Sir Ernest Shackleton experienced the 'third man factor' (Image: Getty)

       Endurance athletes who train alone are susceptible to the ‘third man factor’, according to new research just released.

       The ‘third man factor’ refers to the reported situations where an unseen, imaginary presence, such as a spirit or the apparition of a dead loved one, provides comfort or support during traumatic experiences.

       Those who go climbing, diving, running, cycling or hiking, especially over long distances, are prone to hallucinations or being joined by a ‘spiritual guide’, much like what happened to explorer Sir Ernest Shackleton during his Antarctic expedition in 1917, where he wrote about an incorporeal companion who ‘joined’ him and his men on their gruelling march to safety in the harsh environment of South Georgia.

       Dr Ben Alderson-Day led research by Durham University, who discovered 84 sporting people who had experienced an unknown presence. The study was published in the Psychological Medicine journal.

       They had put out an appeal to organisations including UK Caving, the British Mountaineering Council and Cornish adventure sports firm FreediveUK for people to come forward and take part in the survey.

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       Long-distance swimmers could also be joined by a 'spirit' (Image: Getty)

       Around 20% of people admitted they felt like they had been followed or watched while out training alone. Of these, 30% thought they knew who has been looking over them.

       Dr Ben Alderson-Day described the phenomenon at Cheltenham Science Festival, where he said: “Right at the brink, suddenly they feel like there is a ghostly companion with them, just for that period, and somehow they get through (the physical challenge).”

       Speaking after the talk, Dr Alderson-Day said: “Weekend warriors who are doing extreme exercise, and trying to push through a physical barrier to complete it, should be aware that they may start to feel a presence that isn’t there.

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       Researchers discovered 84 sporting people who had experienced an unknown presence (Image: Getty)

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       “The explanation is thought to be that when you are pushing yourself, and when there is not much sensory input, like in a cave, underwater or on a mountain, you lose your internal sense of where your body is positioned in physical space, so start to sense your own body outside of yourself and believe it is someone else.

       “It seems to be more common in people doing these sports alone, and in those with an endurance element, but it can also happen during something like a marathon.’

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