You may even try going through the motions of strength training with no weight, since you're still lifting the weight of your arms and legs. (healthline.com)
When you are doing a plank, you can not add additional load and increase the resistance, like you do when training with weights. (fitnessandpower.com)
You will have moved past the beginner stages of training, and have been training with weights for at least 18 months. (muscleevo.com)