The age related slow and fast contributions to the overall changes in tibialis anterior contractile features disclosed by maximal single twitch scan

• A non-invasive method for maximal single twitch scan was presented.
• The method allowed to estimate the functional weight of the scanned slow and fast components.
• In older individual this can contribute to understanding the ageing process.

This work aimed to verify if maximal electrically evoked single twitch (STmax) scan discloses the relative functional weight of fast and slow small bundles of fibres (SBF) in determining the contractile features of tibialis anterior (TA) with ageing. SBFs were recruited by TA main motor point stimulation through 60 increasing levels of stimulation (LS): 20 stimuli at 2 Hz for each LS. The lowest and highest LS provided the least ST and STmax, respectively. The scanned STmax was decomposed into individual SBF STs. They were identified when twitches from adjacent LS were significantly different and then subtracted from each other. Nine young (Y) and eleven old (O) subjects were investigated. Contraction time (CT) and STarea/STpeak (A/PT) were calculated per each SBF ST. 143 and 155 SBF STs were obtained in Y and O, respectively. Y: CT and A/PT range: 45–105 ms and 67–183 mN s/mN, respectively. Literature data set TA fast fibres at 34% so, from the arrays of CT and A/PT, 65 ms and 100 mN s/mN were identified as the upper limit for SBF fast ST classification. O: no SBF ST could be classified as fast. Conclusions: STmax scan reveals age-related changes in the relative contribution of fast and slow SBFs to the overall muscle mechanics.