Resistance helps improve strength
Strength training is a beneficial form of exercise for everyone. And no, it's never too late, and you are never too old, to get started. It's important to know a few fundamental principles of strength training:
• Resistance: You have to apply an appropriate resistance to build muscle. The amount of resistance should be above what one is accustomed to in everyday life. Add this resistance by using weight machines, free weights, cable machines, various weighted tools or even your own body weight.
• Balance: Make sure to work the entire musculoskeletal system to avoid postural and strength imbalances and injury. Work several muscle groups at once when possible.
• Rest: Rest between sets of exercise for about 60 to 90 seconds giving your muscles a chance to recover before you attempt the next set. Also, rest 48 hours between bouts of weight training if you are sore.
Source: Life Fitness