CHAPTER 32 • ENDOCRINE CONSIDERATIONS 187•With intense exercise (>80% VO2max) it appears that
catecholamines, not insulin, become the major regula-
tors of glucose homeostasis during and immediately
after a single bout.
- Insulin regains control during recovery and insulin
levels rise (Marliss et al 2002). - During moderate exercise, glucagon and insulin appear
to be the main regulators of glucose production. - Prolonged (>2 h) increases the role of catecholamines
in glucose production (Richter et al 1995). - Increased glucagon and decreased insulin result in
hepatic glycogenolysis and gluconeogenesis. - High levels of catecholamines (high intense exercise)
can prevent glucose stimulation of insulin release
(Marliss et al, 2000). - Insulin levels will increase during recovery because of
immediate decrease in catecholamines aiding in the
replacement of muscle glycogen. - Resistance exercise:Progressive resistance training
has been shown to improve insulin sensitivity and glu-
cose tolerance (Willey and Singh, 2003). - An acute single resistance bout decreased total insulin
response to an oral glucose tolerance test. - In nine subjects with type 2 diabetes, insulin sensitiv-
ity improved by 48% after 4–6 weeks of moderate
intensity resistance training. - Resistance trained rats performed three sets of 10 rep-
etitions at 75% 1-RM, 3 days/week for 1–12 weeks:
- Increased rates of glucose transport were found in
exercise specific muscles. - Resistance exercise may improve insulin’s effect
on glucose uptake and transport in muscles
recruited for exercise (Yaspelkis et al, 2002).
- Chronic exercise: In trained individuals, insulin did
not fall as much as their untrained counterparts. - Blunted decrease may be a result of increased sensi-
tivity to insulin or normoglycemia in trained individ-
uals, increased dependence on free fatty acids(FFA)
(Gyntelberg et al,1977). - An increased number of insulin receptors are found in
trained individuals when compared to untrained coun-
terparts; increased insulin sensitivity continues up to
24 h following exercise (Landry and Allen, 1992).
B. Glucagon- Endurance exercise:Unchanged or increased gluca-
gon levels and decreased insulin increased glucose
production with moderate exercise (Wasserman et al,
1989). - Glucagon: Insulin is the main regulator in glucose
production with moderate exercise. - As exercise increases in duration, glucagon secretion
increases hepatic glucose production. - Resistance exercise:College men participated in a
10-week progressive resistance training program:- No significant change in glucagon was found in a
3-h oral glucose tolerance test following the inter-
vention.
- No significant change in glucagon was found in a
- Chronic exercise:Blunted response may result with
training.
PARATHYROIDHORMONE ANDEXERCISE
A. Parathyroid- Endurance exercise:When examining the effect of a
recovery period between (40 min) two periods of
exercise (2 ×21 min at 70–85% VO2max) versus two
successive exercise sessions with no recovery:
1.Parathyroid hormone(PTH) levels increased sig-
nificantly with both protocols.
2. PTH levels remained high 24 h into recovery with
“no recovery” protocol.
3. “No recovery” caused higher PTH levels when
compared to “recovery.”
4. Ca2+ levels returned to resting after recovery
(Bouassida et al, 2003). - Male marathon runners were examined during training,
during a 3-week training hiatus, and within 2 weeks of
retraining:
TABLE 32-6 Pancreatic Hormones
GLAND HORMONE CONTROL ACTION ENDURANCE RESISTANCE CHRONIC
Pancreas Insulin Glucose levels (+) glucose, fatty acid, and Decreased; dependent on Improves Increased insulin
amino acid transport into increasing intensity and insulin sensitivity; normal
cell; regulate glucose duration; glucose levels sensitivity; drop in insulin during
metabolism with the also drop with similar moderate to an acute bout of ex.
exception of brain; exercise because of intense is significantly less;
anabolic hormone catecholamine release; (50–100% maintained close to
induces more energy 1RM) resting values
from FFA and hepatic
glucose
Glucagon Glucose levels (+) glycogenolysis and Increased with increasing Blunted response similar
gluconeogenesis; exercise to resting values
insulin antagonist