 The long distance track events gained popularity in the 1920s by the achievements of the " Flying <unk> " , such as multiple Olympic champion <unk> <unk> . The successes of Emil <unk> in the 1950s promoted intense interval training methods , but Ron Clarke 's world record @-@ breaking feats established the importance of natural training and even @-@ paced running . The 1990s saw the rise of North and East African runners in long distance events . Kenyan and Ethiopian athletes , in particular , have since remained dominant in these events . 
