Two exercises continue to demonstrate their effectiveness in strengthening the core: the sit-up, which tones the more superficial abdominal muscles – the rectus abdominis in the center and the obliques on the sides – and the plank, which targets the deep transverse abdominis, acting like a corset. (Try these variations of the plank to engage your core from different angles.)

The sit-up is highly effective at activating these superficial muscles due to their vertical orientation, allowing them to synchronize with the straight-up motion of the exercise, says Martin Eriksson-Crommert at Örebro University in Sweden. His research has found that women who place their hands behind their head – as opposed to on their chest or reaching forward – achieve the greatest activation. Other studies have shown that increasing the pace of sit-ups can double the activation of the rectus. Adding a twist further engages the obliques.

Now, let’s discuss the plank. The variations demonstrated here – along with the core-stability challenge of the double-leg stretch – produce transverse activation that exceeds expectations, according to lab research conducted by Shape Brain Trust member Michele Olson, Ph.D., a senior clinical professor of sport science at Huntingdon College in Alabama with over 20 years of experience in testing abdominal exercises. Incorporate them into your sit-up routine or any other core-focused workouts and tips in this article to achieve your fittest, strongest core. (And it’s not just about acquiring a six-pack; here’s why having a strong core is crucial.)

Photo: Rony Shram.

• Spider Plank: Begin on the floor in a plank position, balancing on your hands and toes. Keep your hips level and bend your left knee outward towards your left triceps [shown on the left]. Return to the plank position, switch sides, and repeat to complete 1 repetition. Perform 2 sets of 10 to 12 repetitions.
• Double-Leg Stretch: Lie facing upward on the floor with your arms by your sides. Lift your head and shoulders off the floor, then raise your arms overhead (bringing your biceps towards your ears) and lift your legs up at a 45-degree angle to start. Maintaining a lifted upper body, bring your knees towards your chest and circle your arms around, touching your palms to the outside of your knees [shown in the center]. Extend your legs and raise your arms overhead to return to the starting position, completing 1 repetition. Perform 2 sets of 10 to 12 repetitions.
• Side Plank Twist: Start on the floor in a side plank position, balancing on your left palm and sides of your feet, with your right foot in front of your left. Bend your right elbow and place your palm behind your ear to start [shown on the right]. Rotate your torso to bring your right elbow towards the inside of your left elbow. Return to the starting position to complete 1 repetition. Perform 12 repetitions. Switch sides and repeat. (Want to keep going? Try the 10-minute abs workout Tone It Up’s Karena and Katrina swear by.)

Routines with Integrated Core Strengtheners

Certain workouts also serve as strength training sessions for your abs. “When you increase the intensity or load during full-body movements, your ab muscles naturally brace,” explains Olson. “This action truly works the transverse.” Here’s how to multitask.

• Swing a kettlebell: Your transverse muscles brace to stabilize your core as you bring the kettlebell swing to a complete stop, especially during one-handed movements.
• Lift heavier dumbbells: Add a little more weight to your repetitions – weighted squats, biceps curls, you name it – and “the heavier the load, the more bracing will occur,” says Olson.

(On that note, here are eight advantages of resistance training.)

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