The level of resistance utilized is known as intensity, and it is generally stated as a percentage of the one-repetition maximum (percent 1-RM) for a certain lift. Another approach to express intensity is to state the maximum number of repetitions that may be accomplished for a certain lift. For example, an exercise that can be done 20 times maximum would be considered moderately difficult while one able to be performed only once is described as very hard. Intensity is a key factor in determining how much muscle fiber stimulation and growth occurs during strength training. Intense exercises stimulate more muscle fibers and thus lead to greater growth than less intense ones. However, too much intensity at any time will cause injury because large muscle groups are being used without sufficient rest between sets. There are two ways to increase the intensity of your strength training sessions: by changing the weight you lift or by adding more repetitions to current lifts. Either method will bring about significant changes in your muscles over time. Changing the Weight You Lift As you gain experience with weight lifting, you will find that you become stronger able to use heavier weights then when you first started out. This is because your body gets better at handling heavy loads over time. So, by keeping the weight constant but increasing the number of repetitions you can boost your intensity significantly.