Stick to biceps isolations when looking to eliminate forearm involvement.
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Completely isolating your biceps muscles is virtually impossible, as whenever you perform a biceps exercise, your forearms are working to hold the weight. What you can do, however, is find ways to work the biceps brachii and brachioradialis muscles of the biceps without working your forearm flexors and extensors by performing certain movement variations.
Go Cold Turkey on Compounds
Compound pulling movements, such as barbell rows and chin-ups are an effective way to build your biceps, but the downsides to these is that they also work your forearms. Take the pull-up for example -- getting stronger at pull-ups will increase biceps size over time, but pull-ups also work the forearms, notes strength coach Charles Poliquin. The same goes for any type of row or pulldown movement. Keep these to a minimum to avoid overworking your forearms.
Throw Away the Hammer
If you're currently performing biceps exercises using a neutral grip with your palms facing inward, stop. This grip, known as a hammer grip, activates your forearms more than a regular supinated or underhand grip, writes personal trainer Lee Boyce on the MuscleMag website. When curling, stick with a supinated grip.
Best for Bis
To limit the work your forearms are doing, aim to isolate your biceps as much as possible. One of the best exercises for this is the preacher curl, according to strength coach Kwesi Peters. Resting your arm on the preacher bench pad forces you to keep your form strict and concentrate on working the target muscles. To these, you can also add concentration curls, performed sitting down with one dumbbell at a time and your arm resting against your inner thigh. Regular seated and standing dumbbell, barbell and cable curls also fit the bill, as do crucifix curls, performed by standing in the middle of a cable crossover station with the handles set to the highest setting and curling each side in toward your head.
The Game Plan
Pick three exercises each workout: one type of preacher curl -- either with dumbbells or an EZ bar or on a machine; a seated or standing curl; and another move, such as the concentration or crucifix curl. Keep your reps higher -- somewhere around the 10 to 15 reps per set range. This higher rep range means you'll have to use slightly lighter weights, which won't put as much stress on your grip or forearm muscles. Complete three to four sets per exercise, resting 60 to 90 seconds between sets.