If it feels as if you’re putting in the work but not all your muscles are getting the memo, you might not be imagining it. Today's lead story unpacks why some muscle groups respond faster to strength training than others. From genetics to your workout splits, the factors are more nuanced than you think—but this guide teaches you how to get lagging muscles moving. Push your training even further with this new info on how many reps you need to build muscle, the form cues that are game changers for results, and more.