An examination of the relationships among myosin heavy chain isoform content, isometric strength, and mechanomyographic median frequency

A noninvasive test for estimating myosin heavy chain of the vastus lateralis in females with mechanomyography

This study examined relationships between percent myosin heavy chain (%MHC) expression and mechanomyographic amplitude (MMG_RMS). Fifteen females (age ± SD=21.3 ± 5.3 yrs) completed isometric trapezoidal contractions at 30% and 70% maximal voluntary contraction (MVC). MMG was recorded from the vastus lateralis (VL). Participants gave a muscle biopsy of the VL post-testing. MMG_RMS-torque relationships during the linearly varying segments were log-transformed and linear regressions were applied to calculate b terms (slopes). For the steady torque segment, MMG_RMS was averaged. Correlations were performed for type I%MHC with the MMG variables. Multiple regression was utilized to examine prediction equations for type I%MHC. Type I%MHC was significantly correlated with the b terms during the increasing segment of the 70% MVC (p = 0.003; r = -0.718), and MMG_RMS during steady torque at 30% (p = 0.008; r = -0.652) and 70% MVC (p = 0.040; r = -0.535). Type I%MHC reduced the linearity of the MMG_RMS-torque relationship during the high-intensity linearly increasing segment, and MMG_RMS at a low- and high-intensity steady torque. A combination of MMG variables estimated type I%MHC expression with 81.2% accuracy. MMG recorded during a low- and high-intensity isometric trapezoidal contraction may offer a simple, noninvasive test for estimating type I%MHC expression of the VL in sedentary females.

Noninvasive Assessment of Skeletal Muscle Myosin Heavy Chain Expression in Trained and Untrained Men

Fry, AC, Housh, TJ, Cramer, JB, Weir, JP, Beck, TW, Schilling, BK, Miller, JD, and Nicoll, JX. Noninvasive assessment of skeletal muscle myosin heavy chain expression in trained and untrained men. J Strength Cond Res 31(9): 2355-2362, 2017-Numerous conditions and types of physical activity (e.g., exercise, aging, and muscle-related diseases) can influence muscle fiber types and the proteins expressed. To date, muscle fibers can only be characterized by actually obtaining a tissue sample using the invasive muscle biopsy procedure. Mechanomyography (MMG) is the assessment of the vibration properties of contracting skeletal muscle and has been proposed as a possible noninvasive method for muscle fiber analysis. Therefore, the purpose of this project was to examine the feasibility of using MMG and muscle performance measures to noninvasively assess muscle fiber characteristics. Fifteen men (5 endurance-trained, 5 weight-trained, and 5 sedentary) provided muscle samples from their vastus lateralis muscle. These samples were analyzed for relative myosin heavy chain (MHC) protein expression, which is highly correlated with % muscle fiber type areas. Additionally, each subject performed several muscle performance tests, and MMG of the quadriceps was assessed during a knee extension exercise. Multiple regression was used to develop prediction equations for determining relative muscle content of MHC types I, IIa, and IIx. A combination of MMG and knee extension performance variables estimated types I, IIa, and IIx MHCs with approximately 80% accuracy. Although preliminary, these data suggest that muscle performance tests in addition to MMG assessments during a simple muscle performance task (knee extension) can be used to estimate muscle fiber type composition in a healthy male population. Such methods could ultimately be used to noninvasively monitor muscle health and fitness.

Mechanomyographic mean power frequency during an isometric trapezoid muscle action at multiple contraction intensities

This study examined the mechanomyographic mean power frequency (MMGMPF)-force relationships for five (age = 19.20   ±   0.45 years) aerobically-trained (AT), five (age = 25   ±   4.53 years) resistance-trained (RT), and five (age = 21.20   ±   2.17 years) sedentary (SED) individuals. Participants performed isometric trapezoidal muscle actions at 50, 60, and 70% maximal voluntary contraction (MVC) of the leg extensors that included linearly increasing, steady force, and linearly decreasing segments. MMG was recorded from the vastus lateralis. Linear regressions were fit to the natural-log transformed MMGMPF versus natural log-transformed force relationships (linearly increasing and decreasing segments) with the b (slope) and a (y-intercept) terms used for comparisons. MMGMPF was averaged for the entire steady force segment. The b and a terms were not different among training statuses (P  >  0.05) or linearly increasing and decreasing segments (P  >  0.05). There were muscle action-related differences in the b terms as a function of training status from the 70% MVC. The SED had greater b terms during the linearly increasing than decreasing muscle action (P = 0.010), and the converse was true for the AT (P = 0.013), whereas the RT displayed no muscle action-related differences (P  >  0.05). The unique muscle action-related differences in the b terms as a function of training status may be the result of unique adaptations to motor unit activation and deactivation strategies.