[509] And how does a bhikkhu develop the basis for success (iddhipāda) endowed with concentration due to energy and volitional formations of striving (viriya-samādhi-padhāna-saṅkhāra)?
If a bhikkhu, having made energy (viriya) the dominant factor, obtains concentration (samādhi), obtains one-pointedness (ekaggatā) of mind (citta), this is called concentration due to energy (viriya-samādhi). For the non-arising of unarisen evil unwholesome phenomena (dhammā) he generates desire (chanda), endeavors, arouses energy, exerts his mind, and strives; for the abandoning of arisen evil unwholesome phenomena … ; for the arising of unarisen wholesome phenomena … ; for the persistence, non-loss, increase, abundance, development, and fulfillment of arisen wholesome phenomena he generates desire, endeavors, arouses energy, exerts his mind, and strives. These are called volitional formations of striving (padhāna-saṅkhārā).
Thus this concentration due to energy and these volitional formations of striving — brought together as one and condensed — come to be designated simply "concentration due to energy and volitional formations of striving" (viriya-samādhi-padhāna-saṅkhāra).
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.