Relationship between motor unit activity and muscle unit length dining voluntary contractions

2004 Fiscal Year Final Research Report Summary

• Project/Area Number: 14580064
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: 体育学
• Research Institution: Japan Women's College of Physical Education
• Principal Investigator: KAMO Mifuyu Japan Women's College of Physical Education, Faculty of Physical Education, Assistant professor, 体育学部, 講師 (30224702)
• Project Period (FY): 2002 – 2004
• Keywords: Muscle unit length / Motor unit activity

Research Abstract

To elucidate the relationship between force development and activation pattern in motor units, I simultaneously observed the motor unit spike interval and muscle unit length during human voluntary contraction in vastus medialis muscle using surface electrode methods.
1)The motor unit action potentials recorded >2 cm from the motor-end plate at the distal end of muscle fibers facilitated accurate estimation of muscle unit length in the vastus medialis muscle.
2)The muscle unit length shortened >5% to 15% of maximal voluntary contraction (%MVC). The relationship between spike interval and muscle unit length was not linear.
3)Regardless of spike interval elongation, the muscle unit length gradually shortened 5% during the sustained contraction below 5%MVC for 3min.
4)The muscle unit length gradually shortened during the evoked contraction from tonic vibration, but the amount of shortening was smaller than that of voluntary contraction.
These findings suggested a shortening of muscle unit length during voluntary contraction at a low-level might be caused by both motor unit activity and the activities of other adjacent motor units.