EFFECTS OF LEG IMMOBILIZATION AND RECOVERY RESISTANCE TRAINING ON SKELETAL MUSCLE IN TRAINED VERSUS UNTRAINED ADULTS

PURPOSE: We sought to examine how resistance training (RT) status in young healthy individuals, either well resistance trained (T, n = 10) or untrained (UT, n = 11), affected molecular markers with leg immobilization followed by recovery RT. METHODS: All participants underwent two weeks of left leg immobilization via a locking leg brace. Afterwards, all participants underwent eight weeks (3 d/week) of knee extensor focused progressive RT. Vastus lateralis (VL) ultrasound-derived thickness and muscle cross-sectional area were measured at baseline (PRE), immediately after disuse (MID), and after RT (POST) with VL muscle biopsies also being collected at these time points. RESULTS: Both groups presented lower ultrasound derived VL size metrics at MID versus PRE (p ≤ 0.001), and values increased in both groups from MID to POST (p < 0.05); however, VL size increased from PRE to POST in UT only (p < 0.001). Mean and type II myofiber cross-sectional area values were greater at PRE and POST versus MID (p < 0.05), with T being greater than UT throughout (P ≤ 0.012). In both groups, satellite cell number was not affected by leg immobilization but increased in response to RT (p ≤ 0.014), with T being greater than UT throughout (p = 0.004). Total RNA (ribosome content) decreased (p = 0.010) from PRE to MID, while total RNA and certain endoplasmic reticulum stress proteins increased from MID to POST regardless of training status. CONCLUSION: Immobilization-induced muscle atrophy and recovery RT hypertrophy outcomes are similar between UT and T participants, and the lack of molecular signature differences between groups supports these findings. However, results are limited to younger adults undergoing non-complicated disuse.