Whether you're in the gym every day or every few weeks, abs are one muscle group you'll want to strengthen to improve your overall fitness performance and your day-to-day activities. Ab exercises should be incorporated into all of your workouts, whether it's a deadlift [1] (yes, they work your posterior core [2]) or a Russian twist [3], but when you do the bulk of your ab exercises will vary.
"In my experience, it depends on the objective of the workout or the training block," Ariel V. Foxie [4] an NASM-certified Nike trainer and fitness and wellness adviser told POPSUGAR. "I usually try and incorporate some type of core drill into the warmup but nothing too taxing that will leave you feeling fatigued or sacrifice form/force during large movements," he added.
As an NASM-certified trainer, I recommend beginning your workout with a few core-activating exercises [6] such as dead bug [7], bird dog [8], and plank variations [9] to get your abdominal muscles warmed up and firing. You want to activate your abdominal muscles before training because your abs are involved in all movement. If your abdominal muscles aren't warm there's a possibility you can get injured and you may not be moving as efficiently as possible.
There's nothing wrong with adding core into your main workout, and I often include ab exercises as a form of active recovery. An example of this would be doing an upper-body exercise like the dumbbell bench press [10], followed by a lower-body exercise like a deadlift, and then a plank with knee taps [11].
"If my main purpose of a workout isn't heavily focussed on strength and weighs more on an increased level of intensity, I might mix some ab exercises into a circuit," Ariel said. If the focus of the workout is strength, Ariel said he'll program an ab circuit at the back end of a workout on an accessory day (a day where the focus is targeting specific muscles groups in different ways and improving any imbalances you may have).
Doing core at the beginning of a workout is OK, just make sure you aren't doing exercises that will fatigue you. It's also an option to use ab exercises as active recovery if you aren't focusing on heavy lifting, or you can save your ab work for the end of your workout to finish off with a bang.