So if increasing intensity of your workouts is completely out of the question, you can extend the time of your routine to see a modest boost in calorie burn. (onnit.com)
Then, you can gradually increase the duration and intensity of your workouts as the weeks go on. (verywellfamily.com)
By varying the duration and intensity of a workout session, you can aim to achieve specific results. (bodybuilding-wizard.com)