AUTHOR=Iannetta Danilo , Qahtani Ahmad , Millet Guillaume Y. , Murias Juan M. 

TITLE=Quadriceps Muscles O2 Extraction and EMG Breakpoints during a Ramp Incremental Test

JOURNAL=Frontiers in Physiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2017.00686

DOI=10.3389/fphys.2017.00686

ISSN=1664-042X

ABSTRACT=<p>Muscle deoxygenated breakpoint ([HHb]<italic>BP</italic>) has been found to be associated with other indices of exercise tolerance in the vastus lateralis (VL) muscle but not in the vastus medialis (VM) and rectus femoris (RF).</p><p><bold>Purpose:</bold> To investigate whether the [HHb]<italic>BP</italic> occurs also in the VM and RF muscles and whether or not it is associated with other physiological indices of exercise tolerance, such as the EMG threshold (EMG<sub>t</sub>) and the respiratory compensation point (RCP).</p><p><bold>Methods:</bold> Twelve young endurance trained participants performed maximal ramp incremental (RI) cycling tests (25–30 W·min<sup>−1</sup> increments). Muscle oxygen extraction and activity as well as ventilatory and gas exchange parameters were measured. After accounting for the mean response time, the oxygen uptake (<inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mrow><mml:mtext>V</mml:mtext></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub>) corresponding to the RCP, [HHb]<italic>BP</italic>, and the EMG<sub>t</sub> was determined.</p><p><bold>Results:</bold> Peak power output (PO<sub>peak</sub>) was 359 ± 48 W. Maximal oxygen consumption (<inline-formula><mml:math id="M2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mrow><mml:mtext>V</mml:mtext></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2max</sub>) was 3.87 ± 0.46 L·min<sup>−1</sup>. The <inline-formula><mml:math id="M3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mrow><mml:mtext>V</mml:mtext></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub> at the RCP was 3.39 ± 0.41 L·min<sup>−1</sup>. The <inline-formula><mml:math id="M4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mrow><mml:mtext>V</mml:mtext></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub> (L·min<sup>−1</sup>) corresponding to the [HHb]<italic>BP</italic> and EMG<sub>t</sub> were: 3.49 ± 0.46 and 3.40 ± 0.44; 3.44 ± 0.61 and 3.43 ± 0.49; 3.59 ± 0.52, and 3.48 ± 0.46 for VL, VM, and RF, respectively. Pearson's correlation between these thresholds ranged from 0.90 to 0.97 (<italic>P</italic> &lt; 0.05). No difference was found for the absolute <inline-formula><mml:math id="M5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mrow><mml:mtext>V</mml:mtext></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub> and the normalized PO (%) at which the thresholds occurred in all three muscles investigated (<italic>P</italic> &gt; 0.05). Although in eight out of 12 participants, the [HHb]<italic>BP</italic> in the RF led to a steeper increase instead of leading to a plateau-like response as observed in the VL and VM, the <inline-formula><mml:math id="M6" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mrow><mml:mtext>V</mml:mtext></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub> at the breakpoints still coincided with that at the RCP.</p><p><bold>Conclusions:</bold> This study demonstrated that local indices of exercise tolerance derived from different portions of the quadriceps are not different to the systemic index of the RCP.</p>