title: The effect of exercise repetition on the frequency characteristics of motor output force: implications for Achilles tendinopathy rehabilitation.
abstract: OBJECTIVE
  To investigate the frequency characteristics of the ground reaction force (GRF) recorded throughout the eccentric Achilles tendon rehabilitation programme described by Alfredson.
  
  
  METHODS
  Controlled laboratory study, longitudinal.
  
  
  METHODS
  Nine healthy adult males performed six sets (15 repetitions per set) of eccentric ankle exercise. Ground reaction force was recorded throughout the exercise protocol. For each exercise repetition the frequency power spectrum of the resultant ground reaction force was calculated and normalised to total power. The magnitude of peak relative power within the 8-12 Hz bandwidth and the frequency at which this peak occurred was determined.
  
  
  RESULTS
  The magnitude of peak relative power within the 8-12 Hz bandwidth increased with each successive exercise set and following the 4th set (60 repetitions) of exercise the frequency at which peak relative power occurred shifted from 9 to 10 Hz.
  
  
  CONCLUSIONS
  The increase in magnitude and frequency of ground reaction force vibrations with an increasing number of exercise repetitions is likely connected to changes in muscle activation with fatigue and tendon conditioning. This research illustrates the potential for the number of exercise repetitions performed to influence the tendons' mechanical environment, with implications for tendon remodelling and the clinical efficacy of eccentric rehabilitation programmes for Achilles tendinopathy.
authors: Centre for Musculoskeletal Research, Griffith Health Institute, Griffith University, Australia; Institute of Health and Biomedical Innovation, Queensland University of Technology, Australia. Electronic address: n.grigg@griffith.edu.au.
authors: Nicole L
authors: NL
authors: Grigg
authors: Faculty of Health Sciences and Medicine, Bond University, Australia; Centre of Excellence for Applied Sport Science Research, Queensland Academy of Sport, Australia.
authors: Scott C
authors: SC
authors: Wearing
authors: DeustoTech, University of Deusto, Spain.
authors: John M
authors: JM
authors: O'Toole
authors: Institute of Health and Biomedical Innovation, Queensland University of Technology, Australia.
authors: James E
authors: JE
authors: Smeathers
mesh_terms: D000125:Achilles Tendon / Q000502:physiology*; D000328:Adult; D005081:Exercise Therapy; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D052256:Tendinopathy / Q000534:rehabilitation*
keywords: Eccentric exercise; Fatigue; Physiological tremor; Tendon