Unpowered Knee Exoskeleton Reduces Quadriceps Activity during Cycling

Ronnapee Chaichaowarat, Jun Kinugawa, Kazuhiro Kosuge

Research output: Contribution to journalArticlepeer-review

18 Citations (Scopus)


Cycling is an eco-friendly method of transport and recreation. With the intent of reducing the energy cost of cycling without providing an additional energy source, we have proposed the use of a torsion spring for knee-extension support. We developed an exoskeleton prototype using a crossing four-bar mechanism as a knee joint with an embedded torsion spring. This study evaluates the passive knee exoskeleton using constant-power cycling tests performed by eight healthy male participants. We recorded the surface electromyography over the rectus femoris muscles of both legs, while the participants cycled at 200 and 225 W on a trainer with the developed wheel-accelerating system. We then analyzed these data in time–frequency via a continuous wavelet transform. At the same cycling speed and leg cadence, the median power spectral frequency of the electromyography increases with cycling load. At the same cycling load, the median power spectral frequency decreases when cycling with the exoskeleton. Quadriceps activity can be relieved despite the exoskeleton consuming no electrical energy and not delivering net-positive mechanical work. This fundamental can be applied to the further development of wearable devices for cycling assistance.

Original languageEnglish
Pages (from-to)471-478
Number of pages8
Issue number4
Publication statusPublished - 2018 Aug


  • Augmentation
  • Cycling
  • Electromyography
  • Energy cost
  • Exoskeleton
  • Knee
  • Muscle activity
  • Orthosis

ASJC Scopus subject areas

  • Computer Science(all)
  • Environmental Engineering
  • Chemical Engineering(all)
  • Materials Science (miscellaneous)
  • Energy Engineering and Power Technology
  • Engineering(all)


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