I am not sure how to answer this without the Yoga-perspective.
Yoga can be of two kinds: Hatha
and Raja
, where Hatha Yoga mainly focuses on making the body strong and disease free, which provides the platform for further spiritual progress. And Raja Yoga is more of meditation & less of cumbersome physical activities that finally leads to spiritual awakening.
But since without a healthy body spiritual advancements can not be made these two are deeply inter-linked. And, as the following verse says:
Hatham vinā rājayogho rājayogam vinā hathah
Na sidhyati tato
yughmamānishpatteh samabhyaset||
.............
No success in Râja Yoga without Hatha Yoga, and no success in Hatha
Yoga without Râja Yoga. One should, therefore, practise both of these
well, till complete success is gained.
So, first, i am giving the preliminary signs that indicate that the Sadhaka is achieving success in Hatha Yoga.
Vapuh krśatvam vadane prasannatā
Nādasphutatvam nayane
sunirmale
Aroghatā bindujayoaghnidīpanam
Nādīviśuddhirhathasiddhilakshanam||
..........
When the body becomes lean, the face glows with delight, Anâhatanâda
manifests, and eyes are clear, body is healthy, bindu under control, and appetite increases, then one should know that the Nâdîs are purified and
success in Hatha Yoga is approaching.
In Yoga Sadhana they talk of four Avasthas, that the Sadhaka experiences one after another, with the first such Avastha is the one that gives the preliminary signs of success.
Ārambhaścha ghataśchaiva tathā parichayoapi cha
Nishpattih
sarvayogheshu syādavasthāchatushtayam||
...........
In all the Yogas, there are four states: (1) ârambha or
the preliminary, (2) Ghata, or the state of a jar, (3) Parichaya
(known), (4) nispatti (consumate.)
And, the signs of the Arambha Avastha are as follows:
Divyadehaścha tejasvī divyaghandhastvaroghavān
Sampūrnahrdayah
śūnya ārambhe yogavānbhavet
............
In the ârambha, a Yogî's body becomes divine, glowing, healthy, and
emits a divine smell. The whole of his heart becomes void.
Some, further signs are as follows:
When the Brahma granthi (in the heart) is pierced through by
Prânâyâma, then a sort of happiness is experienced in the vacuum of
the heart, and the anâhat sounds, like various tinkling sounds of
ornaments, are heard in the body.
NOTE: All these verses are taken from the Yoga Treatise called Hatha Yoga Pradipika.
Some further signs are given below. They are taken from another Yoga Treatise called the Shiva Samhita:
But so long as he does not gain it, let him practise observing all the
rules and restrictions laid down above. From the perfection of
pranayama, follows decrease of sleep, excrements and urine (43)
The truth perceiving Yogi becomes free from disease, and sorrow or
affliction. He never gets (putrid) perspiration, saliva and intestinal
worms.
Shiva Samhita's Chapter 2 verses.