With a flurry of punches and kicks, hundreds of Thai "red shirts" undergo self-defence drills as they mobilise to protect the embattled government, stoking fears of a dangerous new phase of civil conflict.
While far from a battle-ready militia, the ranks of sunweathered rice farmers brim with determination to prevent opposition protesters in Bangkok toppling Prime Minister Yingluck Shinawatra.
Drawn from the poor but populous north and northeast, the red-shirts broadly support ousted former premier Thaksin Shinawatra - Yingluck's elder brother.
Their rhetoric has soared over the last few weeks, matching a barrage of legal challenges that could lead to Yingluck's removal from office.
In anticipation of her fall, the red-shirts say they will bring hundreds of thousands of supporters to a Bangkok suburb today for a two-day rally.
The move looks likely to raise the stakes in a six-month political crisis that has left 24 people dead and hundreds wounded in grenade attacks and shootings.
The backdrop is an eight-year struggle between a royalist establishment - supported by the judiciary and the military - and Thaksin's supporters.
"We have lion hearts ... we are real fighters," local red-shirt leader Kwanchai Pripana said on the sidelines of the training camp in the movement's heartland of Udon Thani.
At the camp, around 500 mainly middle-aged men and women gamely rehearsed Muay Thai boxing moves and parade drills despite the sapping heat.
Kwanchai said 40,000 volunteers had already signed up to act as guards for red-shirt protests, with several further rounds of training planned.
"We are building our strength to learn how to defend ourselves," he said, stressing the volunteers would be unarmed.
Kwanchai was shot several times at his home in January in what was believed to have been a politically motivated attack. He now periodically needs a wheelchair.
Still, with fellow firebrand Suporn Attawong - dubbed "Rambo Isaan" - he organised the training camp for the "Democracy Protection Volunteers".
Without a swift cooling of tempers on both sides of Thailand's bitter divide, analysts warn more violence lies ahead.
If Yingluck falls, the red-shirts could seize official buildings and block roads in their strongholds, potentially prompting the army to act to restore order, according to Matthew Wheeler of the International Crisis Group think tank.
"The prospects for the country look grim in the near term. People feel it's going to get worse before it gets better," he added.
Observers say Thaksin's family has been holding back its trump card to use in the event Yingluck falls.
She faces neglect-of-duty charges linked to a loss-making rice subsidy scheme.
"Once Thaksin uses the reds, it may be impossible to control them," said Paul Chambers, director of research at the Institute of Southeast Asian Affairs at Chiang Mai University.
The movement could become "a sort of bucking bronco", he added.