Sports Medicine: Just the Facts

CHAPTER 32 • ENDOCRINE CONSIDERATIONS 189

•Various studies have shown that short-term maximal
exercise results in increased testosterone levels in men
(Hackney AC, 2001).

• Consitt et al (2001) showed increased levels of testos-
  terone in woman who performed 40 min of cycling at
  75% maximum heart rate(MHR) when compared to
  resting controls:
  •Testosterone did not change with three sets of eight
  exercises at 10 RM.
  •Exercise that consists of moderate to hard exercise to
  exhaustion (>2 h) resulted in lowered testosterone
  levels in men (Hackney AC, 2001).


• Resistance exercise: Most research investigating the
  relationship between testosterone and short-term
  resistance training in women have found no significant
  changes even with measurable muscle gains (Consitt
  et al, 2002).
  •Effects of acute resistance exercise and 8 weeks of
  resistance training were measured at pre-ex, immediate
  postexercise:
  
  
  • During the 1st week, 6 weeks, and 8 weeks, testos-
    terone was significantly higher in men at all meas-
    urement points (Kraemer et al, 1998).
  
  
  
  


• Chronic exercise: Decreased testosterone levels were
  found in women after 3 months of endurance training.
  
  
  • This finding was only apparent in the luteal phase
    (Keizer et al 110).
  
  
  
  


• Many studies have shown that testosterone levels of
  endurance-trained men were 60–85% the levels
  (lower) of untrained counterparts (Hackney and Dolny,
  1988; Hackney and Fahrner, 1997; Gulledge et al,
  1996).


• Baseline testosterone levels and testosterone produc-
  tion rates were significantly lower in endurance trained
  men when compared to sedentary counterparts.
  •Blunted values may help the endurance athlete avoid
  excessive muscle mass which could overwhelm
  oxygen delivery during prolonged exercise (Hackney
  et al, 2002).

Type 1 Diabetes and Exercise
•Physiologic adaptations result within the exercising
muscle, energy needs, and regulatory hormones.

• Increased dependence on hepatic glycogenolysis,
  FFAs, blood-borne glucose.
  
  
  • Catecholamines become primary regulators of glu-
    cose as insulin levels decrease with exercise.
  
  
  • Insulin may be needed to regulate ketone production;
    without insulin, exercise-induced increases in glucagon/
    catecholamines will result in increased ketone pro-
    duction.
  
  
  • Normoglycemic athletes: During exercise, use of
    oxygen, muscle and liver glycogen, triglycerides, and
    FFAs increase in exercising muscles. This increased
    mobilization of substrates results from enhanced epi-
    nephrine, glucagon, cortisol, and growth hormone
    action. In addition, the counterregulatory function of
    insulin allows for stable blood glucose regulation
    (Drazin and Patel, 1998).
  
  
  • Plasma insulin decrease with exercise.
  
  
  • Glucagon/catecholamines promote increased hepatic
    glucose production to match the level of glucose
    usage.
  
  
  • Increased insulin sensitivity postexercise, muscle, and
    hepatic glycogen restoration.
  
  
  • Athletes with type 1 diabetes:Plasma insulin levels
    may not decrease during exercise.
  
  
  • Insulin-stimulated glucose uptake may be blunted.
  
  
  • Dependent on injection site, insulin could increase
    with exercise.
  
  
  • Relies more on gluconeogenesis than hepatic glyco-
    genolysis to maintain blood glucose levels.
  
  
  • Glucose production >glucose clearance; less glucose
    oxidation
  
  
  • Increased lipolysis can result in ketogenesis.
  
  
  • Increased risk of hypoglycemia hours after exercise,
    increased insulin sensitivity, decreased levels of
    glycogen stores, and injection site.
  
  
  • Hyperglycemia can result from poor control; insulin
    deficiency can lead to decreased glucose uptake,
    increased lipolysis, and therefore ketogenesis; and
    insulin coma.
    •Benefits of regular exercise
    
    
    1. Cardiorespiratory and muscular fitness
    
    
    2. Improved insulin sensitivity
    
    
    3. Improved vascular endothelial function
    
    
    4. Improved lipid profiles, blood pressure (BP), and
       body fat percentage
    
    
    5. Enhanced quality of life: social, self-confidence,
       and the like.
    
    
    
    
  
  
  
  

TABLE 32-9 Hormones of the Testes

GLAND HORMONE CONTROL ACTION ENDURANCE RESISTANCE CHRONIC

Testes Testosterone LH, FSH Anabolic; protein Increased;intensity and Increased; Resting levels
synthesis; androgenic duration related; may be conflicting may be lower in
influence by decrease in findings in endurance trained
metabolic clearance rate women
(decreased hepatic blood
flow)