A 40-year-old male presents with bilateral upper limb weakness, muscle atrophy, and fasciculations for 1 year. No sensory deficit or urinary incontinence. Examination: shoulder muscle strength grade V, elbow joint muscle strength grade V, wrist joint muscle strength grade IV, opponens pollicis muscle and interosseous muscles strength grade II-III, slightly increased muscle tone in both upper limbs, hyperactive biceps and triceps reflexes (+++), positive Hoffmann's sign on the right, positive Babinski sign on the left, and atrophy of thenar and hypothenar eminences and interosseous muscles bilaterally. If electromyography (EMG) is performed, the findings would most likely show: