The occurrence of fibre-type grouping in healthy human muscle: a quantitative study of cross-sections of whole vastus lateralis from men between 15 and 83 years.

Methods that objectively assess the muscle fibre-type arrangement may improve the detection of fibre-type grouping, a diagnostic sign of a denervation and reinnervation process. To distinguish between a diseased and a normal muscle, there is a need for quantitative data on the fibre-type arrangement in healthy human muscles at different ages. In this study, cross-sections were prepared of whole autopsied vastus lateralis muscle from 24 previously physically healthy men, aged 15 to 83 years. The arrangements of type 1 and type 2 fibers were assessed in terms of the number of enclosed fibres in individual fascicles throughout each muscle. Recent improvements to the enclosed fibre method were used to define measures of randomness which facilitated the combination of several sample areas and the quantification of the fibre-type arrangements. Segregation was typical for young muscles, randomness was most common between 30 and 50 years of age, while some fibre-type grouping was considered "normal" in old muscles. The arrangements of type 1 and type 2 fibres were quantitatively similar, irrespective of the age of the individual. The results imply that the fibre population changes considerably during a lifetime, and that it undergoes a continuous denervation and reinnervation process with normal ageing. Because of its importance, age should be accommodated in the analysis of a muscle sample, irrespective of the statistical model and method used.