"Dorian Yates trains for only 45 minutes, but it's brutal! You can feel the intensity! He uses three exercises per bodypart, three sets each. The first two sets are short of failure, while the last one is an all out effort to failure with assistance from his training partner."

-Dorian Yates Blood & Guts Workout Routine

"What kind of half-ass set was that?" asks your training partner.  "You didn't train to complete muscular failure! How are you going to get big if you don't train to complete muscular exhaustion! You could of did 2 more reps you big pus! What's the matter, did you take your girlfriends birth control pills instead of your GAKIC?" Keep talking smack you think to yourself, continuously training to failure may result in reduced anabolic hormones and may lead to overtraining!  According to the newest study in the Journal of Applied Physiology training to muscular failure each set leads to reductions in anabolic hormones such as IGF-I and testosterone and caused larger increases in cortisol compared to lifters who don't train to failure.  The subjects in the study trained twice a week using a periodized weight training program.  One group trained to complete muscular failure for each set while the other group trained did not complete sets to muscular failure.  The researchers defined muscular failure when the subjects could not perform a full extension or the weight was paused for more than 1 second during a repetition.  At the end of the 16 week study, training to failure over the 16 week study resulted in reductions in circulating IGF-I concentrations and elevations in IGFBP-3 (IGF- Binding Protein 3).  In addition, the group that did not train to failure had reduced resting cortisol concentrations and an elevation in resting serum total testosterone concentration.  Additionally, the group that did not train to failure had similar increases in 1-repetition maximum strength gains in the bench press, parallel squat, and muscle power output of the arms and legs extensor muscles¹.   The group that did train to failure did have increased muscular endurance at the end of the study so unless you are preparing for a bench press competition for reps, training to failure might be the way to go.  If you are trying to maximize size, than not training to failure may lead to enhanced testosterone and lower catabolic activity such as reduced cortisol.  The reduction in anabolic hormones (IGF-I and testosterone) from training to failure goes against decades of advice to train to failure for maximal muscle growth.  Although Dorian Yates trained to failure does not mean you should train to failure.  Training to failure each set may lead to overtraining and lowered testosterone and IGF-I levels.

IGF-I and IGFBP-3(IGF-I Binding Protein 3)

In skeletal muscle, IGF-I can increase the uptake of glucose and Amino Acids enhance protein synthesis and suppress protein breakdown^{3, 4}. Moreover, IGF-I stimulates muscle growth by increasing the stimulation of satellite cells⁵. IGF-I is produced in many tissues, but the main source of circulating IGF-I is the liver, and the main regulators of hepatic IGF-I synthesis are GH and nutrient intake⁶.   Additionally long term resistance training that is of sufficient intensity and volume has been shown to increase IGF-I responses ^{7, 8}, whereas overtraining has been shown to decrease IGF-1 responses^{9, 10}. 

STOP! Step Away from the Bar! Your IFGBP-3 Levels are Dropping!

A large fraction of circulating IGF-I is attached to IGF binding proteins. 

Approximately 95% of the IGF-I and IGF-II are bound to IGFBP-3, which makes this protein the major carrier of IGF's in plasma. One of the principal functions of binding proteins is to extend the half-life of the IGF's from eight minutes to several hours. In this way, IGFBP-3 acts as a stabilizer, providing a constant level of IGF in the blood².  Serum IGFBP-3 concentrations in humans are relatively constant throughout the day, and this is likely to account for the stability of serum IGF-I concentrations¹⁷.  IGFBP-3 serves as a storage pool for serum IGF-I.  Interestingly, aging which is associated with a loss of lean muscle mass results in reduced secretion of GH and/or production of IGF-I which may contribute to the development of an excess of IGFBP-3 relative to IGF-I in aging¹⁹. A rise in IGFBP-3 means the body is trying to maintain IGF-I integrity.  It could be speculated that the reason why circulating levels of IGFBP-3 levels rose in the group that trained to failure was to preserve IGF-I levels from falling, however once the training intensity is high for long periods and overtraining is taking place, IGFBP-3 levels drop to rapidly release IGF-I to the tissues.  The response of IGFBP-3 has been variable between studies; usually the more exhaustive and strenuous a resistance exercise protocol is the bigger the drop in IGFBP-3 is.  For example, IGFBP-3 has been identified as a sensitive marker for overtraining, as IGF-1 levels fall IGFBP-3 decrease to release more IGF-1 in the plasma making it more available¹².  A significant drop in IGFBP-3 has been reported in overtrained soccer players and volleyball players, suggesting that IGFBP-3 level reflect a neuroendocrine adaptation to heavy exercise^{13, 14}.  Kraemer et al. reported that there was no change in IGF-I in response to a resistance exercise protocol in young men but IGFBP-3 levels increased significantly after exercise perhaps preserving IGF-I stability¹¹.  So what happens when you start pushing your body too hard?  There is a drop in both IGF-I and IGFBP-3.  For example, 10 untrained and 10 well trained elite troop soldiers were subjected to 11 weeks of intense physical training.  Both the untrained and trained groups had decreases in IGF-I but the IGFBP-3 responses were different.  The well trained group had no changes in IGFBP-3 whereas the untrained group had significant drops in IGFBP-3 levels indicating that the untrained subjects were in a more catabolic state¹⁷.