Sports Medicine: Just the Facts

174 SECTION 3 • MEDICAL PROBLEMS IN THE ATHLETE

•Regarding infectious diseases, the team physician
should have the ultimate authority in return to play
issues (Boschert, 2002).

IMMUNOLOGY AND EXERCISE

• The immune system has two parts, the innate and the
  acquired. The innate, composed of barrier and non-
  barrier elements, is nonspecific regarding host
  defense. The acquired protects the body against spe-
  cific infectious agents.


• The body’s first lines of defense are physical barriers,
  such as the skin and mucous membranes that can be
  impaired by temperature, wind, sun, humidity, and
  trauma (Simon, 1987).


• Airflow patterns, mechanical barriers, ciliary action,
  and mucosal immunoglobulin-A (IgA) activity affect
  airborne respiratory pathogens (Nieman, 1999).
  1.During nasal breathing at rest, viruses are sus-
  pended until they reach the bronchi and bronchioles
  where the mucous barrier, rich in IgA, impedes fur-
  ther invasion (Shephard and Shek, 1999).
  2. During mouth breathing with exercise, there is
  increased deposition of harmful particles in the
  lower respiratory tract, and increased cooling and
  drying of the respiratory mucosa, slowing ciliary
  movement and increasing mucous viscosity
  (Shephard and Shek, 1999).
  3. Depressed IgA levels have been noted in cross-
  country skiers, cyclists, and swimmers (Eichner,
  1993; Nieman, 1999; Brenner, 1984).
  4. There is thus a decreased clearance of infectious
  particles and a theoretically increased infection
  risk (Nieman, 1999; Shephard and Shek, 1999).


• The nonbarrier components to the innate immune
  system include natural killer (NK) cells, phagocytes,
  cytokines, and neutrophils.
  
  
  1. NK counts (Woods, 1999) and natural killer cell
     activity(NKCA) (Nieman, 1999) increase immedi-
     ately after high intensity exercise lasting less than
     1 h,but fall soon after to below preexercise levels
     (Woods et al, 1999). NKCA is elevated chronically
     in elite versus untrained athletes (Nieman, 2000),
     but not with moderate exercise (Woods et al, 1999).
  
  
  2. Acute exercise increases macrophage count and
     function. Chronic exercise attenuates this
     response, but macrophage function is greater than
     in nonathletes (Woods et al, 1999).
     3.Cytokines mediate communication between
     immune and nonimmune cells. Proinflammatory
     cytokines, like tumor necrosis factor-alpha(TNF-
     alpha), interleukin-1 (IL-1), and interleukin-6
     (IL-6), and anti-inflammatory cytokines, like
  
  
  
  

interleukin-10 and IL-1 receptor antagonist,

increase with acute exercise (Moldoveanu,

Shephard, and Shek, 2001).

4. Neutrophil counts increase with acute intense exer-
   cise, and several hours later. Long-term moderate
   exercise seems to elicit an increase in neutrophil
   activity, but chronic intense exercise seems to sup-
   press it (Woods et al, 1999; Pyne, 1991).

• The acquired immune system, mainly T- and B-lym-
  phocytes and plasma cell-secreted antibodies, attacks
  specific foreign particles that invade the body
  (Goodman, 1991). Overall lymphocyte counts increase
  with any type of acute exercise. Lymphocyte counts and
  B-cell function are decreased after intense exercise but
  not after moderate exercise (Pedersen and Toft, 2000).


• Antibody production, notably IgA, is affected by exer-
  cise. Cross-country skiers and cyclists have low base-
  line salivary IgA levels that drop after racing (Eichner,
  1993; Nieman, 1999; Brenner, 1984; Pedersen et al,
  1996). Longitudinal studies of salivary IgA in elite
  swimmers, however, have reported increases
  (Bruunsgaard et al, 1997), decreases (Gleeson et al,
  1999), and no change with training (MacKinnon and
  Hooper, 1994).


• Among T-lymphocytes are CD4 (T-helper) and CD8
  (T-suppressor) cells. A CD4/CD8 ratio of >1.5 is con-
  sidered necessary for proper immune function.
  Intense exercise decreases CD4 and increases CD8
  counts, decreasing the CD4/CD8 ratio. In one study
  (Bruunsgaard et al, 1997), male triathletes showed
  diminished skin test measures of cellular immunity 48 h
  after a half-ironman triathlon compared to noncom-
  peting triathletes and recreational athletes.


• The brief period of immunosuppression after acute,
  intense physical activity when ciliary action, IgA
  levels, NK count, NKCA, T-lymphocyte count, and
  CD4/CD8 ratio are decreased has been described as
  the immunologic “open window” when infectious
  organisms are theoretically more likely to invade the
  host and cause an infection (Nieman, 1999; Shephard
  and Shek, 1999; Brenner, 1984; Pedersen et al,
  1996).

INFECTIONS AND EXERCISE

• Marathon runners have a higher incidence of self-
  reported upper respiratory tract infections(URI’s) after
  competition (Peters and Bateman, 1983; Nieman et al,
  1990 a). URI incidence was higher with increased
  training volume. Danish elite orienteers have increased
  incidence of URI comparedto controls (Linde, 1987).


• Studies of moderate physical activity, however, have
  had variable results.