Simulated time courses of system variables during transition from rest to moderate muscle work (relative ATP usage activity A_UT = 35) to recovery for the saturating-type A_OX (ESA, each-step activation intensity)-A_UT (relative ATP usage activity) dependence.

<p>A, dependence of , ADP and pH; B, dependence of PCr, P_i and ATP; C, dependence of ATP usage (vUT) as well as of ATP supply by OXPHOS (+ aerobic glycolysis) (vOX), creatine kinase (vCK) and anaerobic glycolysis (vGL). The saturating-type A_OX-A_UT dependence without additional ATP usage is postulated to be present in voluntary exercise below critical ATP usage activity (critical power).</p

Dependence of proton leak intensity (vLK) on protonmotive force (Δp).

<p>State 4, state 3, rest, moderate work and heavy/severe work in skeletal muscle are indicated. vLK in all states is scaled for intact skeletal muscle. Simulations were made using the model version for intact skeletal muscle, as described in the text.</p

Experimental values of the characteristic transition time τ_p of the on-kinetics at different bilateral knee extension exercise intensities for the same group of individuals in each experiment.

<p>Experimental values of the characteristic transition time τ_p of the on-kinetics at different bilateral knee extension exercise intensities for the same group of individuals in each experiment.</p

Simulated phenomenological steady-state V’O₂-ADP relationship in different states.

<p>These states comprise: state 4_id, intermediate state, state 3 _id, rest, moderate work and intensive work in isolated mitochondria and intact skeletal muscle. Inset: enlarged fragment around state 4 and rest. The presented phenomenological V’O₂-ADP relationship involves implicitly the V’O₂-P_i relationship. V’O₂ in isolated mitochondria is scaled for mitochondria in skeletal muscle in order to make a direct comparison.</p

Simulated (lines) and experimental (points) dependence of system variables on relative ATP usage activity A_UT for the saturating-type A_OX (ESA, each-step activation intensity)-A_UT dependence in the presence of the ‘additional’ ATP usage above the critical ATP usage activity.

<p>A, dependence of , ADP and pH; B, dependence of PCr, P_i and ATP. Re-scaled (see sub-section 2.5) experimental data for medial gastrocnemius from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195620#pone.0195620.ref014" target="_blank">14</a>] are presented. The saturating-type A_OX-A_UT dependence with additional ATP usage is postulated to be present in voluntary exercise above critical ATP usage activity (critical power).</p

Experimental -power output dependence.

<p>Experimental dependence of (oxygen consumption at the end of subsequent steps) on the power output (PO) in subsequent steps in step-incremental exercise (increase in PO by 60 W after each 6 or 8 min in two overlapping protocols ‘shifted in phase’ by 30 W, with a baseline of 20 W and 50 W) extracted from Table 1 in [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195620#pone.0195620.ref019" target="_blank">19</a>] is presented.</p

Power-type vs. saturating-type A_OX (ESA, each-step activation intensity)-A_UT (relative ATP usage activity) dependence.

<p>Simulated power-type and saturating-type A_OX-A_UT dependences (lines) are compared with the values of A_OX and A_UT extracted from experimental data for rest, moderate exercise and severe exercise (points) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195620#pone.0195620.ref001" target="_blank">1</a>]. The power-type dependence, described by <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195620#pone.0195620.e009" target="_blank">Eq 1</a>, is postulated to be present in electrically-stimulated muscle, while the saturating-type dependence, described by <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195620#pone.0195620.e010" target="_blank">Eq 2</a>, is postulated to be present during voluntary exercise (cortically-stimulated muscle).</p

Simulated dependence of system variables on relative ATP usage activity A_UT for the saturating-type A_OX (ESA, each-step activation intensity)-A_UT dependence in the absence of the ‘additional’ ATP usage.

<p>A, dependence of , ADP and pH; B, dependence of PCr, P_i and ATP. The saturating-type A_OX-A_UT dependence without additional ATP usage is postulated to be present in voluntary exercise (cortically-stimulated muscle) below critical ATP usage activity (critical power).</p

Dependence of total oxygen consumption (), related to proton leak, related to ATP synthesis, Δp, NADH (% of total NAD) and phenomenological ATP/O₂ ratio on relative activity of ATP usage (relative rate constant, k_UT, or its activation in relation to rest, A_UT) in skeletal muscle for proton leak activity (rate constant) elevated twice in relation to the ‘standard’ value.

<p>Dependence of total oxygen consumption (), related to proton leak, related to ATP synthesis, Δp, NADH (% of total NAD) and phenomenological ATP/O₂ ratio on relative activity of ATP usage (relative rate constant, k_UT, or its activation in relation to rest, A_UT) in skeletal muscle for proton leak activity (rate constant) elevated twice in relation to the ‘standard’ value.</p

Simulated relationship of the characteristic transition time τ_p of the principal phase of the muscle on-kinetics on relative ATP usage activity (A_UT) for the power-type and saturating-type A_OX (ESA, each-step activation intensity)-A_UT dependencies.

<p>The relative activation of OXPHOS during rest-to-work transition A_OX was increased as a function of A_UT according to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195620#pone.0195620.e009" target="_blank">Eq 1</a> for power-type dependence and to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195620#pone.0195620.e010" target="_blank">Eq 2</a> for saturating-type dependence. The power-type A_OX-A_UT dependence without ‘additional’ ATP usage is postulated to be present in electrically-stimulated muscle, while the saturating-type A_OX-A_UT dependence with ‘additional’ ATP usage is postulated to be present in voluntary exercise (cortically-stimulated muscle).</p