No ageing-related increase in fibre type grouping in sprint-trained masters runners: A 10-year follow-up study

Abstract

Background: Previous research suggests that an ageing-associated remodelling and loss of motor units due to motor neuron death contributes significantly to muscle weakness in old age. In histological sections, motor unit remodelling is reflected by increased fibre type grouping. While regular exercise may not attenuate the loss of motor units during ageing, it has been suggested to facilitate reinnervation resulting in larger motor units, and a higher number and larger fibre type groups in histological sections of muscles from aged individuals.

Methods: In a 10-year follow-up study, we assessed changes in the prevalence and size of fibre type groups in the vastus lateralis muscle from 34 male masters sprinters (40-85 years at start).

Results: Over the 10 years, there was an ageing-related reduction in performance in the 60-m sprint (P < 0.001) without significant changes in fibre type composition and fibre cross-sectional area. Neither the number of fibre type groups, defined as a fibre surrounded exclusively by fibres of the same type, nor the group size changed significantly in the 10-year period.

Conclusions: These histological data show that there is limited to no significant fibre type grouping over a 10-year period in masters athletes who continued sprint run training. This observation challenges the paradigm that ageing, at least in systematically trained sprinters, is associated with motor unit remodelling.

Keywords: ageing; longitudinal study; masters athlete; motor unit.

Figure 1

Examples of m. vastus lateralis biopsy cross sections obtained from a participant in (A) 2002 (54‐year‐old) and (B) 2012 (63‐year‐old) and stained for myosin ATPase after pre‐incubation at pH 4.30. Type I fibres were stained black, and type II fibres were stained light. *An enclosed type I fibre. Scale bar = 50 μm. (C) Proportion of type I fibres in 2002 (○) and 2012 (●).

Figure 2

Correlation between 60‐m performance with (A) training hours per week, (B) years of competitive training and (C) age in 2002 (○) and 2012 (●). The outlier is the 85‐year‐old (in 2012, 95‐year‐old) person, but in Panel (C), his data point corresponds with the expected exponential age‐related decline in performance.

Figure 3

Relationship between age and fibre cross‐sectional area (FCSA) of (A) type I and (B) type II fibres, and standard deviation of the fibre cross‐sectional area (SD FCSA) fibres of (C) type I and (D) type II fibres in the vastus lateralis muscle of masters athletes in 2002 (○) and 2012 (●) (n = 34).

Figure 4

Relationship between observed fibre type grouping (A) with age and (B) expected fibre type grouping in the vastus lateralis muscle of masters athletes in 2002 (○) and 2012 (●) (n = 34). The regression lines for observed versus expected grouping in 2002 (solid line) and 2012 (dashed line) are similar.

Figure 5

(A) Fibre group size and (B) number of fibre groups per 1000 fibres in the vastus lateralis muscle of masters athletes in 2002 (○) and 2012 (●) (n = 34).

Figure 6

Relationship between age and shape factor of all pooled fibres in masters athletes in 2002 (○) and 2012 (●) (n = 34).