Dataset DOI: 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: mm²

·       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:
perimeter² / (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.