Pedzisa mutsara unotevera: Larsen akava mukwikwidzi wenyika yeDenmark ye5,000 uye 10,000m muna 1937, achiwana Helsingør IF yekutanga yekumhanya. Akaenderera mberi nekutora mamwe makwikwi gumi emunyika, mapfumbamwe mumarathon (1941, 1943<unk>1950) uye imwe mu20 km (1950), pamwe nekuuya panzvimbo yechitatu mu10,000m muna 1938. Muna 1946 akaisa rekodhi yenyika yeDenmark yemarathon pa2:38:36 uye akakwikwidza muEuropean Athletics Championships yegore iroro, achiisa yechisere mumarathon. Kumira kwake kukuru kwenyika yose kwakatevera kwakanga kuri Mitambo yeOlympic yeZhizha ya1948, kwaakauya ari wechigumi mumunda wevakwikwidzi 41 mu
chiitiko chimwe chete.