Fig. 2.

Isoproterenol enhances force generation of soleus and extensor digitorum longus muscles. Force frequency curves were performed at baseline (○, □) and 30 min post-treatment for control (●) and isoproterenol (■) groups in soleus (SOL) (a, b) and extensor digitorum longus (EDL) (c−f), respectively. Forces are substantially higher than baseline in the presence of ISO in SOL (b). After baseline, a prolonged contraction was performed in each muscle (see Fig. 3), which caused a rundown effect in the EDL muscle with CON values significantly decreasing from baseline (c). Consequently, there were only minor increases in force in the presence of ISO (d). Force frequency curves were therefore performed in another series of EDL muscles without continuous contraction after baseline, CON (e) and ISO (f). In the latter case, forces are clearly higher than baseline in the presence of ISO (f). The corresponding average percentage effect of ISO on force is shown for SOL (g) and EDL (h) muscles. h is derived from results from d and f, with adjustments for rundown in d. Data are expressed as mean ± SE for 5 (e−f), 8 (a−d and g), or 13 (h) muscles. *p < 0.05; **p < 0.01; ***p < 0.001 vs. corresponding treatment by paired t test