Germany, Dec 2023 - back bending
Some yoga poses are very acrobatic. Some yoga styles are also very strenuous and demanding. Nevertheless, practising yoga is not a fitness program. For one thing, practicing the asanas is only part of the journey. Pranayama, meditation and observing a few essential rules of life such as non-violence are also part of it. The intention of yoga is to show the practitioner a way to live in peace with themselves and with the world. Being healthy is part of this. One goal of yoga is enlightenment, even if few people talk about it today. What can one say about it. Only a few people experience this state. It cannot be practiced.
So you can't criticize yoga for not challenging the cardiovascular system enough or that your strength decreases even though you practice yoga for so many hours a day. Yoga is not a fitness program, even if it often looks like one.
In order to stay fit, you have to be active in other ways.
I have discovered strength training and callisthenics, which is also strength training without equipment. To stay strong at an advanced age, you have to do additional exercises. This is not a criticism of yoga.
You have completely different goals in the fitness sector. You want to see a six-pack on your stomach. The percentage of muscle mass should go up, the percentage of fat down. You develop an idea of how aesthetically pleasing your body should look. That may sound superficial. But staying healthy is never just superficial. Training your body according to your own ideas is absolutely OK. People in the fitness community are concerned with nutrition. Exercise sequences are developed further. The direction of sporting activities is completely different from yoga. There is a lot of overlap. One of them is to keep the body in good health.
Yoga and fitness programs are not in competition with each other. They can complement each other perfectly.