Altered Gravity Simulated by Parabolic Flight and Water Immersion Leads to Decreased Trunk Motion

Abstract

Gravity is one of the important environmental factors that influence the physiologies and behaviors of animals and humans, and changes in gravity elicit a variety of physiological and behavioral alterations that include impaired movement coordination, vertigo, spatial disorientation, and perceptual illusions. To elucidate the effects of gravity on human physiology and behavior, we examined changes in wrist and trunk activities and heart rate during parabolic flight and the activity of wrist and trunk in water immersion experiments. Data from 195 person-time parabolas performed by eight subjects revealed that the trunk motion counts decreased by approximately half during ascending legs (hypergravity), relative to the data acquired before the parabolic flights. In contrast, the wrist activity remained unchanged. The results from the water immersion experiments demonstrated that in the underwater condition, both the wrist and trunk activities were significantly decreased but the latter decreased to a much lower level. Together, these data suggest that gravitational alterations can result in differential influences on the motions of the wrist and the trunk. These findings might be important for understanding the degeneration of skeleton and muscular system and performance of astronauts in microgravity.

Fig 1. Influences of parabolic flight on activity of wrist and trunk activities.

(A) Schematic representation of the parabolic flight profile. (B) The gravity levels that occurred during the parabolic flights and the blocks used for data collection (I-V). Block I: prior to parabola; block II: during hypergravity; block III: during hypogravity; block IV: during hypergravity; block V: prior after parabola. The duration of each block was 15 s. (C) The placements of Actiheart and Actiwatch on a human subject. (D) Trunk activity recorded by the Actiheart. The data are presented as the averages of 195 parabolas completed by seven subjects. (E) Wrist activity recorded by Actiwatch. Data are averages from the mean values of eight subjects. Statistical significance was determined with one-way repeated-measures ANOVA with Fisher’s least significance difference (LSD) post hoc test. The data are means ± SEs. The P values are shown to indicate significant differences.

Fig 2. Influences of parabolic flight on activity and heart rate.

(A) Changes in trunk and wrist activities during the five time blocks. The data obtained from seven subjects are presented as the average values of seven subjects, mean ± SE. The values in block I were normalized to 1.0. Statistical significance was determined by Student-t test. Data are mean ± SE, n = 7. (B) The heart rates during the five time blocks. The data obtained from seven subjects are averages of all tests completed by eight subjects. Statistical significance was determined with one-way repeated-measures ANOVA with Fisher’s least significance difference (LSD) post hoc test. Data represent mean ± SE, n = 195.The data are means ± SEs. The P values are shown to indicate significant differences.

Fig 3. Influence of water immersion on wrist and trunk activities.

(A) The placement of the Actiwatchs on a human subject. The Actiwatch on the chest was sealed in double-layered plastic bag and wrapped with bandage around chest along the dashed lines. (B) Wrist and trunk activities recorded by the Actiwatchs. The data represent means ± SEs, n = 22. (C) Changes in the trunk and wrist activities. The data are means ± SEs, n = 22. The values in block I were normalized to 1.0. Statistical significance was determined with Student-t test. (D) Schematic presentation of the changes in motion in the different gravity conditions.