Motoneuron activation via vibration stimulation: Kanazawa University develops a seat which is effective for muscle strengthening

Exercise is important for preventing frailty associated with aging, but it is difficult for prefrail older people to make exercise a habit. A research group comprising Assistant Professor Yuichi Nishikawa, Professor Toshihiko Komatsuzaki, and Associate Professor Takanori Chihara of the Faculty of Frontier Engineering, Institute of Science and Engineering; Professor Shinobu Tanaka of the Faculty of Transdisciplinary Sciences, Institute of Philosophy in Interdisciplinary Sciences and Professor Jiro Sakamoto of the Advanced Manufacturing Technology Institute at Kanazawa University; Chief Researcher Kenji Kawano, Chief Staff Hidetaka Nagayasu, and Assistant Manager Kyoko Mori of Toyota Boshoku Corporation; Professor Kohei Watanabe of Chukyo University; Associate Professor Noriaki Maeda of Hiroshima University, together with Professor Aleš Holobar of the University of Maribor, Slovenia and Professor Allison Hyngstrom of Marquette University in the USA, successfully developed a seat that uses vibration stimulation to activate motoneurons—which transmit commands from the brain to the muscles—while sitting. They demonstrated that muscle strength was increased after using this seat. In the future, use of the seat in office chairs, wheelchairs, automobiles, and aircraft seats is expected to contribute to the prevention of frailty. The work was published in the European Journal of Applied Physiology.

Fourteen young men (24.3 ± 3.6 years old, 172.2 ± 4.8 cm in height, 60.9 ± 6.6 kg in weight) sat on the seat with a built-in vibrator applying vibration to the biceps femoris muscle tendon. The stimulation parameters were as follows: frequency, 80 Hz; amplitude, 0.1 mm; and duration, 30 seconds. Maximum contractions with the knee extensor and motoneuron activities were measured before and after vibration stimulation. High-density surface electromyography was used to analyze motoneuron activity measurements.

As a control, the subjects sat on the seat for the same duration as above without vibration, with measurements of maximum contractions and motoneuron activities before and after the sitting period. The analysis results revealed that the application of vibration stimulation immediately increased muscle activities, causing an increase in motoneuron activities.

Vibration stimulation was also found to contribute to the motoneuron activation occurring at higher thresholds. Motoneurons have the property of starting the activity from smaller ones (size principle). Given the size principle, slow-twitch muscle fibers are activated at low thresholds and fast-twitch muscle fibers are activated at high thresholds. Thus, vibration stimulation was suggested to contribute to activation of fast-twitch muscle fibers. Another finding is that the subjects with larger changes in motoneuron activity gained more muscle strength, indicating that vibration stimulation can contribute to an immediate improvement in physical function.

This study demonstrated that the quadriceps muscle, one of the muscles important for fall prevention, can be activated while sitting. Muscles throughout the body shrink gradually with age. Of the muscles, the quadriceps muscle is used as a predictor of falls and known to be crucial for balance.

The application of the seat developed by the research group to seats and chairs on which people sit for an extended period of time, such as automobile and plane seats and office chairs, is expected to aid in developing devices that easily activate physical functions.

Journal Information
Publication: European Journal of Applied Physiology
Title: Immediate effect of local vibration on motor unit firing behavior and muscle strength in healthy young adult males
DOI: 10.1007/s00421-024-05553-9