CHAPTER 31 • INFECTIOUS DISEASE AND THE ATHLETE 175- High levels of self-reported exercise, occupational,
and leisure time activities were associated with a
20–30% decrease in the annual incidence of URI
in healthy, nonathletic, and middle-aged adults
(Matthews et al, 2002). - A similar study of healthy, elderly people noted an
inverse relationship between the amount of energy
expended in daily moderate activities and URI
incidence (Kostka, 2000). - Runners in short races (5K, 10K, half-marathon)
had no increased incidence of infection after the
race compared to before. Training more than 15 mi
a week showed a nonsignificant trend towards
fewer infections (Nieman, Johanssen and Lee,
1989). Another study (Heath et al, 1991), however,
found running 16–26 mi a week increased the risk
of having ≥1 URI compared to running <9 mi a
week. Running 9–16 mi or >26 mi a week con-
ferred intermediate risk.
EXERCISE, IMMUNOLOGY,
AND INFECTION
- In premenopausal women, no exercise or a 15-week
walking program made no difference in NK cell
counts. NKCA was significantly increased in the
training group at 6 weeks, but was elevated equally in
both groups at 15 weeks. The training group reported
50% fewer days with URI symptoms, but the same
number of separate URIs compared to controls.
NKCA at 6 weeks was negatively correlated with URI
symptom days (Nieman et al, 1990b).
•A similar study (Nieman et al, 1993) of sedentary, eld-
erly women found no significant difference in lympho-
cyte counts, T-cell counts, and NKCA. The exercise
group, however, had significantly fewer URIs than the
control group (3/14 vs. 8/16). A comparison group of
elite elderly athletes had significantly higher NKCA
and lymphocyte activity and even fewer URIs (1/12). - NK counts (Gleeson et al, 2000) and resting neutrophil
oxidative burst capacity (a measure of neutrophil activ-
ity) (Pyne et al, 1995) decreased in 22 elite swimmers
during a 12-week training cycle but were not correlated
with the risk of URI.
•A study (Nieman et al, 2000) of elite female rowers
and sedentary controls found no difference in base-
line measures of granulocyte/monocyte phagocytosis,
neutrophil oxidative burst capacity, and concentra-
tions of IL-6, TNF-alpha, and IL-1ra. NKCA and
lymphocyte proliferative response were significantly
higher in the rowers. Days of self-reported URI
symptoms, however, were similar in both groups and
did not correlate with immunologic changes.- Gleeson (Gleeson et al, 1999) found an inverse corre-
lation between pretraining salivary IgA levels and risk
of infection in elite swimmers and controls, and pre-
dicted an additional infection for each 10% drop in
IgA. Swimmers and controls had equal incidence of
infections, however. A follow-up study (Gleeson et al,
2000) showed no correlation between salivary IgA
levels and infection risk. - Three 30-s Wingate leg cycling tests over 9 min
decreased salivary IgA an average of 27.8% in healthy
adult females, but without an increased incidence of
URI (Fahlman et al, 2001). - Klentrou et al (Klentrou et al, 2002) studied 19 seden-
tary men and women randomized to no exercise or
exercise for 12 weeks. There was a negative correlation
between salivary IgA levels and number of days of ill-
ness and flu symptoms, but not days of cold symptoms. - Studies of immune marker changes with exercise have
failed to show consistent correlation with risk of
infection (Nieman, 2002).
•A popular theory regarding exercise intensity and
infection risk is the “J-curve” proposed by Nieman
(Fig. 31-1). Moderate exercise lowers infection risk
to below that of being sedentary, while strenuous
exercise imposes the highest risk of all (Nieman,
2002). - More evidence is needed, however, as the link
between moderate exercise and infection is less clear
(Shephard and Shek, 1999). Most studies of infection
and exercise are relatively small and rely on patient
recall and self-reporting for diagnosis. Also, other fac-
tors such as pathogen exposure, stress, sleep, nutri-
tion, and environment may play a confounding role
(Shephard and Shek, 1999).
- Gleeson (Gleeson et al, 1999) found an inverse corre-
FIG. 31-1 “J” curve of exercise and susceptibility to infection.