Sports Medicine: Just the Facts

186 SECTION 3 • MEDICAL PROBLEMS IN THE ATHLETE

2. Catecholamines are the prime regulator of glucose
   production (Kriesman et al, 2001; 2002).

• Resistance exercise: On completion of 5 sets of 10
  knee extensions at 40% RM load followed by 2 sets to
  exhaustion:

1. Norepinephrine increased in women, men, and in
   pubescent boys postsubmax exercise and at max
   exercise.


2. Epinephrine increased significantly post submax
   exercise in woman, and significantly in all groups
   after maximal exercise.


3. Woman and boys had twice the values when com-
   pared to preexercise levels (Pullinen et al, 2002).

• Chronic exercise: Training dampened catecholamine
  response in mild to moderate exercise (lower sympa-
  thetic stimulation).

1. During hard to maximal exercise trained individu-
   als experienced increased catecholamines when
   compared to untrained individuals.
   2.Exercise at 60% VO2max caused only slight
   increases; whereas, exercise at 100% VO2max
   resulted in exaggerated epinephrine/norepineph-
   rine levels.


2. Hundred and ten percent VO2maxsprint caused fur-
   ther increases (Kjaer et al, 1986).
   •Training 6 days a week (7 weeks) progressively
   decreased catecholamines in men over the training
   period.


3. The most rapid decrease was found early in the
   training (Winder et al, 1968).
   2.When comparing endurance trained with
   untrained, the trained subjects have higher epi-
   nephrine secretion capacity at identical intensities:
   “sports adrenal medulla” (Kjaer, M., 1998).

THYROIDHORMONE ANDEXERCISE

• Endurance exercise: Twenty weeks of endurance
  training resulted decreased free T3 levels versus base-
  line by the 5th week (6.2%) and 10th week (7.9%).
  
  
  1. Values returned toward baseline levels as they
     approached 20th week.
  
  
  2. TSH levels followed the same pattern.
  
  
  3. Decreased TSH may indicate reduced hypothala-
     mic drive (Baylor and Hackney, 2002).
     
     
     • Six months of intensive training (rowing), resulted in
       a decrease in thyroid volume which was correlated
       with a decrease in LBM (Wesche et al, 2001).
     
     
     • Resistance exercise: In eight trained weight lifters
       performing three sets of six exercises to exhaustion:
       
       
       1. T3 levels were unchanged immediately after exer-
          cise and during nocturnal measurements.
       
       
       2. T4 levels were increased for the 1st 20-min period
          postexercise but lowered at the nocturnal measure-
          ment when compared to the control (no exercise)
          period may suggest nocturnal muscle anabolism
          (McMurray et al, 1995).
          •Twelve hours after an anaerobic exercise session there
          was a decrease in T4:T3; free T4, free T3 did not
          change with aerobic, anaerobic immediate post meas-
          urements (Umschied, 1998).
       
       
       
       
     
     
     • Chronic exercise: Highly trained rowers performed 3
       weeks of high intensity resistance training followed
       by 3 weeks of endurance training with 1 week of
       recovery in between each.
       
       
       • Resistance training resulted in a significant decrease
         in TSH and free T3 (free T4 unchanged).
       
       
       • Endurance training resulted in a significant increase
         in TSH and patterns of increasing values in free T3
         and T4 (nonsignificant).
       
       
       • Changes were independent of body fat suggesting
         that high intensity exercise may decrease the hypo-
         thalamic-thyroid-axis (Simsch et al, 2001).
         •Physically active men had significantly higher T3
         levels than sedentary men; whereas, TSH values were
         significantly lower than their sedentary counterparts
         (Ravaglia et al, 2001).
       
       
       
       
     
     
     
     
  
  
  
  

PANCREATICHORMONES ANDEXERCISE

A. Insulin

• Endurance exercise:Blood glucose levels will likely
  decrease as activity continues.
  
  
  • Insulin is, in part, suppressed by epinephrine thus
    increasing hepatic glucose release.
  
  
  
  


• Intense exercise (80% VO2max) resulted in an approxi-
  mate eightfold increase in glucose production and
  only a fourfold increase in uptake.
  
  
  • Insulin did not change significantly and glucagon
    increased less than twofold (Kreisman et al, 2003).
  
  
  
  

TABLE 32-5 Thyroid Hormones

GLAND HORMONE CONTROL ACTION ENDURANCE RESISTANCE CHRONIC

Thyroid Thyroxine (T4) Hypothalamus; Stimulate metabolic Increased;intensity Conflicting Decrease total T3;
Triiodothyronine TRH; TSH rate; calorigenic, fuel dependent increased free T3
(T3) metabolism, at rest; increased
sympathomimetic turnover without
hyperthyroidism