A functional evaluation of skeletal muscle oxidative metabolism during dynamic knee-extension (KE) incremental exercises was carried out following a 35-day bed rest (BR) (Valdoltra 2008 BR campaign). Nine young male volunteers (age: 23.5 ± 2.2 years [mean ± SD]) were evaluated. Pulmonary gas exchange, heart rate (HR) and cardiac output (Q, by impedance cardiography), skeletal muscle (vastus lateralis) fractional O(2) extraction and brain (frontal cortex) oxygenation (by near-infrared spectroscopy) were determined during incremental KE. Values at exhaustion were considered "peak". Peak HR (147 ± 18 beats(.)min(-1) before vs. 146 ± 17 after BR) and peak (17.8 ± 3.3 L(.)min(-1) before vs. 16.1 ± 1.8 after BR) were unaffected by BR. As expected, brain oxygenation did not decrease during KE. Peak O(2) uptake (VO (2)peak) was lower after vs. before BR, both when expressed as L(.)min(-1) (0.99 ± 0.17 vs. 1.26 ± 0.27) and when normalized per unit of quadriceps muscle mass (46.5 ± 6.4 mL(.)min(-1)(.)100g(-1) vs. 56.9 ± 11.0). Skeletal muscle peak fractional O(2) extraction, expressed as a percentage of the maximal values obtained during a transient limb ischemia, was lower after (46.3 ± 12.1%) vs. before BR (66.5 ± 11.2). After eliminating, by the adopted exercise protocol, constraints related to cardiovascular O(2) delivery, a decrease in VO (2)peak and muscle peak capacity of fractional O(2) extraction was found after 35 days of BR. These findings suggest a substantial impairment of oxidative function at the muscle level, "downstream" with respect to bulk blood flow to the exercising muscles, that is possibly at the level of blood flow distribution/O(2) utilization inside the muscle, peripheral O(2) diffusion, intracellular oxidative metabolism.
Functional impairment of skeletal muscle oxidative metabolism during knee-extension exercise after bed rest.
Marzorati M;Porcelli S;
2011
Abstract
A functional evaluation of skeletal muscle oxidative metabolism during dynamic knee-extension (KE) incremental exercises was carried out following a 35-day bed rest (BR) (Valdoltra 2008 BR campaign). Nine young male volunteers (age: 23.5 ± 2.2 years [mean ± SD]) were evaluated. Pulmonary gas exchange, heart rate (HR) and cardiac output (Q, by impedance cardiography), skeletal muscle (vastus lateralis) fractional O(2) extraction and brain (frontal cortex) oxygenation (by near-infrared spectroscopy) were determined during incremental KE. Values at exhaustion were considered "peak". Peak HR (147 ± 18 beats(.)min(-1) before vs. 146 ± 17 after BR) and peak (17.8 ± 3.3 L(.)min(-1) before vs. 16.1 ± 1.8 after BR) were unaffected by BR. As expected, brain oxygenation did not decrease during KE. Peak O(2) uptake (VO (2)peak) was lower after vs. before BR, both when expressed as L(.)min(-1) (0.99 ± 0.17 vs. 1.26 ± 0.27) and when normalized per unit of quadriceps muscle mass (46.5 ± 6.4 mL(.)min(-1)(.)100g(-1) vs. 56.9 ± 11.0). Skeletal muscle peak fractional O(2) extraction, expressed as a percentage of the maximal values obtained during a transient limb ischemia, was lower after (46.3 ± 12.1%) vs. before BR (66.5 ± 11.2). After eliminating, by the adopted exercise protocol, constraints related to cardiovascular O(2) delivery, a decrease in VO (2)peak and muscle peak capacity of fractional O(2) extraction was found after 35 days of BR. These findings suggest a substantial impairment of oxidative function at the muscle level, "downstream" with respect to bulk blood flow to the exercising muscles, that is possibly at the level of blood flow distribution/O(2) utilization inside the muscle, peripheral O(2) diffusion, intracellular oxidative metabolism.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
