James Hopkinson, a former instructor at the Infantry Battle School in Brecon, has described the challenging conditions that the two soldiers who died would have been up against.
He said that military exercises in the Brecon Beacons were designed to push soldiers "to the edge of their endurance," but that measures would "undoubtedly" have been put in place to mitigate the effects of the hot weather.
He added that while the exact circumstances of the deaths remain unclear, such endurance training is needed to make the British Army "the best in the world".
This photo shows Lance Corporal Craig Roberts, who died during a training exercise in the Brecon Beacons on Saturday.
Photograph removed due to copyright agreement.
The two soldiers who died on the Brecon Beacons on Saturday were taking part in a selection process for the SAS reserves, sources have told the Press Association.
According to the SAS website, the elite force has two reserve units which recruit male personnel from both military and civilian backgrounds.
The website states that they are "tasked to the highest level" and must complete a two-phase selection process demanding about 80 days over 12 months.
The initial 'Aptitude' test is described as "a progressively arduous phase, requiring greater expenditure of physical energy, designed to select volunteers with the right qualities".
Another walker who saw some of the soldiers training in the Brecon Beacons on Saturday has said he saw nothing out of the ordinary. Phil Speck told BBC News:
– phil speck
They did look very hot, they were tired in the afternoon, but it did kind of seem like you would normally see the soldiers when you're walking up there.
I think maybe if we had walked past another walker who was on their own, you might have gone 'Is everything OK? Do you need some extra water?'
They looked very hot and sweaty but when you see the soldiers you do walking in the Brecon Beacons, you see them all the time, you kind of get used to the fact they can cope with those conditions.
– ministry of defence spokesman
It is with great sadness that the Ministry of Defence can confirm the death of LCpl Craig Roberts and another Army reserve soldier during a training exercise in the Brecon Beacons at the weekend.
Our thoughts are with their families and friends at this difficult time.
The families of the soldiers have requested that their privacy is respected at this difficult time.
The Ministry of Defence has named one of the soldiers who died on a training exercise in the Brecon Beacons in Wales as Lance Corporal Craig Roberts.
The other was identified only as "another Army reserve soldier".
The soldiers' families have been informed.
Major Alan Davies told the BBC that the Brecon Beacons is one the most challenging terrains military personnel can encounter:
"On one end of the spectrum you have cadets being taken for mountain walking and at the other end of the spectrum the SAS use it," he said.
He added that the three men may have been carrying very heavy equipment and working to a deadline, which meant they would have been pushing themselves very hard.
The deaths are thought to be related to the hot weather but despite more high temperatures expected an MoD spokesperson told the paper: "There no plans to change any planned exercises, whatever their nature, in light of this."
The two soldiers who died during a training exercise in the Brecon Beacons were serving with the Territorial Army, according to the BBC.
Defence sources suggested the personnel had "succumbed" to unusually hot weather conditions during the drills in Wales.
The TA is a British volunteer reserve force which recently announced plans to increase its manpower to 30,000.