Using a tri-axial accelerometer to quantify the locomotive Patterns before and after 60 days of bed-rest

Abstract

The effects that microgravity induces to the human body are well known. Unfortunately, how to completely counter them is not yet clear. One method among others is very effective to mimic and simulate these effects to study them on Earth – the bed-rest study. To date, the best countermeasure known to preserve the physiological functions during a spaceflight or during bedrest is physical exercise. This thesis aims to quantify, using a tri-axial accelerometer, the changes in locomotive patterns and levels of physical activity (PA) before and after a 60-day bed-rest and the effectiveness of a new training device – Sledge Jump System (SJS) – as countermeasure of bed-rest and, eventually, spaceflights. 23 male subjects, divided in two groups underwent a 60-day bed-rest period. They wore a tri-axial accelerometer on the waist for two consecutive weeks before and after this period. The training group (n=12) trained daily in the SJS, while the control group (n=11) did not perform any kind of activity during the whole period. In the two weeks before and after the bed-rest period, measurements of gait and of PA were taken. To measure the gait parameters (walking, slow run, moderate run, climb up stairs and climb down stairs), one gait course was done before bed-rest to set baseline values and three more gait courses were done after the bed-rest period, one day (R+1), seven days (R+7) after and fourteen days (R+14) after re-ambulation to see the differences in gait parameters and recovery over time. For the PA levels, integrals over the two weeks before and after bed-rest period were calculated from the signal of the accelerometer. Different levels of PA were set based on baseline values. The linear mixed-effects models showed a statistical difference (p<0.05) for the relative values in the time to complete the task, the number of steps, the average speed for the slow run in the control group during the R+1 measurements, and a decrease in the stride length for both groups. A significant increase (p<0.05) in time to complete the task, number of steps as well as a decrease in the average speed have been reported for both groups during R+1 in the moderate run. No significant changes (p<0.05) were found in the PA levels. Results support other findings suggesting the benefits of physical exercise during immobilization, proving a partial effectiveness of the SJS for preventing the effects of bed-rest period.