Definition of Exercise:

1. 1128 γυμναζω gumnazo goom-nad'-zo, to exercise vigorously, in any way, either the body or the mind

Note: the meaning may be very different from this in the Old Testament--see below.

Hebrews 5:14 But strong meat belongs to those who are of full age, even those who by reason of use have their senses vigorously exercised [1128 gumnazo] to discern both good and evil. (read more)

Hebrews 12:11 Now no chastening for the present seems to be joyous, but grievous: nevertheless afterward it yields the peaceable fruit of righteousness to them who are vigorously exercised [1128 gumnazo] in themselves. (read more)

Note: they are vigorously exercised in themselves. The Greek, dia autos, translates to in themselves. The exercising happens within. This is a passive experience of repentance. Repentance is passive in the original language. It is a renewing of the mind, which is spoken of in Romans 12:1-2. Your part is to allow it. Your part is to not contend with God as He gives you a new mind. The process is simple: God leads and gives power--you submit and yield yourself to Him. He foreknew who would do this, but, in the moment, you must submit.

1 Timothy 4:7 But refuse profane and old wives' fables, and vigorously exercise [1128 gumnazo] yourself towards [3842 pros] godliness. (read more)

2:14 Having eyes full of adultery, and that cannot cease from sin; beguiling unstable souls: they have vigorously exercised [1128 gumnazo] their hearts with greedy desires, the curse of addiction [5043 teknon, the metaphorical meaning]:

06031 הנע 'anah aw-naw'
1) (Qal) to be occupied, be busied with
2) to afflict, oppress, humble, be afflicted, be bowed down
2a) (Qal)
2a1) to be put down, become low
2a2) to be depressed, be downcast
2a3) to be afflicted
2a4) to stoop
2b) (Niphal)
2b1) to humble oneself, bow down
2b2) to be afflicted, be humbled
2c) (Piel)
2c1) to humble, mishandle, afflict
2c2) to humble, be humiliated
2c3) to afflict
2d4) to humble, weaken oneself
2d) (Pual)
2d1) to be afflicted
2d2) to be humbled
2e) (Hiphil) to afflict
2f) (Hithpael)
2f1) to humble oneself
2f2) to be afflicted

01497 לזג gazal gaw-zal'
1) to tear away, seize, plunder, tear off, pull off, rob, take away by force
1a) (Qal)
1a1) to tear away, rob
1a2) to seize, plunder (with acc cognate)
1b) (Niphal)
1b1) to be robbed
1b2) to be taken away