For EMG biofeedback of a weak extensor carpi radialis longus, which electrode placement configuration yields signals primarily from that muscle?

• A. Electrodes placed close together to pick up signals from ERL only
• B. Electrodes placed far apart to pick up all forearm activity
• C. Use only intramuscular electrodes
• D. High impedance amplifiers

Answer: (A)

In EMG biofeedback, the goal is to get a reading that reflects activity from a specific muscle, not a mix from many forearm muscles. Signals detected by surface electrodes are volume-conducted, so nearby muscles contribute to what you record. Placing the two recording electrodes very close together over the belly of the extensor carpi radialis longus, aligned with the direction of its muscle fibers, makes the sensor more spatially selective. This tight configuration emphasizes the electrical activity from that muscle and reduces cross-talk from neighboring forearm muscles, giving a cleaner signal for biofeedback.

If electrodes are placed far apart, the pickup field widens and you capture more activity from multiple forearm muscles, muddling which muscle the feedback reflects. Intramuscular electrodes would isolate signals from individual motor units but are invasive and not typical for standard biofeedback practice. High impedance amplifiers affect noise handling but don’t inherently improve muscle specificity.