Foreward when his back legs pushed. BUT! Most horses, when looking at the various stages to a complete stride, are fully airborne or suspended once during that stride. Secretariat had two suspensions! I gathered from the article that he's the only horse known to have been capable of this. It wasn't only his big heart. He had sturdy bones. That match race between him and Sham at the Belmont fractured Sham's cannon bone, I think it was, which was why he limped to the finish and never raced again... and his heart was second only to Secretariat's, according to the vet, but the rest of Secretariat was built to handle the stress his heart put on the body. Research after Secretariat's death showed that the severe freeze that wrecked his pasture and caused his laminitis had another horrible result, spontaneous abortions. The number of miscarriages among mares who grazed on the previously frozen grass compared to mares who weren't put out to pasture is just sickening. But no one knew.