An ultramarathon is technically any running events that is longer than standard marathon distance (26.2188 miles/42.195 kilomtres). Most ultramarathons are at least 50km (31.069 miles) and can go upto multi day events covering many hundreds of miles. Many ultramararthons are also held of road. Many of road events are also classed at trail runs. Role of aid stations
My own personal view is that time also plays a significant part. A very difficult trail race that measures 26.3 miles over very difficult technical and mountainous terrain is going to take loner to complete than a 50 km race set over gently undulating terrian. The key part of ultramarathon and trail running events is enjoyment! Running an ultramarathon is a challenging experience that takes a considerable amount of effort and time. So pick events, courses and terrain that you enjoy running on :)
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