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EMG Study of Hand Muscle Recruitment During Hard Hammer Percussion Manufacture of Oldowan Tools

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EMG Study of Hand Muscle Recruitment During Hard Hammer Percussion Manufacture of Oldowan Tools AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 105:315–332 (1998) EMG Study of Hand Muscle Recruitment During Hard Hammer Percussion Manufacture of Oldowan Tools MARY W. MARZKE,1* N. TOTH,2 K. SCHICK,2 S. REECE,1 B. STEINBERG,1 K. HUNT,2 R.L. LINSCHEID,3 AND K-N. AN3 1Arizona State University, Tempe, Arizona 2Indiana University, Bloomington, Indiana 3Mayo Clinic, Rochester, Minnesota KEY WORDS stone tool-making; electromyography; flexor pollicis longus; fossil hominids ABSTRACT The activity of 17 hand muscles was monitored by electromy- ography (EMG) in three subjects during hard hammer percussion manufac- ture of Oldowan tools. Two of the subjects were archaeologists experienced in the replication of prehistoric stone tools. Simultaneous videotapes recorded grips associated with the muscle activities. The purpose of the study was to identify the muscles most likely to have been strongly and repeatedly recruited by early hominids during stone tool-making. This information is fundamental to the identification of skeletal features that may reliably predict tool-making capabilities in early hominids. The muscles most fre- quently recruited at high force levels for strong precision pinch grips required to control the hammerstone and core are the intrinsic muscles of the fifth finger and the thumb/index finger regions. A productive search for skeletal evidence of habitual Oldowan tool-making behavior will therefore be in the regions of the hand stressed by these intrinsic muscles and in the joint configurations affecting the relative lengths of their moment arms. Am J Phys Anthropol 105:315–332, 1998. ௠ 1998 Wiley-Liss, Inc. Who made Oldowan stone tools? This is a 1988a,b, 1989, 1991, 1994; Susman and recurring question in paleoanthropology, re- Creel, 1979; Susman and Stern, 1979; Sus- cently raised again with the discovery of man et al., 1984; Marzke, 1997). However, Oldowan stone tools in Ethiopia at a level these inferences have been drawn in the dating to 2.5–2.6 Ma (Semaw et al., 1997), absence of data that indicate 1) which contemporary with australopithecines and muscles are most heavily recruited during earlier than the most ancient known mem- Oldowan tool-making, and 2) which skeletal ber of the genus Homo reported by Kimbel et features may be relied upon as predictors of al. (1996). the relative size and moment arm lengths of The route to the answer should be through these muscles. the fossil hominid hands that were capable In the experiments reported here, we di- of making the tools. Several attempts have rectly sought such data from the perspective been made to infer tool-making capabilities of tool-making, as a necessary preparation from available skeletal features in fossil for detailed examinations of fossil bones. hand bones such as muscle attachment ar- Using electromyography (EMG), we identi- eas, bone and joint surface configurations, relative metacarpal robusticity, hand seg- ment proportions, and skeletal topography *Correspondence to: Mary W. Marzke, Department of Anthro- pology, Arizona State University, P.O. Box 872402, Tempe, AZ affecting the length of tendon moment arms 85287-2402. (Napier, 1962; Ricklan, 1987, 1990; Susman Received 30 April 1997; accepted 12 November 1997. ௠ 1998 WILEY-LISS, INC. 316 M.W. MARZKE ET AL. fied muscles that are recruited repeatedly at Toth (Subject 1) was selected because he has high levels when a hammerstone held by one been manufacturing Oldowan tools by hard hand strikes flakes from a core held in the hammer percussion regularly for nearly 20 other hand. Our assumption is that the most years. It can be expected that in the course strongly recruited muscles are likely to have of these years he has settled into grips and generated recognizable periosteal reactions hand movements that expedite the produc- at their attachment sites which could be tion of Oldowan flakes with minimum muscle identified in hand bones of early hominid fatigue and pain-producing stress to the tool-makers. This assumption is currently joints. Schick (Subject 2) was selected be- being tested in our laboratory. cause she also learned to replicate Oldowan In a related kinematics experiment (Mar- tools and has continued the activity over zke et al., submitted), we found that each many years. Because her tool-making activ- thumb muscle, with the exception of the ity has been more sporadic, it was antici- transverse adductor pollicis muscle, has a pated that she might use some muscle re- significantly larger dynamical moment arm cruitment patterns that differ from those of in humans than in chimpanzees for at least Toth. Hunt (Subject 3) served as the novice one axis of rotation and one thumb joint. tool-maker, whose muscle use we thought Thus, we now have a potential additional might differ still more and might thereby source of evidence in fossil hominid hands put into relief the patterns in the more for stone tool-making capabilities, namely, experienced subjects, and those most likely the orientations and dimensions of skeletal to have been arrived at by early hominids features that determine the relative lengths that habitually made Oldowan tools. of moment arms for the tendons of the Toth and Schick are right-handed and muscles that are strongly recruited. A larger Hunt is left-handed. The terms ‘‘dominant’’ moment arm gives a muscle greater me- and ‘‘nondominant’’ will therefore be applied chanical advantage, maximizing the poten- to the specific hand used by a subject. Domi- tial of the muscle to exert torque while nant hand length and breadth were 18.7 3 minimizing the number of muscle fibers 8.6 cm in Subject 1, 17.6 3 8.2 cm in Subject needed, thus conserving the energy required 2, and 19.6 3 8.3 cm in Subject 3. for repetitive muscle contraction. Evolution- The importance of testing at least three ary increase in moment arm lengths thus subjects with differing expertise is that would have enhanced habitual, effective, muscle recruitment patterns found to be hard hammer percussion manufacture of common to all of them are likely to be stone tools, well known by practitioners to patterns that are most compatible with hu- make heavy demands on several groups of man hand morphology. The common pat- hand muscles. How large these demands terns suggest to us the grips and associated are, and upon which muscle groups, are set hand musculoskeletal features that should forth in the following sections. be targeted for analysis in the development of biomechanical models for the functional MATERIALS AND METHODS interpretation of similar morphology in an- The experiments were conducted in the cestral hominids. gait analysis facility of the Mayo Clinic Stone tool materials Orthopedic Biomechanics Research Labora- tory in Rochester, Minnesota. The doctors Stones collected from an Indiana quarry who inserted the electrodes and the staff were used for the experiments. They were who coordinated data acquisition are all medium-grained, river-worn cobbles with regular participants in the EMG analysis of small crystal inclusions which can be flaked clinical disorders of patients who come to equally well in any direction, closely similar the facility, including patients with prob- in composition to stones used by the Old- lems in the hand. owan tool-makers. Subjects Muscles and activities monitored The three authors from Indiana Univer- Seventeen muscles were monitored with sity were the subjects of the experiments. EMG in the course of the study (Table 1), 16 EMG OF HAND MUSCLES IN OLDOWAN TOOL-MAKING 317 TABLE 1. Muscles monitored in the EMG experiments Extrinsic muscles Abbreviation Intrinsic muscles Abbreviation Flexor carpi ulnaris FCU Flexor pollicis brevis FPB Flexor pollicis longus FPL Opponens pollicis OP Flexor digitorum profundus 2 FDP2 Adductor pollicis (transverse) APT Flexor digitorum profundus 5 FDP5 Dorsal interosseus 1 D1 Extensor digitorum communis 2 EDC2 Palmar interosseus 1 P1 Extensor digitorum communis 5 EDC5 Palmar interosseus 3 P3 Extensor pollicis brevis EPB Flexor digiti minimi FDM Extensor pollicis longus EPL Abductor digiti minimi ADM Opponens digiti minimi ODM functioning on the hand and one (flexor human skeletal configurations (FCU, FPL, carpi ulnaris) exclusively on the wrist. Eight FPB, FDM, ODM; see Napier, 1959; Stern are extrinsic and nine are intrinsic muscles. and Susman, 1983; Trinkaus, 1983; Ricklan, Ten channels of A/D conversion were used 1987; Sarmiento, 1988). Third, we focused for receiving muscle signals. One set of ten on muscles of the thumb, index, and fifth muscles in the dominant hand and a slightly finger that seemed to us most likely to be different set of ten muscles in the nondomi- strongly recruited in tool-making, based on nant hand were monitored in the first experi- frequent grips and hand movements ob- ment. A year later, a third set of muscles was served in our earlier study of tool-making monitored in both hands of Subjects 1 and 2, (Marzke and Shackley, 1986). We were including four muscles that were not moni- guided in muscle selection (and later in the tored in Subject 3 in the first experiment interpretation of our data) by predictions of (flexor digiti minimi, adductor pollicis (trans- muscle interaction in moving and stabilizing verse portion) and the first and third palmar link systems of the hand and wrist, based on interosseous muscles), and four muscles that the detailed functional analysis of hand were monitored for only one hand in Subject muscle functions by Brand and Hollister 3 (the extensor pollicis longus muscle in the (1993) and on EMG studies which recorded dominant hand and the flexor pollicis brevis, muscle signals during prescribed grips and first dorsal interosseous, and extensor polli- movements (Forrest and Basmajian, 1965; cis brevis muscles in the nondominant hand). Hall and Long, 1968; Close and Kidd, 1969; Records were obtained from only one hand Long et al., 1970; Long, 1981; Cooney et al., at a time in each session.
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