Heavier resistance training - if your joints are up to it - will build muscle at almost any age. If you can do more that 12 reps it is not heavy resistance training. If you can do 20 reps it might be a great exercise for endurance and possible increased vascular enlargement but will probably not build muscle effectively.
From 40 on you probably tend to lose muscle mass at perhaps 1/2 to 1% per year. It depend on the heavier exercises & activities that you are doing and how much they heavily stress your muscles. Playing just tennis and accelerating to the ball less each year you leg muscles probably do not get enough heavy resistance and will lose muscle mass. If you do heavier resistance exercises you may be able to add, say, 5% to your muscle mass per year - equivalent to several years of your loss from aging.
(That is not
adding 5% of muscle to your body weight since the weight of your muscles is only a portion of your total weight. "An average adult male is made up of 42% of skeletal muscle and an average adult female is made up of 36% (as a percentage of body mass)." http://en.wikipedia.org/wiki/Muscle
Calculator - Converts Reps Performed to One Rep Max
. As reps performed go above 10 the accuracy of the calculator declines.
1) With age there are a few very, very minor
declines so why should I do anything with such certain fate stacked against me.......
2) Heavier weight training builds muscle. Test yourself for about 8 weeks by doing heavy resistance using some joint that is in good shape, arm curls? The test will indicate what you can expect from heavier resistance training.
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