Final answer:
The residual volume that indicates effective reflex training is less than 100 mL.
Step-by-step explanation:
The residual volume that would indicate that reflex training is effective in emptying the bladder is less than 100 mL. When a patient with a spinal cord injury undergoes reflex training, their goal is to improve the ability to empty the bladder through the micturition reflex. By reducing the residual volume to less than 100 mL, it demonstrates that the reflex training is effective in facilitating bladder emptying.