Differences between linear volume resistance training versus variable resistance training in skeletal muscle molecular adaptations

Abstract

Although several studies have examined the strength and hypertrophy adaptations in response to lower versus higher volume resistance training, examining the metabolic and morphological adaptations that occur to both forms of training is still in its infancy. Herein, healthy resistance-trained men (n = 20; 26 ± 3 years old, 25.6 ± 2.1 kg/m2, 2.5 ± 1.1 years of self-reported training) performed eight weeks of unilateral leg resistance training (twice-weekly). In each participant, one leg was randomly assigned to perform a lower volume protocol (PC, Controlled linear volume), which consisted of 4 sets of unilateral leg press followed by 4 sets of unilateral leg extension exercise per workout (9–12 repetitions per exercise to concentric failure). The contralateral leg was subjected to a higher volume training protocol (PV, variable volume) with the same exercises which, over the 8-week period, led to 12.6% more total training volume (p<0.05). A pre-training vastus lateralis biopsy was obtained from a randomized single leg, and biopsies were obtained from both legs 48 h following the last training bout. Tissue was processed to examine metabolic and mitochondrial markers in the sarcoplasmic protein pool, and the myofibril pool was analyzed for the relative abundances of total myosin heavy chain (MHC) and actin proteins. Additionally, sections were stained using a fluorogenic-conjugated phalloidin stain to obtain contractile protein and non-contractile spacing attributes within myofibers. While neither form of training affected most of the assayed sarcoplasmic proteins related to metabolic processes (i.e., CKM, LDHA, PFK, PYGM, GLUT4, LAT1, IDH2. CPT1, or mitochondrial complexes I-IV), both forms of training increased hexokinase 2 protein levels while decreasing a mitochondrial beta-oxidation marker (VLCAD protein content). Interestingly, PV training decreased mitochondrial complex V protein content as well as the relative abundances of MHC and actin (p<0.05). Additionally, PV training decreased myofibril spacing within muscle fibers (p<0.05), and participants that began training with more myofibril packing seemingly experienced a larger increase in non-contractile protein spacing with PV training (association r = -0.714, p=0.006). In conclusion, these data are the second observation from our laboratory suggesting that higher volume training in previously-trained individuals significantly decreases myofibril volume in muscle fibers. However, unlike our previous report, this morphological adaptation did not coincide with metabolic adaptation. Further studies are needed to determine whether this morphological adaptation is transient and/or meaningful.