set) and long rest periods (3-5 minutes). Studies have found a regimen of 3X5RM with 3’ rest to
increase testosterone significantly in men (67,68,72) but not in women (69). It is unknown
whether the transient increase in testosterone following training has an impact on muscle
growth.
IGF-1 is a hormone released from the liver, most likely in response to increases in GH
levels (62). However, the small increases in GH seen with training do not appear to affect IGF-1
levels (73). More likely, IGF-1 is released from damaged muscle cells (due to eccentric muscle
actions) and acts locally to stimulate growth (42,63).
Cortisol is a catabolic hormone meaning that it breaks down larger substances to smaller
(i.e. triglycerides to fatty acids and glycerol, and proteins to amino acids). It is released from the
adrenal cortex in response to stress such as exercise or starvation. Cortisol may have a role in
the tissue remodeling seen with heavy resistance training as it increases protein breakdown at
high levels (1). Increases in cortisol tend to mirror the increases seen in growth hormone (74) and
it has been suggested that the increase in cortisol is a necessary part of the muscle remodeling
stimulus. (65,70) The basis for this is that the breakdown of tissue is necessary to stimulate a
rebuilding of that same tissue.
The major role of catecholamines (adrenaline and noradrenaline) is fuel utilization. As
described previously, increases in levels of adrenaline and noradrenaline increase liver output of
glucose, mobilize fat from adipose tissue, and stimulate glycogen breakdown in muscles. High
intensity weight training with multiple exercises increases catecholamine levels similar to that
seen in sprint training (65,75). The overall effect of the rise in catecholamine levels is an increase
in blood glucose and stimulation of fat breakdown.
Adequate nutrients and energy
Once muscle growth is stimulated, the final requirement for growth to actually occur is an
excess of nutrients and energy (63). Reduced calorie diets put the body in a systemically
catabolic (tissue breakdown) condition due to changes in hormone levels. Low-calorie diets cause
a decrease in growth promoting hormones such as insulin and thyroid while increasing growth
inhibiting hormones such as adrenaline, glucagon, and cortisol (63). Similarly, overfeeding causes
and increase in those same hormones and an increase in lean body mass as well as fat (76). It is
generally impossible, except for beginners or those returning from a layoff, for most individuals to
gain muscle while losing fat at the same time.
Simply put, the body must either be systemically catabolic (for fat loss) or systemically
anabolic (for muscle gain). Attempting to gain significant amounts of muscle while losing fat at
the same time or vice versa tends to minimize the results of either goal. Most individuals find
that focusing on either fat loss or muscle growth yields the best results. The CKD is somewhat
unique among diets in that it couples a catabolic phase (at below maintenance calories) with an
anabolic phase (at above maintenance calories), meaning that the potential to gain muscle and
lose fat simultaneously exists. This topic is discussed in greater detail in chapter 12.