Effects of EVA spacesuit glove on grasping and pinching tasks

Acta Astronautica 96 (2014) 151–158

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Effects of EVA spacesuit glove on grasping and pinching tasks Silvia Appendino n, Alessandro Battezzato, Fai Chen Chen, Alain Favetto, Mehdi Mousavi, Francesco Pescarmona Center for Space Human Robotics@PoliTo, Istituto Italiano di Tecnologia, Corso Trento 21, Torino 10129, Italy

a r t i c l e i n f o

abstract

Article history: Received 18 July 2013 Received in revised form 18 September 2013 Accepted 19 November 2013 Available online 3 December 2013

The human hand has a wide range of degrees of freedom, allowing a great variety of movements, and is also one of the most sensitive parts of the human body. Due to these characteristics, it is the most important tool for astronauts to perform extravehicular activities (EVA). However, astronauts must wear mandatory EVA equipment to be protected from the harsh conditions in space and this strongly reduces hand performance, in particular as regards dexterity, tactile perception, mobility and fatigue. Several studies have been conducted to determine the influence of the EVA glove on manual capabilities, both in the past and more recently. This study presents experimental data regarding the performance decline occurring in terms of force and fatigue in the execution of grasping and pinching tasks when wearing an EVA glove, in pressurized and unpressurized conditions, compared with barehanded potential. Results show that wearing the unpressurized EVA glove hinders grip and lateral pinch performances, dropping exerted forces to about 50–70%, while it barely affects two- and three-finger pinch performances. On the other hand, wearing the pressurized glove worsens performances in all cases, reducing forces to about 10–30% of barehanded potential. The results are presented and compared with the previous literature. & 2013 IAA. Published by Elsevier Ltd. All rights reserved.

Keywords: Extravehicular activity Gloves Hand performance Glove effects EVA glove

1. Introduction Extra vehicular activity (EVA) has been part of space activities since the 1960s. The EVA hours have increased, from the maximum of 50 h/year of the past lunar explorations, to over 200 h/year for the ISS construction. In the forthcoming years NASA plans to significantly increase the number of hours dedicated to EVA operations during space missions, reaching almost 5000 h/year in the lunar exploration foreseen around 2025 [1]. Therefore it is important that the astronaut's equipment allows maximum efficiency during EVA. The most important tools for astronauts are their own hands: they have many degrees of freedom, allowing a great variety of movements, and they are also one of the most sensitive parts of the human body (their projection in the primary motor cortex of the brain is one of the largest ones [2]). Human hand dexterity and perception are the

n

Corresponding author. Tel.: þ39 0110903414; fax: þ 39 0110903401. E-mail address: [email protected] (S. Appendino).

main factors in human superiority over artificial devices in adaptive and complex tasks that cannot be completely defined in advance. During an EVA, not only is the hand a multi-purpose tool but it is also the primary means of locomotion, grasping and tool handling. The current EMU (Extravehicular Mobility Unit) suit is composed of a complex and highly technological multilayer system, pressurized with air, in order to protect the astronauts from the extreme environment in which they operate. Although necessary wearing an EMU suit, imposes strong limitations to the mobility and dexterity of astronauts during missions, increasing the stiffness at each joint and requiring a force greater than normal to perform tasks. Gloves are probably the most critical part of the suit because most operations involve the use of the hands. The stiffness of the suit is particularly relevant at the hands and fingers, sharply increasing fatigue and forcibly limiting the overall duration of EVAs. Several studies have been conducted to determine the influence of the EVA glove on manual capabilities. Six basic hand characteristics have been identified [3]: range of

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motion, strength, tactility, dexterity, fatigue and comfort. These aspects have been studied in several papers [3–9] following different methods. In this paper the influence of the EVA glove characteristics on hand force and fatigue has been investigated in different conditions. In Section 2, materials and methods are discussed. In particular, the methodology adopted to perform tests is presented, the equipment used and the experimental setup are described, as well as the subject population participating in the study. In the following parts of the paper, experimental results are shown and discussed. 2. Material and methods

with one simple criterion: their left hand had to fit well inside the glove. In particular, the volunteer's fingertips had to touch the glove fingertips without feeling uncomfortable and, at the same time, their finger webbings had to correspond to the bases of the glove fingers, in order to prevent finger slipping inside the glove. To ascertain this, each subject was asked to perform the test tasks before the actual start of the test, and to give feedback on their sensations. Those who felt unable to effectively achieve the requested movements, or who felt that the fingers would slip inside the glove during movements, were excluded from the study. The index finger of all chosen subjects has been measured, and the average length was 95 mm, with standard deviation of 2.8 mm.

2.1. EVA glove 2.3. Experimental setup The EVA glove used for the tests (Fig. 1) is a left-handed Russian Orlan-DM glove [10]. The EVA glove used in our tests is composed of three separate elements: an inner rubber glove (bladder) (a), the actual EVA glove (restraint) (b) and the outer Thermal Micrometeoroid Garment (TMG) (c). The experimental tasks were performed wearing all components of the glove. 2.2. Subjects

2.3.1. Pneumatic setup A simple pneumatic setup (scheme in Fig. 2a and picture in Fig. 2b) was realized for performance measurement. A bulb syringe was connected to a constant volume and to a manometer. The subjects pressed the bulb syringe, increasing the air pressure inside the pneumatic circuit. This pressure variation was measured by means of the manometer and recorded.

Thirteen test subjects participated in this study. The test subject pool included 5 females and 8 males, aged between 25 and 36. The average BMI of the test pool was 23.16 (standard deviation of 3.26), and none of the subjects had a particular hand training due to sport activity (e.g. climbing or other). Among the 13 test subjects, 2 were left-handed and 11 were right-handed. All subjects were volunteers and had never worn an EVA glove before. Subjects were selected

2.3.2. Glove box Prod. Type: A glove box (Fig. 3a) was designed and realized in order to simulate glove pressurization. It consists of a 430  440  630 mm aluminum parallelepiped, with 3 aluminum and 3 Plexiglas sides. One of these has an opening which permits the insertion of the forearm in an airtight flange that ends with a joint that is coupled with the forearm joint of the EVA glove. Thus, different EVA gloves

Fig. 1. The Orlan-DM glove used during tests. Rubber bladder (a), EVA glove (b), and outer TMG (c).

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153

Fig. 2. Pneumatic setup for pressure measurement: functional scheme (a) and picture with EVA glove (b).

can be tested by substituting the flange with another flange, custom-made for the particular glove under test. Three sides of the box are transparent in order to grant visual feedback and one side may be opened to insert or remove instrumentation in/from the glove box when the vacuum pump is off. Air tightness is guaranteed by gaskets along the perimeter. The pneumatic circuit consists of a vacuum pump, a manually adjustable safety valve and a vacuum manometer. Thus, the relative pressure level inside the glove box can be adjusted down to -0.6 bar and be kept constant. As mentioned above, the EVA glove is fixed to a flange by means of the ORLAN suit-glove coupling, which has been reproduced on the flange. The presence of an internal rubber bladder permits separation between the external environment pressure and internal pressure, thus obtaining the same pressure differential as in actual EVA operation (scheme in Fig. 3b, where white is environment pressure and gray is the desired underpressure). All the tests were performed at a differential pressure of 0.4 bar (  0.4 bar underpressure within the box), which is the typical value of the Orlan-DM suit pressurization.

2.4. Test protocol The literature identifies and classifies several types of hand grips, mainly divided into power and precision grips, according to the forces exerted [11]. Power grips involve muscles on the forearm, whereas precision grips make an extensive use of muscles inside the palm of the hand. Precision grips are typically performed by two or three fingers and are called pinches. In this study, four different tasks, shown in Fig. 4, have been chosen to represent common activities astronauts perform. The choice of the

Fig. 3. Glove box used for testing: picture during test execution (a) and functional scheme (b).

tasks to be performed stems from a study [12] claiming that 2 fingers can perform 40% of the possible hand tasks, 3 fingers can accomplish 90% and 4 can complete 99%. Therefore, it is interesting to examine the influence of the glove while varying the number of fingers involved in each task. Grip nomenclature is not universal, thus the chosen grips have been named as follows: a. Power grip (Fig. 4a): power grasp performed using all five fingers, with the thumb opposing the other fingers b. Two-finger pinch (Fig. 4b): precision pinch performed using only the thumb and index finger c. Three-finger pinch (Fig. 4c): precision pinch performed with the thumb opposing the index and middle finger d. Lateral pinch (Fig. 4d): intermediate pinch performed with the thumb opposing the side of the fist.

All the subjects were shown the pictures of the grips they should perform (Fig. 4) and received the following instructions: 1. Hold the bulb syringe with your left hand as shown in the picture. 2. Apply the strongest force you can. 3. Maintain this configuration for about 1s. 4. Return to relax position. 5. Repeat until you feel too tired to continue or it becomes too painful.

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Fig. 4. Tasks chosen for the tests: power grip (a), two-finger pinch (b), three-finger pinch (c) and lateral pinch (d).

These instructions were given for each test, for a total of 12 tests per subject (4 grips per session, performed barehanded, wearing the unpressurized EVA glove and wearing the pressurized EVA glove). The subjects performed one test session in the morning and one in the afternoon at most, in order to guarantee that each task started with no initial fatigue. A test session is a complete series of repetitions of a single task, performed barehanded or wearing the unpressurized EVA glove or wearing the pressurized EVA glove. Since the instructions did not impose a fixed number of hand grips, subjects would stop after a varying number of repetitions. In most cases, apart from fatigue, motivation was another possible influence on the amount of performed cycles. For each grip execution (i.e. a single performance of points 2–4 on the instruction list), the maximum pressure was recorded. Force is directly related to the maximum pressure value, whereas fatigue can be associated both with the decrease of maximum pressure value in time and with the total number of cycles performed for each test. The latter, however, is probably less significant, since fatigue is a subjective physiological and mental effect that can be strongly influenced by factors like motivation, commitment, and wellness at the time of the test [3]. 3. Results The results of the tests show that the effects of wearing the EVA glove on performances are specific to the task executed, whereas the effect of pressurization drastically worsens performances in all cases.

Fig. 5(a–d) shows, as an example, the results obtained from one subject, for the four different executed tasks, in the three conditions: barehanded, wearing the unpressurized EVA glove and wearing the pressurized EVA glove. The values on the y-axis are expressed as percentages of the maximum force exerted by the subject (maximum voluntary contraction, %MVC) for that task, whereas the x-axis reports the number of repetitions. Crosses represent barehanded tests, gray squares are related to the tests performed wearing the unpressurized EVA glove and black dots are related to tests with the pressurized EVA glove. The linear regression of each series of data is represented with a black line. Wearing the unpressurized EVA glove, forces exerted for the power grip drop to about 50% of the ones obtained in barehanded condition, whereas the forces obtained for the three-finger pinch barely change. As regards the two-finger pinch, the initial force is almost the same, but it decreases more and more rapidly when wearing the EVA glove. Finally, for the lateral pinch task, the forces exerted when wearing the EVA glove are reduced to about 80% of the ones exerted in barehanded conditions. When the EVA glove is pressurized performances are dramatically reduced for all tasks. This shows that the effect of pressure is much more relevant than the mechanical stiffness of the glove itself. These effects are not equivalent for all subjects, although they are similar. Fig. 6 shows all collected data; since forces are expressed in percentages of each subject's maximum contraction, it is possible to view all data on the same graph.

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Fig. 5. Effects of wearing the EVA glove in different conditions on (a) power grip performances, (b) two-finger pinch performances, (c) three-finger pinch performances and (d) lateral pinch performances.

Although single points in the plots of Fig. 6 are hard to distinguish, they give an intuitive overall view of the effects of wearing the EVA glove on performances for the different tasks. In particular, the position of the point clouds on the graph covers particular regions, similar to the ones of the single subject depicted in Fig. 5, hinting a possible common trend. All collected data have been analyzed performing multiple linear regression and analysis of variance (ANOVA, [13]). Initially, 4 variables were considered as independent: gender, maximum voluntary contraction, number of cycles and handedness. However, gender was soon found not to be an independent variable: it is correlated to the maximum voluntary contraction (MVC) of the subject. As an example, for power grip the maximum pressure value (directly related to the MVC) obtained by female subjects is between 0.38 and 0.5 bar, whereas for male subjects it is between 0.56 and 0.68. Handedness was excluded, too, since it resulted not significant from the analysis of variance significance test (pE0.9). Thus, the regression was finally executed with 2 independent variables, resulting in a model with the following general equation: y ¼ b0 þb1 x1 þ b2 x2

ð1Þ

where x1 is the performed number of cycles, x2 is the maximum voluntary contraction, and y is the percentage of the maximum voluntary contraction for each repetition. ANOVA was performed for the different tasks and conditions: for all tasks, in all conditions, all the correlation

p-values are extremely small. This shows that there is a strong correlation between the chosen variables and the experimental results, and that the data clouds can be approximated by a multiple linear regression. The numerical results are summarized in Tables 1–3. As previously stated, the pressurized EVA glove hinders hand performances for all tasks, whereas this is not completely true for the unpressurized glove, whose effects are different according to the task being executed. In particular, the following can be observed: for power grip and lateral pinch, performances wearing the unpressurized EVA glove are inferior to bare handed ones, and performances wearing the pressurized EVA glove are even worse, both as regards forces and number of repetitions. On the other hand, as regards two- and three-finger pinches, wearing the unpressurized EVA glove seems to produce little effect on performances. These observations may be verified by analyzing the formulas obtained with the multiple linear regression. When representing %MVC as a function of the number of repetitions, the effect on the maximum performance of a subject can be found by adding up the value of the intercept (b0) and the value of the MVC times its coefficient b2. So the value of the intercept, indicated with int, may be written as: int ¼ b0 þ b2 MVC

ð2Þ

Considering the whole set of subjects, int varies between a maximum and a minimum value, according to the maximum and minimum values of MVC of those

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Fig. 6. Effects of wearing the EVA glove in different conditions on (a) power grip performances, (b) two-finger pinch performances, (c) three-finger pinch performances and (d) lateral pinch performances. Table 1 Barehanded case: coefficients and p-values.

Table 3 Pressurized glove: coefficients and p-values.

Task

p0

Intercept b0

No of MVC repetitions b2 b1

Task

p0

Intercept b0

No of MVC repetitions b2 b1

Power grip Two finger pinch Three finger pinch Lateral pinch

3.23E  59 1.27E  26 1.35E 09 3.49E  47

0.599 0.636 0.787 0.835

 0.005  0.006  0.003  0.005

Power grip Two finger pinch Three finger pinch Lateral pinch

1.07E 56 1.26E  46 4.42E  45 2.98E  74

0.083 0.13 0.12 0.046

 0.005  0.008  0.004  0.008

0.609 0.929 0.291 0.424

Table 2 Unpressurized glove: coefficients and p-values.

0.838 1.436 0.121 3.015

Table 4 Values of int in different tests and conditions.

Task

p0

Intercept b0

No of MVC repetitions b2 b1

Power grip Two finger pinch Three finger pinch Lateral pinch

3.05E  79 3.09E  71 8.37E  74 1.07E 14

0.227 0.642 0.457 0.523

 0.005  0.007  0.006  0.005

0.956 0.826 1.47 0.97

subjects. Table 4 reports, for each task and condition, the range of values obtained for int when substituting the results of the regression (see Tables 1–3) in Eq. (2). It can be seen how power grip and lateral pinch have similar trends, in particular the value of int drops down when wearing the unpressurized glove, and even more with pressurization. As already observed, for the two- and three-finger pinches the behavior is different: the value of

Power grip Barehanded Unpressurized glove Pressurized glove

2 Finger pinch

3 Finger pinch

Lateral pinch

0.83–1 0.78–0.91 0.85–0.89 0.89–0.97 0.42–0.67 0.76–0.87 0.93–0.96 0.65–0.79 0.12–0.3 0.17–0.26 0.12–0.14 0.11–0.53

int is very similar in barehanded conditions and wearing the unpressurized glove, but drop down significantly with pressurization. 4. Discussion of the results The results for the pressurized and unpressurized EVA glove will be discussed separately, since they differ so much.

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garment. The results show how performances drastically decline for all tasks performed in these conditions. Our results are slightly different from those that can be found in the literature. Several papers reporting tests executed on different EVA gloves (either developmental or current NASA gloves) state that performances do decline when wearing a pressurized EVA glove, but not as dramatically. Some authors [4] report grip strength reduced by 70% of that in barehanded conditions for men and by 47% for women, and pinch strength reduced by 25% for men and 20% for women. Other authors [9], report grip strength reduced by 55% of that in barehanded conditions, while lateral pinch strength is reduced by 14% and two-finger pinch strength increases by 15% when wearing the pressurized glove. In another study [3], grip strength is reduced by 47% of that in barehanded conditions, while lateral pinch is reduced by 10% and two-finger pinch maintains the same performances as those in barehanded conditions. From the data collected for this study, it appears that pressurization restrains hand performance by about 80% to 90% of barehanded performance for all tasks, which is a much more relevant drop. This may be due to the geometry of the grasped object: in most cases, especially for pinch tasks, the subjects found it very hard to hold the bulb syringe in the correct position or felt it could easily slip away from their grasp. It has been mentioned that the EVA glove pressurization was obtained by depressurizing the glove box. Since the measurement system was also inside the glove box, as a side effect the bulb syringe would slightly inflate, thus worsening the grasping conditions. In some cases, the subject would suspend the task execution not due to fatigue, but because they found it was too painful to continue. They were aching, either at the fingertips or at the finger crotches because of the local stiffness of the glove. As already stated for the unpressurized glove, but even more necessarily in this case, it would be interesting to check what results would arise with different shapes and sizes of the object being grasped.

4.1. Unpressurized glove Although the results of the tasks performed with the unpressurized glove may seem puzzling, in particular for the pinches, they are in line with previous research. The literature states [4] that grip strength is reduced by 50% for men and by 30% for women when wearing an unpressurized EVA glove, whereas pinch strength is not modified. Other studies [3] also assess an average strength reduction of 40% for grip force and a negligible reduction of pinch force due to the unpressurized EVA glove. This leads to the consideration that one of the main problems when wearing an unpressurized EVA glove may be its bulk, especially between the fingers, perhaps even more than its stiffness. Supporting this claim, the results of our tests show that, when wearing the EVA glove, the performances with the whole hand (i.e. power grip) are even worse as when using only three fingers, as if the ring finger and the little finger were too far away, too weak or too hampered to help. On the contrary, wearing the EVA glove barely hinders three-finger pinch performances: it is interesting to notice that barehanded power grip performances are very close to the three-finger pinch performances, both barehanded and wearing the unpressurized glove, as confirmed by the numerical values from the multiple linear regression. Table 5 reports the ranges of values of the intercept (calculated according to Eq. (2)) in the conditions mentioned before: the similarity between them is evident. This may be due to the glove itself or to the shape and dimension of the bulb syringe used for the tests: it would be interesting to check if similar results arose with grasped objects of different shapes and sizes.

4.2. Pressurized glove When wearing a pressurized EVA glove, it is immediately perceived as a very stiff, rigid, uncomfortable Table 5 Values of int in different conditions.

Barehanded Wearing unpressurized glove

157

Power grip

3-finger pinch

4.3. Estimation of exerted forces

0.83–1 (0.42–0.67)

0.85–0.89 0.69–0.93

An estimation of exerted forces may be performed, calculating the force as the product between the pressure

Table 6 Comparison between exerted force estimations and literature, forces expressed in [N].

Barehanded Present study Mesloh et al. [9] Bishu et al. [4] Unpressurized glove Present study Mesloh et al. [9] Bishu et al. [4] Pressurized glove Present study Mesloh et al. [9] Bishu et al. [4]

Power grip

Two-finger pinch

Lateral pinch

409 410 432

67 53 88

71 93 N.A.

255 220 265

60 57 84

57 84 N.A.

103 190 185

17 53 71

22 71 N.A.

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inside the bulb syringe and the surface on which the pressure is exerted. The pressure is the one that has been measured, whereas the surface is calculated as the sum of the contact surfaces between the fingers performing the grip or pinch and the bulb syringe. Table 6 compares the estimated force values obtained in the present study with the forces measured in previous ones, for different tasks and conditions. The estimated forces, in barehanded conditions and wearing the unpressurized glove, are fairly close to the results presented by the cited previous authors ([4,9]). The effect of pressurization, however, is different. In particular, pressurization reduces forces much more significantly in the present study than in [4] and in [9]. It must be pointed out that the tested gloves are different from the Orlan-DM: [4] presents results obtained with the Shuttle 3000 training glove and with two advanced developmental gloves, whereas [9] shows results of a Phase IV glove. Moreover, in the case of Mesloh et al. [9], the glove was pressurized to a lower pressure differential (0.43 psid, corresponding to about 0.3 bar), which probably explains the higher force values in pressurized condition. Finally, it is possible that the volunteer subjects who performed the tasks – both in [4] and in [9] – had already used EVA gloves before and thus were able to perform tasks better than subjects of the present study, who had never worn an EVA glove before. 5. Conclusions and future work This study provides many indications on how (and how much) wearing an EVA glove hinders human hand performances. It is very interesting to notice that the effects, especially in unpressurized conditions, are specific to the task being executed. Further research is however required to obtain a thorough knowledge of these effects. In particular, investigation of the forces by means of grip and pinch dynamometers would give actual strength values in order to confirm the estimated forces. Future work will comprise the study of different tasks, involving different hand movements, including common EVA tools and tasks [14]. A modular test bench is under development, comprising different tools and force/torque acquisition instruments to be inserted into the glove box. Further research on physiological fatigue will be carried out by recording surface electromyography data during task execution. So far, the execution of the tests has only been performed with the left hand and a single type of glove, but we are planning to extend the measurements to the right hand

and to other kinds of gloves in the future. The use of a particular EVA glove (Orlan-DM) in this series of tests does not limit the application of the related methodology. Thus it would be interesting to repeat the tests on different EVA gloves and with different pressurizations.

Acknowledgments The authors would like to thank all the volunteer subjects who participated in the study. References [1] C. Walz, M. Gernhardt, Extravehicular activity—challenges in planetary exploration, in: Third Space Exploration Conference & Exhibit, Denver, Colorado, February 2008. [2] A. Rigutti, Atlante di anatomia, (Ed.) Giunti S.p.A., Firenze–Milano, 2000, pp. 28–29; 86–87. [3] J.M. O'Hara, M. Briganti, J. Cleland, D. Winfield, Extravehicular Activities Limitations Study. Volume II: Establishment of Physiological and Performance Criteria for EVA Gloves-Final Report Report number AS-EVALS- FR-8701, NASA Contract no NAS-9-17702, 1988. [4] R.R. Bishu, G. Klute, The effects of extra vehicular activity (EVA) gloves on human performance, Int. J. Ind. Ergon. vol. 16 (1995) 165–174. [5] M.H. Welsh, D.L. Akin, The effects of extravehicular activity gloves on human hand performance, in: 31st International Conference on Environmental Systems, Orlando, FL, July 2001. [6] S. Rajulu, E. Benson, S. England, M. Mesloh, S. Thompson, Use of traditional and novel methods to evaluate the influence of an EVA glove on hand performance, in: 40th International Conference on Environmental Systems, Barcelona, Spain, July 2010. [7] D.C. Buhman, J.A. Cherry, L. Bronkema-Orr, R. Bishu, Effects of glove, orientation, pressure, load, and handle on submximal grasp force, Int. J. Ind. Ergon. 25 (2000) 247–256. [8] S. Thompson, M. Mesloh, S. England, E. Benson, S. Rajulu The effects of extravehicular activity (EVA) glove pressure on tactility, in: 54th Annual Meeting of the Human Factors and Ergonomics Society, San Francisco, CA, September 2010. [9] M. Mesloh, S. England, E. Benson, S. Thompson, S. Rajulu The effects of extravehicular activity (EVA) glove pressure on hand strength, in: Third International Applied Human Factors and Ergonomics, Miami, FL, July 2010. [10] A.I. Skoog, I.P. Abramov, Russian Spacesuits, Springer-Verlag, New York, 2003 (ch. 5). [11] T. Feix, R. Pawlik, H. Schmiedmayer, J. Romero,.D. Kragic, A Comprehensive Grasp Taxonomy, in Robotics, Science and Systems: Workshop on Understanding the Human Hand for Advancing Robotic Manipulation, June 2009. [12] A.H. Mishkin, B.M. Jau, Space-Based Multifunctional End Effector Systems: Functional Requirements and Proposed Designs Technical Report 88-16, NASA JPL, 1988. [13] B.B. Gerstman, Basic Biostatistics: Statistics for Public Health Practice, Jones & Bartlett Learning, 2008—Ch. 15. [14] NASA-STD-3000 Space Flight Human-System Standard vol. 1, section 14, Extravehicular Activity (EVA), 〈http://msis.jsc.nasa.gov/ sections/section14.htm〉.