Help with Product Selection and Build Tips for Electrical Muscle Stimulator

I am working on designing a device that uses electrical muscle stimulation to activate muscles in the forearm. I was able to find the specs on a similar device. I need help with choosing the right controller and, if needed, add ons to be capable of achieving similar outputs. I’ve attached the specs of the similar device. Please respond with any questions or answers you may have to help me. Thanks.

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I should also say that the similar device runs on a 3.7V, 280-350 mAh Lithium ion rechargeable battery.