A study investigated the effects of strength training (ST) on resting metabolic rate (RMR) and body composition across different ages and genders (Lemmer JT, et., al., 2001). After 24 weeks of ST, results showed:
Both young and older participants experienced a 7% increase in RMR.
Men saw a 9% rise in RMR, while women had no notable change.
Even when accounting for body fat, men still showed a significant boost in RMR.
Physical activity levels outside of training didn't alter due to ST.
In summary, ST influences RMR based on gender but not age, and doesn't affect external physical activity levels.
J T Lemmer 1, F M Ivey, A S Ryan, G F Martel, D E Hurlbut, J E Metter, J L Fozard, J L Fleg, B F Hurley. Effect of strength training on resting metabolic rate and physical activity: age and gender comparisons. Med Sci Sports Exerc. 2001 Apr;33(4):532-41.