Effects of different restrained foot positions on hand force exertion capability-implications for microgravity operations

Abstract

An experiment was conducted to determine restrained foot positions that increase hand force exertion capability (HFEC) over that available under the existing restrained foot position utilized by NASA astronauts during Extra Vehicular Activity (EVA). With the feet immobilized to simulated the actual boundary conditions of a Portable Foot Restraint (PFR), participants performed a series of static push, pull, and lateral exertions. These exertions were performed in each of three experimental foot positions consisting of a control and two treatments. The existing foot position within the PFR utilized by NASA is symmetric about the mid-sagittal and frontal planes with the feet rotated laterally by 15', and was adopted as the control in this study. The existing foot position was compared against two experimental foot positions defined as spread and spread/slant. For the spread design, the feet were separated by 1 O' in the sagittal plane with the feet rotated lateraaly by 150, right foot forward, and remained symmetric about the frontal plane. The spread/slant foot position differs from the spread stance in that the anterior foot was set to 20' of dorsiflexion and the posterior foot to 20' of plantar flexion. An analysis of the data using ANOVA showed at the cc =.05 level that the spread/slant foot position produces greater HFEC than the existing design during pushing. For pulling, the spread/slant design produced greater HFEC than the spread and existing foot positions. For lateral exertions, neither foot position produced significantly higher hand forces. This study shows that the spread/slant foot position increases maximal hand forces for push and pull exertions. For pushing, the difference between the means of the existing and spread/slant foot positions fell between 16 and 88 N ((x =.05), which is a relative increase between 7 and 35%. For pulling, the difference between the means of and 3 5 N (cc =. 0 5), which is a relative increase between 4 and 19%. Similarly, the difference between the spread and spread/slant foot positions fell between 20 and 62 N (cc =.05), which is a relative increase between 7 and 23%.