I saw on TV, a mountain biker towing another mountain biker, then today I saw 2 people riding, one being towed using some sort of rope. Are they using this for training, or are they helping out the weaker rider? What kind of rope would be best for this? I'm thinking that on longer flat trail rides I could tow my kids at their pace to help lighten the load for them, especially on up hills. Where would I attach the rope?