A person that is over 40 years old needs to hold each stretch for a minimum of sixty seconds. This helps to prevent injuries after you have exercised to build muscle. Try psychometric Hard Boost XL exercises. This type of exercise develops the fast-twitch muscle fibers that stimulate muscle growth. Plyometric exercises are a different kind of exercise that rely more on acceleration than strength. For instance, when doing plyometric push-ups, you let your hands jump off the floor and explode as high as you can. You can cut corners a bit when you lift, although always be safe. If you feel your targeted muscle groups getting fatigued, then put some body behind the last few reps. Be careful not to do this to the extreme. Always keep your rep speed controlled.