lunging

As, I am beginner i have not much idea that how can i train my horse perfectly. I was thinking to buy lunge lines but once my colleague told me that it can hurt my horse. Is it true or just a myth?

One of my ex racehorses has always been a pig to lunge. At the minute he needs lunging as he’s in due to bad weather and mudfever. Some days when you least expect it he lunged like a dream. Most days however he gets quick and choppy no matter how much I talk to him and try to steady him he’s...