DOI: 10.5061/dryad.9p8cz8wwr
title: Capillary differences with age and fiber type are attenuated by accounting for fiber shape

description: This dataset contains quantitative measurements of skeletal muscle fiber
 morphology and capillarization in young and older women. Muscle biopsies
 were obtained from both a rested leg and a leg that had performed a single
 bout of heavy resistance exercise five days prior to sampling. Variables
 include muscle fiber cross-sectional area, perimeter, and Shape Factor
 Index (SFI), as well as multiple indices of capillarization, including
 capillary density, capillary-to-fiber ratio, individual capillary-to-fiber
 ratio, and morphology-adjusted capillarization metrics. The dataset
 enables analysis of age-, fiber type-, and condition-related differences
 in muscle fiber geometry and capillary supply.
description: # Capillary differences with age and fiber type are attenuated by
 accounting for fiber shape Dataset DOI:
 [10.5061/dryad.9p8cz8wwr](10.5061/dryad.9p8cz8wwr) ## Description of the
 data and file structure This dataset derives from a study of skeletal
 muscle capillarization in young and older women. Muscle biopsies were
 collected from both legs of each participant. One leg performed a single
 bout of heavy resistance exercise five days prior to sampling (Exercised
 leg), while the contralateral leg served as the rested control (Rested
 leg). Each sample is identified by a unique alphanumeric sample ID
 corresponding to participant and leg. Muscle biopsies were embedded,
 frozen, cryosectioned, and immunohistochemically stained for type I myosin
 heavy chain (fiber type identification), laminin (fiber borders), and CD31
 (capillaries). From these sections, muscle fiber cross-sectional area,
 perimeter, and the derived Shape Factor Index (SFI) were quantified.
 Capillarization was evaluated using several established and
 morphology-adjusted indices. All data are provided in a single spreadsheet
 file (Dryad-Data-Deposition.xlsx) with two sheets, described below:
 **Sheet: “CD+CF”** This sheet contains whole-section capillarization
 metrics quantified at the sample level (i.e., not fiber type–specific).
 **Variables:** ·       **A: Sample ID**\ Unique identifier for each biopsy
 sample (participant × leg). ·       **B: Age group**\ Categorical variable
 indicating participant age group (Young or Old). ·       **C: Leg**\
 Experimental condition of the leg (Rested or Exercised). ·       **D:
 Total tissue area quantified**\ Total analyzed tissue area per sample.\
 *Unit: mm^2^* ·       **E: Total number of myofibers**\ Total number of
 muscle fibers counted within the analyzed area. ·       **F: Total number
 of capillaries**\ Total number of capillaries identified within the
 analyzed area. ·       **G: Capillary density (CD)**\ Number of
 capillaries per unit tissue area.\ *Unit: capillaries/mm²* ·       **H:
 Capillary-to-fiber ratio (C:F)**\ Average number of capillaries per muscle
 fiber. 
 
 **Sheet: “CSA+Per+SFI+CAF+CFi”** This sheet contains fiber type–specific
 and mixed-fiber capillarization and morphology metrics. Values represent
 averages derived from approximately 25 fibers per fiber type per sample.
 **Variables:** ·       **A: Sample ID**\ Unique identifier for each biopsy
 sample. ·       **B: Age group**\ Categorical variable indicating
 participant age group (Young or Old). ·       **C: Leg**\ Experimental
 condition of the leg (Rested or Exercised). ·       **D: Fiber type**\
 Categorical variable indicating fiber type: o   Type I (MyHC I positive)
 o   Type II (MyHC I negative) o   Mixed (average of Type I and Type II
 fibers) ·       **E: Cross-sectional area (CSA)**\ Average muscle fiber
 cross-sectional area.\ *Unit: µm²* ·       **F: Fiber perimeter**\ Average
 muscle fiber perimeter.\ *Unit: µm* ·       **G: Shape Factor Index
 (SFI)**\ Dimensionless geometric index describing fiber shape
 irregularity, calculated as:\ perimeter^2^ / (4π × CSA) ·       **H:
 Capillaries around fiber (CAF)**\ Average number of capillaries in direct
 contact with each muscle fiber. ·       **I: Individual capillary-to-fiber
 ratio (C:Fi)**\ Average number of capillaries per muscle fiber, adjusted
 for capillary sharing between adjacent fibers. ·       **J:
 Capillary-to-fiber perimeter exchange index (CFPE)**\ C:Fi normalized to
 muscle fiber perimeter. ·       **K: Capillary-to-fiber cross-sectional
 area exchange index (CFCE)**\ C:Fi normalized to muscle fiber
 cross-sectional area. ·       **L: Shape-adjusted CFPE
 (CFPE_SFI-adjusted)**\ CFPE multiplied by SFI to account for differences
 in muscle fiber geometry. ## Human subjects data All participants provided
 explicit written consent for their data to be made publicly available in
 de-identified form. Prior to sharing, all direct identifiers were removed.
 The resulting dataset contains no information that could be used to
 re-identify individuals.