Reactive Jumps Preserve Skeletal Muscle Structure, Phenotype, and Myofiber Oxidative Capacity in Bed Rest
Dieter Blottner, Maria Hastermann, Robert Weber, Regina Lenz, Guido Gambara, Ulrich Limper, Jörn Rittweger, Alessandra Bosutti, Hans Degens, Michele Salanova
Abstract
Identification of countermeasures able to prevent disuse-induced muscle wasting is crucial to increase performance of crew members during space flight as well as ameliorate patient`s clinical outcome after long immobilization periods. We report on the outcome of short but high impact reactive jumps (JUMP) as countermeasure during 60 days 6° head-down tilt (HDT) bed rest on myofiber size, -type composition, capillarisation and oxidative capacity in tissue biopsies (pre/post/recovery) from the knee extensor vastus lateralis (VL) and deep calf soleus (SOL) muscle of 22 healthy male participants (RSL study 2015-2016, DLR:envihab, Cologne). Bed rest induced a slow-to-fast myofiber shift (type I -> II) with an increased prevalence of hybrid fibers in SOL after bed rest without jumps (CTRL, p = 0.016). In SOL, JUMP countermeasure in bed rest prevented both fast and slow myofiber CSA decrements (p=0.005) in CTR group. In VL, bed rest only induced capillary rarefaction, as reflected by the decrease in local capillary to fiber ratio (LCFR), for both type II (pre vs post/R+10, p= 0.028/0.028) and type I myofibers (pre vs. R+10, p= 0.012), which was not seen in the JUMP group. VO2maxFiber (pL x mm-1 x min-1) calculated from SDH-stained cryosections (OD660nm) showed no significant differences between groups. High-impact jump training in bed rest prevented disuse-induced myofiber atrophy, phenotype transition in SOL, and attenuated capillary rarefaction in the prime knee extensor VL however with little impact on oxidative capacity changes.