How many years have you been training and racing hard? I am 41 and have been at it since I was 13 y.o. I have had a similarly inexplicable drop off in performance at the age of 38 (from a 34 min to a 38 min 10 km in a year or so) and an inability to push hard in, or recover from, any hard workout or race. Still not sure why, but I did come across this research:
Skeletal muscle pathology in endurance athletes with
acquired training intolerance
L A Grobler, M Collins, M I Lambert, C Sinclair-Smith, W Derman, A St Clair Gibson, T D Noakes
Background: It is well established that prolonged, exhaustive endurance exercise is capable of inducing
skeletal muscle damage and temporary impairment of muscle function. Although skeletal muscle has a
remarkable capacity for repair and adaptation, this may be limited, ultimately resulting in an accumulation
of chronic skeletal muscle pathology. Case studies have alluded to an association between long term, high
volume endurance training and racing, acquired training intolerance, and chronic skeletal muscle
pathology.
Objective: To systematically compare the skeletal muscle structural and ultrastructural status of endurance
athletes with acquired training intolerance (ATI group) with asymptomatic endurance athletes matched for
age and years of endurance training (CON group).
Methods: Histological and electron microscopic analyses were carried out on a biopsy sample of the
vastus lateralis from 18 ATI and 17 CON endurance athletes. The presence of structural and ultrastructural
disruptions was compared between the two groups of athletes.
Results: Significantly more athletes in the ATI group than in the CON group presented with fibre size
variation (15 v 6; p = 0.006), internal nuclei (9 v 2; p = 0.03), and z disc streaming (6 v 0; p = 0.02).
Conclusions: There is an association between increased skeletal muscle disruptions and acquired training
intolerance in endurance athletes. Further studies are required to determine the nature of this association
and the possible mechanisms involved.
It is well established that prolonged, exhaustive endurance
exercise can induce skeletal muscle damage and temporary
impairment of muscle function.1–10 Although skeletal
muscle has a remarkable capacity for repair and adaptation,
5 6 11–13 research on exercise induced muscle
damage,1 3 4 8 14–16 aging,17–20 and the overtraining syndrome
21 22 suggest that this capacity may be limited.
Under experimental conditions in which the skeletal
muscle is damaged in a controlled manner and the research
subject is forced to rest, allowing the muscle adequate time to
repair and adapt, the regeneration process is complete, and
normal muscle function and morphology are fully
regained.11 23–27 In reality, however, most endurance athletes
train six or seven days a week and often begin training again
within 24–48 hours after a race. This despite evidence that
the repair process after a 42.2 km road race takes 1–10 weeks
to be completed.8 10 Many endurance athletes train and race
in this manner for several years, incurring repeated muscle
damage which requires repair and regeneration. This raises
the question: what are the long term, cumulative effects of
repeated bouts of muscle damaging endurance training and
racing, and potentially incomplete repair, on skeletal muscle
function and morphology?
Case studies suggest an association between long term,
high volume endurance training and racing and chronic
skeletal muscle damage. For example, St Clair Gibson et al16
described a 28 year old international male runner who
experienced a sudden decline in running performance and
an inability to tolerate high training loads. Analysis of a vastus
lateralis biopsy sample revealed a predominance of type I fibres
with no signs of inflammation, necrosis, or excessive regeneration.
The mitochondria, however, were grossly abnormal. In
contrast, a biopsy sample from the triceps muscle of the same
subject showed no signs of abnormality.
Sjo¨stro¨m et al3 studied a previously well trained (10000 km/
year) 46 year old man, who ran a distance of 3529 km in
seven weeks. After the race, signs of neuromuscular pathology
and skeletal muscle ultrastructural abnormalities were
revealed by light microscopic analysis, and the subject’s
running speed continuously decreased. Although no causality
between the ultrastructural abnormalities and running speed
was established, it is tempting to speculate that the decreased
performance resulted from the chronic skeletal muscle
damage and the inability of the muscles to recover fully
from this state of damage/degeneration.
Rowbottom et al28 reported a decrement in performance
capacity of a previously elite ultraendurance male cyclist who
developed chronic fatigue syndrome. Although no skeletal
muscle ultrastructural abnormalities were noted, the case
further supports a possible association between ultraendurance
activity, chronic fatigue, and decreased performance
capacity. Similarly, Derman et al29 described a group of
endurance athletes with exercise associated chronic fatigue.
The clinical condition of these athletes was called ‘‘fatigued
athlete myopathic syndrome’’. The common characteristics
among these athletes were a history of high volume
endurance training and racing, a precipitous decline in
running performance that was not related to ordinary aging,
and an inability to tolerate and adapt to previously
accustomed exercise training loads. The clinical profile of
these athletes was dominated by skeletal muscle symptoms,
including excessive delayed onset muscle soreness and
muscle stiffness, tenderness, and weakness. On investigation,
structural and ultrastructural abnormalities of the skeletal
muscle typical of exercise induced muscle degeneration/
regeneration were noted. The physical symptoms were not
consistent with the acute consequences of overtraining, as, in
most cases, the training loads of the athletes were significantly
reduced, and extensive rest periods did not alleviate
the symptoms, as would occur with overtraining.29 30
No study has systematically examined the impact of
repeated bouts of muscle damage and repair over a number
of years on the structure and function of skeletal muscle.
Accordingly, the aim of this study was to compare the
presence of chronic skeletal muscle structural and ultrastructural
pathology in endurance athletes who presented
with a similar clinical and physiological profile to the subjects
previously defined by Derman et al29—that is, decreased
performance, training intolerance, and exercise associated
chronic fatigue—with asymptomatic endurance athletes
matched for age and years of endurance training.