Variability in skeletal muscle fibre characteristics during repeated muscle biopsy sampling in human vastus lateralis

Abstract

The percutaneous muscle biopsy procedure is an invaluable tool for characterizing skeletal muscle and capillarization. Little is known about methodological or biological variation stemming from the technique in heterogeneous muscle. Five muscle biopsies were taken from the vastus lateralis of a group of young men (n = 29, 22 ± 1 years) over a 96-h period. We investigated the repeatability of fibre distribution, indices of muscle capillarization and perfusion, and myofibre characteristics. No differences between the biopsies were reported in myofibre type distribution, cross-sectional area (CSA), and perimeter. Capillary-to-fibre perimeter exchange index and individual capillary-fibre contacts were unchanged with respect to the location of the muscle biopsy and index of capillarization. The variability in the sampling distribution of fibre type specific muscle CSA increased when fewer than 150 muscle fibres were quantified. Variability in fibre type distribution increased when fewer than 150 muscle fibres were quantified. Myofibre characteristics and indices of capillarization are largely consistent throughout the vastus lateralis when assessed via the skeletal muscle biopsy technique. Novelty Markers of muscle capillarization and perfusion were unchanged across multiple sites of the human vastus lateralis. Myofibre characteristics such as muscle cross-sectional area, perimeter, and fibre type distribution were also unchanged. Variation of muscle CSA was higher when fewer than 150 muscle fibres were quantified.

Vitamin D3supplementation does not enhance the effects of resistance training in older adults

“…prior to introduction to resistance training (Supporting Information, Figure S2). Similar issues have been previously reported for such analyses, 107 although not in all studies 108,109 and are likely exacerbated in older adults, for whom larger spatial heterogeneity are present in muscle fibre characteristics compared with young adults, 110 possibly relating to the age‐related remodeling of motor units 111 . Despite these issues, the data provided sufficient resolution to disclose marked increases in muscle fibre CSA and changes in muscle fibre proportions over the entirety of the training intervention, as previously presented ( Figure 4 and Supporting Information, Figure S1).…”

Individual physiological and mitochondrial responses during 12 weeks of intensified exercise

“…However, neither fiber type composition nor MHC mRNA expression significantly changed with 12‐weeks of HIIT at either the group or individual level. It is recommended that for better accuracy a minimum of 150 fibers to be used for estimation of fiber type proportions (Nederveen et al, 2020 ), and these guidelines were followed whenever possible (i.e., large enough sample) in our study, and the absolutely minimum number of fibers considered was 100. However, even though we were careful to reduce variability within the data whenever possible, it is possible that the large noise to ratio observed by these techniques might have hindered any significant changes in our cohort (Murach et al, 2019 ).…”

“…Fiber type distribution was quantified using Fiji software and values are presented in percentage distribution. We have attempted where possible to keep our fiber counts above 150 as previously suggested (Nederveen et al, 2020 ), and a minimum of 100 fibers was considered the lowest threshold for analyses.…”

No benefits of prolonged vitamin D3 supplementation for adaptations to resistance training in old adults

“…Similar issues have been previously reported for such analyses, 104 though not in all studies. 105,106 Speculatively, older adults (with or without COPD) may display larger spatial heterogeneity in muscle fibre characteristics compared to young adults, possibly relating to the age-related remodeling of motor units. 107 This may have contributed to the high heterogeneity.…”