Exercising must serve life.
Below is an amazing testimony that closed-chain exercise are suprior to open-chain exercise to gain functional strength and mobility.
The body is more resilient than what we think. But if we judge strength via open-chain we can make a big mistake.
For example, I, Ageless Eylon, can lift and jump very high, but leg extension in air I find difficult, not joking.
The same concept of closed-chain exercise was validated in my experience while I was providing Physical Therapy services Canada's Public domain Hospitals.
I found that rolling sideways in bed is much more beneficial than open chain (lift your legs in the air) exercise.