The American track & field legend is in Jamaica to film a BBC documentary with Bolt, and feels the Jamaican megastar has what it takes to lower his world record over the distance.
“He is good enough to run 42 seconds, but he will have to develop his strength-and-speed endurance,” said Johnson, whose record stands at 43.18 seconds.
“Nobody is ever going to hold the world record at 100m, 200m, and 400m again if he (Bolt) does it.”
Bolt has shunned the 400 because of the type of training it demands, and Johnson agrees that he would definitely have to change his training regime.
“The training is going to be much more significant for the 400m than the 100 and 200,” he said.
“That natural ability and gift that he has, has helped him to be great at 100 and 200, but at 400 that gift is still there and is still important. But the longer the distance, the less it becomes.
“Training, endurance, and most important speed-endurance become a more important factor.”
