during resistance exercise, muscles are __________.
Resistance exercise is any form of exercise that forces your skeletal muscles (not the involuntary muscles of your heart, lungs, etc.) to contract. An external resistance (such as heavy weights) is used to cause the contractions, and those contractions lead to increases in muscular mass, strength, endurance and tone.
1 Resistance training increases muscle strength by making your muscles work against a weight or force. 2  Different forms of resistance training include free weights, weight machines, resistance bands and your own body weight.  A beginner needs to train two or three times per week to gain the maximum benefit.