Kettlebell Swings as Muscle Builders? Increases in Cortisol & GH & Decreases in Testosterone Which Position the KB Swing Rather as a HIT Fat Burner Than Muscle Builder

Kettlebell swings - According to the results from the study at hand, probably great to shed body fat. not exactly what you should be doing to gain tons of muscle.
Ok, here is my confession: I hate kettle bell training (probably, because I am a pussy ;-). Now that it's out there and you know my bias, it's about time to take a look at the results of a recent study from the University of North Texas in Denton (Budnar Jr. 2014) that investigated the hitherto unknown hormonal response to kettlebell training among strength and conditioning professionals.

I know, there is no reliable evidence that the GH, testosterone and cortisol response to exercise is a good predictor of the exercise induced muscular adaptations - including muscle and strength gains and fat loss, but there are a few neat associations due to which looking at the study results probably isn't totally useless.
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Based on the previously cited study by West et al. (2009 & 2012), the things we should be looking for are elevations of cortisol and growth hormone, but not those of testosterone, which were not associated with either lean muscle mass or type I / type II fiber cross sectional area (CSA).
As you can see in Figure 1, we could expect increases in muscle fiber size with significant increases in cortisol, and increases in total lean body mass if the amount of GH that's circulating in the blood of the ten healthy male volunteers' n (19–30 years; mean 24 years, 175 cm, 78.7 kg) was significantly increased in response to performing 12 rounds of 30 seconds of kettlebell swings alternated with 30 seconds of rest.

The subjects of which the scientists say that they were recreationally trained,  had been engaged in resistance exercise >2 times a week for at least the previous 3 months. They had no history of anabolic steroid use, but more importantly, they had no experience with the kettlebell swing exercise and were thus the perfect candidates for maximal hormonal responses (and strength outcomes) in response to an unaccustomed workout. As Budnar Jr. et al. point out, ...
"[...] Lake and Lauder (2012) have previously demonstrated that training using this exercise protocol improves lower-body strength and power. A 16-kg kettlebell (Perform Better, Cranston, RI, USA) was used by all participants because it is the recommended starting weight for men and has previously been used in evaluating the effect of kettlebell swings on strength training adaptations and acute aerobic responses (Lake. 2012)." (Budnar Jr. 2014) 
Fasted blood samples were collected using intravenous catheter before the warm-up (PRE), immediately postexercise (IP), 15 minutes postexercise (P15), and 30 minutes postexercise (P30) and were analyzed for testosterone (T), growth horomone (GH), cortisol (C), myoglobin, and lactate concentrations.
Table 1: 1.Heart rate (HR) and rating of perceived exertion (RPE; range, 6–20) at rest (HR only) and immediately after each round of kettlebell swings and number of swings per round (Budnar Jr. 2014)
A brief glimpse at the RPE data (rate of perceived exertion; 20 = max) in Table 1 reveals that the workout was pretty exhausting. After only one swing the RPE level had reached 50% of the 20 point maximum. No wonder, considering the fact that the subjects
"[...]completed 12 consecutive rounds of kettlebell swing exercise with each round consisting of 30 seconds of exercise followed by 30 seconds of rest. Investigators provided verbal encouragement to the participant to complete as many swings in the 12-minute period as possible." (Budnar Jr. 2014)
Immediately after the completion of the exercise bout, the participant was seated and the IP blood sample was obtained. The participant remained seated comfortably for the remainder of the session, including during the collection of the P15 and P30 blood samples.
Figure 1: Human growth hormone, cortisol and testosterone response to <15 min of kettlebell swings (Budnar Jr. 2014)
Figure 1 shows the results of the blood samples. The first thing you should notice are the huge differences in cortisol and GH response with one "hyper-responder" who probably went hypo right after his first swing (low glucose ➲ high coritsol + high GH during workouts).
Bottom line: Overall, the increase in growth hormone (GH) and cortisol (C), would suggest that there will be long-term beneficial effects on the total lean body mass and type I & II fiber size, as they were observed by West et al. (2012) in the previously cited study. Plus: The decrease in testosterone, that occurs in all subjects is not exactly what you'd like to see from a muscle builder. Previous studies do after all show that it's increased in response to classic hypertrophy workouts, even if there is no significant association between the T increase and the subsequent muscle gains.

The kettlebell swing would be a great addition to regular resistance training and could be listed in every workout in the fat loss episode of the "Step By Step Guide to Your Own Workout Routine" | read more
Considering the fact that the kettlebell swing exercise was performed for a relatively short duration (11.5 minutes in total: 6 minutes of exercise and 5.5 minutes of rest), the results are quite impressive and speak in favor of performing kettlebell swings as a high intensity, but not necessarily a muscle building workout. But just as Budnar Jr. et al. (2014) point out, there debate concerning the physiological importance of the acute hormonal response to resistance exercise for long-term strength and hypertrophy adaptations is still ongoing and the connection is rather putative (Phillips.

Against that background I would rather stick to the tried and proven, if your goal is maximal muscle hypertrophy. Due to the degree of exhaustion and the overall high energy demand, kettlebell swings would yet make an effective and highly time-efficient high intensity addition to a classic resistance training workout | Comment on Facebook!
  • Budnar Jr, Ronald G., et al. "The acute hormonal response to the kettlebell swing exercise." Journal of strength and conditioning research/National Strength & Conditioning Association (2014).
  • Lake, Jason P., and Mike A. Lauder. "Kettlebell swing training improves maximal and explosive strength." The Journal of Strength & Conditioning Research 26.8 (2012): 2228-2233. 
  • Phillips, Stuart M. "Strength and hypertrophy with resistance training: chasing a hormonal ghost." European journal of applied physiology 112.5 (2012): 1981-1983.
  • West, Daniel WD, et al. "Resistance exercise-induced increases in putative anabolic hormones do not enhance muscle protein synthesis or intracellular signalling in young men." The Journal of physiology 587.21 (2009): 5239-5247.
  • West, Daniel WD, and Stuart M. Phillips. "Associations of exercise-induced hormone profiles and gains in strength and hypertrophy in a large cohort after weight training." European journal of applied physiology 112.7 (2012): 2693-2702.
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