TY - JOUR
T1 - EMG of the human flexor pollicis longus muscle
T2 - Implications for the evolution of hominid tool use
AU - Hamrick, Mark W.
AU - Churchill, Steven E.
AU - Schmitt, Daniel
AU - Hylander, William L.
N1 - Funding Information:
We are grateful to Dr Jack T. Stern Jr for providing the computer program used in the r.m.s. analysis and we are especially grateful to the volunteers that participated in this study. Digitizing equipment and hardware were provided by the Duke University Morphometrics Laboratory under the direction of Dr J. Mercer. We thank Mr Kirk Johnson for technical assistance and Drs D. Begun, M. Marzke, M. Rose, E. Trinkaus and C. Wall for helpful comments on the manuscript. Funding for this research was provided by Duke University and NIH (DE-04531) and NSF (SBR-9420764) research grants to WLH. This research was completed under Duke Medical Center Human Research Subjects Protocol IRB-028-96-1.
PY - 1998/2
Y1 - 1998/2
N2 - Modern humans possess a distinct and well-developed flexor pollicis longus muscle, an extrinsic thumb flexor which is "either rudimentary or absent" in great apes (Straus, 1942, p. 228). Previous workers (e.g., Napier, 1962; Susman, 1988) have related the origin of a well-developed flexor pollicis longus muscle to the acquisition of precision grasping and stone tool making capabilities in early hominids. The proposed functional association between flexor pollicis longus activity, precision grasping, and stone tool manufacture has, however, never been tested experimentally. This study uses electromyographic techniques (EMG) to investigate the role of flexor pollicis longus during a variety of tool making, tool using, and manipulatory behaviors in order to determine the functional and evolutionary significance of the human flexor pollicis longus muscle. Our results indicate that flexor pollicis longus is recruited during forceful tool using and stone tool making behaviors, regardless of the power or precision grip used to hold the tool. In particular, both stone tool use and stone tool making employing three- and four-jaw chuck precision grips elicit consistently high levels of FPL activity. Flexor pollicis longus activity increases most when resistance is increased to the thumb's volar pad during these hammering, cutting, and knapping behaviors. In contrast, we observed relatively low levels of flexor pollicis longus activity during the fine manipulation of food items, the making of slender wooden probes, and the use of these probes as tools. The paleontological, archaeological, and experimental data suggest that a well-developed flexor pollicis longus muscle functioned initially in the hominid lineage to stabilize the terminal pollical phalanx against loads applied to the thumb's apical pad during the frequent and forceful use of unmodified stones as tools.
AB - Modern humans possess a distinct and well-developed flexor pollicis longus muscle, an extrinsic thumb flexor which is "either rudimentary or absent" in great apes (Straus, 1942, p. 228). Previous workers (e.g., Napier, 1962; Susman, 1988) have related the origin of a well-developed flexor pollicis longus muscle to the acquisition of precision grasping and stone tool making capabilities in early hominids. The proposed functional association between flexor pollicis longus activity, precision grasping, and stone tool manufacture has, however, never been tested experimentally. This study uses electromyographic techniques (EMG) to investigate the role of flexor pollicis longus during a variety of tool making, tool using, and manipulatory behaviors in order to determine the functional and evolutionary significance of the human flexor pollicis longus muscle. Our results indicate that flexor pollicis longus is recruited during forceful tool using and stone tool making behaviors, regardless of the power or precision grip used to hold the tool. In particular, both stone tool use and stone tool making employing three- and four-jaw chuck precision grips elicit consistently high levels of FPL activity. Flexor pollicis longus activity increases most when resistance is increased to the thumb's volar pad during these hammering, cutting, and knapping behaviors. In contrast, we observed relatively low levels of flexor pollicis longus activity during the fine manipulation of food items, the making of slender wooden probes, and the use of these probes as tools. The paleontological, archaeological, and experimental data suggest that a well-developed flexor pollicis longus muscle functioned initially in the hominid lineage to stabilize the terminal pollical phalanx against loads applied to the thumb's apical pad during the frequent and forceful use of unmodified stones as tools.
KW - A ustralopithecus
KW - Grips
KW - Paranthropus
KW - Stone tools
KW - Thumb morphology
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U2 - 10.1006/jhev.1997.0177
DO - 10.1006/jhev.1997.0177
M3 - Article
C2 - 9503091
AN - SCOPUS:0032004110
SN - 0047-2484
VL - 34
SP - 123
EP - 136
JO - Journal of Human Evolution
JF - Journal of Human Evolution
IS - 2
ER -