Exercise has an established ability to alter human
physiological systems. However to this time much of the
research in this area, and particularly that in
relation to the human immune system, has focused on
exercise that has required predominantly aerobic
metabolism. Little research has been carried out into
the physiological effects of intense interval exercise,
commonly used as a training regime by athletes in
sports such as track & field, ball sports and swimming.
This study investigated the effects of intense interval
running on selected physiological parameters, with
special reference to the immune system and the function
of neutrophils.
Trained male subjects performed intense interval
running protocols both in the laboratory and on a 400
metre running track. The protocols required significant
anaerobic energy production as indicated by the
elevated post-exercise whole blood lactate
concentrations of 7.6 mmol.L-1 and 14.0 to 16.0
mmol.L -1 relating to the laboratory and "track" running
protocols, respectively.
Intense interval exercise induced a series of
biochemical and morphological changes consistent with
the multi-faceted activation of neutrophils. Such activation in vivo may have important implications for
both tissue damage induced during, and immunocompetence
immediately after, intense interval exercise.
A single session of intense interval exercise produced
significant perturbation of other physiological systems
known to be capable of .altering immune function. This
was manifested as a significant elevation in the plasma
concentrations of several hormones, minor fluctuations
in plasma cytokines concentrations and iron status
parameters as well as a characteristic pattern of
leucocyte mobilisation.
After exercise neutrophils displayed phenotypic changes
characteristic of activation in vivo. The plasma
concentration of elastase (derived from the primary
granules of neutrophils) was elevated significantly at
1 hr post-exercise (p<O.OS), while the expression of
complement receptor 3 (:::R3;CD11b/CD18), a ts2-integrin
stored intracellularly in association with the
secondary granules, was increased significantly after
exercise (p<0.01). These changes imply that
degranulation of neutrophils in vivo was induced by
intense interval exercise. Neutrophil expression of
LECAM-1, a member of the selectin "family" of cell
adhesion molecules, was significantly decreased after
exercise (p<0.01). Neutrophils isolated after exercise showed a reduced
ability to generate ROS when stimulated in vitro with
phorbol myristate acetate (PMA) and opsonized zymosan
(OZ), as assessed by both reduction of ferricytochrome
c and by luminol-enhanced chemiluminescence,
respectively (both p<O.OS). A key component of the
neutrophil's NADPH-oxidase system, p47-phox,
translocated to the plasma membrane during exercise.
The reduced ability of neutrophils isolated after
intense interval exercise to generate ROS appears to
constitute a post-exercise "refractory" period and be
secondary to both assembly and activation of the
NADPH-oxidase system during exercise. Increased plasma
concentrations of immunosuppressive hormones cortisol
and epinephrine during and after intense interval
exercise may accentuate the post-exercise refractory
period induced after this form of exercise.
Our findings indicate that intense interval exercise
induced a multi-faceted activation of neutrophils in
vivo and imply that both the increased susceptibility
of athletes to infection during and after periods of
intense competition and training, and tissue damage
induced by exercise may be due to activation of
neutrophils in vivo during exercise