Heterogeneous atrophy occurs within individual lower limb muscles during 60 days of bed rest

Abstract

To better understand disuse muscle atrophy, via magnetic resonance imaging, we sequentially measured muscle cross-sectional area along the entire length of all individual muscles from the hip to ankle in nine male subjects participating in 60-day head-down tilt bed rest (2nd Berlin BedRest Study; BBR2-2). We hypothesized that individual muscles would not atrophy uniformly along their length such that different regions of an individual muscle would atrophy to different extents. This hypothesis was confirmed for the adductor magnus, vasti, lateral hamstrings, medial hamstrings, rectus femoris, medial gastrocnemius, lateral gastrocnemius, tibialis posterior, flexor hallucis longus, flexor digitorum longus, peroneals, and tibialis anterior muscles (P ≤ 0.004). In contrast, the hypothesis was not confirmed in the soleus, adductor brevis, gracilis, pectineus, and extensor digitorum longus muscles (P ≥ 0.20). The extent of atrophy only weakly correlated (r = -0.30, P< 0.001) with the location of greatest cross-sectional area. The rate of atrophy during bed rest also differed between muscles (P < 0.0001) and between some synergists. Most muscles recovered to their baseline size between 14 and 90 days after bed rest, but flexor hallucis longus, flexor digitorum longus, and lateral gastrocnemius required longer than 90 days before recovery occurred. On the basis of findings of differential atrophy between muscles and evidence in the literature, we interpret our findings of intramuscular atrophy to reflect differential disuse of functionally different muscle regions. The current work represents the first lower-limb wide survey of intramuscular differences in disuse atrophy. We conclude that intramuscular differential atrophy occurs in most, but not all, of the muscles of the lower limb during prolonged bed rest.

Non-uniform recruitment along human rectus femoris muscle during transcutaneous electrical nerve stimulation

“…Also, other groups reported that adaptation of the muscle volume to resistance training and bed rest is spatially localized within this muscle (Matta et al 2014;Miokovic et al 2012). These localized neural and morphological responses can be partly explained by a unique neuroanatomy, i.e., the proximal and other regions are innervated by different motor nerve branches (Sung et al 2003;Yang and Morris 1999).…”

High-intensity flywheel exercise and recovery of atrophy after 90 days bed-­rest­

“…Prolonged bed-rest is also a model of clinical disuse 8 and can be informative clinically on which musculature is most affected and hence how to target rehabilitation programmes. While a series of works have examined muscle atrophy in the lower limb in disuse, [9][10][11][12][13][14][15][16][17] yet less is known about atrophy of the deep muscles of the hip and the lower leg. A secondary aim of the current study was to examine which muscles of the lower limb atrophy the most.…”

Gluteal muscle function and size in swimmers

“…26 There are a number of factors that may contribute to the lack of difference in whole muscle size observed between controls and swimmers in this study. These include intermittent rather than continuous exposure to deloading; sufficient land-based training (similar 'past BPAQ' scores to control) to negate deloading related changes; or the inability of measures of whole muscle size (volume) to detect segmental changes within the muscle, 27 or other morphological adaptations such as muscle fibre atrophy or changes in tendon and connective tissue stiffness. 28 These results may have implications on the land-based function of swimmers.…”