Training to failure increases growth hormone, testosterone, and cortisol (i.e., catabolic hormone) acutely or in the short term, but training to failure reduces testosterone in the long term. Whether the acute increases in GH and testosterone affect muscle growth is debatable.



  • Forced reps result in increased cortisol and more muscle damage
  • Acute anabolic hormones (GH and testosterone) do not impact muscle growth


You have already learned that it’s unnecessary to train to failure, and there is no difference in muscle growth between those going to failure and those who do not. Check out the article A NEW STUDY SUGGESTS TRAINING TO FAILURE PROVIDES LITTLE BENEFIT TO MUSCULAR GROWTH COMPARED TO STOPPING SHORT OF FAILURE. Studies suggest that when monitored over a period of weeks, not training to failure is better for anabolic hormones.

Izquierdo and colleagues found that training to failure resulted in suppressed levels of muscle-building hormones (i.e., reduced IGF-1 levels). In contrast, the non-training failure group had lower cortisol levels and higher testosterone levels.[1]

Cortisol can block anabolic signaling events in the muscle and interfere with the binding of testosterone to receptors in the muscle.[2] Therefore, it is essential to keep cortisol balanced and allow for recovery for optimal training and subsequent adaptations.

Training to failure increases growth hormone, testosterone, and cortisol (i.e., catabolic hormone) acutely or in the short term, but training to failure reduces testosterone in the long term. Whether the acute increases in GH and testosterone affect muscle growth is debatable.

The combined effects of resistance exercise and exercise-induced anabolic hormones may lead to an upregulation of anabolic signaling pathways, which likely augments net protein synthesis and hypertrophy.[3] However, most studies suggest that acute increases in anabolic hormones have no impact on muscle growth.


Professor Stuart Phillips has led the charge in debunking the role of acute anabolic hormones and muscle growth. In a 2016 study, subjects trained with either a heavy weight, low repetitions (~75%-90% of a 1RM), or high repetitions (~30–50% of a 1RM). Despite an acute increase in anabolic hormones, there was no correlation between acute anabolic hormones and muscle growth; both groups increased muscle mass similarly.[4]

One exciting finding from this study was that local androgen receptor concentration was correlated with increased muscle mass, suggesting that rather than systemic hormones (i.e., testosterone, GH), androgen receptor concentration is more important for muscle growth.

The current research suggests that acute anabolic hormones play a lesser role in muscle growth than previously thought. Subjects were trained with either arm curls (low anabolic hormone exposure) or arm curls plus leg press and leg extension/leg curl at ∼90% of 10 RM (high anabolic hormone levels).

It has been well documented that large multi-joint exercises like the leg press produce greater anabolic hormones than smaller joint exercises like the bicep curls. If acute anabolic hormones led to muscle growth, the arms training with leg training that resulted in greater anabolic hormone exposure should have resulted in greater muscle growth.

Despite arms plus legs workouts producing large increases in GH, testosterone, and IGF-1 levels, they found no differences in the arm size exercised under low or high anabolic hormone conditions after 15 weeks of training.[5]


Based on the sum collection of all the studies, the acute anabolic hormone rise from exercise has a minor effect on muscle growth.[6] One study found that after 12 weeks of resistance training, the resistance exercise changes in testosterone had no direct correlation with muscle fiber growth.[7]

Keep in mind that women can gain substantial increases in muscle size in response to a resistance exercise program, despite having lower testosterone levels than men.[8] If the acute increases in GH contributed to the muscle growth process, one would expect that training in the morning, in which the body’s naturally occurring GH levels are higher, would result in more muscle growth.

The study’s sum collection does not show that training in the morning is more effective than in the afternoon for muscle growth, despite having higher GH in the morning.[9]

More than likely, you don’t need to worry about the acute anabolic effects of testosterone and GH in response to exercise and muscle growth. Tension in the muscle is more important than the acute anabolic hormone response.


It’s common to see lifters use a spotter to assist them with the last few reps of a set. Based on the above finding that reps taken to failure do not result in more muscle growth than sets that are stopped several reps short of failure, I have little faith that forced reps will stimulate more muscle growth.

No study to date has examined forced reps’ responses to traditional exercise for muscle hypertrophy. Still, I would assume that it would be similar to the training to failure vs. non-failure training, which favors non-failure training.

A 2003 study found that forced reps resulted in greater GH and increased cortisol responses than a traditional resistance exercise protocol. This means that there was greater workout stress associated with forced reps.

Recovery time after the workout was prolonged in the forced rep group for three days post-exercise.[10] Forced reps result in greater recuperation time between workouts. Forced reps also cause greater peripheral and central fatigue. Furthermore, forced reps have not been found to increase strength compared to traditional resistance exercises.[11]


·      Acute anabolic hormones (GH and testosterone) do not impact muscle growth.

·      Forced reps result in increased cortisol and more muscle damage.


1.     Mikel Izquierdo et al., “Differential Effects of Strength Training Leading to Failure versus Not to Failure on Hormonal Responses, Strength, and Muscle Power Gains,” Journal of Applied Physiology 100, no. 5 (2006): 1647–56.

2.     Barry A. Spiering et al., “Effects of Elevated Circulating Hormones on Resistance Exercise-Induced Akt Signaling,” Medicine and Science in Sports and Exercise 40, no. 6 (June 2008): 1039–48.

3.     Nima Gharahdaghi et al., “Links Between Testosterone, Oestrogen, and the Growth Hormone/Insulin-Like Growth Factor Axis and Resistance Exercise Muscle Adaptations,” Frontiers in Physiology 11 (2021): 1814.

4.     Robert W. Morton et al., “Neither Load nor Systemic Hormones Determine Resistance Training-Mediated Hypertrophy or Strength Gains in Resistance-Trained Young Men,” Journal of Applied Physiology 121, no. 1 (July 1, 2016): 129–38.

5.     Daniel W. D. West et al., “Elevations in Ostensibly Anabolic Hormones with Resistance Exercise Enhance Neither Training-Induced Muscle Hypertrophy nor Strength of the Elbow Flexors,” Journal of Applied Physiology 108, no. 1 (January 2010): 60–67.

6.     E. Todd Schroeder et al., “Are Acute Post–Resistance Exercise Increases in Testosterone, Growth Hormone, and IGF-1 Necessary to Stimulate Skeletal Muscle Anabolism and Hypertrophy?,” Medicine & Science in Sports & Exercise 45, no. 11 (November 2013): 2044–51.

7.     G. E. McCall et al., “Acute and Chronic Hormonal Responses to Resistance Training Designed to Promote Muscle Hypertrophy,” Canadian Journal of Applied Physiology = Revue Canadienne de Physiologie Appliquee 24, no. 1 (February 1999): 96–107.


8.     Monica J. Hubal et al., “Variability in Muscle Size and Strength Gain after Unilateral Resistance Training.,” Medicine and Science in Sports and Exercise 37, no. 6 (June 2005): 964–72.

9.     Jozo Grgic et al., “The Effects of Time of Day-Specific Resistance Training on Adaptations in Skeletal Muscle Hypertrophy and Muscle Strength: A Systematic Review and Meta-Analysis,” Chronobiology International 36, no. 4 (April 2019): 449–60.

10.  J. P. Ahtiainen et al., “Acute Hormonal and Neuromuscular Responses and Recovery to Forced vs. Maximum Repetitions Multiple Resistance Exercises,” International Journal of Sports Medicine 24, no. 6 (August 2003): 410–18.

11.  Eric J. Drinkwater et al., “Increased Number of Forced Repetitions Does Not Enhance Strength Development with Resistance Training,” Journal of Strength and Conditioning Research 21, no. 3 (August 2007): 841–47.

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