Transverse section of human muscle fibers, preserved in epoxy resin.

<p>A representative area of a part of vastus lateralis muscle stained with the mixture of toluidine and methylene blue is showed. The arrows indicate the cross section of capillaries.</p

Values of peak power output, selected cardio-respiratory variables and plasma lactate concentration obtained at exhaustion during the incremental exercise test performed before and after 20 weeks of endurance training.

<p>Values of peak power output, selected cardio-respiratory variables and plasma lactate concentration obtained at exhaustion during the incremental exercise test performed before and after 20 weeks of endurance training.</p

Models fitted to subject 3 data collected during baseline-heavy-intensity exercise transition before training and the corresponding residuals.

<p>The arrow represents the size of the slow component, which is defined as the difference between the value reached at the end of the exercise, and the value of the first (fast) exponential component (represented with the broken line).</p

Mean (± SD) values of pulmonary oxygen uptake (V’O₂) for 12 subjects during baseline and during heavy-intensity transition.

<p>Note the training-induced attenuation of the slow component of the V’O₂ on-kinetics during high-intensity cycling.</p

Physical performance (cycling and running) before and after the 20 weeks of cycling endurance training.

<p>Physical performance (cycling and running) before and after the 20 weeks of cycling endurance training.</p

Plasma lactate concentration [La^-]_pl during an incremental exercise test before (white circles) and after (black circles) 20 weeks of endurance training.

<p>The power output was increased by 30 W every 3 minutes up to 240 W. Note the right-ward shift of the lactate curve after training and especially the difference (<i>P</i> < 0.02 Wilcoxon signed rank test) between [La^-]_pl at 180 W i.e. near to the power output at which the V’O₂ on-kinetics has been determined, before and after the training. Data are given as means ± SD for 11 subjects.</p

Oxygen uptake on-kinetics during high-intensity cycling exercise, before and after 20 weeks of training.

<p>Oxygen uptake on-kinetics during high-intensity cycling exercise, before and after 20 weeks of training.</p

Experimental V’O₂ and simulated muscle V’O₂, metabolite concentrations and ATP usage/supply fluxes during low-intensity (baseline) and high-intensity cycling exercise in untrained and trained muscle.

<p>(A) Experimental and simulated V’O₂, simulated ADP and pH. (B) Simulated PCr, P_i and ATP. (C) Simulated ATP usage (UT), ATP supply by OXPHOS (OX), ATP supply by anaerobic glycolysis (GL), ATP supply by creatine kinase (CK). Experimental baseline-heavy-intensity exercise transition: after 3 min. Simulated baseline-heavy-intensity exercise transition: after 3.4 min (the delay by 24 s corresponds to the cardio-dynamic phase of the pulmonary V’O₂ on-kinetics). The muscle V’O₂ is calculated based on the assumption that during baseline-intensity exercise (20 W) muscle V’O₂ constitutes ~75% and during heavy-intensity exercise ~85% of the pulmonary V’O₂ (see Ref. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0154135#pone.0154135.ref040" target="_blank">40</a>]).</p