A waist twisting disc provides an unstable surface which requires the small stabilizers of your core to work harder.

Bicycle crunches effectively activate several muscles of your abdomen. Use them as part of a comprehensive core-strengthening routine.

Ordinarily, bike riding doesn't work the lower abs very much. Add these embellishments to turn your bike ride into an ab workout.

Adding a twist to a traditional scissor kick exercise works the obliques along the sides of the torso as well as the abdominal muscles.

Cable crunches are effective at stimulating your abs but cable machines are big and expensive. You can perform the same exercise using dumbbells.

Sit-ups are an integral part of any workout routine. For extra resistance and to add difficulty to this simple exercise, just add dumbbells!

A stability ball is a tool to amp up your abs workout. Doing something as simple as bouncing on the ball can effectively train your whole core.

Exercise intolerance is a common symptom among those who suffer from heart disease, mitochondrial disease or metabolic disorders. In such cases, the normal conversion of food or oxygen into energy is disrupted, leaving the patient without an adequate supply.

Situps make up one of the primary ab exercises today. However, some fitness experts question this popular exercise, saying that it may not be the best way to tone the core region. Additionally, situps have been linked to injury such as back and neck strain, resulting in recommendations for alternate exercises.

Crunches can be a real pain in the neck. Although this popular exercise strengthens your rectus abdominis at the front of your waistline, if you're a newbie to exercise with weak abdominals, or if your form is poor, it can do more harm than good.

The Romanian deadlift -- originally developed by Romanian weightlifter, Nicu Vlad -- strengthens your lower back and hamstrings. Your trapezius and abdominals get recruited for power and stability.

Crunches are an abdominal exercise that can effectively work the muscles of your core. This exercise can be performed a number of ways and can often result in neck injury.