If you find that you have no energy to exercise, especially in the morning, you can start with just light cardio like bicycling, walking on the treadmill or doing the cross trainer at low effort level. Once your muscles are warmed up sufficiently, try a few exercises that is targetted at your core muscles like the following:
In this exercise, you slowly lean backwards and then raise your legs about 45 degrees. Make sure your back is straight and that you are not straining your lower back. Tuck in your stomach.
As you are doing this exercise, you would like feel involuntarily (uncontrolled) squeezing of the muscles in your inner stomach. When you are no longer able to maintain this pose at proper posture because it is too streneous, take a short break. Then repeat the exercise again. You will feel that there is more energy.
Another post is the plank pose- which also activates the core.
I am sharing this through my own experience- because sometimes when I try to workout especially early in the morning, my limbs felt as if they are still asleep. And if I were to push on, it requires a lot of effort. I discover the method by chance when after doing some core exercises, I find that my limbs seemed to have woken up and I have more energy to complete my usual running.
The reason why this is effective is probably the core, also at similar position of the ‘da tien’ or the center of energy (located 2 fingerwidths below the navel) – somehow when you do these simple but demanding core exercises- you could end up activiting your ‘da tien’ -and the energy surge is passed through the limbs and around the body.
However, if you have more energy doing workouts but ended up feeling flat out few hours later, then the method may not be suitable to you because you may have ended up using your body’s reserve- that would leave you feel ‘very tired on the insides’.