We recently reported that resistance trained (T, n=10) and untrained (UT, n=11) young adults experience vastus lateralis (VL) muscle atrophy following two weeks of disuse, and 8 weeks of recovery resistance training (RT) promotes VL hypertrophy in both participant cohorts. However, angiogenesis targets and muscle capillary number were not examined and currently no human studies that have sought to determine if disuse followed by recovery RT affects these outcomes. Thus, we examined whether disuse and/or recovery RT affected these outcomes. All participants underwent two weeks of left leg immobilization using locking leg braces and crutches followed by eight weeks (3d/week) of knee extensor focused progressive RT. VL biopsies were obtained at baseline (PRE), immediately after disuse (MID), and after RT (POST). Western blotting was used to assay angiogenesis markers and immunohistochemistry was performed in 16/21 participants to determine type I and II muscle fiber capillary number. Significant main effects of time (p<0.05) were observed for protein levels of VEGF (MID<POST), VEGFR2 (PRE&MID<POST), TSP-1 (PRE<POST), TIMP1 (MID<POST), phosphorylated/pan eNOS (Ser1177) (POST<PRE), and pan eNOS (PRE<POST). VEGFR2 exhibited a training status*time (p=0.018), but no differences existed between T and UT at any time point. A significant main effect of time was observed for type II fiber capillary number (PRE<POST), and type II fiber cross-sectional area (fCSA) increased from MID to POST (+25%, p<0.001) and PRE to POST (+20%, p=0.019). No significant correlations exist for percentage changes in type II fiber capillary number and type II fCSA from PRE-to-MID (r= 0.020), MID-to-POST (r= 0.392), or PRE-to-POST (r= -0.120) across all participants (p>0.100). Although disuse and recovery RT affect skeletal muscle angiogenesis-related protein targets, prior training history does not differentially affect these outcomes.
New and noteworthy: This is the first study to examine how limb immobilization and recovery resistance training affect molecular outcomes related to angiogenesis in younger adults with or without a prior training history. Regardless of resistance training history, the molecular responses are largely similar between participant cohorts and is suggestive of a reduced (pre-mid) and increased (mid-post) angiogenic response, with disuse and subsequent recovery resistance training.