Presentation Title

Disagreement Between Two Popular Methods for Assessing Human Skeletal Muscle Fiber Type

Faculty Mentor

Andrew Galpin

Start Date

17-11-2018 12:30 PM

End Date

17-11-2018 2:30 PM

Location

HARBESON 60

Session

POSTER 2

Type of Presentation

Poster

Subject Area

health_nutrition_clinical_science

Abstract

Introduction: Human skeletal muscle expresses multiple fiber types that exist across a spectrum from slow- to fast-twitch. The amount of each fiber type (FT%) present in a muscle greatly influences its function. A common approach is to homogenize (HG) samples and assess relative expression of the three myosin heavy chain (MHC) isoforms (I, IIa, & IIx). Alternatively, isolation of single fibers (SF) for distribution allows resolution of the pure and “hybrid” (I/IIa, IIa/IIx, I/IIa/IIx) fiber types. No study to date have directly compared the two approaches (HG vs. SF). Purpose: Compare two common methods of assessing FT% in human skeletal muscle. Methods: Resting vastus lateralis biopsies were performed on 21 highly resistance-trained participants (15 women, 6 men; age = 26±2 y, height = 166±9 cm, body mass = 76±25 kg). Each sample was partitioned into ~10 mg section and stored in solution at -20°C for at least seven days before being analyzed for MHC content via SDS-PAGE. HG samples were diluted between 1:20 and 1:100 while SF samples (N = 2,147; 102 ± 3 fibers per person) were mechanically isolated. All other conditions (gel density, running time, staining methods, etc.) were similar between HG and SF. Results: HG overestimated MHC I (23±9 vs. 31±9%, p=0.005) and IIx (0±0 vs. 3±6%, p=0.046) distribution. HG likely misclassified MHC IIa/IIx fibers as IIx as the two were highly correlated (r=0.96, p<0.001). The heaviest five participants accounted for 91% of the MHC IIa/IIx fibers, thus body mass was also correlated to IIa/IIx content for both the women (r=0.46, p=0.04) and men (r=0.76, p=0.080). Conclusion: These data 1) highlight the rarity of pure MHC IIx fibers in healthy men and women, 2) indicate a potential link between IIa/IIx frequency and body mass, and 3) question the fidelity of HG as a measure of FT% distribution.

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Nov 17th, 12:30 PM Nov 17th, 2:30 PM

Disagreement Between Two Popular Methods for Assessing Human Skeletal Muscle Fiber Type

HARBESON 60

Introduction: Human skeletal muscle expresses multiple fiber types that exist across a spectrum from slow- to fast-twitch. The amount of each fiber type (FT%) present in a muscle greatly influences its function. A common approach is to homogenize (HG) samples and assess relative expression of the three myosin heavy chain (MHC) isoforms (I, IIa, & IIx). Alternatively, isolation of single fibers (SF) for distribution allows resolution of the pure and “hybrid” (I/IIa, IIa/IIx, I/IIa/IIx) fiber types. No study to date have directly compared the two approaches (HG vs. SF). Purpose: Compare two common methods of assessing FT% in human skeletal muscle. Methods: Resting vastus lateralis biopsies were performed on 21 highly resistance-trained participants (15 women, 6 men; age = 26±2 y, height = 166±9 cm, body mass = 76±25 kg). Each sample was partitioned into ~10 mg section and stored in solution at -20°C for at least seven days before being analyzed for MHC content via SDS-PAGE. HG samples were diluted between 1:20 and 1:100 while SF samples (N = 2,147; 102 ± 3 fibers per person) were mechanically isolated. All other conditions (gel density, running time, staining methods, etc.) were similar between HG and SF. Results: HG overestimated MHC I (23±9 vs. 31±9%, p=0.005) and IIx (0±0 vs. 3±6%, p=0.046) distribution. HG likely misclassified MHC IIa/IIx fibers as IIx as the two were highly correlated (r=0.96, p<0.001). The heaviest five participants accounted for 91% of the MHC IIa/IIx fibers, thus body mass was also correlated to IIa/IIx content for both the women (r=0.46, p=0.04) and men (r=0.76, p=0.080). Conclusion: These data 1) highlight the rarity of pure MHC IIx fibers in healthy men and women, 2) indicate a potential link between IIa/IIx frequency and body mass, and 3) question the fidelity of HG as a measure of FT% distribution.