Avoid Burnout

To see if you’re overtraining, check your pulse first thing in the morning the day after a workout. If it’s 10 beats per minute or more above normal, your body is still recovering.

Multiply Your Muscles

Follow this simple formula to build more muscle: Multiply the amount of weight you lift for a particular exercise by the total number of times you lift it. Try to increase that number every workout by lifting heavier weights, increasing your repetitions, or doing more sets.

Strengthen Your Core

Situps increase your range of motion, which makes your abdominals work harder and longer. (Doing crunches on a Swiss ball or with a rolled-up towel under your lower back has a similar effect.) Just avoid situps with anchored feet, which can hurt your lower back.

Keep Muscles Limber

If you’re under 40, hold your stretches for 30 seconds. If you’re over 40, hold them for 60 seconds. As you reach your 40s, your muscles become less pliable, so they need to be stretched longer.