Abstract
We sought to determine if manipulating resistance training (RT) variables differentially altered the expression of select sarcoplasmic and myofibril proteins as well as myofibrillar spacing in myofibers. Resistance-trained men (n = 20; 26 ± 3 years old) trained for 8 weeks where a randomized leg performed either a standard (CON) or variable RT protocol (VAR: manipulation of load, volume, muscle action, and rest intervals at each RT session). A pre-training (PRE) vastus lateralis biopsy was obtained from a randomized single leg, and biopsies were obtained from both legs 96 h following the last training bout. The sarcoplasmic protein pool was assayed for proteins involved in energy metabolism, and the myofibril protein pool was assayed for relative myosin heavy chain (MHC) and actin protein abundances. Sections were also histologically analyzed to obtain myofibril spacing characteristics. VAR resulted in ~12% greater volume load (VL) compared to CON (p < 0.001). The mean fiber cross-sectional area increased following both RT protocols [CON: 14.6% (775.5 μm2), p = 0.006; VAR: 13.9% (743.2 μm2), p = 0.01 vs. PRE for both], but without significant differences between protocols (p = 0.79). Neither RT protocol affected a majority of assayed proteins related to energy metabolism, but both training protocols increased hexokinase 2 protein levels and decreased a mitochondrial beta-oxidation marker (VLCAD protein; p < 0.05). Citrate synthase activity levels increased with CON RT (p < 0.05), but not VAR RT. The relative abundance of MHC (summed isoforms) decreased with both training protocols (p < 0.05). However, the relative abundance of actin protein (summed isoforms) decreased with VAR only (13.5 and 9.0%, respectively; p < 0.05). A decrease in percent area occupied by myofibrils was observed from PRE to VAR (−4.87%; p = 0.048), but not for the CON (4.53%; p = 0.979). In contrast, there was an increase in percent area occupied by non-contractile space from PRE to VAR (10.14%; p = 0.048), but not PRE to CON (0.72%; p = 0.979). In conclusion, while both RT protocols increased muscle fiber hypertrophy, a higher volume-load where RT variables were frequently manipulated increased non-contractile spacing in resistance-trained individuals.
Highlights
Resistance training (RT) is an effective strategy to increase skeletal muscle fiber cross-section area
In a subsequent study with a separate cohort of resistance-trained men, we demonstrated that a higher load and lower volume resistance training (RT) protocol [lifts ~80–90% of one repetition maximum (1-RM)] relative to that used by Haun et al increased type II fiber cross-section area (fCSA) and reduced the relative abundances of myosin heavy chain (MHC) and actin protein by only ~3% (Vann et al, 2020a)
We demonstrated that frequent manipulation of RT variables does not affect several proteins in the sarcoplasmic fraction such as enzymes related to energy production (CKM, lactate dehydrogenase A (LDHA), PFK, and PYGM), nutrient transporters (LAT1 and glucose transporter 4 (GLUT4)), mitochondrial enzymes (IDH2 and CPT1), or markers of mitochondrial volume (COX I, COX II, COX III, COX IV, and COX V proteins, except the citrate synthase (CS) activity which increased for change scores of the training protocols (CON))
Summary
Resistance training (RT) is an effective strategy to increase skeletal muscle fiber cross-section area (fCSA; Kraemer and Ratamess, 2004; American College of Sports Medicine, 2009; Haun et al, 2019b). We demonstrated that progressively higher RT volume (up to 32 sets of 10 repetitions per muscle group per week) reduced the relative abundance (per milligram of dry tissue) of MHC (combined isoforms) and actin (combined isoforms) by ∼30% in vastus lateralis muscle of resistance-trained young men (Haun et al, 2019a). These findings were further validated with actinphalloidin staining, which showed decreases in actin density per muscle fiber with this training style. No study to date has compared the effects of manipulating RT variables on these aforementioned markers
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