Alysia Johnson Montano of the U.S. starts her women's 800 metres heat at the IAAF World Championships at the National Stadium in Beijing, China August 26, 2015. REUTERS/Lucy Nicholson

Alysia Johnson Montano of the U.S. lies on the track after she fell at the finish line in her women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Kai Pfaffenbach (RUSSIA - Tags: SPORT ATHLETICS)

Alysia Johnson Montano of the U.S. cries after falling at the finish line in the women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Kai Pfaffenbach (RUSSIA - Tags: SPORT ATHLETICS)

Eunice Jepkoech Sum of Kenya (L) celebrates as she wins the women's 800 metres final while Alysia Johnson Montano of the U.S. (R) falls at the finish line during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Kai Pfaffenbach (RUSSIA - Tags: SPORT ATHLETICS)

Eunice Jepkoech Sum of Kenya (R) crosses the finish line to win the women's 800 metres final ahead of second place finisher Mariya Savinova of Russia (2nd R), Alysia Johnson Montano of the U.S., (top L) Ekaterina Poistogova of Russia and Ajee Wilson of the U.S. (bottom L) during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Fabrizio Bensch (RUSSIA - Tags: SPORT ATHLETICS)

Alysia Johnson Montano of the U.S. reacts after she fell at the finish line of the women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Phil Noble (RUSSIA - Tags: SPORT ATHLETICS TPX IMAGES OF THE DAY)

Alysia Johnson Montano of the U.S. cries after placing fourth in the women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Lucy Nicholson (RUSSIA - Tags: SPORT ATHLETICS)

Alysia Johnson Montano of the U.S. cries after placing fourth in the women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Lucy Nicholson (RUSSIA - Tags: SPORT ATHLETICS)

Alysia Johnson Montano of the U.S. cries after placing fourth in the women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Lucy Nicholson (RUSSIA - Tags: SPORT ATHLETICS)

Alysia Johnson Montano of the U.S. lies on the track after falling in her women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Fabrizio Bensch (RUSSIA - Tags: SPORT ATHLETICS)

Ajee Wilson of the U.S. walks with her compatriot Alysia Johnson Montano (L) after the women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Lucy Nicholson (RUSSIA - Tags: SPORT ATHLETICS)

Alysia Johnson Montano of the U.S. (C) falls to the track after her women's 800 metres final as Ajee Wilson of the U.S. (R) and Nataliia Lupu of Ukraine run past her during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Fabrizio Bensch (RUSSIA - Tags: SPORT ATHLETICS)

Ajee Wilson of the U.S. speaks to her compatriot Alysia Johnson Montano (L) after the women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Lucy Nicholson (RUSSIA - Tags: SPORT ATHLETICS)

Ajee Wilson of the U.S. speaks to her compatriot Alysia Johnson Montano (R) after the women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Lucy Nicholson (RUSSIA - Tags: SPORT ATHLETICS)

Ajee Wilson of the U.S. speaks to her compatriot Alysia Johnson Montano (L) after the women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Lucy Nicholson (RUSSIA - Tags: SPORT ATHLETICS)

Ajee Wilson of the U.S. speaks to her compatriot Alysia Johnson Montano (L) after the women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Lucy Nicholson (RUSSIA - Tags: SPORT ATHLETICS)

Eunice Jepkoech Sum of Kenya (R) crosses the finish line to win the women's 800 metres final ahead of second place finisher Mariya Savinova of Russia (2nd R), Alysia Johnson Montano of the U.S., (top L) Ekaterina Poistogova of Russia and Ajee Wilson of the U.S. (bottom L) during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Fabrizio Bensch (RUSSIA - Tags: SPORT ATHLETICS)

Alysia Johnson Montano of the U.S.reacts after she fell at the finish line of the women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Phil Noble (RUSSIA - Tags: SPORT ATHLETICS)

Eunice Jepkoech Sum (R) of Kenya reacts as she wins ahead of Alysia Johnson Montano of the U.S. in the women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Lucy Nicholson (RUSSIA - Tags: SPORT ATHLETICS TPX IMAGES OF THE DAY)

Alysia Johnson Montano of the U.S. is comforted by compatriot Ajee Wilson (R) after she fell at the finish line of the women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Phil Noble (RUSSIA - Tags: SPORT ATHLETICS)

Eunice Jepkoech Sum (R) of Kenya reacts as she wins ahead of Mariya Savinova (L) of Russia and Alysia Johnson Montano of the U.S. in the women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Lucy Nicholson (RUSSIA - Tags: SPORT ATHLETICS)

Alysia Johnson Montano of the U.S. is comforted by compatriot Ajee Wilson (R) after she fell at the finish line of the women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Phil Noble (RUSSIA - Tags: SPORT ATHLETICS)

Eunice Jepkoech Sum (R) of Kenya reacts as she wins ahead of Ekaterina Poistogova and Mariya Savinova of Russia and Alysia Johnson Montano of the U.S. (L-2R) in the women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Lucy Nicholson (RUSSIA - Tags: SPORT ATHLETICS)

Eunice Jepkoech Sum of Kenya (R) wins the women's 800 metres final ahead of second place finisher Mariya Savinova of Russia (2nd R), Ekaterina Poistogova of Russia (2nd lane from bottom) and Ajee Wilson of the U.S. (bottom), as Alysia Johnson Montano of the U.S. (923) falls to the ground, during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Fabrizio Bensch (RUSSIA - Tags: SPORT ATHLETICS TPX IMAGES OF THE DAY)

Alysia Johnson Montano of the U.S. is comforted by compatriot Ajee Wilson (R) after she fell at the finish line of the women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Phil Noble (RUSSIA - Tags: SPORT ATHLETICS)

Eunice Jepkoech Sum of Kenya celebrates as she wins the women's 800 metres final while Alysia Johnson Montano of the U.S. falls as Mariya Savinova and Ekaterina Poistogova of Russia (L) finish during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Phil Noble (RUSSIA - Tags: SPORT ATHLETICS)

Eunice Jepkoech Sum of Kenya celebrates as she wins the women's 800 metres final while Alysia Johnson Montano of the U.S. falls during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Phil Noble (RUSSIA - Tags: SPORT ATHLETICS)

Eunice Jepkoech Sum of Kenya celebrates as she wins the women's 800 metres final while Alysia Johnson Montano of the U.S. falls as Mariya Savinova and Ekaterina Poistogova of Russia (L) run during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Phil Noble (RUSSIA - Tags: SPORT ATHLETICS)

Eunice Jepkoech Sum of Kenya (2nd R) celebrates winning the women's 800 metres final as Alysia Johnson Montano of the U.S. falls to the ground (R) during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Dylan Martinez (RUSSIA - Tags: SPORT ATHLETICS TPX IMAGES OF THE DAY)

Eunice Jepkoech Sum (R) of Kenya celebrates winning the women's 800 metres final as Alysia Johnson Montano of the U.S. falls at the finsih line during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Gary Hershorn (RUSSIA - Tags: SPORT ATHLETICS)

Alysia Johnson Montano of the U.S. reacts after the women's 800 metres final during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Lucy Nicholson (RUSSIA - Tags: SPORT ATHLETICS)

Eunice Jepkoech Sum of Kenya (R) celebrates winning the women's 800 metres final ahead of Ekaterina Poistogova of Russia (L) and second place finisher Mariya Savinova of Russia (2nd L) as Alysia Johnson Montano of the U.S. falls to the ground during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Gary Hershorn (RUSSIA - Tags: SPORT ATHLETICS TPX IMAGES OF THE DAY)

Eunice Jepkoech Sum (R) of Kenya celebrates winning the women's 800 metres final ahead of Mariya Savinova (L) of Russia and Alysia Johnson Montano of the U.S. during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Gary Hershorn (RUSSIA - Tags: SPORT ATHLETICS)

Eunice Jepkoech Sum of Kenya (R) celebrates winning the women's 800 metres final ahead of Ekaterina Poistogova of Russia (L) and second place finisher Mariya Savinova of Russia (2nd L) as Alysia Johnson Montano of the U.S. falls to the ground during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 18, 2013. REUTERS/Gary Hershorn (RUSSIA - Tags: SPORT ATHLETICS)

Alysia Johnson Montano of the U.S. (R) wins her women's 800 metres semi-final ahead of compatriot Brenda Martinez (L) and Nataliia Lupu of Ukraine (C) during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 16, 2013. REUTERS/Phil Noble (RUSSIA - Tags: SPORT ATHLETICS)

Brenda Martinez of the U.S., Lenka Masna of Czech Republic, Nataliia Lupu of Ukraine, Halima Hachlaf of Morocco and Alysia Johnson Montano of the U.S. (L-R) compete in the women's 800 metres semi-final heat event of the IAAF World Athletics Championships at the Luzhniki Stadium in Moscow August 16, 2013. REUTERS/Lucy Nicholson (RUSSIA - Tags: SPORT ATHLETICS)

Alysia Johnson Montano of the U.S. (R) leads Nataliia Lupu (C) of Ukraine and Halima Hachlaf of Morocco to the finish line in their women's 800 metres heat during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 15, 2013. REUTERS/Denis Balibouse (RUSSIA - Tags: SPORT ATHLETICS)

Alysia Johnson Montano of the U.S. (2nd R) crosses the finish line ahead of Nataliia Lupu (2nd L) of Ukraine in their women's 800 metres heat during the IAAF World Athletics Championships at the Luzhniki stadium in Moscow August 15, 2013. REUTERS/Phil Noble (RUSSIA - Tags: SPORT ATHLETICS)

Alysia Johnson Montano of the U.S. (L) and Romania's Elena Mirela Lavric recover after their women's 800m semi-final during the London 2012 Olympic Games at the Olympic Stadium August 9, 2012. REUTERS/David Gray (BRITAIN - Tags: OLYMPICS SPORT ATHLETICS TPX IMAGES OF THE DAY)

Alysia Johnson Montano of the U.S. (L) and Romania's Elena Mirela Lavric recover after their women's 800m semi-final during the London 2012 Olympic Games at the Olympic Stadium August 9, 2012. REUTERS/David Gray (BRITAIN - Tags: OLYMPICS SPORT ATHLETICS)

(L to R) Third placed Morocco's Halima Hachlaf, first placed Alysia Johnson Montano of the U.S. and second placed South Africa's Caster Semenya congratulate each other after the women's 800m round 1 heat during the London 2012 Olympic Games at the Olympic Stadium August 8, 2012. REUTERS/David Gray (BRITAIN - Tags: OLYMPICS SPORT ATHLETICS)

South Africa's Caster Semenya (L) and Alysia Johnson Montano of the U.S. prepare to start their women's 800m round 1 heat during the London 2012 Olympic Games at the Olympic Stadium August 8, 2012. REUTERS/David Gray (BRITAIN - Tags: OLYMPICS SPORT ATHLETICS TPX IMAGES OF THE DAY)

South Africa's Caster Semenya (R) and Alysia Johnson Montano of the U.S. prepare to start their women's 800m round 1 heat during the London 2012 Olympic Games at the Olympic Stadium August 8, 2012. REUTERS/David Gray (BRITAIN - Tags: OLYMPICS SPORT ATHLETICS TPX IMAGES OF THE DAY)

South Africa's Caster Semenya (L) and Alysia Johnson Montano of the U.S. prepare to start their women's 800m round 1 heat during the London 2012 Olympic Games at the Olympic Stadium August 8, 2012. REUTERS/David Gray (BRITAIN - Tags: OLYMPICS SPORT ATHLETICS)

South Africa's Caster Semenya (R) and Alysia Johnson Montano of the U.S. prepare to start their women's 800m round 1 heat during the London 2012 Olympic Games at the Olympic Stadium August 8, 2012. REUTERS/David Gray (BRITAIN - Tags: OLYMPICS SPORT ATHLETICS)

South Africa's Caster Semenya (L) and Alysia Johnson Montano of the U.S. prepare to start their women's 800m round 1 heat during the London 2012 Olympic Games at the Olympic Stadium August 8, 2012. REUTERS/David Gray (BRITAIN - Tags: OLYMPICS SPORT ATHLETICS)

South Africa's Caster Semenya (R) and Alysia Johnson Montano of the U.S. prepare to start their women's 800m round 1 heat during the London 2012 Olympic Games at the Olympic Stadium August 8, 2012. REUTERS/David Gray (BRITAIN - Tags: OLYMPICS SPORT ATHLETICS)

First placed Alysia Johnson Montano (L) of the U.S. and second placed South Africa's Caster Semenya congratulate each other after the women's 800m round 1 heat during the London 2012 Olympic Games at the Olympic Stadium August 8, 2012. REUTERS/Lucy Nicholson (BRITAIN - Tags: OLYMPICS SPORT ATHLETICS)

(L to R) Third placed Morocco's Halima Hachlaf, first placed Alysia Johnson Montano of the U.S. and second placed South Africa's Caster Semenya congratulate each other after the women's 800m round 1 heat during the London 2012 Olympic Games at the Olympic Stadium August 8, 2012. REUTERS/Lucy Nicholson (BRITAIN - Tags: OLYMPICS SPORT ATHLETICS)

South Africa's Caster Semenya (L) and Alysia Johnson Montano of the U.S. run in the women's 800m round 1 heat during the London 2012 Olympic Games at the Olympic Stadium August 8, 2012. REUTERS/Lucy Nicholson (BRITAIN - Tags: OLYMPICS SPORT ATHLETICS)

Alysia Johnson Montano of the U.S. runs in her women's 800m round 1 heat during the London 2012 Olympic Games at the Olympic Stadium August 8, 2012. OLY-ATHL-ATW800-R1-DAY12/ REUTERS/Lucy Nicholson (BRITAIN - Tags: OLYMPICS SPORT ATHLETICS)

Mariya Savinova of Russia (2nd L) reacts winning the women's 800 meters event in front of second placed Caster Semenya of South Africa (R) Ekaterina Kostetskaya of Russia (3rd R) Janeth Jepkosgei Busienei of Kenya (2nd R) and Alysia Johnson Montano of the U.S. (L) at the IAAF World Championships in Daegu September 4, 2011. REUTERS/Michael Dalder (SOUTH KOREA - Tags: SPORT ATHLETICS)

Mariya Savinova of Russia (C) celebrates as she sprints to the finish line winning the women's 800 metres final ahead of Caster Semenya of South Africa (R) and Alysia Johnson Montano (L) of the U.S. at the IAAF World Athletics Championships in Daegu, September 4, 2011. REUTERS/David Gray (SOUTH KOREA - Tags: SPORT ATHLETICS)

Alysia Johnson Montano of the U.S. falls to the track at the end of the women's 800 metres final behind winner Mariya Savinova of Russia at the IAAF World Athletics Championships in Daegu September 4, 2011. REUTERS/David Gray (SOUTH KOREA - Tags: SPORT ATHLETICS IMAGE OF THE DAY TOP PICTURE) 

(L-R) Alysia Johnson Montano of the U.S., Mariya Savinova of Russia and Liliya Lobanova of Ukraine cross the finish line during the woman's 800 metres semi-final heat 2 at the IAAF World Championships in Daegu September 2, 2011. REUTERS/Michael Dalder (SOUTH KOREA - Tags: SPORT ATHLETICS)

(L-R) Alysia Johnson Montano of the U.S., Mariya Savinova of Russia and Emma Jackson of Great Britain cross the finish line during the woman's 800 metres semi-final heat 2 at the IAAF World Championships in Daegu September 2, 2011. REUTERS/Michael Dalder (SOUTH KOREA - Tags: SPORT ATHLETICS)

Janeth Jepkosgei Busienei of Kenya (R) runs with Alysia Johnson Montano of the U.S. in their women's 800 metres semi-final at the IAAF World Championships in Daegu September 2, 2011. REUTERS/Lee Jae-Won (SOUTH KOREA - Tags: SPORT ATHLETICS)

Mariya Savinova of Russia (R) crosses the finish line ahead of Alysia Johnson Montano of the U.S. in their women's 800 metes semi-final heat at the IAAF World Athletics Championships in Daegu, September 2, 2011. REUTERS/David Gray (SOUTH KOREA - Tags: SPORT ATHLETICS)

Janeth Jepkosgei Busienei of Kenya crosses the finish line ahead of Ekaterina Kostetskaya of Russia (L), Alysia Johnson Montano of the U.S. (2nd L) and Marilyn Okoro of Britain (R) during their women's 800 metres heat at the IAAF World Championships in Daegu September 1, 2011. REUTERS/David Gray (SOUTH KOREA - Tags: SPORT ATHLETICS)

Gold medallist Mariya Savinova (C) of Russia, silver medallist Jennifer Meadows (L) of Britain and bronze medallist Alysia Johnson of the U.S. pose during the ceremony for the women's 800 metres at the 2010 IAAF World Indoor Athletics Championships at the Aspire Dome in Doha March 14, 2010. REUTERS/Stringer (QATAR - Tags: SPORT ATHLETICS)