.8211 (LBNP) + 0.7899 while the GRF generated with original CSA followed the equation: GRF = −1.5079 (LBNP) + 0.3995. These data support our hypothesis that GRFs generated by LBNP are directly proportional to the waist CSA. Using this new concept, astronauts may generate GRFs at lower LBNP levels to prevent pre‐syncopal symptoms during exercise in space.Support or Funding InformationSupported by NASA grants NNX13AJ12G and NSSC19K0409.Average weight measurements with varying pressures for six volunteers; red is original CSA of subject's waist and blue is larger CSA.Figure 1