Figure 8. Muscle force production is unaffected during manipulation of adrenoreceptor activation .

During single tetanic contractions at 100 Hz, active force produced by GM in young (n = 6; open symbols, means ± SEM) and old (n = 2, individual solid symbols) mice was similar across contraction durations as well as between control conditions and superfusion with either NA (10⁻⁹  m) or phentolamine (10⁻⁶  m).