So I’ve been paddling for fitness for many years. I mostly paddle long distances (3-5 miles) at 80-90% nonstop in a 16-17 foot sea kayak. I also use a lot of core rotation while paddling (I try to use my arms as little as possible.)
Last night I read a fitness-related article online about the importance of core strength (a common theme), and they were talking about doing planks. The article said if you can hold a plank for 60 seconds, you’re doing well. If you can hold one for 90 seconds, you’re doing REALLY well…and if you can hold one for 2 minutes, you’re at an “elite level.”
I thought “Hmm…I wonder if I could do 2 minutes?” I really didn’t think I could…so got down on the floor…and did it! (With zero cheating.)
I’m not bragging. I’m 63 years old, and while I’m pretty fit for my age, I’m far from being a male model who is ripped with 6-pack abs. I despise weight training and gyms in general. 100% of my exercise is outdoors—paddling, hiking (with elevation gain) and cycling. And my diet is just okay. I eat healthy foods, but also eat pizze, greasy burgers and fries and put sugar in my coffee.
But I can hold a plank for TWO MINUTES…and I credit that 100% to lots of paddling with core rotation!
So paddling is a GREAT upper body/core exercise…especially if you work on using as much of your core (and as little of your arms) as possible to drive the boat forward.
Now if I could just eat more veggies and less carbs and sugar, I probably would get ripped with a 6-pack, LOL. But I think it’s fine to enjoy some less-than-stellar foods in life…and my goal isn’t to be a male model. 
As long as I keep getting an “A” on my annual physicals, I’m happy.