Muscle fatigue, pedalling technique and the VO2${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ slow component during cycling

Above the first lactate threshold, the steady-state <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:msub> <mml:annotation>${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$</mml:annotation></mml:semantics> </mml:math> is delayed or prevented due to the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:msub> <mml:annotation>${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$</mml:annotation></mml:semantics> </mml:math> slow component ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>SC</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{SC}}}}$</mml:annotation></mml:semantics> </mml:math> ). This phenomenon has been associated with muscle fatigue, but evidence for a causal relationship is equivocal. Moreover, little is known about the contribution of pedalling technique adjustments to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>SC</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{SC}}}}$</mml:annotation></mml:semantics> </mml:math> during fatiguing cycling exercise. Eleven participants completed constant power trials at 10% above the second lactate threshold. Muscle fatigue was assessed, utilizing femoral nerve stimulation and instrumented pedals, while <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:msub> <mml:annotation>${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$</mml:annotation></mml:semantics> </mml:math> , quadriceps oxygenation, electromyography (EMG) and pedal force components were measured. Correlations between physiological and mechanical variables were estimated at group and individual levels. Group correlations revealed moderate values for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>SC</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{SC}}}}$</mml:annotation></mml:semantics> </mml:math> with quadriceps twitch force (r = -0.51) and muscle oxygenation (r = -0.52), while weak correlations were observed for EMG amplitude (r = 0.26) and EMG mean power frequency (r = -0.16), and with pedalling mechanical variables such as peak total downstroke force (r = -0.16), minimum total upstroke force (r = -0.16) and upstroke index of effectiveness (r = 0.16). The findings here align with prior literature reporting significant correlations between the magnitude of muscle fatigue and that of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>SC</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{SC}}}}$</mml:annotation></mml:semantics> </mml:math> , although there was large interindividual variability for all the reported correlations. Considering the heterogeneity in the data, it is difficult to determine the relative impact of pedalling technique adjustments on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>SC</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{SC}}}}$</mml:annotation></mml:semantics> </mml:math> overall, but the present study opens the possibility that in some cases, increases in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:msub> <mml:annotation>${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$</mml:annotation></mml:semantics> </mml:math> secondary to technical adjustments may be 'superimposed' on the underlying <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>SC</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{SC}}}}$</mml:annotation></mml:semantics> </mml:math> .