Muscle damage
A recent doctorate thesis at the Norwegian School of Sport Sciences shows that eccentric muscle activity (whereby muscles act as ‘brakes’) can result in inflammation with an accumulation of white blood cells in the muscle.
| 19.06.2009 
Gøran Paulsen, Photo: Torunn Gjerustad
Strenuous muscle activity can result in inflammation of the muscles.
Eccentric muscle activity (whereby muscles act as ‘brakes’) can result in inflammation with an accumulation of white blood cells in the muscle.
Since such inflammatory reaction is frequently very much exaggerated, it has been speculated whether inflammatory reaction in the muscle following use of the muscle actually increases the extent of damage and thereby delaying the restitution process.
Muscle damage and the accumulation of white blood cells (red in colour) around and in the muscle fibre (indicated by the green membrane colour; cell nuclei are coloured blue).
However, observation indicates that an inflammatory reaction primarily arises when parts of the muscle fibre die. This results in an accumulation of white blood cells which are drawn to area so as to repair the damage.
This concentration of white blood cells thus appears to be a consequence of comprehensive muscle damage rather than the cause.
Not due to inflammation
Tender and sore muscles are frequently encountered following abnormal muscular activity, particularly when the muscle is employed as a ‘brake’.
– It has been suggested that muscle stiffness is the result of muscle damage and a subsequent inflammation reaction in the muscle, but our findings contradict this, says Gøran Paulsen.
The degree of muscle stiffness following training varies considerably from one individual to the next, and does not appear to provide reliable information on how the muscle is restored.
Protects the muscle fibres
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Muscle fibres, which comprise the skeletal muscles, have an inner cell skeleton of structural proteins which are used in transferring muscular power (the cytoskeleton).
During strenuous muscular activity such as heavy body-building, the inner cell skeleton is challenged, with a risk of damage. In order to prevent this, the muscle fibres contain special proteins – stress proteins (or ‘heat shock proteins’) which can attach themselves to the inner cell skeleton in order to stabilise and protect this. |
The red-yellow colour indicates the accumulation of stress proteins in parts of a muscle fibre where damage has occurred during activity. |
– We have seen how some of these stress proteins react during and following eccentric muscle work. The aim of the project was to gain a better insight into muscular restitution process, Gøran Paulsen explains.
The objective of the project ‘Restitution following muscular work with strong power development’ was to improve our understanding of processes commencing and following muscular activity with considerable power development (for example body building), and new knowledge of how the skeletal muscles undergo restitution and adapt themselves to strenuous physical activity.
– In order to study this, we chose to subject a number of trial subjects to muscular activity where the muscles (knee and arm flexors) worked exclusively as ‘brakes’ (eccentric muscle activity). Purely eccentric muscle activity with maximum activation is particularly demanding and results in a strong reduction of the muscular function (maximum strength) and a restitution period lasting from days to weeks.
The aim was to follow the restitution process throughout several days simultaneous to taking samples (biopsies) of the muscles in order to study the underlying cell processes Gøran Paulsen concludes.
Background
Gøran Paulsen defended his dissertation ‘Exercise-induced muscle damage in humans: Heat shock proteins and inflammation in recovery, regeneration, and adaptation’ for the degree of PhD at the Department of Physical Performance at the Norwegian College of Sport Science on 16 June, 2009.