Without hitting failure, these masters remain unsure whether they've trained with sufficient intensity. (lasting-weight-loss.com)
However, it had not been possible until recently to observe such interactions at X-ray wavelengths because there was no X-ray source that could produce X-rays of sufficient intensity. (sciencedaily.com)
But the exercise must be performed correctly to be effective, and that means using sufficient intensity, and keeping your rest periods between exercises and sets down to 60 seconds or less. (truthaboutabs.com)