Comparison of the background electromyogram activity. The background SEMG amplitudes of the soleus: JM (17.21 ± 0.64% NF), HP (17.42 ± 0.67% NF), R (14.13 ± 0.48% NF), and TC (13.53 ± 0.61% NF). *p < .01667; standard errors are shown. R indicates rest; TC indicates teeth clench, which consists of biting on an individualized mouth guard with maximal force; HP indicates clenched hand pull, which consists of trying to pull the hands apart against interlocked fingers; and JM indicates a specific Jendrassik maneuver, which consists of both clenched hand pull and teeth clench.