Maximal strength training and increased work efficiency: contribution from the trained muscle bed

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Abstract
Maximal strength training (MST) reduces pulmonary oxygen uptake (V̇o2) at a given submaximal exercise work rate (i.e., efficiency). However, whether the increase in efficiency originates in the trained skeletal muscle, and therefore the impact of this adaptation on muscle blood flow and arterial-venous oxygen difference (a-vO2diff), is unknown. Thus five trained subjects partook in an 8-wk MST intervention consisting of half-squats with an emphasis on the rate of force development during the concentric phase of the movement. Pre- and posttraining measurements of pulmonary V̇o2(indirect calorimetry), single-leg blood flow (thermodilution), and single-leg a-vO2diff(blood gases) were performed, to allow the assessment of skeletal muscle V̇o2during submaximal cycling [237 ± 23 W; ∼60% of their peak pulmonary V̇o2(V̇o2peak)]. Pulmonary V̇o2peak(∼4.05 l/min) and peak work rate (∼355 W), assessed during a graded exercise test, were unaffected by MST. As expected, following MST there was a significant reduction in pulmonary V̇o2during steady-state submaximal cycling (∼237 W: 3.2 ± 0.1 to 2.9 ± 0.1 l/min). This was accompanied by a significant reduction in single-leg V̇o2(1,101 ± 105 to 935 ± 93 ml/min) and single-leg blood flow (6,670 ± 700 to 5,649 ± 641 ml/min), but no change in single-leg a-vO2diff(16.7 ± 0.8 to 16.8 ±0.4 ml/dl). These data confirm an MST-induced reduction in pulmonary V̇o2during submaximal exercise and identify that this change in efficiency originates solely in skeletal muscle, reducing muscle blood flow, but not altering muscle a-vO2diff.

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