Many people work out and wonder why they tremble as they fatigue. The answer to that is your transverse abdominal muscle aka your core is not activated/no longer active. In fact, after we as human learn to walk as toddlers or children and develop muscle strength in our legs and back, we can compensate with new muscles. Making the core weak as we progress through life.
So how do you reactivate your core muscle? Relatively simple. You reactivate first by pulling your navel/ belly button in towards your spine and hold for 30 seconds. Once done, make it a habit through out your day and increase the durations of your hold by 30 seconds.
Next, below are some planking exercises that will not only strengthen your core, but help trembling reside and make your reps more solid, complete, and efficient. As a former NASM, AFFA, and ACE certified trainer, this is how I would start everyone off on their road to their individual goals. Hope this helps whomever is interested in improving core strength and making your hard work pay off greater than it did before. One love and keep at it.