The walkout by resident doctors – the new name for junior doctors – is due to begin at 07:00 BST on Friday.
"Senior doctors cannot physically be in two places at once," said Dr Runswick.
"We think the vast majority of planned and scheduled care should be shifted."
During previous strikes in 2023 and 2024 non-urgent work was cancelled in large quantities so senior doctors could provide cover in emergency and urgent services.
This came after NHS England told hospitals that rescheduling bookings and appointments was going to be "sadly essential" to maintain safe care.
At some hospitals up to half of planned care was cancelled.
But this new approach is being overseen by Sir Jim Mackey, who became chief executive of NHS England in the spring after Amanda Pritchard stepped down.
Sources at NHS England said he was determined to minimise the disruption, pointing out that cancelling non-urgent work comes at a risk to patients too.
Dr Runswick also defended the sums being charged by senior doctors for covering resident doctors during the strike. The BMA has suggested consultants charge over £300 an hour for night shifts.
Dr Runswick said sometimes the NHS needed to "incentivise" doctors to provide cover outside their normal work.
