Researchers found 12 weeks of regular aerobic exercise increased testosterone levels for overweight and obese men.
Lead researcher Hiroshi Kumagai, of Tsukuba University in Japan, and colleagues recently presented their findings at the American Physiological Society's Integrative Biology of Exercise VII Meeting in Phoenix, AZ.
Testosterone is a predominantly male sex hormone, mainly produced by the testicles.
In men, testosterone is responsible for sustaining sperm production, sex drive, facial and body hair, muscle size and strength, fat distribution, red blood cell production, and bone density.
According to the Mayo Clinic, men's testosterone levels typically start to decrease from the age of 30 or 40, falling around 1 percent each year.
Kumagai and colleagues note that obesity is a leading risk factor for low testosterone levels. A 2015 study from the team established a link between diet and exercise and increased testosterone levels in men who were overweight or obese.
For the new study, the researchers set out to determine how regular aerobic exercise alone might affect the testosterone levels of overweight or obese men.
Overweight, obese men saw rise in testosterone with exercise program
The study involved 44 men, of whom 28 were overweight or obese and 16 were a normal weight. None of the men engaged in regular exercise.
All participants were required to take part in an aerobic exercise program that involved 40-60 minutes of walking or jogging 1-3 days a week for 12 weeks.
The men's testosterone levels were measured before and after the exercise program.
While the program had no impact on the testosterone levels of normal-weight men, men who were overweight or obese saw a significant increase in levels of the hormone by the end of the 12 weeks.
In detail, overweight or obese men saw their total testosterone levels increase from 15.4 nanomoles per liter to 18.1 nanomoles per liter.
Overweight or obese men who exercise most vigorously during the 12-week program saw the highest increase in testosterone levels, the team notes.
Exercise, not weight loss, 'a main factor for increasing testosterone levels'
The researchers point out that the testosterone levels of the overweight or obese men were still lower than those of the normal-weight men following the exercise intervention, but their findings remain promising.
Overweight or obese men did show some weight loss with the exercise program, which the researchers speculate may have contributed to the rise in testosterone levels.
"However, the degree of weight loss is small, and we found that the increase in vigorous physical activity was independently associated with the increase in serum testosterone levels," notes Kumagai.
"So, it seems the increase in physical activity, especially vigorous physical activity, is the main factor for increasing serum testosterone levels."