The relationship between contraction and relaxation during fatiguing isokinetic shoulder flexions. An electromyographic study

  • Jessica Elert
  • Björn Gerdle


Knowledge of the strength, endurance and coordination of the shoulder muscles during dynamic contractions in healthy women would contribute to the understanding of symptoms in that part of the body in patients with myalgia. Twenty clinically healthy women performed single maximal forward shoulder flexions at four different angular velocities (0.57–3.14 rad·s−1). The same subjects also took part in two endurance tests (at angular velocities of 0.57 and 2.09 rad·s−1, respectively) consisting of 150 repeated maximal shoulder flexions. Electromyographic activity (EMG) was registered from four shoulder flexors using surface electrodes. Work was used as the mechanical variable. During the endurance tests subjects rated their perception of fatigue in the shoulder muscles. Work and the amplitude of the EMG signals decreased with angular velocity. The mean power frequency of the EMG was constant in the span of angular velocities investigated. During the endurance tests, work and the mean power frequency decreased during the initial 40–60 contractions followed by stable levels. The relative work level was higher at 2.09 than at 0.57 rad·s−1. Greater relative increases of the signal amplitudes of EMG occurred at 2.09 than at 0.57 rad·s−1. The EMG activity between the flexions (during the supposed passive extension) was higher at 2.09 than at 0.57 rad·s−1. Such a high activity was associated with a low mechanical performance at 2.09 rad·s−1. It is suggested that the initial sharp decreases in work and in mean power frequency reflect the fatiguing of the fast twitch motor units. Dynamic work consisting of continuous activity could predispose to muscle complaints.

Key words

Electromyography Fatigue Female Human Muscle 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Borg G (1982) Psychophysical bases of perceived exertion. Med Sci Sports Exerc 14:377–381PubMedGoogle Scholar
  2. De Luca CJ, Merletti R (1988) Surface myoelectric signal crosstalk among muscles of the leg. Electroencephalogr Clin Neurophysiol 69:568–575PubMedGoogle Scholar
  3. Edwards RHT (1988) Hypothesis of peripheral and central mechanisms underlying occupational muscle pain and injury. Eur J Appl Physiol 57:275–281CrossRefGoogle Scholar
  4. Fridén J (1983) Exercise induced muscle soreness. Medical dissertation, Umeå University, SwedenGoogle Scholar
  5. Fugl-Meyer AR, Mild KH, Hörnsten J (1982) Output of skeletal muscle contractions: a study of isokinetic plantar flexion in athletes. Acta Physiol Scand 115:193–199PubMedGoogle Scholar
  6. Fugl-Meyer AR, Gerdle B, Långström M (1985) Characteristics of repeated isokinetic plantar flexions in middle-aged and elderly subjects with special regard to muscular work. Acta Physiol Scand 124:213–222PubMedGoogle Scholar
  7. Gerdle B, Fugl-Meyer AR (1985) Mechanical output and iEMG of isokinetic plantar flexion in 40–64-year-old subjects. Acta Physiol Scand 124:201–211PubMedGoogle Scholar
  8. Gerdle B, Hedberg R, Jonsson B, Fugl-Meyer AR (1987) Mean power frequency and integrated electromyogram of repeated isokinetic plantar flexions. Acta Physiol Scand 130:501–506PubMedGoogle Scholar
  9. Gerdle B, Wretling ML, Henriksson-Larsén K (1988) Do the fibre-type proportion and the angular velocity influence the mean power frequency of the electromyogram? Acta Physiol Scand 134:341–346PubMedGoogle Scholar
  10. Gerdle B, Elert J, Henriksson-Larsén K (1989) Muscular fatigue during repeated isokinetic shoulder forward flexions in young females. Eur J Appl Physiol 58:666–673CrossRefGoogle Scholar
  11. Henneman E, Olsen CB (1965) Relation between structure and function in the design of skeletal muscles. J Neurophysiol 28:581–598PubMedGoogle Scholar
  12. Jonsson B (1978) Kinesiology. With special reference to electromyographic kinesiology. Contemp Clin Neurophysiol [EEG Suppl 34]:417–428Google Scholar
  13. Kilbom Å, Persson J, Jonsson BG (1986) Disorders of the cervicobrachial region among female workers in the electronics industry. Int J Ind Ergonomics 1:37–47Google Scholar
  14. Lorentzon R, Johansson C, Sjöström M, Fugl-Meyer AR (1988) Fatigue during dynamic muscle contractions in male sprinters and marathon runners. Acta Physiol Scand 132:531–536PubMedGoogle Scholar
  15. Maeda K (1977) Occupational cervicobrachial disorder and it's causative factors. J Hum Ergol 6:193–202Google Scholar
  16. Moritani T, Gaffney FA, Carmichael T, Hargis J (1985) Interrelationship among muscle fibre types, electromyogram and blood pressure during fatiguing isometric contraction. In: Winter DA, Norman RW, Wells RP, Hayes KC, Patla AE (eds) Biomechanics IX-A, International series on Biomechanics, vol 5A. Human Kinetics Publishers, Champaign, Illinois, pp 287–292Google Scholar
  17. Morrenhof JW, Abbink HJ (1985) Cross-correlation and crosstalk in surface electromyography. Electromyogr Clin Neurophysiol 25:73–79PubMedGoogle Scholar
  18. Rourke M, Erlandson RF, Jaynt RL (1984) Quantitative analysis of computer-stimulated EMG interference patterns. Muscle Nerve 7:570Google Scholar

Copyright information

© Springer-Verlag 1989

Authors and Affiliations

  • Jessica Elert
    • 1
  • Björn Gerdle
    • 2
  1. 1.Work Physiology UnitNational Institute of Occupational HealthUmeåSweden
  2. 2.Department of Clinical PhysiologyUniversity of UmeåUmeåSweden

Personalised recommendations