no. Its all the time really. When lunging as well. I know 100% that its not the saddle fit because he jsut started this a week or so ago. I've been using this saddle for 2-3 years
While if he behaves just the same when you're not riding, there's a fair bet something else is going on, just because you've been using the same saddle for years doesn't mean it fits. If you haven't had it checked & adjusted lately, there's actually a better chance it doesn't. Because horses & saddles both change shape over time & they should be checked for comfort & fit every 6 months or so. Also a horse's behaviour doesn't necessarily make problems like this obvious. Many horses will 'grin & bear it' until such time as it may become too acute to ignore. Some horses put up with chronic pain for years without 'complaining'. For more info on evaluating saddle fit, Balance International have heaps on their site.
what other information do you need? Is there a good chance he's getting arthritis, because he is 17. Should I be showing this year if he has arthritis?
Information; feed, management, type of riding, how much exercise & play he gets in the paddock, hoofcare, symptoms, hoof & confo pics.... Need lots more to even guess whether it *might* be arthritis & couldn't say for sure purely on a forum - for that you need a vet & maybe xrays.
Just because he's 17yo(middle aged) doesn't mean he's just going to get arthritis. It's a 'disease' meaning it happens because of problems; joint stress, infection, nutrition, for eg. Not just something that a horse will get at x age.
If he's lame, regardless of whether it's arthritis I would be very hesitant to ride him, without finding out what's wrong at least - if in doubt, get the vet. If it's something like arthritis tho, *if* he's not too bad & you're a good, light rider it may be OK, because *generally* lots of light, low impact exercise is good. If whatever showing you're considering fits that bill, then fine. If you mean jumping, dressage, etc, etc, then he's probably not the best prospect, at least until his lameness is treated, if that's possible.