Affiliations: [a] Department of Biosurgery and Surgical Technology,
Division of Surgery, Oncology, Reproductive biology and Anaesthetics (SORA),
Faculty of Medicine, Imperial College London, Charing Cross Hospital, London W6
8RF, UK
Note: [] Address for correspondence: Dr. Paul H. Strutton, The Nick Davey
Laboratory, Biosurgery and Surgical Technology, Division of Surgery, Oncology,
Reproductive biology and Anaesthetics (SORA), Faculty of Medicine, Imperial
College London, Room 7L15, Charing Cross Hospital, London W6 8RF. Tel.: +44
(0)20 8383 8837; Fax: +44 (0)20 8383 8835; E-mail: p.strutton@imperial.ac.uk
Abstract: Poor trunk extensor endurance is implicated in low back pain, less
is known regarding contributions of different regions of the erector spinae to
maximum torque production particularly after fatigue. This study examines
torque and electromyographic (EMG) activity following a maximal voluntary
contraction (MVC) hold in these muscles. 16 students (9 male, 7 female, mean
age 21.3 ± 0.6 years) participated. Testing was performed
using a Cybex isokinetic dynamometer with synchronous bilateral EMG recordings
(during MVCs of 5 second duration) from the left and right the erector spinae
(ES) muscles at vertebral levels T12 and L4, prior to and immediately after the
effort and then at 1, 5 and 10 min following a 60 s MVC. A small decrease in
maximum torque was observed during 60 s MVC, followed by a non significant
step-wise increase. The highest torque value was recorded 10 min post MVC.
There was a trend for the ratios of left:right EMG RMS amplitudes to be higher
following the fatigue in the lower back and to decrease in the upper back,
suggesting the task involved differential use of left and right sides in
addition to upper and lower back muscles. This study suggests that 60 s MVC
induces differential activation of left and right sides and upper and lower
parts of the trunk extensors. The apparent potentiation in force and asymmetry
of activation following the 60 s MVC task requires further investigation.
Keywords: Fatigue, torque, EMG, back extensors, isokinetic
