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

The effectiveness of whey protein plus potassium bicarbonate enriched-diet (WP+KHCO₃) to mitigate disuse-induced changes in muscle fibre oxidative capacity and capillarization was investigated in a 21-day crossover design bed rest study. Ten healthy men (31±6 years) once received WP+KHCO₃ and once received a standardized isocaloric diet. Muscle biopsies were taken two days before and during the 19^th day of bed rest (BR) from the soleus (SOL) and vastus lateralis (VL) muscle. Whole body aerobic power (VO_2max), 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<0.05), and the fiber oxidative capacity (P<0.001) and VO_2max (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<0.001). WP+KHCO₃ attenuated the disuse-induced reduction in fiber oxidative capacity in both muscles (P<0.01). In conclusion, following 19 days bed rest, the decrement in fiber oxidative capacity is proportionally larger than the loss of capillaries. WP+KHCO₃ appears to attenuate disuse-induced reductions in fiber oxidative capacity.

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