Methodological issues with the interpolated twitch technique.
A number of methodological issues in the use of the interpolated twitch technique were investigated for their effect on true maximum force (TMF) and activation (ACT): timing of control (pre- vs post-contraction) and superimposed twitches (first vs second); type of twitch stimulus (primarily magnitude); and the type of extrapolation utilised. On three occasions subjects performed a series of maximal and sub-maximal contractions of the knee extensors, with electrically evoked twitches delivered before, during and after each contraction. The twitch-voluntary force relationship was concave for all types of twitch stimuli, and extrapolation using this relationship typically calculated TMF 39N (7%) higher, and ACT 7% lower than linear extrapolation. The timing of the control (2-4%) and superimposed twitches (approximately 4%) both influenced TMF and ACT. Despite the different twitch stimuli being a range of magnitudes (13-32% maximum voluntary force) they did not affect TMF and ACT. A novel finding was that prior potentiation changed the shape of the twitch-voluntary force relationship. For precise measurement of TMF and ACT it is recommended that: extrapolation is based on the twitch-voluntary force relationship of the experimental model; and post-contraction potentiated twitches be used, as the superimposed twitch on a high level contraction appears to be potentiated.
Folland
Jonathan P
JP
School of Sport and Exercise Sciences, Loughborough University, Loughborough, Leicestershire, UK. j.p.folland@lboro.ac.uk
Williams
Alun G
AG
D000328:Adult; D004558:Electric Stimulation / Q000379:methods*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007717:Knee / Q000502:physiology; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*