This question is an exact passage from the text, found in the section titled Attilaisms: Selected thoughts of Attila." The quote you're referring to is precisely that: "Strong chieftains stimulate and inspire the performance of their Huns." This thought is the seventh "Attilaism" that is listed. As the your question is asserted verbatim in the text in the form of a statement, it could indeed be said that that strong chieftains have a positive effect on their subjects in terms of Hun culture. The essential qualities of leadership according to Attila count both emotional and physical stamina as chief among them.
It is said that lofty positions of leadership have an extraordinarily draining effect on the emotional strength of leaders. Leaders must be able to take disappointment and defeat in stride and "bounce back quickly," rather than let it consume them. This extends as well to physical strength. Chieftains are only fit to lead the charge if they are strong in body, and as it is stated, a chieftain cannot "lead from their bedside." This is only one of the many qualities that Attila deems necessary for leadership, however. Other important qualities include loyalty, courage, desire, empathy, decisiveness, anticipation, timing, competitiveness, self-confidence, accountability, responsibility, credibility, tenacity, dependability, and stewardship, all of which are detailed within the text.