Experimental Brain Research

, Volume 175, Issue 4, pp 745–753 | Cite as

Motor unit synchronization measured by cross-correlation is not influenced by short-term strength training of a hand muscle

  • Dawson J. Kidgell
  • Martin V. Sale
  • John G. SemmlerEmail author
Research Note


The purpose of the study was to quantify the strength of motor unit synchronization and coherence from pairs of concurrently active motor units before and after short-term (4–8 weeks) strength training of the left first dorsal interosseous (FDI) muscle. Five subjects (age 24.8 ± 4.3 years) performed a training protocol three times/week that consisted of six sets of ten maximal isometric index finger abductions, whereas three subjects (age 27.3 ± 6.7 years) acted as controls. Motor unit activity was recorded from pairs of intramuscular electrodes in the FDI muscle with two separate motor unit recording sessions obtained before and after strength training (trained group) or after 4 weeks of normal daily activities that did not involve training (control group). The training intervention resulted in a 54% (45.2 ± 8.3 to 69.5 ± 13.8 N, P = 0.001) increase in maximal index finger abduction force, whereas there was no change in strength in the control group. A total of 163 motor unit pairs (198 single motor units) were examined in both subject groups, with 52 motor unit pairs obtained from 10 recording sessions before training and 51 motor unit pairs from 10 recording sessions after training. Using the cross-correlation procedure, there was no change in the strength of motor unit synchronization following strength training (common input strength index; 0.71 ± 0.41 to 0.67 ± 0.43 pulses/s). Furthermore, motor unit coherence z scores at low (0–10 Hz; 3.9 ± 0.3 before to 4.4 ± 0.4 after) or high (10–30 Hz; 1.7 ± 0.1 before to 1.9 ± 0.1 after) frequencies were not influenced by strength training. These motor unit data indicate that increases in strength following several weeks of training a hand muscle are not accompanied by changes in motor unit synchronization or coherence, suggesting that these features of correlated motor unit activity are not important in the expression of muscle strength.


Motor Unit Maximum Voluntary Contraction Strength Training First Dorsal Interosseous Hand Muscle 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



This work was supported by the National Health and Medical Research Council of Australia grant (274307) awarded to JGS.


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Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • Dawson J. Kidgell
    • 2
  • Martin V. Sale
    • 1
  • John G. Semmler
    • 1
    Email author
  1. 1.Discipline of Physiology, Research Centre for Human Movement Control, School of Molecular and Biomedical ScienceThe University of AdelaideAdelaideAustralia
  2. 2.School of Exercise and Nutrition SciencesDeakin UniversityBurwoodAustralia

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