Training for Endurance and Strength: Lessons from Cell Signaling

Training for Endurance and Strength: Lessons from Cell Signaling.
SYMPOSIUM
Medicine & Science in Sports & Exercise. 38(11):1939-1944, November
2006.

BAAR, KEITH
Abstract:
The classic work of Hickson demonstrated that training for both
strength and endurance at the same time results in less adaptation
compared with training for either one alone: this has been described
as the concurrent training effect. Generally, resistance exercise
results in an increase in muscle mass, and endurance exercise results
in an increase in muscle capillary density, mitochondrial protein,
fatty acid-oxidation enzymes, and more metabolically efficient forms
of contractile and regulatory proteins.

In the 25 yr since Hickson's initial description, there have been a
number of important advances in the understanding of the molecular
regulation of muscle's adaptation to exercise that may enable
explanation of this phenomenon at the molecular level. As will be
described in depth in the following four papers, two serine/threonine
protein kinases in particular play a particularly important role in
this process. Protein kinase B/Akt can both activate protein
synthesis and decrease protein breakdown, thus leading to
hypertrophy, and AMP-activated protein kinase can increase
mitochondrial protein, glucose transport, and a number of other
factors that result in an endurance phenotype. Not only are PKB and
AMPK central to the generation of the resistance and endurance
phenotypes, they also block each other's downstream signaling. The
consequence of these interactions is a direct molecular blockade
hindering the development of the concurrent training phenotype. A
better understanding of the activation of these molecular pathways
after exercise and how they interact will allow development of better
training programs to maximize both strength and endurance.