A new study out of Australia demonstrates rats’ heart cells not only get bigger as a result of exercise, but they can also increase in number when endurance training takes place at young ages. What’s more, the additional cells remain present into adulthood, even after the rats have become sedentary.
Scientists long thought exercise-related benefits to the mammalian heart were because of increased size and function of existing cells, not the creation of new cardiomyocytes. The full complement of heart cells was assumed to be locked in at a certain number after birth.
But in the study, conducted by Deakin University’s Glenn Wadley, PhD, and colleagues, male juvenile rats who began a four-week exercise training program at 5 weeks old achieved a 36 percent increase in cardiomyocytes, equivalent to 20 million cells, which they maintained into adulthood. Adolescent (11 weeks old) and adult (20 weeks old) mice were also tested. While they too demonstrated cardiac hypertrophy, fewer additional cardiomyocytes were found in the adolescent rats and no additional cells for those who began the exercise program in adulthood.
“A few weeks of moderate intensity endurance training during juvenile life can lead to sustained and physiologically relevant increases in heart mass, LV (left ventricular) wall thickness, cardiomyocyte number and size in adulthood,” Wadley and colleagues wrote in The Journal of Physiology. “Also, the ability of endurance training to increase cardiomyocyte number appears to diminish with age, with the effect being completely lost by adulthood.”
The rats’ exercise program consisted of treadmill running five days per week for four weeks. They began running 20 minutes at a time and eventually increased the workouts to 60 minutes.
Wadley et al. noted having a greater number of cardiomyocytes would likely increase an organism’s functional reserve, “potentially rendering the hearts better equipped for the structural and functional challenges in adult life.” This could include boosting the odds of surviving a heart attack or protecting against heart failure.
The authors suggested future studies examine whether these findings also apply to female rats, and then to humans.
“Should our findings translate to humans they would provide support for exercise training programs in school curricula and suggest that there are long-term cardiac benefits of exercise training to all children, even if the children do not continue with regular exercise training in adulthood,” they wrote. “Nevertheless, whilst the effects of endurance training on the heart in the present study are promising, resistance training is likely to have difference effects and may require investigation.”
Daniel joined TriMed’s Chicago editorial team in 2017 as a Cardiovascular Business writer. He previously worked as a writer for daily newspapers in North Dakota and Indiana.