A: As you age and become less active, your muscle function is reduced. Generally, you will see the largest reduction in your lower limbs and trunk extensors (i.e. lower back, etc.). Additionally, there is more loss of your type II fibers – the one’s mainly responsible for power and strength and aiding in your anaerobic activity.
Though your strength to mass ratio also decreases, your ability to adapt to a resistance training program is not affected by aging. Consider, for instance, if a 25 year old and a 65 year old man were to start the same strength training program they would both have roughly the same percentage of strength gains. In this example, the only difference is that the younger man would start off as having a higher muscle mass to begin with.
This is why it is so important for older adults to continue doing strength training as they grow older — there are many rewards to be had. Specifically, benefits include increased muscle fiber size (hypertrophy), reduced body fat percentage, increased muscle contractile strength, improved physical functioning as you age, and more.