לָא בִגְבוּרְתָּא דִרְכִיבִין עַל סוּסֵי יִצְבֵי לָא בְשׁוֹקֵי גוּבְרִין רַחֲמָנִין יִצְבֵי.
1. He does not desire | לֹא... יֶחְפָּץ – See Rashi, Radak and others that the subject of the verbs of the sentence is Hashem, with the connotation being that Hashem does not desire one who trusts in either the might of horses or of men. Cf. the anonymous Northern French commentary who alternatively suggests that the subject of the verse is man: "He [i.e humans] should not desire the might of the horse...."
2. the thighs of man | בְשׁוֹקֵי הָאִישׁ – This is likely a metaphor for the swiftness of man (Hoil Moshe).