Muscle outlines from Body Muscles by Ivan Vulović, Apache 2.0 — regrouped and recoloured for Muscle Train.
Stand with feet hip-width apart, dumbbells in each hand, palms forward. Keeping elbows close to your body, curl one dumbbell, flexing your elbow and rotating your palm up. Lift until your bicep is fully contracted. Pause, squeeze, then slowly lower back to the start. Alternate arms.
Control the movement to engage biceps. Avoid body swing and shoulder involvement; keep elbows stable. Exhale on the lift, inhale on the lower. Use a full range of motion. Start with lighter weights to ensure proper form.
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