From the fact you are 4 weeks out I think you could begin walking now.i usually allow my patients to workout about 4 to 6 weeks after breats lift.
These are questions for your surgeon to review with you since you just had surgery and he knows what the incisions look like.
Small openings or dehisences after breast reductions or lifts are not uncommon. If they are small and non infected in appearance you do not need to excessively worry as they are likely to heal over soon. Should you be overexerting yourself with frequent pulling at your incisions this unfortunately may contribute not only to them not healing as quickly but also ultimately to widened scars. Although I sympathize with you and the difficulty to keep sedentary for several weeks after surgery try to at minimum avoid exercises causing direct tension at the incision sites or unsupported cardio until they are fully healed. It may also be of benefit to support the non-opened portions of the incision sites with stere-strips or surgical tapes to assist with your overall healing and outcome. Warm Regards, Dr Quinton Chivers