Skeletal Muscle Fiber Type and Morphology in a Middle-Aged Elite Male Powerlifter Using Anabolic Steroids

Powerlifting regularly exposes athletes to extreme stimuli such as chronic heavy resistance training(HRT),and many powerlifters choose to augment their performance with anabolic-androgenic steroids(AAS).However,little is known about the myocellular adaptations that occur from long-term HRT and AAS use,especially into middle age.We were presented with the unique opportunity to study muscle cells from an elite-level powerlifter(EPL;age 40 years)with≥30 years of HRT experience and≥15 years of AAS use.The purpose of this case study was to identify myocellular characteristics[myosin heavy chain(MHC)fiber type,fiber size,and myonuclear content]in EPL,as well as compare these data to existing litera-ture.The participant underwent a resting vastus lateralis muscle biopsy and single fibers were analyzed for MHC content via SDS-PAGE.A subset of fibers underwent MHC-specific imaging analysis via confocal microscopy to identify cell size(cross-sectional area,CSA)and myonuclear domain(MND)size.MHC fiber type distribution was 9% I,12% I/IIa,79% IIa,and 0% other isoforms.This pure MHC IIa(fast-twitch)fiber content was amongst the highest reported in the literature.Imaging analysis of MHC IIa fibers revealed a mean CSA of 4218±933μm^(2) and MND of 12,548±3181μm^(3).While the fast-twitch fiber CSA was comparable to values in previous literature,mean MND was smaller than has been reported in untrained men,implying greater capacity for growth and repair.These findings showcase the unique muscle cell structure of an elite powerlifter,extending the known physiological limits of human muscle size and strength.

Going nuclear: Molecular adaptations to exercise mediated by myonuclei

Muscle fibers are multinucleated,and muscle fiber nuclei(myonuclei)are believed to be post-mitotic and are typically situated near the periphery of the myofiber.Due to the unique organization of muscle fibers and their nuclei,the cellular and molecular mechanisms regulating myofiber homeostasis in unstressed and stressed conditions(e.g.,exercise)are unique.A key role myonuclei play in regulating muscle during exercise is gene transcription.Only recently have investigators had the capability to identify molecular changes at high resolution exclusively in myonuclei in response to perturbations in vivo.The purpose of this review is to describe how myonuclei modulate their transcriptome,epigenetic status,mobility and shape,and microRNA expression in response to exercise in vivo.Given the relative paucity of high-fidelity information on myonucleus-specific contributions to exercise adaptation,we identify specific gaps in knowledge and provide perspectives on future directions of research.