The eyes told you they had gone to the edge of exhaustion. Big players, physically strong, were being held up by team-mates at the end of it.

Carlisle United's activities at Cassius Camps this week were not for show. They subjected Keith Curle's squad to sharp and serious pain.

A circuit, in the hot sun near Windermere, appeared the hardest of it. The players were split into three teams, and from each, one player would step forward to undertake the course.

There were huge tyres to be lifted, heavy logs to be hauled, sandbags to be lugged and demanding squats, push-ups and crawls to be attempted.

It was an endurance test of body and mind, also examining United's attitude to teamwork. The other players in each of the teams walked or jogged along with the man taking the circuit, urging him along.

Some, like Luke Joyce, powered through it superbly. Others, such as Tom Miller, Mike Jones, Shaun Miller and the youngsters, Cameron Salkeld and Jordan Holt, also came home impressively.

For others the challenge proved harder, slower. The idea was to push each individual to their own limits, supported by genuine camaraderie.

Around Shaun Brisley they clustered, urging the big defender on until he had ran over the final line, shattered. Kelvin Etuhu, the midfielder known as "machine" to team-mates, looked like the experience had taken him to another place, emotionally.

When Danny Grainger paused, briefly letting go of two weighty water bottles because he was in so much agony, others in blue shirts crowded round and made sure he continued. It briefly looked as though Tom Parkes' legs would give way after the final sprint, before the new signing regained his balance.

In 17 days, United will start their League Two season. What they did here was designed to tell them they would achieve nothing unless they were prepared to escape their comfort zones, whilst working tightly together.

At the outdoor training centre, on the Graythwaite Estate, other activities included a cross-country run, a punishing range of upper and lower-body exercises with hay bales for support, a hill climb with logs for company. Monday afternoon, meanwhile, tested the emotional bravery of Curle and his men with a 250ft abseil. Even the manager himself joined in that one.

It is the third successive summer United have undertaken this experience. In the company's headquarters, there are motivational slogans, and signed shirts from footballers and rugby players who claim to have benefited from the camp's rigours.

After breakfast, Cassius founder Philip Ercolano addressed the players. He explained that it was all about exiting each other's comfort zone, and respecting 12 "pillars" which ought to give an individual and team a chance of coming through the inevitable hard times a long season brings.

These included leadership, communication, self-awareness, "personal brand", motivation and self-discipline. When Ercolano asked the group if any of them had ever struggled with "self-belief", it was striking to see several hands honestly raised. Players were given forms and asked to rate themselves in the 12 different areas.

They were also asked if they had any phobias. Two admitted to disliking open water, several were afraid of heights, one did not enjoy confined spaces. Nicky Adams chipped in: "What's a confined space? Like a wardrobe?"

The mood was light, but Ercolano also highlighted the effect the camp two seasons ago had had on Jabo Ibehre's form at the start of his Carlisle career. As Curle looked on, sipping a lemon and ginger tea, Ercolano used an image similar to those often deployed by United's boss. "If you build a house with crap foundations, when that wind blows it will fall down. At some point in the season you know that wind is coming. So build yourself ready for it."

Several coaches guided the players through the physical challenges, among them Adam Smith, who runs a sports injury and rehab clinic in Ambleside and has previously worked on the strength and conditioning of the England rugby team, Olympic athletes and rugby players in Australia and New Zealand.

Smith demanded discipline and good form. "If I think you are swinging it, I'll tell you," he told Curle's small squad. Any player tempted to sit down after one of the disciplines was told to get back up. Maximum effort, though, was praised. On midfielder Jones, after a session of press-ups and squats, Smith said: "He's the guy to beat. He was in pieces. He gave 100 per cent."

Curle often approached a cluster of players to add his own encouraging voice. United's boss clearly values this experience. "I came across Phil a couple of times through different contacts in the game," he said. "Lee Dykes had a conversation with Phil, set up a meeting, I came here, he gave a presentation and explained the physical, mental and team dynamics that Cassius could involve with teams and individuals within teams.

"He enthused me."

Ercolano, who previously worked for a sports agency, said he established Cassius Camps after initially working with four footballers for an extended period, claiming it helped them make big strides in their careers. "The findings at the end of that year were incredible," he says. "So we needed a location. The Graythwaite Estate is exclusive - it's 5,000 acres, it's remote, it's a partnership with the estate and it's good because the players feel they're in the middle of nowhere. I don’t think you can replicate that anywhere else."

How did he assess Carlisle's performance? "I think they were receptive to it. From a comfort zone perspective, they're open-minded. They got better as the day went on.

"The challenge they did in the morning would challenge anyone, whether it's Wladimir Klitschko or Jack Bonham."

While Tuesday morning's session involved some management games, with a focus on leadership and communication, Monday's physical slog appeared to resonate the most. Midfielder Joyce, a man known for his devotion to fitness, enjoyed reflecting on the pain.

"We did the run first thing in the morning, up and down hill, setting off at different intervals, 15 seconds between everyone, and the aim was to overtake that man in front of you," he said. "I set off last and managed to get past six or seven lads, so I'm quite happy with that."

"By the time you stop your lungs are burning. Then it's straight into physical tests - upper bodies, lower bodies, your chest is burning, your arms, quads, glutes...everything's burning. Then the circuits, you're up against your teammates, three lanes, three lads going for it, man against man and you want to win, and you've got a team around you helping you on."

Did he really enjoy it, or was it the hell it looked? "It's a good combination," he smiled. "It's horrendous while you're doing it, and there's times when you just want to stop, and there's people screaming stuff in your ear. But you've got to grind through it.

"There's going to be times in the season when we're going to have tough points and difficult times. This gives you a good eye-opener for lads who are going to graft for you and get through it."