Trotting between the two markers in saa’i should be done in all laps

Yes, one should walk fast between the two markers in all laps
of saa’i, from al-Safa to al-Marwah and from al-Marwah to al-Safa. 

Ibn Qudaamah said in al-Mughni (10/236), when
describing saa’i between al-Safa and al-Marwah: 

It means coming down from al-Safa and walking until you are
level with the marker, which is the green mark that is attached to the
corner of the mosque. When you are about six cubits away from it, you should
walk quickly until you come in line with the other marker, then you should
stop trotting and walk (normally) until you come to al-Marwah, then stand to
face the qiblah and say du’aa’ as you did at al-Safa. … Then come down and
walk in the place for walking, and trot in the place for trotting. End
quote. 

The scholars of the Standing Committee for Issuing Fatwas
were asked about that and said: 

Yes, it is the same when going from al-Marwah to al-Safa as
when going from al-Safa to al-Marwah, because the Prophet (peace and
blessings of Allaah be upon him) did that, as is proven in the saheeh
ahaadeeth. 

And Allaah is the Source of strength. May Allaah send
blessings and peace upon our Prophet Muhammad and his family and companions.
End quote. 

Standing Committee for Academic Research and Issuing Fatwas 

Shaykh ‘Abd al-‘Azeez ibn ‘Abd-Allaah ibn Baaz, Shaykh ‘Abd al-Razzaaq ‘Afeefi, Shaykh ‘Abd-Allaah ibn Qa’ood.