AN 7.51 so you think working out at the gym is healthy and harmless?

If you're serious about full liberation, and keeping celibacy, you really want to study this sutta carefully.

Don't take this as advice not to exercise! Just be prudent about how you go about it. I exercise solo about 99% of the time.  Exercise is preventative medicine. I do plenty of it, it's as essential as eating and sleeping.

AN 7.51 Bound and Unbound 

51. Saṃyogasutta	51. Bound and Unbound
“Saṃyogavisaṃyogaṃ vo, bhikkhave, dhammapariyāyaṃ desessāmi.	“monks, I will teach you an exposition of the teaching on the bound and the unbound.
Taṃ suṇātha … pe …	Listen and pay close attention, I will speak.
katamo ca so, bhikkhave, saṃyogo visaṃyogo dhammapariyāyo?	And what is the exposition of the teaching on connection and disconnection?
Itthī, bhikkhave, ajjhattaṃ itthindriyaṃ manasi karoti—	A woman focusses on her own femininity:
itthikuttaṃ itthākappaṃ itthividhaṃ itthicchandaṃ itthissaraṃ itthālaṅkāraṃ.	her feminine moves, feminine appearance, feminine ways, feminine desires, feminine voice, and feminine adornment.
Sā tattha rajjati tatrābhiramati.	She’s stimulated by this and takes pleasure in it.
Sā tattha rattā tatrābhiratā bahiddhā purisindriyaṃ manasi karoti—	So she focusses on the masculinity of others:
purisakuttaṃ purisākappaṃ purisavidhaṃ purisacchandaṃ purisassaraṃ purisālaṅkāraṃ.	masculine moves, masculine appearance, masculine ways, masculine desires, masculine voice, and masculine adornment.
Sā tattha rajjati tatrābhiramati.	She’s stimulated by this and takes pleasure in it.
Sā tattha rattā tatrābhiratā bahiddhā saṃyogaṃ ākaṅkhati.	So she desires to bond with another.
Yañcassā saṃyogapaccayā uppajjati sukhaṃ somanassaṃ tañca ākaṅkhati.	And she desires the pleasure and happiness that comes from such a bond.
Itthatte, bhikkhave, abhiratā sattā purisesu saṃyogaṃ gatā.	Sentient beings who are attached to their femininity are bound to men.
Evaṃ kho, bhikkhave, itthī itthattaṃ nātivattati.	This is how a woman does not transcend her femininity.
Puriso, bhikkhave, ajjhattaṃ purisindriyaṃ manasi karoti—	A man focusses on his own masculinity:
purisakuttaṃ purisākappaṃ purisavidhaṃ purisacchandaṃ purisassaraṃ purisālaṅkāraṃ.	his masculine moves, masculine appearance, masculine ways, masculine desires, masculine voice, and masculine adornment.
So tattha rajjati tatrābhiramati.	He’s stimulated by this and takes pleasure in it.
So tattha ratto tatrābhirato bahiddhā itthindriyaṃ manasi karoti—	So he focusses on the femininity of others:
itthikuttaṃ itthākappaṃ itthividhaṃ itthicchandaṃ itthissaraṃ itthālaṅkāraṃ.	feminine moves, feminine appearance, feminine ways, feminine desires, feminine voice, and feminine adornment.
So tattha rajjati tatrābhiramati.	He’s stimulated by this and takes pleasure in it.
So tattha ratto tatrābhirato bahiddhā saṃyogaṃ ākaṅkhati.	So he desires to bond with another.
Yañcassa saṃyogapaccayā uppajjati sukhaṃ somanassaṃ tañca ākaṅkhati.	And he desires the pleasure and happiness that comes from such a bond.
Purisatte, bhikkhave, abhiratā sattā itthīsu saṃyogaṃ gatā.	Sentient beings who are attached to their masculinity are bound to women.
Evaṃ kho, bhikkhave, puriso purisattaṃ nātivattati.	This is how a man does not transcend his masculinity.
Evaṃ kho, bhikkhave, saṃyogo hoti.	This is how one is bound.
Kathañca, bhikkhave, visaṃyogo hoti?	And how does one become unbound?
Itthī, bhikkhave, ajjhattaṃ itthindriyaṃ na manasi karoti—	A woman doesn’t focus on her own femininity:
itthikuttaṃ itthākappaṃ itthividhaṃ itthicchandaṃ itthissaraṃ itthālaṅkāraṃ.	her feminine moves, feminine appearance, feminine ways, feminine desires, feminine voice, and feminine adornment.
Sā tattha na rajjati, sā tatra nābhiramati.	She isn’t stimulated by this and takes no pleasure in it.
Sā tattha arattā tatra anabhiratā bahiddhā purisindriyaṃ na manasi karoti—	So she doesn’t focus on the masculinity of others:
purisakuttaṃ purisākappaṃ purisavidhaṃ purisacchandaṃ purisassaraṃ purisālaṅkāraṃ.	masculine moves, masculine appearance, masculine ways, masculine desires, masculine voice, and masculine adornment.
Sā tattha na rajjati, tatra nābhiramati.	She isn’t stimulated by this and takes no pleasure in it.
Sā tattha arattā tatra anabhiratā bahiddhā saṃyogaṃ nākaṅkhati.	So she doesn’t desire to bond with another.
Yañcassā saṃyogapaccayā uppajjati sukhaṃ somanassaṃ tañca nākaṅkhati.	Nor does she desire the pleasure and happiness that comes from such a bond.
Itthatte, bhikkhave, anabhiratā sattā purisesu visaṃyogaṃ gatā.	Sentient beings who are not attached to their femininity are not bound to men.
Evaṃ kho, bhikkhave, itthī itthattaṃ ativattati.	This is how a woman transcends her femininity.
Puriso, bhikkhave, ajjhattaṃ purisindriyaṃ na manasi karoti—	A man doesn’t focus on his own masculinity:
purisakuttaṃ purisākappaṃ purisavidhaṃ purisacchandaṃ purisassaraṃ purisālaṅkāraṃ.	his masculine moves, masculine appearance, masculine ways, masculine desires, masculine voice, and masculine adornment.
So tattha na rajjati, so tatra nābhiramati.	He isn’t stimulated by this and takes no pleasure in it.
So tattha aratto tatra anabhirato bahiddhā itthindriyaṃ na manasi karoti—	So he doesn’t focus on the femininity of others:
itthikuttaṃ itthākappaṃ itthividhaṃ itthicchandaṃ itthissaraṃ itthālaṅkāraṃ.	feminine moves, feminine appearance, feminine ways, feminine desires, feminine voice, and feminine adornment.
So tattha na rajjati, tatra nābhiramati.	He isn’t stimulated by this and takes no pleasure in it.
So tattha aratto tatra anabhirato bahiddhā saṃyogaṃ nākaṅkhati.	So he doesn’t desire to bond with another.
Yañcassa saṃyogapaccayā uppajjati sukhaṃ somanassaṃ tañca nākaṅkhati.	Nor does he desire the pleasure and happiness that comes from such a bond.
Purisatte, bhikkhave, anabhiratā sattā itthīsu visaṃyogaṃ gatā.	Sentient beings who are not attached to their masculinity are not bound to women.
Evaṃ kho, bhikkhave, puriso purisattaṃ ativattati.	This is how a man transcends his masculinity.
Evaṃ kho, bhikkhave, visaṃyogo hoti.	This is how one is unbound.
Ayaṃ kho, bhikkhave, saṃyogo visaṃyogo dhammapariyāyo”ti.	This is the exposition of the teaching on connection and disconnection.”