Whey protein with potassium bicarbonate supplement attenuates the reduction in muscle oxidative capacity during 19 days of bed rest

<jats:p> The effectiveness of whey protein plus potassium bicarbonate-enriched diet (WP+KHCO<jats:sub>3</jats:sub>) in mitigating disuse-induced changes in muscle fiber oxidative capacity and capillarization was investigated in a 21-day crossover design bed rest study. Ten healthy men (31 ± 6 yr) once received WP+KHCO<jats:sub>3</jats:sub> and once received a standardized isocaloric diet. Muscle biopsies were taken 2 days before and during the 19th day of bed rest (BR) from the soleus (SOL) and vastus lateralis (VL) muscle. Whole-body aerobic power (V̇o<jats:sub>2 max</jats:sub>), muscle fatigue, and isometric strength of knee extensor and plantar flexor muscles were monitored. Muscle fiber types and capillaries were identified by immunohistochemistry. Fiber oxidative capacity was determined as the optical density (OD) at 660 nm of succinate dehydrogenase (SDH)-stained sections. The product of fiber cross-sectional area and SDH-OD (integrated SDH) indicated the maximal oxygen consumption of that fiber. The maximal oxygen consumption supported by a capillary was calculated as the integrated SDH in its supply area. BR reduced isometric strength of knee extensor muscles ( P &lt; 0.05), and the fiber oxidative capacity ( P &lt; 0.001) and V̇o<jats:sub>2 max</jats:sub> ( P = 0.042), but had no significant impact on muscle capillarization or fatigue resistance of thigh muscles. The maximal oxygen consumption supported by a capillary was reduced by 24% in SOL and 16% in VL ( P &lt; 0.001). WP+KHCO<jats:sub>3</jats:sub> attenuated the disuse-induced reduction in fiber oxidative capacity in both muscles ( P &lt; 0.01). In conclusion, following 19 days of bed rest, the decrement in fiber oxidative capacity is proportionally larger than the loss of capillaries. WP+KHCO<jats:sub>3</jats:sub> appears to attenuate disuse-induced reductions in fiber oxidative capacity. </jats:p>