Some motorbikes have heavy clutches. It may just be a default thing. This does not mean that you can not do anything about it but it may be a good idea do try and find other motorists experienced same model of bike with the same production year and region. One example I am thinking is a friend's tenere 700ish (not the liter bike version) where the clutch is by default heavy. There are things you can do for a lighter clutch. Here are few.
- lubricate your clutch cable
Clutch cables "need" periodic oiling and regular change. However few motorists really bother. Knowing that you have an old bike, it may still have its original cable in a very bad condition
- Remove your clutch lever. Grease the bolts and the slot. Don't over tighten the bolt when assambling back.
The part where your lever is attached to the handlebar might be causing a lot of friction as well. Again considering you are dealing with an old bike it is not a bad idea to grease few moving parts.
- Leaver length is also important.
Make sure your levers are properly sized. Some people slap on short levers to their street bikes for reasons beyond my understanding. If that is the case you will have a harder time pulling the clutch as well. This will help you pull with all of your fingers on a spot where you will have a greater leverage.
If you are not "sitting" on the bike properly this may cause tension on your arms as well. While you are riding the bike your wrists should be almost straight with no twist. It should be straight within the range of throttle free play. After an hour of riding if you have any sorts of body fatigue anywhere other than your legs you may have a poor riding position. If you don't have any fatigue in your legs you should squeeze the gas tank more :).
This video is intended for dirt bikers but I see no reason why they should not apply. As far as I know (which is not a lot) almost all motorbikes have similar multidisk clutch assemblies. You can try the advices here that may apply to your bike. Please consider this as a last resort as it involves with messing around engine internals. I have this impression (which may not have a really good basis) that ducatis are not abuse proof. Please keep in mind that I am not a proffesional mechanic. Everything apart from the last is unlikely to harm your bike but there might be other solutions that are not manifested here. A possible expert on this might be ducatikiller if he wishes to write an answer here.
Edit1: I just remembered there are kits on the market that turn your cable clutch into a hydrolic clutch. Those kits are somewhat expensive and not very easy to fit. Considering that your bike is old, it may not worth the investment.