Figure 3. ΔO₂ for 80 stimuli as a function of time between stimuli (interpulse interval).

Eighty stimuli given within 1 s (80 Hz or interpulse interval of 0.0125 s) consumed an average of 0.747 μmol g⁻¹ O₂ but as the interpulse interval increases, the ΔO₂ increased about 2.6-fold until a maximum was reached at the interpulse interval of 0.5 s (2 Hz). The ΔO₂ remained constant thereafter as the interpulse interval increased. Hence, for these experiments we used an interpulse interval of 0.5 s to determine the ΔO₂ (and ATP utilization) for the first twitch. Error bars shown are ±SEM. n = 6–11 for all points except for 0.5 Hz where n = 4. These measurements were performed in the absence of BTS, and hence include the crossbridge ATP utilization. In another set of experiments where ΔO₂ was measured in the presence of BTS, ΔO₂ rose 4.13-fold from 0.378 ± 0.026 μmol g⁻¹ (n = 4) at 80 Hz to 1.56 ± 0.021 μmol g⁻¹ (n = 4) at 2 Hz.