Strikes - the first for 40 years by junior doctors - went ahead on 12 January after emergency talks through the conciliation service ACAS broke down.
More than 150 pickets took place across England, the BMA has said, and figures reported by NHS England show that more than 60% of junior doctors took part in strikes.
A second day of action is scheduled for 26 January, with junior doctors again set to provide emergency cover only.
Junior doctor strikes
If a third day of planned strikes takes place on 10 February, junior doctors will go a step further with a full withdrawal of labour.
The last round of talks through ACAS came to an acrimonious end, with the BMA and government accusing each other of misrepresenting the level of progress achieved in negotiations.
NHS England said 39% of 26,000 junior doctors worked on Tuesday, with 1,279 inpatient cases and 2,175 day cases cancelled across England.
BMA junior doctors committee chairman Dr Johann Malawana said: 'We deeply regret the level of disruption caused, but this is a fight for the long-term safety of patients and junior doctors’ working lives. The biggest threat to patient care is the government’s insistence on removing safeguards which prevent junior doctors from being forced to work dangerously long hours without breaks, with patients facing the prospect of being treated by exhausted doctors.'