Why the Bottom Half of Your Rep Builds the Most Muscle

People love to lock out their reps to show they finished the job, but if you want to build actual size, you need to respect the stretch. Over the past few years, sports science has confirmed what old-school lifters always felt in their muscle bellies: training a muscle at long muscle lengths, meaning when it is fully stretched, drives disproportionate growth. A landmark meta-analysis reviewed partial versus full range of motion training and found that doing partial reps exclusively in the stretched position often outperforms full range of motion for hypertrophy (see [1]). That means the deepest, hardest part of a dumbbell fly, a Romanian deadlift, or a Bulgarian split squat is doing the heaviest lifting for your gains.

This does not mean you should abandon full range of motion entirely. It means you cannot afford to skip or rush the bottom of the movement where the muscle is under maximum tension in a lengthened state. When you bounce out of the hole on a squat or cut your lat pulldowns short before your arms are fully extended overhead, you are robbing yourself of stretch-mediated hypertrophy. A fascinating study on leg extensions demonstrated that just doing the bottom half of the movement built significantly more quad mass than just doing the top half where you squeeze at lockout (see [2]). You have to own that deep, uncomfortable stretch if you want the fibers to adapt and grow.

If you are currently stalling on a plateau, look at your execution before you start completely overhauling your routine. Next time you are in the gym, slow down the lowering phase, pause for a split second in the deepest part of the stretch, and force the target muscle to move the weight out of that hole. Keep a close eye on your body when you make this shift, because training at long muscle lengths causes more initial muscle damage and soreness. You can monitor your readiness to handle this extra structural stress by checking the Recovery score on your /dashboard before your next heavy session. Put the work in where it is the most mechanically difficult, recover like it is your job, and the size will follow.