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. AN 3 1 Arizona State University, Tempe, Arizona 2 Indiana University, Bloomington, Indiana 3 Mayo 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 recurring question in paleoanthropology, re- cently raised again with the discovery of Oldowan stone tools in Ethiopia at a level dating to 2.5–2.6 Ma (Semaw et al., 1997), contemporary with australopithecines and earlier than the most ancient known mem- ber of the genus Homo reported by Kimbel et al. (1996). The route to the answer should be through the fossil hominid hands that were capable of making the tools. Several attempts have been made to infer tool-making capabilities from available skeletal features in fossil hand bones such as muscle attachment ar- eas, bone and joint surface configurations, relative metacarpal robusticity, hand seg- ment proportions, and skeletal topography affecting the length of tendon moment arms (Napier, 1962; Ricklan, 1987, 1990; Susman 1988a,b, 1989, 1991, 1994; Susman and Creel, 1979; Susman and Stern, 1979; Sus- man et al., 1984; Marzke, 1997). However, these inferences have been drawn in the absence of data that indicate 1) which muscles are most heavily recruited during Oldowan tool-making, and 2) which skeletal features may be relied upon as predictors of the relative size and moment arm lengths of these muscles. In the experiments reported here, we di- rectly sought such data from the perspective of tool-making, as a necessary preparation for detailed examinations of fossil bones. Using electromyography (EMG), we identi- *Correspondence to: Mary W. Marzke, Department of Anthro- pology, Arizona State University, P.O. Box 872402, Tempe, AZ 85287-2402. Received 30 April 1997; accepted 12 November 1997. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 105:315–332 (1998)  1998 WILEY-LISS, INC.