Effects of verbal encouragement on force and electromyographic activations during exercise.

Background: The aim of the present study was to examine the effects of verbal encouragement on isometric force and associated electromyographic (EMG) parameters during a handgrip task.

Methods: Twenty-three participants (12 women and 11 men) performed maximal voluntary isometric handgrip contractions following three conditions: 1) verbal encouragement (VE) condition: participants executed isometric contractions while being verbally encouraged; 2) non-verbal encouragement (nVE) condition: the same starting and stopping signal but without encouragement; 3) non-concentration and non-motivation (nCM) condition: self-initiated contractions without concentration and motivation. Start and stop of the contraction were self-initiated. The maximal voluntary force (MVF) and the maximal rate of force development (MRFD) were measured. Integrated EMG corresponding to MVF (iEMGMVF) and to MRFD (iEMGMRFD) were collected from flexor digitorum superficialis (FDS) and extensor digitorum communis (EDC) muscles.

Results: MVF was higher during VE compared with nVE (+11.7%; P<0.05) and nCM (+23.2%; P<0.05) conditions. Likewise, MRFD was significantly higher during VE, compared with nVE (+21.7%; P<0.05) and nCM (+55.4%; P<0.05) conditions. iEMGMVF increased for FDS and EDC during VE, compared to nVE (+26.19%, +20.5%) and nCM conditions (+68.85%, +48.91%), respectively. iEMGMRFD increased for FDS and EDC during VE, compared to nVE (+21.2%, +46.07%) and nCM conditions (+23.79%, +42.32%). Furthermore, the reproducibility of all these indices was higher with VE condition.

Conclusions: Taken together, force production (MVF and MRFD) and EMG data supported the view that muscles activity is considerably influenced by the verbal encouragements during isometric force exercise.