When we are developing training programs for clients we try to not only maximize their potential, we also try to maximize their time. If you have been doing some core exercises in your workout for a long time, mix up the workout by super-setting the exercise. Super-Setting is moving from one exercise to the other with limited or no rest. Have a group of two or three exercises you are confident in and try this.
You will save time and still burn the same calories. Here is a few videos you can watch to see how to do a super-setted leg workout. Try to do a few sets of each before you increase the weight. Contact us if you have more questions.