Resistance training can increase the production of sex steroids in the muscles of older men, a new study shows.
If borne out by further research, the findings could have important implications for a wide range of conditions experienced by many aging individuals and linked to a decline in sex steroid hormones, say Koji Sato, PhD, and colleagues from Ritsumeikan University in Kyoto, Japan in their report in the Journal of the Federation of American Societies for Experimental Biology published online January 17.
"Resistance-training–induced increased muscular sex steroid hormone may positively affect age-related concerns such as accidental falls, diabetes, sarcopenia, and osteoporosis and may improve the quality of life for older individuals," they note.
More and more men are using testosterone supplements in the hope of improving their strength, energy, and sexual performance. But this use has become increasingly controversial, because many experts believe such supplementation is not necessary and there is also mounting evidence of concerning side effects associated with the use of testosterone, particularly in older individuals.
Just last week, the US Food and Drug Administration (FDA) announced it is investigating the potential that FDA-approved testosterone products increase the risk for serious adverse cardiovascular outcomes. The agency cited two studies, the most recent of which shows that men treated with testosterone were significantly more likely to have a myocardial infarction (MI) in the first 90 days after starting the medication.
The second study, of Veterans Affairs (VA) patients, published last year, also found that testosterone therapy in men was linked with an increased risk of death, MI, or ischemic stroke.
Sex Hormones in Skeletal Muscles Boosted by Training
In their new paper, Dr. Sato and colleagues explain that while the testes, ovaries, and adrenal cortex produce most steroid sex hormones in humans, recent animal work has shown that skeletal muscle can also synthesize testosterone, estradiol, dehyroepiandrosterone (DHEA), and dihydrotestosterone (DHT). However, a previous study in men and women in their 20s showed no immediate sign of an increase in these hormones in the quadriceps muscle following training ( J Appl Phys. 2008;105: 1754-1760).
To see what effect resistance training might have on older men over a longer period of training, the Japanese researchers recruited 13 men with a mean age of 67.2 years and 6 men with a mean age of 24.3.
The subjects were moderately active, but none regularly performed resistance exercises.
The older men performed knee extensions and flexions 3 times a week on alternate days, using starting weights that were 70% of each subject's single-repetition maximum strength. Trainers retested this measurement and adjusted weights for each of these men every 4 weeks. The study lasted 12 weeks.
Levels of sex steroid hormones and precursors in each man's vastus lateralis (the largest muscle in the quadriceps) were measured by biopsy before the weight training. The same measurement was taken again in the older men after the weight training.
The researchers also sampled the hormones in the men's blood and measured the size of their quadriceps before and after the training.
The older men had much lower levels of steroidogenic enzymes as well as sex steroid hormones and insulinlike growth factor (IGF-1) than the younger men in both their blood and their muscles. The older men were also weaker and had smaller quadriceps.
Nevertheless, the levels of sex steroid hormones increased significantly in the older men's muscles after the weight training. The older men's isokinetic extension strength and quadriceps sizes also increased significantly.
Muscular Hormone Levels
|DHEA (pg/mL)||Free testosterone (pg/mL)||DHT (pg/mL)||IGF-1 (ng/mL)|
|Older men before training||666||8.18||47||112.1|
|Older men after training||841*||10.6||56*||120.3|
*Statistically significant difference compared with older men before training ( P < .01)
Serum Testosterone Not Significantly Increased
In the blood, however, although the older men had significantly increased serum DHEA and DHT levels after training ( P < .01), their serum free testosterone did not rise significantly ( P = .052), nor did serum IGF-1 ( P = .055).
Levels of steroidogenic enzymes, as well as their androgen-receptor protein expression, did significantly increase, however.
The muscular steroid hormone levels significantly correlated with muscle strength and size, leading the investigators to conclude that "progressive resistance training seems to restore muscle sex steroid hormone levels via enhancement of steroidogenesis-related enzyme expressions in the skeletal muscle and may partly contribute to the increase in muscle strength and [size]."
Asked to comment on the findings, Jakob Vingren, PhD, an associate professor of kinesiology at the University of North Texas Denton, said that the results reinforce the importance of resistance training. "There are definitely benefits to aerobic exercises and there are definitely benefits to resistance training, and they combine, but there are unique benefits to both," he said.
Dr. Vingren added that men who are on androgen-deprivation therapy, for example, for prostate and other cancers, might particularly benefit from resistance training, since these findings indicate it could help strengthen them without increasing their serum testosterone.