Mechanical advantage of the thumb muscles

W. Paul Smutz, Apichai Kongsayreepong, Richard E. Hughes, Glen Niebur, William P. Cooney, Kai Nan An

Research output: Contribution to journalArticle

88 Scopus citations


The purpose of this study was to measure the moment arms of four extrinsic muscles (flexor pollicis longus, extensor pollicis longus, extensor pollicis brevis, and abductor pollicis longus) and four intrinsic muscles (flexor pollicis brevis, abductor pollicis brevis, adductor pollicis, and opponents pollicis) of the thumb at the interphalangeal, the metacarpophalangeal, and the carpometacarpal joints in the same cadaver specimens and to examine the specific role of each muscle. Measurements were made on seven fresh frozen cadaver hands. The moment arms were measured during flexion/extension of the interphalangeal joint, flexion/extension and adduction/abduction of the metacarpophalangealjoint, and flexion/extension and adduction/abduction of the carpometacarpal joint. Moment arms were computed using the slope of the tendon excursion-joint angle relationship. The specific function of each muscle was determined by multiplying the measured moment arms by the maximum force that each muscle can generate. It was found that the flexor pollicis longus was a pure flexor while flexor pollicis brevis was an adductor as well as a flexor, the extensor pollicis longus was an extensor and an adductor, extensor pollicis brevis was an extensor and a mild abductor, the abductor pollicis longus was an extensor as well as an abductor, the abductor pollicis brevis was mainly an abductor, the adductor pollicis was a major flexor as well as an adductor, and the opponents pollicis was a flexor and an abductor.

Original languageEnglish (US)
Pages (from-to)565-570
Number of pages6
JournalJournal of Biomechanics
Issue number6
StatePublished - Jun 1 1998


  • Biomechanics
  • Moment arms
  • Thumb

ASJC Scopus subject areas

  • Biophysics
  • Orthopedics and Sports Medicine
  • Biomedical Engineering
  • Rehabilitation

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  • Cite this

    Paul Smutz, W., Kongsayreepong, A., Hughes, R. E., Niebur, G., Cooney, W. P., & An, K. N. (1998). Mechanical advantage of the thumb muscles. Journal of Biomechanics, 31(6), 565-570.