Figure 2. Representative tracings of shortening and force in the 15 min exercise protocol (1^st bout).

Tracings of shortening (upper panel) and force (lower panel). A) The in vivo prepared muscle was stimulated intermittently with 1s on, 1s off. As stimulation starts, force rises from resting base line tension (T_bl) until it reaches the pre-set afterload (33% of F_max). From here, the force is maintained while the muscle starts to shorten and reaches the maximal shortening (S_max). When stimulation ceases (after 1 s) the muscle is passively stretched to resting length (L₀), and subsequently force declines. B) Representative tracing of a 15 min exercise protocol (1^st bout). Note the three phases marked with roman numbers; during the first 20 s exercise there is a prominent fall in S_max (upper panel); at 100 s there is a further reduction in S_max accompanied by a transient rise in T_bl (lower panel); at 15 min there is still reduction in S_max while T_bl is restored to initial values.